Historical reconstructions of environmental conditions and land uses in coastal aeolian sedimentary systems of the Canary Islands (Spain)

Programa de Doctorado en Oceanografía y Cambio Global TESIS DOCTORAL HISTORICAL RECONSTRUCTIONS OF ENVIRONMENTAL CONDITIONS AND LAND USES IN COASTAL AEOLIAN SEDIMENTARY SYSTEMS OF THE CANARY ISLANDS (SPAIN) Aarón Moisés Santana Cordero Abril 2017 Las Palmas de Gran Canaria D. PABLO MÁYER SUÁREZ, SECRETARIO DEL DEPARTAMENTO DE GEOGRAFÍA DE LA UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA, CERTIFICA, Que el Consejo de Doctores del Departamento, o la Comisión Académica de la Facultad, en su sesión de fecha ................................. tomó el acuerdo de dar el consentimiento para su tramitación, a la tesis doctoral titulada “Historical reconstructions of environmental conditions and land uses in coastal aeolian sedimentary systems of the Canary Islands (Spain)” presentada por el doctorando D. Aarón Moisés Santana Cordero y dirigida por los Doctores Luis Hernández Calvento y María Luisa Monteiro Quintana. Y para que así conste, y a efectos de lo previsto en el Artº 6 del Reglamento para la elaboración, defensa, tribunal y evaluación de tesis doctorales de la Universidad de Las Palmas de Gran Canaria, firmo la presente en Las Palmas de Gran Canaria, a.........de............................de dos mil............................. UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA Departamento de Geografía Programa de doctorado de Oceanografía y Cambio Global Título de la Tesis “Historical reconstructions of environmental conditions and land uses in coastal aeolian sedimentary systems of the Canary Islands (Spain)” Tesis Doctoral presentada por D. Aarón Moisés Santana Cordero Dirigida por el Dr. D. Luis Hernández Calvento Codirigida por la Dra. Dª. María Luisa Monteiro Quintana El Director, la Codirectora, el Doctorando, Luis Hernández Calvento María L. Monteiro Quintana Aarón M. Santana Cordero Las Palmas de Gran Canaria, a 26 de abril de 2017. Programa de Doctorado en Oceanografía y Cambio Global Escuela de Doctorado de la Universidad de Las Palmas de Gran Canaria HISTORICAL RECONSTRUCTIONS OF ENVIRONMENTAL CONDITIONS AND LAND USES IN COASTAL AEOLIAN SEDIMENTARY SYSTEMS OF THE CANARY ISLANDS (SPAIN) Reconstrucciones históricas de las condiciones ambientales y usos del suelo en sistemas sedimentarios eólicos costeros de las Islas Canarias (España). Dirigida por: Dr. Luis Hernández Calvento Dra. María Luisa Monteiro Quintana El Director La Co-directora El Doctorando En Las Palmas de Gran Canaria, a 26 de abril de 2017. CONTENTS Presentación ------------------------------------------------------------------------- 1 0. Abstract/Resumen ------------------------------------------------------------------------- 3 1. Introduction ------------------------------------------------------------------------- 11 1.1. Coastal areas: recent evolution and current state ---------------------------- 11 1.2. Historical Ecology ---------------------------------------------------------------- 12 1.2.1. Origins and evolution of the discipline 1.2.2. Definition and major objectives 1.2.3. Sources and methods 1.3. Historical reconstruction of the characteristics of coastal ecosystems and landscapes of the Canary Islands ---------------------------------------------- 14 1.4. This dissertation: justification and aims ------------------------------------- 16 2. Historical reconstruction of environmental conditions ---------------------------- 18 Santana-Cordero AM, Monteiro Quintana ML, Hernández-Calvento L (2014) Reconstructing the environmental conditions of extinct coastal dune systems using historical sources: the case of the Guanarteme dune field (Canary Islands, Spain). Journal of Coastal Conservation 18: 323-337. Doi: 10.1007/s11852-014-0320-5 3. Historical reconstructions of land uses --------------------------------------------- 48 Santana-Cordero AM, Monteiro Quintana ML, Hernández-Calvento L, Pérez-Chacón Espino E, García Romero L (2016) Long-term human impacts on the coast of La Graciosa, Canary Islands. Land Degradation & Development 27:479-489. Doi: 10.1002/ldr.2369 Santana-Cordero AM, Monteiro-Quintana ML, Hernández-Calvento L (2016) Reconstruction of the land uses that led to the termination of an arid coastal dune system: the case of the Guanarteme dune system (Canary Islands, Spain), 1834-2012. Land Use Policy 55: 73-85. Doi: 10.1016/j.landusepol.2016.02.021 4. Conclusions and prospects ------------------------------------------------------ 93 5. References ------------------------------------------------------------------------ 95 1 Presentación Esta tesis doctoral ha sido realizada por Aarón M. Santana Cordero, y dirigida por los Dres. María Luisa Monteiro Quintana y Luis Hernández Calvento. Ha sido desarrollada en el seno del grupo de investigación Geografía Física y Medio Ambiente, integrado en el Instituto de Oceanografía y Cambio Global, IOCAG, perteneciente a la Universidad de Las Palmas de Gran Canaria, ULPGC. La línea de investigación en la que encaja este trabajo es la de “Sistemas de dunas litorales” cuyo responsable es el Dr. Luis Hernández Calvento. El modelo adoptado por esta tesis es el de compendio de publicaciones, con lo cual su organización ha sido la siguiente: 0) Resumen; 1) Introducción; 2) Reconstrucción histórica de las condiciones ambientales (artículo Santana-Cordero et al. 2014); 3) Reconstrucción histórica de los usos del suelo (artículos Santana-Cordero et al. 2016a; 2016b); 4) Conclusiones y perspectivas; y 5) Referencias. Para la elaboración de esta tesis doctoral, su autor ha sido beneficiario de una beca predoctoral del programa propio de la Universidad de Las Palmas de Gran Canaria, en el período 2012-2016. Este trabajo académico supone una contribución científica a los siguientes proyectos del Plan Nacional de I+D+i del Gobierno de España, cofinanciados con fondos FEDER: Diagnóstico ambiental de los sistemas de dunas de Canarias para la elaboración de modelos sostenibles de gestión territorial (Ref. CSO2010-18150), Caracterización de procesos eco-antrópicos de los sistemas playa-dunas de Canarias como base para su gestión sostenible (Ref. CSO2013-43256-R) y Análisis de procesos naturales y humanos asociados a los sistemas playa-duna de Canarias (Ref. CSO2016-79673-R). Agradecimientos Me gustaría agradecer a todas las personas que han tenido que ver conmigo y/o con mi trabajo de investigación a lo largo de estos años. En primer lugar, agradecer a mi 2 familia: Pedro, Rosi, Ale, Nana y Mesi, el hecho de haber estado ahí en todo momento y apoyarme. En segundo lugar, quiero agradecer a Luis Hernández Calvento su confianza depositada en mí para llevar adelante esta investigación y haberme escuchado y ayudado en los momentos personales más duros. ¡Gracias amigo! Por otra parte, a mi codirectora, María Luisa Monteiro Quintana, Magüi, por su incondicional apoyo y su valiosa aportación a la hora de crear y analizar las fuentes orales que han formado parte de mi trabajo. Al resto de mis compañeros de grupo de investigación: Emma PérezChacón Espino, Pablo Máyer Suárez, Emilio Fernández Negrín, Lidia Esther Romero Martín, Carolina Peña Alonso, Nicolás Ferrer Valero, Leví García Romero, Antonio Hernández Cordero, Elisabeth Fernández Cabrera, Natalia Cruz Avero y Laura Luisa Cabrera Vega. En especial a Emma por su gran ayuda en los escollos administrativos y académicos con los que nos hemos tenido que enfrentar durante el desarrollo de mi tesis doctoral. Mención aparte merecen también el Dr. Eduard Ariza y el Dr. Francesc Romagosa, con quienes trabajé durante mi primera estancia científica en la Universitat Autònoma de Barcelona. Al Dr. Matthias Bürgi y la Dra. Anna Hersperger, por el trabajo realizado conjuntamente conmigo en Zúrich (Suiza), durante mi segunda estancia científica, realizada en su institución, el Swiss Federal Institute for Forest, Snow and Landscape Research WSL. A Tobias Plieninger, de la Universidad de Copenhague (Dinamarca), por supervisar mi tercera estancia científica y aportarme nuevos puntos de vista en mi investigación. A Péter Szabó (Academy of Sciences of the Czech Republic, Department of Vegetation Ecology, República Checa), por sus aportaciones y sus interesantes discusiones sobre la Historical Ecology que hemos tenido. A mis amigos Ancor, Yamilé, Zeus, Nau, Chedey, Luis, Josep, José Luis, Mark y José Vicente por ser quienes son y estar siempre ahí. A todos, mil gracias y un fuerte abrazo. Espero no haberme olvidado de nadie, pero si es así, ruego me disculpe. 9 comentar que la duna de caída del sistema, que quedaba justo encima del estadio Insular (antiguo estadio de fútbol) era usada como grada por los aficionados para ver los partidos. El último uso, referente a la extracción de arena, se llevó a cabo, de acuerdo a las fuentes orales, de norte a sur y de manera sistemática. La arena sirvió como material de relleno de grandes obras, como el Puerto de La Luz y de Las Palmas, a la vez que servía como materia prima para fabricar ladrillos en la fábrica de Eufemiano Fuentes, operativa desde el año 1924. A su vez, grandes cantidades de arena eran extraídas por las personas a título personal para construir sus viviendas, cuestión que, según observó uno de los informantes, se llevó a cabo en el barrio de Guanarteme. En la discusión se habla de los resultados y de la metodología empleada. Respecto a los resultados, se hacen comparaciones entre el sistema de dunas de Guanarteme y varios lugares en el mundo, como la región mediterránea, EEUU y Japón, en los que este tipo de sistemas han sido alterados o destruidos. Respecto a la metodología, se justifica el tipo de análisis aplicado a las fuentes cartográficas utilizadas, debido a la imposibilidad de trabajar con ellas mediante SIG, por sus características geométricas. Las conclusiones de esta tesis doctoral son las que siguen: 1. Desde el punto de vista metodológico, considerando conjuntamente las fuentes de información y los métodos, es necesario, al abordar un estudio de reconstrucción histórica, evaluar la fiabilidad de las fuentes. En este sentido, el método desarrollado en esta tesis consiste en la aplicación de un enfoque crítico hacia las fuentes, con base en la evaluación de sus características y su contribución al estudio. Las variables utilizadas fueron: 1) el tipo de fuente, 2) el nivel de detalle o resolución de la información que proporcionaban, y 3) los análisis que les pueden ser aplicados. 2. Por lo que respecta a los factores de alteración histórica de los sistemas sedimentarios eólicos costeros áridos, la eliminación de la vegetación leñosa resulta ser uno de los principales factores. Dado que ésta estabiliza el sustrato, su eliminación tiene la capacidad de cambiar la dinámica de estos sistemas, tal y como se detecta en La Graciosa. 3. La extracción de arena también tiene consecuencias decisivas en la alteración de estos sistemas, llegando a suponer la desaparición de todo un sistema sedimentario eólico. Tal 10 es el caso del campo de dunas de Guanarteme, debido a la amplia magnitud de la superficie afectada y la alta intensidad en la que se desarrolló este proceso extractivo. 4. Las motivaciones que subyacen detrás de las acciones que conllevan la alteración o desaparición de un sistema de este tipo son económicas y económico-sociales. Esto ha quedado comprobado tanto en el caso de La Graciosa, donde se pretende mejorar las condiciones de vida de los pobladores de la isla, como en el de Guanarteme, en cuyo origen se encuentra la decisión política de construir una infraestructura (un nuevo puerto) y la ampliación de la ciudad de Las Palmas hacia el norte. Por su parte, las perspectivas de este trabajo se exponen a continuación: Perspectivas. 1. La creación de un archivo de memoria ambiental para las islas Canarias. Este estaría basado en el conocimiento del pasado inmediato de nuestro territorio, involucrando a los ciudadanos como donantes de memoria, e influenciaría al progreso científico de Canarias. Este archivo sería construido en torno a fuentes orales, fotografías y videos, y sus interpretaciones, sobre los elementos físicos y las realidades sociales de nuestros ecosistemas y paisajes. 