Riparian or phreatophile woodland and shrubland vegetation in the Central Chilean biogeographic region: phytosociological study

243Mediterranean Botany 40(2) 2019: 243-258 Mediterranean Botany ISSNe 2603-9109 https://dx.doi.org/10.5209/mbot.63049 Riparian or phreatophile woodland and shrubland vegetation in the Central Chilean biogeographic region: phytosociological study Javier Amigo Vázquez1, Lorena Flores-Toro2 & Verónica Caballero-Serrano3 Received: 21 January 2019 / Accepted: 10 June 2019 / Published on line: 7 November 2019 Abstract. The Mediterranean territory in Chile is an extensive area whose natural vegetation has suffered the impact of manmade activities far more severely than anywhere else in the country. Its northernmost section (the Atacama and Coquimbo regions) is characterised by ombroclimates that range from ultra-hyperarid to arid, and by highly irregular river courses with limited spaces for phreatophilic vegetation that have been exploited by humans as fertile farmlands. However, in the river valleys of the Central Chilean biogeographic province, where the ombroclimate is at least semiarid, there may be permanent watercourses that drain from the Andean mountain range towards the Pacific Ocean that contain representations of riparian or phreatophilic vegetation linked to riverbanks or alluvial terraces, in spite of the inevitable human influence. We studied the most conspicuous plant communities with the most highly developed biomass in these riparian environments, namely willow stands dominated by Salix humboldtiana and accompanied by some autochthonous woody species, in order to clarify their floristic composition and their correct ordination within the syntaxonomy of Chilean vegetation. The data collected suggest the existence of a phytosociological association: Otholobio glandulosi-Salicetum humboldtianae ass. nova, as the majority association in the Central Chilean province. Another possible association which replaces this (Baccharido salicifoliae-Myrceugenietum lanceolatae prov.) is also proposed in the transition to a humid ombroclimate and Temperate macrobioclimate. The floristic contents of these Chilean communities are compared with other associations dominated by Salix humboldtiana described for other territories bordering Chile: Argentina, Bolivia and Peru. However, given that they are all located in a Tropical macrobioclimate and their companion flora is therefore clearly different from the flora present in the Chilean communities, we propose the creation of a new phytosociological class to include these syntaxonomically: Mayteno boariae-Salicetea humboldtianae class. nova. This work also ascribes the association Tessario absinthioidis-Baccharidetum marginalis (representing a prior dynamic stage to Otholobio glandulosi-Salicetum humboldtianae) to the class Tessario integrifoliae-Baccharidetea salicifoliae. Keywords: Baccharis salicifolia; Mediterranean rivers; Salix humboldtiana; Syntaxonomy; Willow woodlands. Los bosques y comunidades arbustivas freatófilos riparios en la Región biogeográfica Central Chilena: un estudio fitosociológico Resumen. El territorio mediterráneo de Chile constituye una amplia superficie cuya vegetación natural ha sufrido el impacto antrópico como ninguna otra en el resto del país. Su tramo más septentrional (regiones de Atacama y Coquimbo) caracterizada por ombroclimas de ultrahiperárido a árido presenta unos cursos fluviales muy irregulares y los reducidos espacios para vegetación freatófila han sido aprovechados por el hombre como fértiles terrenos de cultivo. Pero en los valles fluviales de la provincia biogeográfica Chilena Central, cuando el ombroclima es al menos semiárido, ya se pueden presentar cursos de agua permanente que drenan desde la cordillera andina hacia el Pacífico y en los que se