2. La creación de una plataforma online de SIG histórico, a través de un geoportal o de una infraestructura de datos espaciales, que contendría todo nuestro conocimiento histórico sobre nuestros ecosistemas y paisajes, al que la población en general podría acceder y enriquecer (mediante sus aportaciones). 11 1. Introduction Global change is a phenomenon negatively affecting the entire planet Earth. Thus, all ecosystems on the planet are influenced by human activities (Vitousek et al. 1997), with changes in land use being one of the most important (Foley et al. 2005). Although human influence on the planet has a historical character, recently this influence has become a notable pressure on our natural systems (Ellis et al. 2013). 1.1. Coastal areas: recent evolution and current state Coastal areas have historically been affected by humans (Nordstrom 1994). As in other environments, human pressure on these areas has become more and more significant with time. Furthermore, intense coastal population growth in recent decades (Bajocco et al. 2012) has put increasing pressure on these domains. Martínez et al. (2007) report that currently 41% of the world population lives in these areas. This intense coastal development has notably been undertaken over sandy beach ecosystems (Defeo et al. 2009). In the case of Spain, as well as the broader Mediterranean coastal region, this has been a trend and it has resulted in accelerated and intense urban development in these areas (Ariza 2011). Globally, agriculture, natural resource extraction and settlement are the most influential forms of land use (Klein Goldewijk 2013). However, Bajocco et al. (2012) indicate that fires, intensive agricultural practices, land abandonment, urban sprawl, and concentrated mass tourism are the land uses that most degrade coastal landscape characteristics in typical Mediterranean regions. Of these land uses, tourism has largely been an activity carried out in coastal areas worldwide (Gormsen 1997) with inevitable environmental consequences (Davenport and Davenport 2006; Gössling 2002). Its development has a strong relationship with international travel, which has increased since 1950 (Gormsen 1997). Additionally, most of the time, tourism implies urbanization, therefore these two land uses are somehow linked. Thus, urban sprawl at the coast can be a result of tourism and the migration of people towards the coasts (Bajocco et al. 2012), which boosts residential land use. However, vegetation and sand extraction have negative 12 consequences for sedimentary landscapes. This situation is especially harmful in islands, due to their fragility from the environmental point of view. The Canary Islands are a good example of this phenomenon, since they have experienced significant development in their coastal areas that has exerted an important human pressure on valuable ecosystems and their processes (Santana-Cordero et al. 2016). 1.2. Historical Ecology 1.2.1. Origins and evolution of the discipline Humans have always shown a certain interest in their relationship with the natural world. This interest became a field of study that evolved as various subdisciplines during the formation and establishment of the sciences in the 18th and 19th centuries. Thus, some ecological problems with historical implications arose in those centuries. For instance, in 1769, Barrington proposed that sweet chestnut (Castanea sativa) was not native to Britain. Another example was the Ruined Landscape theory which indicates that the degradation of the Mediterranean landscapes was caused by deforestation in the past. These kinds of ideas were treated by various subdisciplines, such as landscape history, environmental history, historical geography, environmental archaeology, forest history or historical ecology, which were developed within at least four academic disciplines: history, ecology, geography and anthropology (Szabó 2015). There have been different approaches through which to address this topic, and that is why several trends in historical ecology coexist. There are three main trends in historical ecology: the anthropological (Crumley 1994; Balée 2006), ecological, and conservation/restoration ecological and ecological planning (Bürgi and Gimmi 2007). Regarding the first one, Crumley (1994) argues that anthropology theoretically adapts to historical ecology by bridging the natural and social sciences and the humanities through its approach. The ecological trend integrates the human dimension in the analysis of patterns and processes in landscapes and ecosystems (Domon and Bouchard 2007; Bürgi et al. 2015). Within this trend some experimental research normally focused on ecosystems (e.g., woodlands) can be 13 considered, in which sediment, compositional/dendrochronological and statistical/modeling analyses play a central role (Hermy et al. 1999; Ireland et al. 2011; Mladenoff et al. 2002). The conservation/restoration ecological and ecological planning trend, also called applied historical ecology (Swetnam et al. 1999), applies historical knowledge to conservation/restoration tasks (Egan and Howell 2005; Grossinger et al. 2007). This last trend has been developed above all in North America. The work undertaken here has been performed in line with the ecological trend of historical ecology. 1.2.2. Definition and major objectives There are many definitions of historical ecology in the literature (Szabó 2015). Although it is not an objective of this work to define historical ecology, efforts will lead to highlight the different definitions and propose some of them to be the most complete ones. In his review, Szabó (2015) offers a list of definitions gathered by examining the historical ecological literature. If we effectively assume that three trends of historical ecology exist, there will be several definitions that fit adequately with the term historical ecology. Therefore, accordingly, three definitions are provided. For the anthropological trend, Balée (2006) states that historical ecology is a research program ‘concerned with comprehending temporal and spatial dimensions in the relationships of human societies to local environments and the cumulative global effects of these relationships’. For the ecological trend, historical ecology encompasses ‘the scientific attempts to elucidate the past of ecosystems; it aims at uncovering past ecosystem dynamics and their drivers, using and combining a large variety of historical data sources’ (Gimmi and Bugmann 2013). Finally, the restorationists/conservationists define historical ecology as ‘a restorationist’s guide to reference ecosystems’ (Egan and Howell 2001). Some authors have highlighted the major objectives of historical ecology. Firstly, Bürgi and Gimmi (2007) suggest the following three objectives: (1) preserving cultural heritage in ecosystems and landscapes, (2) understanding historical trajectories of patterns and processes in ecosystems and landscapes, and (3) informing ecosystem and 14 landscape management. Secondly, Crumley (2007) establishes that ‘the goal of historical ecologists is to use scientific knowledge in conjunction with local knowledge to make effective and equitable management decisions’. Thirdly, Rick and Lockwood (2013) identify another goal: ‘to understand past and present human-environment interactions, but it is also concerned with understanding natural variation before and after human arrival’. 1.2.3. Sources and methods One characteristic of historical ecology is the use of different sources to work with. Bürgi and Gimmi (2007) consider the following sources as typical in historical ecology: ‘historical documents, such as maps, management plans, land survey records, repeat photography, aerial or terrestrial, and oral history interviews. Biological archives, such as tree rings, pollen, diatoms and charcoal sediments, fire scars and bark peelings, archaeological evidence and ecosystems and landscapes themselves’. When working with a variety of sources we must carry out a source critical approach (Bürgi et al. 2010). Forman and Russell (1983) establish a procedure to critically evaluate the sources used in four steps: (1) firstor second-hand observation; (2) purpose or possible bias of the statement; (3) author’s knowledge of the subject and; (4) context of the statement. Similarly, Santana-Cordero et al. (2014) (one of the papers of this dissertation) developed a method to determine the reliability of the sources. Regarding the methods, to my knowledge no literature exists that addresses this topic in the field of historical ecology. Nevertheless, documentary analysis and spatio-temporal analysis through historic maps, aerial photographs and pictures seem to be present in many studies. Furthermore, the GIS tool is quite usual in study cases. 1.3. Historical reconstruction of the characteristics of coastal ecosystems and landscapes of the Canary Islands In the Canary Islands, several general studies of landscape reconstruction have been undertaken. Santana Santana (1992) studied the reconstruction of plant landscapes in 15 Gran Canaria, based on bibliographic, historical sources as well as toponymy. Naranjo Cigala and Hernández Calvento (1995) carried out a change analysis in the landscapes on the Gran Canaria mountain peaks. Martín Galán (2001) reconstructed the landscape of Las Palmas de Gran Canaria and the process of city growth with time. At coastal areas, Hernández Calvento (2006) studied the evolution of the coastline in the Maspalomas dune field (Gran Canaria) through photo-interpretation and bibliographic sources. Finally, in these same areas (i.e., coastal areas) a line of investigation by the Grupo Geografía Física y Medio Ambiente of the Universidad of Las Palmas de Gran Canaria has been developed. In this regard, Santana-Cordero et al. (2010, 2012) studied the historical evolution of the Maspalomas and Guanarteme dune fields (Gran Canaria) by integrating different kinds of sources. Thus, the island of Gran Canaria constitutes an interesting example of the development of these types of studies. The main interests in reconstructing the characteristics of coastal sedimentary systems of the Canary Islands are: (1) retrieval of territory memory through oral and other sources, as patrimonial elements (cultural and natural) of our history. This serves as background to the harmful short-term management of the landscapes of the archipelago. (2) From (1) we can learn how to reconstruct landscapes and avoid the harmful impacts of such management practices. An interesting paradox arises when the environmental characteristics of the coastal sedimentary systems are threatened by the development of tourism-related facilities, i.e., the most important economic activity of the archipelago is destroying the environment that makes tourism possible. Undoubtedly, the key question here is the planning and management of these resources to avoid their degradation. The above mentioned ideas have led us to select the Guanarteme dune field and La Graciosa island for this dissertation. The Guanarteme dune field has disappeared due to the development of the Port of La Luz and Las Palmas and the growth of the city of Las Palmas. We have been able to reconstruct the dune field (environmentally and culturally), thus discovering the natural and human processes that led to its disappearance. La Graciosa has been less affected by human activity. Nevertheless, our study reveals how human actions have modified the natural dynamics. These two cases show different phases in the evolution of these kinds of landscapes. 16 1.4. This dissertation: justification and aims Prior to the research that supports this dissertation, the historical dimension in the study of the dune fields of the Canary Islands had not been addressed. Earlier studies focused on these systems were developed in the fields of aeolian geomorphology and vegetation cover and management, all of which were related to tourism development (especially for the Maspalomas dune field, Gran Canaria). Nevertheless, it is important to state that these previous studies provided views of the temporal evolutions of the dune fields from the first aerial photographs available to the present, i.e., since the 1960s. To expand the temporal dimension in these kinds of studies was essential to understand the current natural dynamics and the degree that human pressure had exerted on them. This approach allows us to get mid-term history of the systems studied and to understand the evolution model of these systems (e.g., the case of Guanarteme, Gran Canaria), spanning several centuries and observing how it evoluted from its original natural state to its present complete disappearance. This model can be used to compare the evolution of other dune fields of the Canary Islands, which are in different evolutionary phases than Guanarteme, and alert us to the impacts that our activity has on them. On the other hand, to overcome the limitations involved in the use of aerial photographs, we had to use other type of sources, such as historical written documents, historical maps, old pictures and oral sources. The challenge in using these was how to work with each one and how to integrate the information provided by each source. In order to solve these issues, the reading of international scientific literature was a key question, as well as to contact and work with national and international scientist from other research institutions, whose support in analyzing the data helped us greatly. Having summarized the scientific background, the main aim of this dissertation is "the study of the historical relationship between the natural processes and the human activities in the aeolian sedimentary systems of the Canary Islands". This aim can be divided in three objectives: (1) the establishment of a methodology to integrate different historical sources; (2) the study in depth of different aspects of the history of the aeolian 17 sedimentary systems of the Canary Islands, to characterize their nature and dynamics, as well as the human uses on them; and (3) the determination of the interference degrees of the human activities on the natural processes of these systems. 18 2. Historical reconstruction of environmental conditions Reconstructing the environmental conditions of extinct coastal dune systems using historical sources: the case of the Guanarteme dune field (Canary Islands, Spain) Aarón Santana Cordero, María L. Monteiro Quintana, Luis Hernández Calvento Journal of Coastal Conservation (2014) 18:323–337 DOI 10.1007/s11852-014-0320-5 25 Friends of the Country of Gran Canaria [hereinafter SEAPGC]), and the unpublished manuscript of González Velazco (Las dunas ó médanos del Ystmo de Guanarteme en la Gran Canaria, dated between 1875 and 1884, according to Martín Galán (2001)). - Historical maps: these maps have been consulted in archives and in published map collections. For this study five historical maps have been used: military map by Próspero Casola (1599, approximate scale (a.s.) 1:13500); three maps of Las Palmas city, 1742 a.s. 1:10800, 1773 a.s. 1:11400 and 1792 a.s. 1:9800 (made by Antonio Riviere, Joseph Ruiz Zermeño, and Luis Marqueli, respectively) (Marqueli 1995; Riviere 1995; Ruiz Zermeño 1995); and the ‘Plano de la bahía de Las Palmas’ (Map of the Bay of Las Palmas) from 1879 (Dirección de Hidrografía 1995; a.s. 1:20000). They have played a key role in the geomorphological reconstruction of the study area to as far back as 1599. However, it is important to bear in mind that their main original purpose was to map the city rather than those areas that were not occupied at the time. - Street-level photographs: the digital photography catalogue of the Fundación para la Etnografía y el Desarrollo de la Artesanía Canaria, FEDAC (Cabildo Insular de Gran Canaria) (Foundation for Ethnography and the Development of the Canary Craft, Gran Canaria Island Council) was consulted. Only some of the available photos were used in this study. These photographs were essential for the identification of specific elements in the territory from the end of the 19th century up until 1954. - Aerial photographs and ortophotos: the oldest aerial photograph, 1954, has been particularly useful. Its scale is 1:2650 and its spatial resolution 0.73 m. The city was still spreading at that time, so the photo shows some sandy areas. Current ortophotos have also been of considerable use in the identification of certain landmarks, such as buildings and other infrastructure, used in this study as spatial references to apply geometrical adjusts to the aerial photography. - Travelers/explorers written accounts: data given by geologist Léopold Von Buch, based on his field observations, have been essential to determine the high of the dunes to the early 19th century (1815). On the other hand, descriptions written by journalist Olivia Stone, in 1883–84, have been relevant for the present analysis. - Oral sources: five interviews were carried out, and they enabled us to gather very useful information about the dune field and their immediate surroundings. This technique has been developed based on Fogerty (2005), considering an interview as a semi-structured conversation between an interviewer and an interviewee. The interviewees, born between 1924 and 1947, contributed significant information based on their early memories of some areas (Santa Catalina, Guanarteme or La Isleta). The interviews were 26 done between February, 2010, and June, 2012. We should point out that these oral sources represent a fundamental part of our research as there are very few documentary sources available on this study area, particularly for the second third of the 20th century.  Bibliographic references. - The most relevant references for this study have been: Martín Galán (2001), who performes a deep analysis on the urban evolution of Las Palmas de Gran Canaria; and Santana Santana (1992), who studies the historical evolution of landscapes of Gran Canaria, through documentary sources, since 15th to 19th century. Fig. 3 Sources used, classified by type, environmental factor and century they provide information about. Further divided by periods of study considered: 15 th century - 1850; 1851–1954 For the 16th century we have the first image of the study area where we can see, with certain limitations, the environmental factors studied to determine its configuration. The 18th century maps are an improvement because they allow the possibility to analyse and contrast the represented elements. This comparative analysis has been done by graphic information extraction of aeolian landforms, overlaying the maps, to obtain an image that integrates the information contained in them. For the nineteenth century we have travelers/explorers written accounts, street-level photographs, a historic map and historical documents that allow us to analyse data and supplement the information provided by all the sources. Finally, for the 20th century we have references, oral sources and the aerial photograph of 1954 (Fig. 3). 27 Considering the availability and quality of the sources, the study period was divided into two parts: 15th century-1850. This decision is based on improving the spatial accuracy that present historical maps from the late nineteenth century and the incorporation of street-level photography as a new source. Methodology Using aeolian geomorphology and vegetation featuring of the system as guidance, the information extracted from each source consulted has merged according to a chronological order (Fig. 3) to obtain several pictures of the natural state of this system throughout the period studied. To assess the reliability of the sources we have adopted a source critical approach on the basis of their characteristics and contribution to the study. The variables chosen for this evaluation have been: 1) the type of source, 2) the detail level and/or resolution of the information provided, and 3) the analyses that could be applied. Each variable has several categories: thus, we have established two categories of source type, direct and indirect. The first one refers to those sources that provide information that has not been interpreted, e.g. street-level and aerial photographs; the second one refers to those documents containing information that has been previously interpreted (bibliographic sources, historical written documents, explorers/travelers written accounts, oral sources and historical cartography). A value of 1 is assigned to direct sources and 0.5 to indirect ones. The detail level/spatial resolution determines the extent and quality of information that can be extracted from the sources. To assign one of these categories for each source we have paid attention to the “scale” that is expressed in the information and/or the level of detail. For example, we have considered whether each source provides information of regional, insular or local (municipal) scale. The categories of this variable are “low”, “medium” and “high”, and their values 0.25, 0.5 and 1, respectively. Three distinct analyses were applied: (i) analogy; (ii) contrasting of information between two or more sources and; (iii) the possibility for extraction of spatial information. By analogy we mean the possibility to establish similarities and differences between the study area and other similar systems, such as Maspalomas in this case, by comparing their respective elements and dynamics. Contrasting of information involves verifying the data provided by a source through its comparison with other sources of the same or different nature. The extraction of spatial information refers to the ability of the sources to show or describe the location of territorial elements. The latter analysis is particularly interesting for historical cartography and aerial and street-level photography. For each of these analyses a value of 0.1 is added, so that the maximum score that each source can acquire for this variable is 0.3. The values of reliability obtained by each source, within the range 0.75–2.3, were 28 standardized on a 0–1 scale indicating the relative reliability of each source. Normalizing values (reliability level value (rlv)) have been obtained by dividing the sum of the values of all categories (Σcv) between 2.3; therefore, Σcv/2.3=rlv. Finally, we have established three categories regarding reliability levels: low (<0.33), medium (0.33 to 0.66) and high (>0.66). Table 1 presents the assessment criteria, showing the values of each category. Table 1 Criteria selected to evaluate the reliability of historical sources Results The reconstruction of the natural characteristics of the Guanarteme dune field has been undertaken bearing in mind two of the most relevant factors linked to these types of natural systems: aeolian geomorphology (major landforms) and vegetation. In addition, an assessment of the reliability of the sources has been conducted using the method developed. Assessment of the reliability of the sources The evaluation of the sources reveals that the aerial photography (AP), street-level photographies (SLP1,2), an explorers/travelers written accounts (WA1), a historic map (HM5) and one oral source (OS2) have a high reliability (>0.66). Next, in the group of sources of medium reliability (0.33 to 0.66), bibliographical sources (BS1,2),HM1–4, historical written documents (HWD1,2), a WA2 and OS1,3,4,5 are found. No low reliability sources have been used. In order to better appreciation of results shown in Table 2, the data of the reliability of each source is depicted in a graph (Fig. 4) with a time scale. It can be appreciated how in the second period, near to the present time, there are more sources available and more reliable information. 