pueden encontrar representaciones de la vegetación riparia o freatófila ligada a márgenes fluviales o terrazas aluviales, a pesar de la inevitable influencia humana. Se estudiaron las comunidades vegetales más desarrolladas en biomasa y más conspícuas de estos ambientes riparios, que son las saucedas dominadas por Salix humboldtiana al que acompañan algunas especies leñosas autóctonas. Los datos recopilados sugieren la existencia de una asociación fitosociológica: Otholobio glandulosi-Salicetum humboldtianae ass. nova, mayoritaria en la provincia Chilena Central, más otra posible asociación (Baccharido salicifoliae- Myrceugenietum lanceolatae prov.) que sustituye a la anterior entrando en ombroclima húmedo y bioclima Templado. Se comparan los contenidos florísticos de estas comunidades chilenas con otras asociaciones dominadas por Salix humboldtiana que se han descrito de otros territorios vecinos a Chile: Argentina, Bolivia y Perú. Pero dado que todos ellos se sitúan bajo bioclima Tropical y por ello su flora acompañante es claramente diferente a las comunidades chilenas, se propone la creación de una nueva clase fitosociológica para encajar a éstas sintaxonómicamente: Mayteno boariae-Salicetea humboldtianae classis nova. Asimismo, en este trabajo se adscribe la asociación Tessario absinthioidis-Baccharidetum marginalis (que representaría una etapa dinámica previa a Otholobio glandulosi-Salicetum humboldtianae) a la clase Tessario integrifoliae-Baccharidetea salicifoliae. Palabras clave: Baccharis salicifolia; Ríos mediterráneos; Salix humboldtiana; Saucedas riparias; Sintaxonomía. 1 Laboratorio de Botánica, Facultad de Farmacia, Universidade de Santiago de Compostela. E-15782 Santiago de Compostela (Galicia, España). E-mail: javier[email protected] 2 Facultad de Ecología y Recursos Naturales, Universidad Andrés Bello, sede Viña del Mar, calle Quillota 980, Viña del Mar, Chile. 3 Faculty of Science, Escuela Superior Politécnica de Chimborazo, Panamericana Sur 1 ½ km², Riobamba, Ecuador. PHYTOSOCIOLOGICAL NOMENCLATURE SECTION 244 Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 Introduction The potential natural vegetation of Chile is reasonably well known, and has been disseminated via several successful mapping approaches (Gajardo, 1994; Luebert & Pliscoff, 2006a, 2017; Amigo et al., 2017). One of the mostly widely accepted opinions among authors is the high degree of anthropisation and degradation of the natural vegetation in the territory in Central Chile, coinciding with the regions of greatest population density or the highest agricultural yields. The adjoining regions of Valparaíso, Metropolitana, O’Higgins and Maule all share these characteristics and the natural ecosystems in these places are all in clear regression. With the possible exception of high-mountain formations (high-Andean scrublands, hygrophilous pastures or chionophilous communities), the sclerophilous or deciduous woodland formations characteristic of the Mediterranean climate can be signalled as being the most endangered, despite the fact that this Central Chilean area lies within a major biodiversity hotspot (Arroyo et al. 2004). It should be noted that there have been different opinions regarding the concept of Mediterranean climate (Blumler, 2005) which have led as a result to the consideration of a larger or smaller territorial area in Chile depending on the case; this diversity of criteria for the Chilean Mediterranean is concisely described in Luebert & Pliscoff (2006b), who ultimately accept the map delimitation contained in the models of Rivas-Martínez (2004) as being the most appropriate, for which there is a somewhat more updated version in Rivas-Martínez et al. (2011a). We have used this most recent version as a reference for the present work, although these authors differ slightly (Luebert & Pliscoff, op. cit.; Rivas-Martínez et al., op.cit.) in their definition of the southernmost limit of the Mediterranean Macrobioclimate. Riparian woodlands must be included in the woodland types that form part of the group known as “Chilean Mediterranean woodlands with a very reduced extension”. The spaces previously covered by these woodlands have suffered massive deforestation and exploitation throughout the whole of Mediterranean Chile, and this phenomenon is even more pronounced in drier climates, as the river valleys are the main –and almost always the only– option for producing the crops required for any human settlement. The part that is climatically least affected by drought, which we identify with the Mediterranean pluviseasonal bioclimate (sensu Rivas-Martínez et al., op. cit.), is home to a woodland type presided by laurisclerophilous mesophanerophytes characteristic of streams and tributaries within the thermomediterranean thermotype that do not –or only scarcely– dry out. This woodland receives the name Beilschmiedio miersi-Crinodendretum pataguae, and has tall trees with microphanerophytes, creepers and diverse herbaceous plants in its understorey, and a notable set of associated species which connects it with the alliance Cryptocaryion albae (Lithraeo causticae- Cryptocaryetea albae). Amigo & Flores-Toro (2012) described some samples of its floristic composition (average richness 25 species/relevé) although it had previously been assessed as a community of significant rarity. However, there are other types of autochthonous riparian tree and shrub formations that have attracted very little interest from geobotanists in Chile for reasons that will be described below, but which play a crucial role in protecting the riverbanks and the fertility of the sediments that they help to retain. Oberdorfer (1960) was the first to call attention to them, when he found scrubland formations on the floodplains of major rivers on banks with accumulations of gravel, or gravel and sand, sometimes extending for several kilometres along the length of the riverbank. Although he collected scarcely four relevés in these scrublands, he noted their ecological position, which he assessed as a vicariant of the European scrublands classified within the class Salicetea purpureae; continuing this parallelism he assigned a provisional association name to this single table of four relevés: Tessario absinthioidis-Baccharidetum marginalis, and proposed their syntaxononomical affiliation to a possible Salicetea chilenae (sic), also as a provisional name. Although the association was defined as a community of shrubs measuring barely 1–2 m in height, he acknowledged the participation of other taller woody species such as Otholobium glandulosum and Salix humboldtiana. It is also worth noting that the companion species in this table of relevés included exotic tree species whose role as invasive elements in the riverbeds of the Chilean Mediterranean rivers has continued to grow to the point that in many sections they have displaced this natural vegetation. To maintain Oberdorfer’s original reasoning (op. cit.), we will continue to call this natural vegetation “Salicetea chilenae” until we propose a valid name according to the International Code of Phytosociological Nomenclature (Weber et al., 2000; Izco & Del Arco, 2003), which will be addressed in the Discussion section. We have explored and sampled a large part of the Mediterranean territory in search of well conserved examples of these willow/shrub formations, avoiding wherever possible the riverbanks invaded by exotic trees, which is the first risk factor for this type of vegetation as a result of the pressure from anthropisation. The communities they form in Chile are apparently quite well defined, but the task of placing them within a syntaxonomical hierarchy is more complex given the wide territorial range of some of their characteristic species in South America. Study area The territory covered extends through the centre of Chile from the south of the Coquimbo region to the south of the Bio-Bio region, between latitudes 31º 44’ and 37º 49’ S; throughout this territory the studied samples were always located at low altitudes with extreme values of between 25 m and 820 m asl. The dispersion of the sampling can be seen in Figure 1, which shows the absence of specimens in non-Andean areas between latitudes 33º and 36º south, as these 245Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 are areas that are intensively used for agriculture and where the river networks have undergone a very serious degree of anthropisation. Biogeographically it is part of the Middle-Chilean Patagonian region and the Central Chilean province, following the classification of Rivas- Martínez et al. (2011b), which is the model we will use for all the biogeographic units mentioned in this work (see later on Figure 5). The northernmost samples are located at the limits with the desertic Mediterranean Chilean province which begins in the Choapa River valley and extends northwards; from this point the ombroclimate becomes generally more arid, in contrast to the semiarid character of the territory to the south of the river. At the southernmost limits of the sampling, in the Ñuble and Bio-Bio regions, some samples were taken on riverbanks at points located within the Valdivian- Magallanic biogeographical region, given that a little further to the south of parallel 36º the Chilean flank of the Andes, up to certain levels of its foothills, lies within the Temperate macrobioclimate. A A B B C D D Figure 1. Administrative map of Central Chilean territory showing geographical dispersion of river points where samples gathered in Table 1 were taken. The thick lines delimit the biogeographical provinces according to Rivas-Martínez et al. (2011b): A) Central Chilean. B) Mediterranean Andean. C) Desertic Mediterranean Chilean. D) Valdivian. Figure 2. Substrate heterogeneity on the riverbanks: always sand, but also gravels and rocks. Rio Claro, Tinguiririca tributary, O’Higgins region (34° 44′ S). Subhumid mesomediterranean thermotype. Figure 3. Typical landscape of a river in a broad valley with riverbank vegetation linked to smaller streams prone to dry out; the willow stand can be seen to be separate from the other phreatophilic scrublands. River Cachapoal, O’Higgins region (34° 22′ S). Dry mesomediterranean thermotype. Figure 4. Dense willow stand of Salix humboldtiana in a narrow valley. The abundance of the allochthonous herb Galega officinalis is significant. Rio Claro, Pangal tributary, O’Higgins region (34° 16′ S). Dry mesomediterranean thermotype. 246 Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 Riverbanks were sought throughout this entire territory with autochthonous willow/shrub formations located in rivers with a very variable flow: from small, with a width of barely 6 m between their banks (Estero Pupío, rel. 3, Table 1), to very large (400 m in the Itata River, rel. 20, Table 1). We visited the most important rivers in this territory, whose main reach or some of whose tributaries flow into the Pacific, and collected samples; the following rivers are thus represented: Choapa (with its tributaries Zapallar and Limahuida), Petorca (with Pedernal), Aconcagua, Maipo, Rapel (with Pangal and Tinguiririca), Mataquito (with Teno and Lontué), Maule (with Longaví), Itata (with Ñuble) and Bio-Bio (with Laja, Queuco and Bureo). Bioclimatically most of the localities can be assigned to the mesomediterranean thermotype, although the thermicity levels of all the sites in the Coquimbo region