29 Table 2 Calculation of reliability level for each source, according the assessment criteria. a AP: Guanarteme dune field and the city of Las Palmas de Gran Canaria (CECAF 1954); SLP1: Vegetation planted in rows near to Las Canteras beach, 1890-1895 (FEDAC 2011); SLP2: Row of Traganum moquinii on Las Canteras beach, 1875-1880 (FEDAC 2011); BS1: Análisis y reconstrucción de los paisajes históricos (Santana Santana 1992); BS2: Las Palmas ciudad y puerto: cinco años de evolución (Martín Galán 2001); HWD1: Boletín 68 (SEAPGC 1868); HWD2: “Las dunas ó médanos del Ystmo de Guanarteme en la Gran Canaria” (González Velazco 1875–1884); WA1: Descripción física de las Islas Canarias (von Buch 1999);WA2: Tenerife and its six satellites; or, The Canary Island Past and Present (Stone 2004); HM1: Planta del sitio de Canaria by Próspero Casola 1599 (Archivo General de Simancas); HM2: Antonio Riviere, circa 1742 (Riviere 1995); MH3: Joseph Ruiz Zermeño, 1773 (Ruiz Zermeño 1995); MH4: Luis Marqueli, 1792 (Marqueli 1995). (Dirección de Hidrografía, 1995); OS1–5; interviews conducted between 02/2010 and 06/2012. Fig. 4 Level of reliability of the sources and their temporal location (level of reliability from Table 2). Three categories were established: low (<0.33); medium (0.33–0.66); and high (>0.66). The vertical line indicates the split established in the study period (upper lines indicate 30 the numbers of the two sub-periods). Aeolian geomorphology and vegetation before 1850 The information that dates back the furthest comes from Santana Santana (1992) in his reconstruction of the historic landscapes of Gran Canaria. This author states that, by the 15th century, psammophile communities, palm groves and thermophile forests were present in the study area and its immediate environs. In all probability, the psammophile community would have been the most widespread, given the large expanse of the dune field. According to this author, the species dominating this community would have been the following: Traganum moquinii, Zygophyllum fontanesii, Cyperus laevigatus and Schizogyne glaberrima. These species are just widely extended nowadays on Maspalomas dune field, as well as on other dune fields of the Canary Islands. In terms of the geomorphology of the area studied, the oldest source that enables us to classify it is a military map drawn up by the engineer Próspero Casola in 1599 (Fig. 5). Its level of detail and the inclusion by its author of certain place names render it extremely useful for this study, both as the oldest cartographic reference source available and due to the quality of the information it provides. According to the map, the dune field at that time was a long landform running NNE—SSW, near to Las Canteras beach, of a notable size and linked to the place name “médanos de arena” (sandbanks, i.e. dunes); at the same time, numerous hummock dunes are depicted across the whole area, which we deduce must have been produced by the interaction of vegetation with the moving sand, as it happens today in other parts of the islands with similar characteristics. So, we have deduced the existence at that time of a transverse ridge that was stabilised or semistabilised due to the vegetation and/or by topographic effects, near to the west coast of the study area, as well as small dunes in the rest of the area conditioned to a greater or lesser extent by the vegetation. 31 Fig. 5 ‘Planta del sitio de Canaria’ (Map of Canaria besieged). Drawn up by Próspero Casola, 1599 (AGS 2011) The historic reconstruction of the 18th century geomorphology was carried out based on three maps of the city of Las Palmas de Gran Canaria (dated circa 1742 (by Antonio Riviere), 1773 (by Joseph Ruiz Zermeño) and 1792 (by Luis Marqueli), see Fig. 6) on which the dune field appears. Examination of these maps reveals once again the presence of the above-mentioned large dune associated with the name monte de arena (sand hill) on those dating from 1742 to 1792, which would have been located perpendicular to the effective winds and parallel to the fluvial terrace, some 50 m above sea level (Fig. 7). Fig. 6 18th century maps (a: Antonio Riviere, circa 1742 (Riviere 1995); b: Joseph Ruiz Zermeño, 1773 (Ruiz Zermeño 1995); c: LuisMarqueli, 1792 (Marqueli 1995)). 32 The appearance of this long dune in various sources leads us to contemplate two possibilities: i) firstly, that the authors have copied from each other, which would lead us to consider only the oldest map as valid; ii) secondly, that the various documents really do represent the different locations of the above-mentioned dune. As far as the first possibility is considered, it is worth remembering that the copying of part, or all, of pre-existing maps was a common practice at the time. In this sense, visual analysis suggests that there are some coincidences that can be consider suspicious, at least in some elements of the territory, such as the coastline. Nevertheless, it is also true that notable differences were detected, particularly in terms of the relief, and if we look at the different shapes of the drawings intended to illustrate the presence of the fluvial terrace. These same singularities can be seen in the representation of the road links. Thus, we can see how the road that linked the city to the port adapts to the topography, presumably as a result of the movement of the dunes. Fig. 7 Location of the dunes on the different dates analysed. The points outlined above lead us to expect that the various maps would roughly reflect, from their authors’ perspectives, the position of the main mounds of sand located on the 33 Guanarteme isthmus at each moment. This possibility is supported by the representation of the dunes dating back to the 16th century, which gives a general configuration of the terrain that is fairly similar to that found in the 18th century maps analysed. If we bear in mind all the above-mentioned documents, we will find that the dune has neither exactly the same shape nor position, which would suggest that each map reflects the situation as it was at the time the map was drawn up, and that they therefore present the evolution of the above-mentioned aeolian landforms. Other elements are also represented in the same area, possibly smaller dunes that change in shape and position, and sometimes disappear completely. However, it is important to remember that dunes constitute exotic landforms and in some case landscape landmarks, hence the associated toponymy (médanos de arena). The above-mentioned long dune must has been of a really extraordinary size, which would explain why it was included in the maps (whereas the other smaller dunes were often left out) and given the toponym monte de arena (sand hill). The fact that this dune maintained a similar shape for nearly 200 years (from 1599 to 1792) is also of interest. However, as we can see in the 18th century maps, one part of the dune, the SW tip, is always in the same position, while the other, to the NE, appears to move. This may be explained by the aeolian dynamics of the topographical obstacle represented by the above-mentioned high sedimentary terrace. In turn, on the eastern edge appears to move, as it takes on a N-S direction in the 1742 map, but it is curved in shape in the 1773 map (facing NE) and 1792 (facing NNE). It would therefore correspond to a transverse ridge, although some parts of the front might be a bit sinuous, as it occurs in the Maspalomas dune field, so it could also be classified as a barchanoid ridge. The eyewitness reports of the geologist Léopold von Buch 1815 (von Buch 1999) are particularly useful for the first half of the 19th century. He reports 30 or 40 foot high dunes on the Guanarteme isthmus, i.e. the sandy mounds at that time were between 8.35 m and 11.14 m high. These heights are entirely comparable with the deposits observed in other dune systems in the Canary Islands, such as those of Maspalomas (Gran Canaria), and Corralejo (Fuerteventura). Aeolian geomorphology and vegetation from 1850 to 1954 During this period, the city of Las Palmas de Gran Canaria grew out to the north from the original old town with the constitution of the district of Arenales, while some settlements were also founded around the La Luz bay as a result of the construction of the port (Puerto de la Luz y de Las Palmas). Olivia Stone, who visited the island between 1883 and 1884, gives the following description of the dune field: “the sand is disposed in hills, valleys, small tablelands, and plateaus, over which when one begins to walk their extent seems to be much greater than would be supposed from 34 a distant view”. In reference to the vegetation cover, this author says that “looking at this stretch of dune, nothing appears but sand and a few stunted tamarisk bushes” (Stone 2004) […] to that, SEAPGC (1868) adds that “planted there in an attempt to stabilize the sand”. We can therefore assume that at the end of the 19th century, the landscape was dominated by aeolian landforms and that the transport of sediment prevailed over the presence of vegetation. This quote suggests the possibility that tamarisk (Tamarix canariensis) could be found in the dune field, although its presence would not seem to be due to natural causes, but rather to the fact that the inhabitants of the city of Las Palmas had planted these shrubs (Fig. 8) as part of an activity proposed by the SEAPGC to fix the dunes, which were threatening to invade the crops, the port installations and the transport infrastructures (SEAPGC 1868). Fig. 8 Vegetation planted in rows near to Las Canteras beach (1890–1895). Tamarisks, among other species, can be seen (FEDAC 2011a). On the other hand, the street-level photographs show some clearly differentiated areas within this dune system. One such is the foredune, which is characteristic of these systems. Just as we can see on the upper part of the El Inglés beach, which is the input area to Maspalomas dune field from, there is some evidence to show that on Las Canteras beach, which acted as the entry system for sand to the Guanarteme dune field, there were rows of Traganum moquinii plants (Fig. 9). These rows of Traganum 41 the Canary Islands, however, those methods could be applied to other dune systems, but always in areas where the material or the underlying substrate are stabilized since these dune systems have high rates of mobility (Cabrera-Vega et al. 2013). We neither have the ability to conduct a comprehensive study using historical cartographic documents and ancient texts, such as those carried out by Gautreau (2010), Levin et al. (2010) and Hunter and Sluyter (2011), due to lack on this type of documents for the entire study period. This is one of the reasons that justifies having sources of diverse nature in the development of this research, something that, on the other hand, has enriched and completed it. Nevertheless, the reference conditions have been identified for various stages along the evolution of this system. Despite this, it is obvious that its disappearance makes impossible the application of restoration efforts based on such information. However, the establishment of reference conditions is a basic step for understanding the natural functioning of this system. Similarly, these data are needed to reconstruct its environmental history, which helps to know the relationship of a society with its natural area (Hughes 2006). The method implemented is a key part of this study, which validates the sources by reliability levels. It is a simple and direct method which could be applied in other studies within the framework of Historical Ecology, whenever working with different types of sources and/or accuracy. In this regard, several methods have been proposed (e.g. Bertolo et al. 2012; Bürgi and Russell 2001; Grossinger et al. 2007), but new methodological contributions are claimed from the scientific literature. This research is innovative in comparison to other studies carried out to date in these kinds of areas, the arid dune systems, as it is based on the integration of sources and techniques drawn from a variety of scientific disciplines. It is also relevant its contribution to bringing History to Ecology, notably distanced scientific areas (Szabó and Hédl 2011), using an integrative approach. Thus, we have used geographic technologies (maps and the interpretation of aerial photographs) together with sources and other analyses typically used in History, such as Oral History, which is a characteristic technique of this type of studies (Bürgi and Gimmi 2007). In this sense, in this field the integration of these techniques is necessary. Conclusions and prospects If we consider the results obtained in terms of the methodology used, three main conclusions arise: firstly, the application of a historical approach, in which different sources have been used and integrated, has enabled us to fill a large part of the gap existing in the environmental information available for the extinct Guanarteme dune field. 