justify their attribution to the thermomediterranean thermotype, in common with some sites in the north of the Valparaíso region. However, as mentioned above, some southern localities can be assigned to the mesotemperate thermotype. There is an acceptable number of Mediterranean meteorological stations listed in Amigo & Flores-Toro (2017), in addition to the global data for all Chile in Luebert & Pliscoff (2006b, 2017). The ombroclimate covers the whole upward precipitation gradient known throughout this Central Chilean province: from the Choapa valley to the capital Santiago, almost all the stations have a semiarid character with some exceptions nearer the coast. Between parallels 33º and 34ºS there is a predominantly dry ombroclimate, and an absolute prevalence of the subhumid to the south of this latitude. This refers to altitudinal levels of less than 1000 m asl, which is where most of the human population is located (and the meteorological recording stations); in this case it also coincides with the preferences of “Salicetea chilenae” formations, as no examples of willow stands were found above this limit. The relevés belonging to localities with a Temperate macrobioclimate can probably, without exception, be assigned to a humid ombroclimate. Species such as Salix humboldtiana are known to have a very broad distribution, not only towards northern Chile, but also throughout tropical South America as far as Mexico, and in Chile itself it is known from Arica to Malleco in Araucanía (San Martín & Véliz 2006). However, in the arid ombroclimate (that is, also including hyper-arid and ultra-hyper-arid values) that covers all Chilean regions from the Peruvian border to the southern Coquimbo region, the anthropisation of the river courses is extremely intense, and the presence of these tree formations with varying degrees of naturalness can be said to be incidental. We therefore did not attempt to cover this vast territory due to the scant results to be yielded from our efforts. Nor did we work in the Araucanía region as the Mediterranean/temperate limit prevails in the northern section of this region even at the level of the Central Depression. Northern Araucanía also marks the absolute limit of the southern distribution of Salix humboldtiana in Chile (Hauenstein et al., 2005) so the presence of autochthonous willow formations at these latitudes can be assumed to be scarce and of little interest. 14.1 12.4 13.8 13.6 15.4 16.1 16.2 Figure 5. Biogeographical map of South America sensu Rivas-Martínez et al. (2011b). The rectangle indicates the Central Chilean province and the ellipses denote the tropical areas that contain the willow communities shown in Table 3. Biogeographical provinces concerned (numeric codes are the same as in the map from Rivas-Martínez et al. (op.cit.): 12.4: Southwest Amazonian; 13.6: West Cerrado; 13.8: Benian; 14.1: North Chacoan; 15.4: Bolivian-Tucumanan; 16.2: Hyperdesertic North Peruvian; 16.2: Hyperdesertic Tropical Chilean-Arequipan. 247Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 Table 1. Otholobio glandulosi-Salicetum humboldtianae ass. nova (rel. 1−22) Baccharido salicifoliae-Myrceugenietum lanceolatae ass. nova prov. (rel. 23−26) Riverbank composition: R/r = rocks (> 50 cm); G/g = gravel (< 50 cm); S/s = sand; L/l = silt. Capitals indicates abundant, lowercase scarce. (x) = xenophytic plant Altitude (m asl) 760 280 130 780 620 820 820 675 135 715 700 725 150 25 415 450 290 345 36 40 560 410 535 470 530 560 Area (m2) 120 150 100 80 80 100 80 100 75 200 160 200 100 80 200 100 100 125 200 160 100 120 120 100 75 240 Slope (º) < 5 0< 5 0< 5 < 5 0< 5 < 5 0 0 0 0 0 10 < 5 5 0 < 5 30 < 5 < 5 0< 5 0 5 Cover E1 (%) 90 100 95 100 100 95 80 100 95 90 100 95 80 90 75 75 95 60 70 40 80 95 95 100 100 50 High tree layer (m) 2−8 2–8 2–4 4–7 7–8 3–8 2–8 2–7 3–7 1–7 1–6 1–8 3–5 2–6 1–6 1–3 2–6 1–4 2–7 1–4 2–6 1–6 1–5 2–4 2–5 1–2 Riverbank composition gsL gSl rgsL rGsl gSL RgSl RgSl GSl SL rGsl rGSl rGSl sL Sl rGS rGSl GS Rgl Sl RSl rGSl GsL RGs RGsl GSL RGS Latitude 31º44 31º44 31º51’ 31º53’ 31º56’ 32º08’ 32º08’ 33º01’ 37º42’ 34º16’ 34º44’ 34º59’ 36º05’ 36º25’ 36º33’ 37º20’ 37º18’ 37º49’ 37º 18’ 36º35’ 36º38’ 35º54’ 35º51’ 36º14’ 36º16’ 36º38’ N. species 23 14 15 14 15 16 22 16 21 15 17 17 11 24 27 28 21 21 14 14 21 27 20 23 23 17 Relevé N. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Characteristics Otholobium glandulosum 4 2 1 3 3 + 1 4 . 2 3 . + 2 2 3 3 3 1 2 1 4 4 2 1 . Salix humboldtiana 4 3 . 4 4 3 4 2 4 5 5 4 4 4 3 2 1 . 4 2 2 1 . . . . Equisetum bogotense 1 2 . . 3 1 + 1 . . 1 1 . . 1 + 1 . . + 1 1 + . 1 . Aristotelia chilensis + 1 . . 1 . . . . . + . . . + . . . . . . 3 + 1 + . Maytenus boaria . 3 1 2 . 1 . + . . 1 . . . . . . . . . . + . 1 . . Stemodia durantifolia . . + . . r 1 . . 1 . . . + r 1 . . . . . . . . . . Escallonia myrtoidea 1 . . . . + . . . + + . . . . . . . . . . + 1 . . . Rhodoscirpus asper . . 1 . . + + + . . + . . . + . . . . . . . . . . . Tessaria absinthioides + 4 3 2 . . . . . . . 2 . . . . . . . . . . . . . . Discaria trinervis 1 . . . 1 . . . . . . . . . . . . . . . 2 . . . . 1 Luma chequen 2 . . . 1 . + 1 . . . . . . . . . . . . . . . . . . Myrceugenia exsucca . . . . . . . . . . . + 1 . . . . . . . . . . . . . Northern Variant Baccharis confertifolia 2 4 4 1 4 + 1 3 . . . . . . . . . . . . . . . . . . Escallonia illinita + . . . + 4 1 3 . . . . . . . . . . . . . . . . . . Equisetum giganteum . 1 1 2 . . . . . . . . . . . . . . . . . . . . . . Southern Variant Baccharis salicifolia . . . . . . . . . + 1 4 + 1 4 4 1 4 . 1 1 1 4 1 + 3 Myrceugenia lanceolata . . . . . . . . . . . . . . r . . . 1 2 4 4 4 5 5 2 Sophora cassioides . . . . . . . . . . . . . . . . . . . . . . . 2 1 . Xenophytic trees Populus nigra+canadensis (x) . . . . . . . . 2 1 2 2 . 2 1 2 1 . 2 1 . . . . . + Salix babylonica (x) . . . 2 . . . . 2 2 . . . + . 1 5 2 1 . . . . . . . Salix viminalis (x) . . . . . . . . + . . . . + . + 3 + 3 + . . . . . . Acacia dealbata (x) . . . . . . . . r . . . . 2 2 . . . . + . 1 . . . . Salix sp. aff. pedicellata (x) . . . . . . . . . . . . . + + + . . . . . . . . . . Native hygrophilous plants Polypogon australis + . 1 + + . 1 . . + 1 1 . . . 1 + + . . 1 . . . . . Eleocharis bonar.+dombeyan*. . . 1 . 1* +* . 1 . 1 + . . . 1 2 . . + . . . . . . 248 Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 Relevé N. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Juncus dombeyanus + . . . . . . . 2 1 . . 2 . 1 2 + . . . 1 . . . . r Verbena litoralis + . 1 . . . + 1 . . . + . . 1 + + . . . . . . . . . Cortaderia gr. selloana + . . 1 . . . . . . . 1 . . 1 . . + . . 1 . 1 . . + Hydrocotyle cf.chamaemorus 2 . . . . r 1 . . 1 . . . . . . + . . . + . . . . . Isolepis cernua . . . . . . . . . 1 . . . + . . . . . . 2 . . . . + Companion species Rubus ulmifolius (x) . + . . . . . . . . 2 + 1 + + 1 2 + 4 + . . 1 2 2 . Lotus uliginosus (x) . . . . . . . . 1 . 2 1 + + 1 1 . 1 . . 1 1 1 + . 1 Galega officinalis (x) . . . 2 . . . 4 . 4 5 5 + 1 . . 2 1 4 . . 1 + . . . Cyperus eragrostis . . . . . . . 1 + + . . . 1 1 1 1 + 1 . 1 1 . . . + Veronica becabunga (x) + . . + + . . . . 1 1 + 1 1 . . + . . . . . . . . . Baccharis linearis + . . . . + + . . . . + . . . . . + . . + + . . . + Schinus polygamus parviflorus + . . . + 2 3 + . . . . . . . . . . . . . + + . . . Agrostis capillaris (x) . . . . . . . . + . . 1 . . 1 1 . 2 . . + . . . . . Mentha pulegium (x) . . . . . + + . . . . . 1 . . . . 2 1 . . . . + . . Dysphania ambrossioides . . . . . . + . . . . . . r + . + . + . r . . . . . Prunella vulgaris (x) . . . . . . . . . . . . . . . 