42 Secondly, this study makes a methodological contribution through the method developed to assess the reliability of sources. Thirdly, the analogy with other still-active dune systems of similar characteristics such as the dune system of Maspalomas on Gran Canaria (beyond being one of the applied analyses), is important because it has enabled us to address the structure and functioning of this dune field, and to come up with an image of what the landforms and processes of the past might have looked like. Similarly, some of the species of vegetation that were found in the outlying areas of this singular system have been identified. The results obtained from this study point the way for future work that may be considered as three-fold: firstly, more in-depth work is needed on the Guanarteme dune field, broadening the scope of the data through further archive material and interviews, in order both to gather more information in terms of the territory that has been the object of this study and also to help to develop and polish the methodological aspects of this type of studies. Secondly, this type of methodologies could also be applied to the reconstruction of the natural characteristics of other dune systems in the Canary Islands and surrounding area, opening up the time-span considered to date, which has been limited by the availability, or lack thereof, of aerial photographs to the end of the 1950s. The inclusion of oral sources enables us to look several decades further back, although it is true that this aspect needs to be addressed urgently, given the fact that potential eye-witnesses are already quite old. Thirdly, proposals that go beyond the scope of this study include the specific interest of working with GIS using historical content, not just as a research tool but also as a source of information for society at large, that can be consulted on-line, through Geoportals or Spatial Data Infrastructure (SDI), to help to understand the space and time dimensions of land. In this way, and in relation with the prospects already mentioned, there is an urgent need for the creation of an archive of environmental memory for the Canary Islands, by means of which our knowledge of the immediate past of our territory could be broadened, involving citizens at large as “memory donors”, in the scientific progress of the Canary Islands. Finally, dune fields are ideal objects of study when examining historical changes in territory, as 1) their landforms are very dynamic and their current state can tell us about natural processes and/or human alterations that may have taken place there, and 2) their elements (at least the most noteworthy among them) tend to be depicted on historical maps, which enriches the historical approach to their study. Acknowledgments 43 This piece of work is a contribution to project CSO2010-18150 of the Spanish National Plan of R&D + I (innovation), co-financed by European Regional Development Funds. 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Cabildo Insular de Gran Canaria, Las Palmas de Gran Canaria, Spain, p 82 Santana Santana A (1992) Propuesta metodológica, cartográfica e informática para el análisis y reconstrucción de los paisajes históricos: aplicación a la isla de Gran Canaria (1478–1865). Unpublished – PhD thesis. Universidad de Las Palmas de Gran Canaria (Spain) Sloan S (2008) Oral History and Hurricane Katrine: reflections on shouts and silences. Oral Hist Rev 35(2):176–186 48 3. Historical reconstructions of land use Long-term human impacts on the coast of La Graciosa, Canary Islands Aarón Santana Cordero, María L. Monteiro Quintana, Luis Hernández Calvento, Emma Pérez-Chacón Espino, Leví García Romero Land Degradation and Development (2016) 27:479–489 DOI 10.1002/ldr.2369 49 Abstract Global change is affecting coastal areas and leading them to degradation. This is severe in sand dunes and sand plains, because they are very fragile ecosystems. The objective of this paper is to characterize the relationship between the historical land uses and the aeolian sedimentary dynamics in an arid coastal system, the island of La Graciosa (Canary Islands) since the second half of the 18th century. The methodology is based on the interpretation of historical documents, aerial photographs and oral testimonies to characterize the changes in the island, in terms of both land use and aeolian geomorphology. The results suggest the existence of six stages during which the intensity of human pressure on the environment changed. Keywords: Historical ecology; Historical land uses; Land use/land cover changes; Alteration; La Graciosa; Canary Islands. Introduction The Earth’s system is being affected by global change, and there is a need to understand the origin of these changes, their processes and rates and to contribute to developing an adequate framework for studying it (Harris et al., 2006; Jackson & Hobbs, 2009; Alphan, 2012). Vitousek et al. (1997) indicate that no ecosystem is currently free from human influence, and Foley et al. (2005) suggest that land use is the main process responsible for the global change. In this context, coastal areas represent priority locations for human settlements (Steffen et al., 2004), and therefore, these areas are subject to continuous degradation by human activity (Lin, 1996; Bajocco et al., 2012). In this sense, coastal dune systems are one of the most altered coastal environments (Thomas & Wiggs, 2008), which have traditionally been impacted by many activities such as grazing, agriculture or forestry (Granados Corona et al., 1988; Kutiel et al., 2004; Levin & Ben-Dor, 2004) and more recently by the building trade and tourism. These activities diminished the extension of the natural systems, despite the efforts performed in their appropriate management and conservation during recent decades (Jackson & Nordstrom, 2011). On the other hand, research about the landscape history involving various types of ecosystems have been developed in recent decades. These studies provide the keys to understand their function and current status. At the same time, they contribute to the basic knowledge on which to base their management and/or ecological restoration (Bellarosa et al., 1996; Swetnam et al., 1999; Rhemtulla & Mladenoff, 2007; Stringer & Harris, 2014). It has been defined a common conceptual framework in the field of historical ecology (Egan & Howell, 2005), where the reconstruction of the features of a natural system is a main issue to address. This topic tries to identify and characterize the elements and environmental dynamics of an ecosystem and/or human activities that influence it at a certain historical period from different sources. These reconstructions were carried out in different environments, such 50 as wetlands (Grossinger et al., 2007; Stein et al., 2010), forest systems (Gimmi & Bürgi, 2007; Gautreau, 2010), river environments (McAllister, 2008), arid environments (Hoffman & Rohde, 2007; McLeman et al., 2010) and coastal areas (Bajocco et al., 2012; Roig-Munar et al., 2012; Santana Cordero et al., 2014), among others. The use of multiple sources and methods is one of the main characteristics of historical ecology studies (Bürgi & Gimmi, 2007; de Mûelenaere et al., 2014; Raska et al., 2015). Some of these are historical maps, written accounts by travellers/explorers, conventional photographs, aerial photographs and oral sources (Rhemtulla & Mladenoff, 2007; Gimmi & Bugmann, 2013). This range of source types enables one to widely explore the history of a place, in both temporal and spatial sense. Furthermore, for these works, with an inherent geographical focus, of special interest are the broad possibilities supplied by geographic information systems (GIS) (Rumsey & Williams, 2002; McLeman et al., 2010). Most of the studies analysing the consequences of the historical uses on aeolian sediment dynamics of the coastal systems have focused on temperate regions, there being few that address these changes in arid systems. In temperate regions, the impacts on aeolian sedimentary dynamics and soils and the apparition of erosion processes have been mainly induced by the use of herbaceous vegetation by grazing activities (Granados Corona et al., 1988; Cerdà & Lavee, 1999; Kutiel et al., 2004; Levin & BenDor, 2004; Mekuria & Aynekulu, 2013; Angassa, 2014). However, in the coastal dunes at arid regions, where shrub species are more commonly found than herbaceous species (Johnson, 1977, 1982; Doing, 1985), the impacts by grazing are lower. In this study, we hypothesize that aeolian sedimentary dynamics in sand arid systems has been historically altered by the direct utilization of wood by humans, instead of herbaceous vegetation by grazing activities. To test this hypothesis, we conducted an investigation on an island laboratory (La Graciosa, Canary Islands, Spain), which was gradually colonized since the 18th century, using a multi-source-based methodology. We have sufficient historical sources to determine the land uses developed since then and their consequences on aeolian sedimentary dynamics. From this hypothesis, the aim of this paper is to explain the relationship between the land uses and covers, and the aeolian sedimentary dynamics. This island can be defined as a laboratory for testing hypotheses around some issues regarding aeolian sedimentary dynamics in arid environments because it meets four conditions: (1) the climate is arid; (2) it presents aeolian sedimentary mantles; (3) human activities are present since the 18th century; and (4) the use and exploitation of its resources and its environmental consequences are documented in historical sources. Materials and methods 57 Fig. 3 Houses and inhabitants evolution at Caleta del Sebo from 1910 (Cabrera Socorro, 1997; González et al., 1996; and INE, 2013); evolution of the surface occupied by buildings at Caleta del Sebo (aerial photographs from 1954, 1977, 1987 and 2009); percentage distribution of vegetation coverage (>50% cover) and moving sand layer at meridional aeolian sedimentary system (aerial photographs from 1954 to 2009). Additionally, in the aerial photography taken in 1954, the dense vegetation cover (>50% cover) occupies less than 40% of the sedimentary field at the southern area (which is closest to Caleta del Sebo), while mobile sand layers occupy about 17% of the surface of this same area (Figure 4). Fig. 4 State of vegetation around Caleta del Sebo from 1954 (A) to 2009 (B). From the point of view of sediment stability, it is important to consider not only the increase in the number of houses but also the change in building materials. Thus, from the previous traditional buildings, they now build stronger houses, introducing the use 58 of lime as mortar. This involves the cutting of bushes to feed the lime kilns. From the oral testimonies gathered, it appears that for the construction of a family home, the material produced by a lime kiln and half of another (three lime kilns for every two houses) were necessary. Each of these kilns’ consumption implied ‘20 camel loads’ (plant material) continuously burning ‘over one night and two days’. Also keep in mind that, at this stage, there was not only an increase in the number of houses but also the renovation of the existing houses so far. Thus, during this period and until 1967, when according to oral sources the last lime kiln burning in the island occurred, at least 5100 camel loads should be required, only for the rehabilitation of existing houses and construction of new ones. Additional loads should be considered for the construction of public infrastructure (water tanks, school, cemetery and spring), funded by the Canarian Economic Command. In this sense, the fieldwork has identified 14 lime kilns in different states of preservation. Oral sources indicate the existence of some other in what today is the very core of Caleta del Sebo, but which disappeared after the current expansion of the buildings. According to these same sources, as a general rule, the location of the lime kilns was associated directly with the presence of rocky material, because of the two resources needed (calcareous sandstone and wood); rocks are the heaviest to transport. It is significant, however, that during the fieldwork we noticed the existence of some kilns not associated with the location of the rock material. The wood was also a key resource in the homes of La Graciosa, not only for cooking but also for supplying small industries such as bakeries. According to oral sources, this wood was gathered initially around population centres, where it was forbidden to collect firewood for lime kilns. However, some witnesses have provided information on the collection of firewood in the north-western edge of the island, which could be indicative of resource depletion in the vicinity of these population centres for intensive use. These same reports indicate that the best wood for cooking was the thickest species (Traganum moquinii Webb ex Moq. in D. C. and Nicotiana glauca R. C. Graham), compared with thinner species used for lime kilns (Launaea arborescens (Batt.) Murb. being the species mostly used). Another use of longer exploitation that had an impact on the stability of the sediment was grazing. The inhabitants of the island, although mostly devoted to fishing, complemented its resources with the farms. In this regard, the sources indicate that each family had about four livestock (goats), although some possessed a higher number. The dedication of the inhabitants of the island to fishing required the services of a community shepherd attending to livestock, leading to grazing all over the island. The clearing of vegetation should also occur for another reason: the growing of dry farms in areas of the island allowed by the soil quality. This agricultural use continuously developed during the decades of the 1940s and 1950s, being gradually abandoned since the 1960s. 59 The sand moved from north to south, accumulating in certain places. In this regard, some testimonies refer to the existence of three large dunes: one in the village itself of Caleta del Sebo, leaning on a home in those years located in the periphery of Caleta del Sebo (nowadays this house is inside the village); another one was located in El Salado (about 200m from the village to the south); and, finally, the largest dune was behind the cemetery (about 500m from the village, to the southwest), and it was used to aggregate extraction. 1967–1987 The pressure related to the agrarian mode of production is greatly reduced, and thus, a gradual natural regeneration of vegetation begins, which will contribute to the stabilization of sands. The causes that led to this change are basically three: first, the decline in the number of people living in La Graciosa, because many of them migrate to Lanzarote to work in tourism or in the harbour of the fishing industry, in Arrecife; second, the arrival of gas for domestic fuel and thereby the lower demand of wood for homes, joint with the availability of electricity for 12 h a day, from 1977, and the final electrical connection since 1985; and third, the termination of use of vegetation as fuel for lime kilns, because, according to testimonies gathered, this activity ended up in 1967. The only use with an impact on aeolian dynamics that survives during this stage is farming, not having evidence of any variations in the number of cattle grazing during this stage. From 1987 The island is declared as a natural park together with the rest of the northern islands of Lanzarote and the ridge of Famara as stated by the Law 12/1987, of 19 July, Declaration of Natural Sites in the Canary Islands. This statement confirmed the declaration made by the Canary Islands Government a year earlier (Decree 89/1986, of 9 May). From that moment, the whole island is classified as a protected rural land, except Caleta del Sebo. The direct consequence is a change in land use, which also involves the housing of livestock. These changes in traditional agricultural uses, which had led to the alteration of aeolian sedimentary dynamics, favors the gradual stabilization of the sands (Figure 5). 60 Fig. 5 Evolution of the land use from 1730 to 2012 and relative pressure over vegetation. However, a new land use appears, which again alters this aeolian dynamics in a short period. Albeit generally less extensive, it is more intensive where it occurs. We refer to certain tourism-related activities, such as the extraction of aggregates for the building trade or track opening for the increasingly widespread use of motor vehicles, especially during the summer months. Recent Evolution of Land Covers (1954–2009) The aforementioned analysis is completed from the spatial point of view by comparing aerial photographs between 1954 and 2009 (Figure 6). With respect to the farm fields, Table III shows the agricultural area in 1954 and 2009. In 1954, most of these lands were abandoned. Oral sources indicate that cereals were cultivated only in the years when it rained, collecting most of the time much grain, which was finally sold in Lanzarote. The trend of abandonment extends to the present day, when only 5.25 ha is cultivated. 61 Fig. 6 Changes in land use from 1954 to 2009 (cartographic source: digital orthophoto from 2009, Canary Islands Government, production date: 2012). Table 3 Active and inactive farm surface at 1954 and 2009. Changes along these decades have led to a transformation of the land use of these plots and thus the agricultural landscape of the island. At present, only some plots located in the central area of the island are in use, linked to the existence of a water tank. Today, these plots have a number of water irrigation hours a week, which has changed their use, as well as the products obtained. Thus, production has changed from cereal dry farming to orchards. While in the 1950s the crop was a complement to food and surpluses were sold at the markets, at present, this is practically a ‘leisure’ activity. With respect to the urban side, it should be noted that the change in the main economic 62 activity on the island, which is now based on tourism, represents a significant growth of Caleta del Sebo village, which almost doubled its surface area from 1977 to 2009 (Figure 7). Despite this increase in the surface occupied, the pressure on vegetation has decreased given the change in fuel use, running from the wood burning to fossil fuels. Fig. 7 Urban expansion at Caleta del Sebo from 1954 to 2009. Another significant change is the expansion of the port, and both the passenger and freight traffic through it. Meanwhile, the network of roads and trails is intensified, and also the number of people and vehicles on it. Although living conditions have improved and the island has secured a constant supply of water and energy, some environmental problems associated with this change in the economic model are detected: deterioration in some areas by the extraction of building trade materials and difficulties in the management of solid waste or wastewater discharges, among others. Some recent steps (closing of landfills, regulation of authorized roads, cleaning campaigns, etc.) have helped to reduce the environmental problems described previously. 63 Discussion The evolution and current status of aeolian sedimentary systems depend directly on the existing environmental conditions around them, especially those related to climate (Jackson & Cooper, 2011). Similarly, such evolution depends on human activities that developed in them and/or around them (Jackson & Nordstrom, 2011). Aeolian sedimentary systems in La Graciosa are the result of special conditions that link these two sets of processes. So, first, we must attend to the arid nature, as performed with the rest of aeolian sedimentary systems in the Canary Islands (Cabrera-Vega et al., 2013). This determines a potential sand mobility greater than that produced in aeolian sedimentary systems at temperate regions. The xeric shrub vegetation stabilizes the soil, and occasionally, when it rains, seasonal herbaceous species grow for short periods. Second, there is a direct relationship between land uses developed on the island and the stability or instability of their aeolian sand fields. In this regard, the results of this research indicate that during the first third of the 18th century, the vegetation cover stabilized the sedimentary substrate. In fact, for that period, before 1730, there are not any documented evidences that suggest altering aeolian sedimentary dynamics by sand remobilization. Considering this information, we estimate that the pressure exerted on the environment was limited, as well as discontinuous in time. We therefore consider that during this period the stability of the sand should be significant in the island. However, human occupation of the island, from those dates, implemented activities of the traditional economic model (grazing, firewood extraction, etc.). So, during this stage (1730–1880), the pressure on the environment, although regulated and limited, surely affected the stability of the sediment, due to the permanence of a larger number of animals and shepherds than in the previous stage and throughout the year. In the next stage, this trend of increasing pressure over vegetation continues, so we can estimate that during this period (1880–1943), there was a significant increase in the remobilization of sands. This same trend has been confirmed for the next phase (1943– 1967), when it can be assumed that at some point the vegetation has almost disappeared from large parts of the island, thus making possible the remobilization of sand by wind. In this regard, some oral testimonies indicate that the island became ‘totally bare’. This fact could be the result of the location of the last lime kilns, which were moved to ‘still non-exploited zones’ by the lack of vegetation in regular wood sources. Another important reason that led the island to that situation was an increment in the number of animals. Assuming an average of four heads of animals per house, between 1940 and 1970, the number of goats grazing on the island increased continuously from 368 (92 houses in 1940) to 680 (170 houses in 1970). To these, an unknown number of donkeys and camels, common animals in farming, must be added. Moreover, it has to be considered that also during this period there were sand mining, as this is a necessary resource for mixing mortar in buildings. Therefore, the consequence of these pressures of land use on vegetation and sand had to be the modification of aeolian sedimentary 64 dynamics, producing sand remobilization and southward transport due to effective wind action. As one contemporary individual described, the island became ‘like a bald man head’. However, this trend was reversed after 1987, and it can be estimated that the pressure diminished to levels of 1730. Figure 5 shows the evolution of land uses as well as the relative pressure that they should have on the vegetation of the island and therefore on sedimentary dynamics. Thus, as raised in the initial hypothesis of this study, the activities related with the use of woody plants are the main factors that produced the alteration of these systems. Nevertheless, in temperate regions where permanent or semi-permanent herbaceous cover stabilizes these systems, grazing is a major cause for destabilizing these systems (Granados Corona et al., 1988; Kutiel et al., 2004; Levin & Ben-Dor, 2004). In this case, this can be checked by facing the first stage, when only seasonal herbaceous are used, against the following stages, when there were permanent human settlements and thus a continuous use of woody plants. The increase of the population and, therefore, the pressure on the vegetation produced a greater intensity in the alteration of sedimentary stability. The system recovered as soon as the pressure on the vegetation ceased. Hence, the change of the economic model in La Graciosa, with its legal protection as a natural area, led to the disappearance of the primary activities involved in their aeolian sedimentary systems. The result was the recovery of the vegetation cover, hence stabilizing the sand again, a phenomenon also studied in other aeolian systems (Granados Corona et al., 1988; Kutiel et al., 2004; Levin & Ben-Dor, 2004; Hoffman & Rohde, 2007). Regarding the methodology used, some issues that this work try to overcome must be addressed. First, historical sources generally impose temporary barriers because of the difficulty to work with pre-19th century documents. Therefore, most of the historical ecology studies span as much as the past 200 years (Szabó & Hédl, 2011). Nevertheless, this work has explored times previous to 1800, such as few other works, like for example Santana Cordero et al. (2014). Second, our methodology links oral history information and GIS in a successful way; this process has also been tackled by other studies, such as that of Trueman et al. (2013). Third, information integration has played a key role in the final interpretation of the results (Trueman et al., 2013). Conclusions From a historical perspective on traditional land uses, we consider that the alteration of arid aeolian sedimentary systems is mainly induced by the removal of woody vegetation that stabilizes the substrate. Thus, the main human exploitation activities that caused depletion of the vegetation cover are related to the extraction of wood for homes, bakeries and buildings (roofs and lime kilns). To these should be added the harsh weather conditions that make vegetation development difficult in arid environments. 65 However, in temperate regions, cattle grazing use eliminates herbaceous vegetation cover, which is what stabilizes the sandy substrate. Acknowledgement This work is a contribution to the projects CSO2010-18150 and CSO2013-43256-R funded by the R&D + I (innovation) Spanish National Programme, cofinanced with FEDER funds. It has been made possible by a contract of the Organismo Autónomo Parques Nacionales of Spain. Leví García Romero and Aarón Santana Cordero develop their research within the ULPGC Funding Programme. Authors would like to thank Antonio I. Hernandez-Cordero for his comments, especially on vegetation species in arid dune systems, and Lluís Gómez-Pujol and two other anonymous reviewers for their comments, which have allowed us to improve the manuscript. Likewise, we would like to thank the inhabitants of La Graciosa and an environmental agent involved in this research. References Alphan H (2012) Classifying land cover conversions in coastal wetlands in the Mediterranean: pairwise comparisons of Landsat images. 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Journal of Historical Geography 36:194–204 73 Specific objectives of this research are the following: (1) to identify and characterize the land uses that occurred in the study period (1834–2012), as this is the period when human activities that led to the demise of this dune system were carried out; (2) to analyze the underlying socioeconomic forces that boosted the changes; and (3) to establish a consistent methodology able to work and integrate multi-source information. Study area The Guanarteme arid dune system was located in the northeast of the island of Gran Canaria (Canary Islands, Spain), covering the isthmus that connects the island of Gran Canaria with the volcanic complex of La Isleta, located to the NE. It had an area of 243.7 ha (2.44 km2) and the dynamics of the dunes were conditioned by the prevailing winds in a NW-SE direction, resulting from changes in the direction of the trade winds, mainly from the NE, by the interposition of La Isleta (Fig. 1). Fig. 14 Study area: 1) tombolo; 2) High sedimentary terrace. The traveller Olivia Stone, who visited Gran Canaria between1883 and 1884, provides a description about this dune field as follows: ‘the sand is disposed in hills, valleys, small tablelands, and plateaus, over which when one begins to walk their extent seems to be much greater than would be supposed from a distant view’(Stone, 1887). The system consisted of two distinct areas from a topographical point of view: on the one hand, the tombolo (also known as the ‘Guanarteme isthmus’), consisting of a flat 74 surface formed by Pleistocene and Holocene sedimentary materials underlying the aeolian deposit; on the other hand, a Pleistocene wedge-shaped sedimentary terrace of about 50 meters height in the south. In terms of dynamics, it was an arid transgressive dune system, whose sand was sourced from the beach in the northwest (Las Canteras beach), crossed the tombolo as sand ridges and returned to the sea along the east coast (Las Alcaravaneras beach) (Santana Cordero et al., 2014). Currently, the only one elements of this system that can still be observed are the sand input and output areas, the beaches of Las Canteras and Las Alcaravaneras, respectively. The rest of the dune field has been entirely occupied by the city of Las Palmas de Gran Canaria. From an economic point of view the dune field was, until the late XIX century, an unproductive land, a marginal area regarding land use. Sometimes it was even a handicap to the development of the activities that took place around it. Thus, during high wind periods, sand invaded the agricultural fields located to the south of this aeolian sedimentary system. Anyway, this system represented a potential area of growth for Las Palmas de Gran Canaria, which developed its urban fabric from the mid-XIX to the mid-XX century, by spreading from the historic old town to join up with La Isleta. Regarding the political context, changes in the national policy system throughout the study period had an effect on urban planning policies. From the 1830s to the Spanish Civil War (1936–1939), several legislative reforms affecting urban planning were introduced, promoted by various political regimes. Then, from 1939 to1975 during Franco’s regime, urban planning changed again. During the dictatorship, patronage and corruption dominated urban planning and in most Spanish cities urban development plans consisted of poor quality draft proposals, at least until the 1950s (Cardesín, 2015). At the local scale it should be mentioned that the first urban plan for the city was made by Laureano Arroyo and dates back to 1898. This plan increased the available area for building, although at this moment the expansion of the city was already under way (Cáceres, 1983). Therefore, the city’s expansion was carried out in absence of rational urban planning nor, of course, any regulation in coastal management. As a result, by 1940, the urban occupation of much of this territory was a fact: ‘This miracle of transformation of sand to orchard, of desert to one of the densest present-day urban agglomerations, has occurred and is still occurring right under our eyes. 40% of the urban extension of Las Palmas currently occupies land that belonged entirely to the domain of the sands and dunes until the last years of the last century’ (Miranda Guerra, 1940). Materials and methods 75 Sources In this study the following sources have been used: Bibliographical references Encompasses from scientific papers to local publications about the study area. These play a determining role in the entire paper, since they provide specific information about the landscape as well as the international scientific context. Historical maps 9 historical maps from different dates were collected from various historical archives and digital platforms. The use of these documents has been of great interest because they show the different land uses developed in the study area and its environs over a century (from 1834 to 1938), when the system dynamics were natural and semi-natural (Fig. 2). Table 1 contains the details of all these maps. Table 4 Basic data from historical maps collected. Abbreviations: Dir. Hidrografía: Dirección de Hidrografía; S.G. Madrid: Sociedad Geográfica de Madrid; BNE: Biblioteca Nacional de España; BNF: Bibliothèque Nationale de France; TNA: The National Archives (UK). Aerial photographs and orthophoto These allow direct observation of the study area in the years 1949 and 1954. These images were obtained by the Air Force of Spain. The frames used in this research were acquired from the Centro Cartográfico y Fotográfico del Ejército del Aire de España (Cartography and Photography Centre of the Air Force of Spain) (CECAF, 1949, 1954). Their approximate scales are 1:1085 and 1:2650, and their spatial resolution 0.38 and 0.73 metres, respectively. Once the corresponding geometric adjustments were performed on these documents, it was possible to make accurate measurements. These documents have been particularly useful in identifying sand mining areas during the study period and the analysis of their evolution during the five years between the two flights. Conventional photographs These were obtained from the catalogue of the Fundación para la Etnografía y el Desarrollo de la Artesanía Canaria (Foundation for Ethnography and Development of Canarian Craft) (FEDAC). A set of 20 photographs was examined in order to identify 76 certain elements in the territory and/or confirm their existence and characteristics according to the information from other sources. Oral sources These sources have been a key element of this study in the characterization of the use and exploitation of the study area in the second third of the XX century. Their application has been of great interest for the study of different aspects that have been addressed in this work. Moreover, oral sources are necessary to validate the information derived from other historical sources and/or fill gaps in the information (Robertson and McGee, 2003). The importance of oral sources in this study is motivated, in part, by the lack of information about the study area, it being an area that has attracted little economic interest, similar to what happened in other places (McAllister, 2008). Oral sources have been constructed through interviews with 10 elderly people who still remember the Guanarteme dune system. Their average age is 82 years, ranging from 66 to 89 years. Each informant is identified by the letter I and a number, in the form I1, I2, etc. throughout the text. Interviews in this research were designed according to the definition of Fogerty (2005): ‘a semi-structured conversation between two people’ (the interviewer and narrator). A script that contains the topics of interest in the conversation, old photographs of the study area and pictures of plant species were used in order to correctly identify certain elements of the landscape. Data analysis Document analysis This analysis has been conducted according to Bowen’s conception: a procedure that ‘entails finding, selecting, appraising (making sense of), and synthesising data contained in documents’ with information of interest (Bowen, 2009). To do so, this analysis has involved, mainly, bibliographical and oral sources. On the one hand, scientific literature has been useful to put our investigation into an international