1 . + . . + + . + 1 . Muehlenbeckia hastulata . + . . . . . . . . . . . . + . . . . . . + 1 + . . Rosa rubiginosa (x) . . . . . . . + . . . . . . . . . + . . . . . 1 + + Cissus striata 1 + . . . . . . . . . . . . . . . . . . . . . 1 1 . Mentha aquatica+piperita (x) 1 . . . 1 . + . . . . . . + . . . . . . . . . . . . Saponaria officinalis (x) . . . . . . . . . . . . . . + + . + . . . . . . . + Balbisia gracilis . . . . . . . . . . . . . . . . . . . . . 1 1 . . 1 Cestrum parqui . . . . 1 + 1 . . . . . . . . . . . . . . . . . . . Sophora macrocarpa . . . . . . . + . . . . . . . . . . . . . + . + . . Typha domingensis . . + . . . . . + 2 . . . . . . . . . . . . . . . . Melilotus alba (x) . . . + . . . . . . . + . . . . . + . . . . . . . . Eleocharis macrostachya . . . . . . . . + . . . . . . + + . . . . . . . . . Schoenoplectus pungens . . . 1 . . . . . . . . . 3 . . + . . . . . . . . . Paspalum distichum . . . . . . . . 3 . . . . 1 . . . . . 1 . . . . . . Anagallis alterniflora . . . . . . + . . . . . . . . + 1 . . . . . . . . . Discaria chacaye . . + . . . . . . . . . . . . 1 . + . . . . . . . . Lithraea caustica . r . . . . . . . . . . . . . . . . . . . 3 + . . . 249Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 Relevé N. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Xanthium strumarium (x) . . . . . . . . 1 . . . . . . . . . 1 1 . . . . . . Polygonum hydropiperoides . . . . . . . . 1 . . . . 1 . r . . . . . . . . . . Hypericum perforatum (x) . . . . . . . . . . . . . . 1 1 . + . . . . . . . . Juncus effusus . . . . . . . . . . . . 2 . + . . . + . . . . . . . Plantago lanceolata (x) . . . . . . . . . . . . . . + . . 1 . . . . . . . 1 Holcus lanatus (x) . . . . . . . . + . . . . . 1 . . . . . . 1 . . . . Other species: Characteristics of Baccharido-Myrceugenietum: Fuchsia magellanica + in 23, 26; Azara celastrina 2 in 24, 3 in 25; Libertia chilensis 1 in 24, 2 in 25; Buddleja globosa 1 en 23; Colliguaja dombeyana 1, Escallonia rubra var. macrantha 2 in 24; Podocarpus saligna 1 in 25. Companion species: Apium nodiflorum 1 in 2, + in 3; Schinus molle + in 2, 2 in 3; Mimulus luteus r in 5, 1 in 7; Anthemis cotula 1 in 6, 7; Ludwigia peploides 1 in 9 and 14; Cyperus reflexus + in 16, 17; Nothofagus dombeyi + in 21, 1 in 22; Chusquea cumingii 2 in 24, 3 in 25; Blechnum hastata + in 24, 1 in 25; Lardizabala biternata 1 in 24, 25; Galium hypocarpium +, Carex excelsa, Eucalyptus sp. 1 in 1; Solanum pinnatum +, Valeriana bracteosa 1 in 3; Tristerix tetrandrus + in 5; Phyla nodiflora + in 7; Proustia pyrifolia and Vinca major + in 8; Calystegia sepium, Schoenoplectus californicus, Alisma plantago-aquatica 1, Salix purpurea 2, in 9; Baccharis sagitalis r, Mimulus glabratus + in 11; Lythrum hyssopifolia +, Cyperus aristatus var. inflexus 1, Salix aff. fragilis 2 in 14; Eryngium paniculatum + in 15; Isolepis nigricans +, Carex excelsa, Festuca arundinacea 1 in 16; Eragrostis curvula + in 18; Juncus balticus + in 19; Rorippa sp., Calystegia sepium + in 20; Nothofagus obliqua (pl.) r, Baccharis gr. obovata +, Symphyotrichum vahlii 1 in 21; Drimys winteri, Crinodendron patagua, Trifolium repens, Sporobolus indica, Leontodon taraxacoides and Paspalum dilatatum 1 in 22; Cryptocarya alba, Aldama revoluta, Ribes punctatum, Blechnum chilense and Proustia pungens + in 23; Amomyrtus luma + in 24; Lardizabala biternata, Cryptocarya alba 2, Luma apiculata 1, Aextoxicon punctatum, Bomarea salsilla, Leptocarpha rivularis, Sanicula crassicaulis, Valeriana crispa + in 25; Aldama revoluta r, Baccharis aff. paniculata 1 in 26. Localities: Province, Comuna; Administrative Regions: 1–5, Coquimbo; 6–7, Valparaíso; 8, Metropolitana; 10–11 O’Higgins; 12–13, 22–25, Maule; 14, 15, 20, 21, 26, Ñuble; 9, 16–19, Bio-Bio. 1: Choapa, Salamanca; from Cunlagua to S Agustín, Zapallar river (31º 44’ 02” / 70º 53’ 16”) 2: Choapa, Los