scientific context regarding the situation of coastal environments of the world, to the studies of their human impacts, and to historical ecological research. On the other hand, some publications treating local issues and oral sources have constituted the material to obtain part of the results of this paper. Cartographic analysis Interpretation of historical maps has been made using drawing software, since the geometric characteristics of these documents do not allow us to treat them with GIS (see Section 5). However, these maps have spatial coherence, aside from the 1895 map which was excluded from the analysis. This fact has allowed us to detect landscape elements in the maps. Thus we have obtained 9 scenarios (one from each map) that show the changes in land uses from 1834 to 1938. The boundaries of the system 77 (coastlines) are taken from the 1882 map; this is for two reasons: first, the accuracy of its coastlines and, second, because the rest of the maps fit quite well within these boundaries, which facilitates the superposition and change analysis. On the other hand, the two aerial photographs have been analyzed with GIS, through which areas of aggregate extraction were identified for mapping. Additionally, the calculation of their extension in both aerial photographs available was carried out. Finally, the comparison between the latter aerial photograph (1954) and the current orthophoto (2012) has been made in order to illustrate the complete disappearance of the system. With this information a map that identifies and integrates land uses for the XX century was made. Fig. 2 Historical maps used. 78 Results Before 1900 Agriculture This use was located in the SE part of the dune system in the 1853 map. It constituted a quasi-rectangular parcel, or a group of parcels, that evolved through time changing in size and shape. It should be noted that this activity was developed along a sector of the east coast on active zones of the system. The type of crop was vegetables, generally on large plots, as some pictures show. Urbanization Settlements and related infrastructure were developed through the XIX century. In the 1834 map, the study area was free of human elements, excluding three unidentified landmarks. In the 1853 map a new settlement appears (La Isleta) (Fig. 3), although it is located outside of the sandy surface. In 1879, La Isleta grows and a new road parallel to the eastern coastline is constructed. Additionally, two groups of unidentified elements appear, one beside the crop parcels and another one where today the Guanarteme neighbourhood is found. In the period 1882–1885 La Isleta and the unidentified elements group of Guanarteme grew, with new features appearing: two telegraph houses (one close to each coastline) and new port infrastructures. The 1894 map does not represent all of the land uses that already existed (especially in the south of the area), but it shows the evolution of a road network and the growth related to the occupation of the eastern coast. Finally, the 1896 map clearly shows the establishment and advancement of an incipient urban fabric, that develops from north to south (Fig. 4). From 1900 Agriculture Agricultural land use continued to be located in the SE part of the dune system as evidenced by oral sources and aerial photographs. Nevertheless, this activity was reduced by the urbanization process; by the mid-XX century it was relegated to the Estadio Insular area and the northern part of Ciudad Jardín (see Fig. 3). In this regard, informant I2 talks about the existence of tomato farms in Ciudad Jardín, noting that ‘there was no longer any sand.’ The informant refers to an area where there were already marked plots for construction and/or cultivation, after the sand was removed. On the other hand, in aerial photographs (especially in 1949) there is agricultural activity on the high sedimentary terrace, which had fallen into disuse, that is also referred to in the testimony of I1, who explains that ‘all La Minilla was a farm’. This fact is confirmed by the current name ‘Finca de La Minilla’ (Farm of La Minilla) 79 observable in the cartography regarding this area. We conclude that this use was recessive during the period when the dune system disappeared. So, on the one hand, it seems that large extensions are lost in some areas, especially in the traditional farming areas; on the other hand, a small gain associated with new residential areas is produced. Fig. 3 Urban evolution of the city of Las Palmas. Sites and facilities of reference: A. Estadio Insular, B. headquarters, C. Bernardo de La Torre Street (end), D. Mesa y López High School, E. Loma del Ingeniero Salinas (Engineer Salinas’ hill). Urbanization 80 In this period the consolidation of the urban fabric can be observed, as well as the gradual disappearance of the dune field. Also, the port infrastructures are seen to expand into the dunes. In addition to the urbanization, and according to some testimonies, some areas of the dune field at one time fulfilled the function of providing shelter to ‘homeless’ people. This is determined by the ‘marginal’ character of the dune field in the context of the city of Las Palmas. The period when this spontaneous settlement occurred has been identified by informant I1 in the 1950s. In this regard, this informant remembers ‘I saw the Moors living there. The Moors came [. . .] made their little houses and stayed there [. . .]. And poor people from here also lived there in shacks.’ In this regard, informant I2 highlights the coexistence of groups of poor local people, economically disadvantaged, with groups of North Africans. They all had very poor living conditions in common: ‘that settlement was an isolated thing there, where those people lived there. [. . .] Unfortunately I must say it. [. . .] That was a situation of terrible poverty, that area there [. . .]. Few were those who came out of there to go somewhere.’ The informants I6, I7 and I8 comment that ‘it was like another world, there was no relationship between the locals and the Moors who lived in the camp.’ From the previous two paragraphs we can highlight two fundamental ideas: first, the dune field was, during those times (coinciding with the end of its period of operation) and in specific areas (areas that had not been urbanized), a place with little economic value in agricultural terms; on the other hand, it was considered to be a marginal area from the social point of view. Still, it was a resource for the disadvantaged people who settled there. Regarding the spatial distribution, these settlements have a certain clustering shape. On this last point, the informants identified several sites for these slums: occupying the western and central parts of the dune field (currently Mesa y López High School— Estadio Insular—Aviation Headquarters) (I1); at the end of the current Bernardo de La Torre street (I2 and I6); between the Santa Catalina and Guanarteme neighbourhoods (I2); at the confluence of the current Mesa y Lopez Avenue with Guanarteme (I2) and between the Estadio Insular and Central Market (I9) (Fig. 2). It seems that this use did not have any influence on the disappearance of the Guanarteme dune field. Rather, it was a use ‘adapted’ to the mobility of the system itself, without permanent structures, so that settlements could move around according to the environmental conditions (Fig. 5). Recreational use According to the informants, the study area sustained some recreational activities. Firstly, the dunes were a very important place for the amusement of children. In this 81 regard, informants I3, I4 and I5 describe how one of the main activities was to climb the dunes and then jump off them, then back up, and so on. There were other games, such as building small houses with ‘walls’ of sand or climbing a dune to see the train passing by (informant I4), which apparently was an attraction for children. They also played with wagons at the brickyard (informants I6, I7 and I8). Secondly, this area was also used by poor families as a place to go on Sundays. Informant I3 remembers that, at least until the mid-1940s (1945–1946): ‘We went to the sands only on Sundays, because we did not have anything else. Nothing else [. . .]. We took off our shoes, we put them down, then climbed, climbed, jumped and threw ourselves up and down . . .’ Fig. 4 Land uses evolution during the XIX century. These maps show agricultural parcels (dotted lines), buildings (black/white-filled polygons), roads (lines) and unknown elements (dots). The grey shaded area corresponds to the dune system extension. 82 Fig. 15 Land uses evolution in the first third of the XX century. These maps show buildings (white and black-filled squares) and roads (lines). Third and finally, it is worth mentioning that the last existing dune in this system was supported on the Engineer Salinas’ hill associated with the high terrace. It also had recreational use, since there were people who accessed to the top of the dune to see football matches at the Estadio Insular which was just below. On this question, informant I2 said that this was a military zone and that the military granted access to the dune in order to allow them to see the football games. Then he says: ‘. . . I remember going there in the 1950s to see football games, just sitting there in the sand [. . .]’ (Fig. 6). Fig. 16 Children playing in the dunes (left); the dune used as a stand to see the football matches (right) (Vittet, 1966 (left), unknown author and date (right), FEDAC, 2015). Aggregate extraction We estimate that this activity was developed massively from 1883, with the operations to build the Port of La Luz, given that the construction of this infrastructure required material as a filler. The port construction and its subsequent operation stimulated various economic activities of relevance in the context of the Archipelago. The port 89 References Anderson NJ, Bugmann H, Dearing JA, Gaillard MJ (2006) Linking pelaeoenvironmental data and models to understand the past and to predict the future. Trends Ecol Evol 21:696–704 Ariza E (2011) An analysis of beach management framework in Spain. Study case: the Catalonian coast. 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Conclusion 1.1: this dissertation makes a methodological contribution to the assessment of the reliability of sources. The method developed consists of an application of a source critical approach on the basis of the assessment of their characteristics and their contribution to the study. The variables chosen for this evaluation are: 1) the type of source, 2) the detail level and/or resolution of the information provided, and 3) the analyses that could be applied. Conclusion 1.2: the consolidation of the oral sources in the development of this dissertation has been a key question. Thanks to these sources, we are able to better describe and analyze the physical features of these systems, as well as the social reality that exists in and around them. Conclusion 2: Important findings. Conclusion 2.1: from a historical perspective on traditional land uses, we consider that the alteration of arid aeolian sedimentary systems is mainly induced by the removal of woody vegetation that stabilizes the substrate. This activity has the capacity to change the dynamics of the systems. This is the case that we observe in the sedimentary systems of La Graciosa island. Conclusion 2.2: aggregate extraction (sand mining) had the most serious consequences for the disappearance of the Guanarteme dune system, by the surface affected, the intensity it developed, and the impact it generated. Conclusion 2.3: we find that an important political decision on the construction of a key communication infrastructure (a new harbor in the XIX century) is the origin of the major landscape change process that occurred at Guanarteme. Prospects Prospect 1: the creation of an archive of environmental memory for the Canary Islands. 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