Vilos; Limáhuida, no-name estero (31º 44’ 56” / 71º 09’ 53”); 3: Choapa, Los Vilos; road to Caimanes, Pupío Estero (31º 51’ 53” / 71º 20’ 18”); 4: Choapa, Salamanca; Coirón, Choapa river (31º 53’ 52” / 70º 46’ 19”); 5: Choapa, Los Vilos; between Caimanes and Mauro, Pupío Estero (31º 56’ 59” / 71º 04’ 14”); 6, 7: Petorca, Petorca; from Chalaco to Pedernal, Pedernal river (32º 08’ 17” / 70º 47’ 58”); 8: Chacabuco, Til-Til; road bifurcation Til-Til/Caleu, Til-Til estero (33º 01’ 13” / 70º 55’ 05”); 9: Bío-Bío, Mulchén; at the entrance of Mulchén, Bureo river (37º 42’ 54” / 72º 13’ 47”); 10: Cachapoal, Requinoa; between Gultro and Coya, bridge over Claro river, tributary of Pangal river (34º 16’ 21” / 70º 35’ 10”); 11: Colchagua, San Fernando; from El Llano to Sierra BellaVista, Claro river, tributary of Tinguiririca river (34º 44’ 39” / 70º 46’ 09”); 12: Curicó, Romeral; bridge at the East of Los Queñes, Teno river (34º 59’ 59” / 70º 47’ 32”); 13: Linares, Parral; road to Cauquenes, no-name river, tributary of Perquilauquén (36º 05’ 42” / 71º 55’ 28”); 14: Ñuble,Trehuaco; at the entrance of Trehuaco, Lonquén river (36º 25’ 39” / 72º 39’ 49”); 15: Ñuble, San Fabián; San Fabián bridge, Ñuble river (36º 33’ 42”/71º 33’ 52”); 16: Bío-Bío, Quilleco; from Antuco to Quilleco, Rucué river (37º 20’ 36” / 71º 47’ 46”); 17: Bío-Bío,Tucapel; at the entrance of Tucapel, Laja river (37º 18’ 04” / 71º 58’ 05”); 18: Bío-Bío, Mulchén; Bío-Bío river, west of Ralco, downstream of the Queuco river junction (37º 49’ 17” / 71º 40’ 46”); 19: Concepción, La Laja; at the entrance of La Laja, Bío-Bío river (37º 18’ 06” / 72º 42’ 38”); 20: Ñuble, Quillón; Ñipas bridge on the north bank of Itata river (36º 35’ 44” / 72º 32’ 28”); 21: Ñuble, San Fabián; Los Puquíos, at the East of San Fabián, Ñuble river (36º 38’ 21” / 71º 24’ 36”); 22: Linares, Linares; at the South of Roblería, Ancoa river (35º 54’ 14” / 71º 17’ 12”); 23: Linares, Linares; close to Chupallar, Ancoa river (35º 51’ 31” / 71º 12’ 54”); 24: Linares, Parral; road to Bullileo dam, no-name left side tributary of Longaví river (36º 14’ 27” / 71º 26’ 25”); 25: Linares, Parral; at Bullileo village, Bullileo river (36º 16’ 22” / 71º 24’ 58”); 26: Ñuble, San Fabián; Los Puquíos, at the East of San Fabián, Ñuble river (36º 38’ 23” / 71º 24’ 34”). 250 Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 Materials and Methodology Numerous expeditions were made in search of river courses whose banks fulfilled the topographic conditions that favour the deposit of materials dragged from the headwaters of these rivers; the ecology of Salix humboldtiana prevents it from colonising rocky riverbanks formed exclusively of boulders, as it requires at least minimal deposits of fine materials (sand or silt) to become established. In all cases we sought out river shrubland formations dominated by autochthonous species with or without the presence of Salix humboldtiana, as the communities of “Salicetea chilenae” tend to disappear when rivers flow near anthropised areas (farmlands, dammed river reaches, etc.) due to the destruction of their habitat or to massive invasions of allochthonous trees. A set of 35 relevés were taken in all the selected localities following the sygmatist phytosociological method (Braun-Blanquet, 1979 updated by Dierschke, 1994). Two tables were built grouping both sets of relevés by floristic affinities, in order to profile communities that reflected our judgement of what may represent the class “Salicetea chilenae” proposed by Oberdorfer (1960) in Chile. We follow Zuloaga et al. (2009) and Rodríguez et al. (2018) as a taxonomic reference for all the vascular flora; however we make an exception in the case of the composite Baccharis confertifolia Bert. ex Colla, a taxon assumed by both references to be merely a synonym of Baccharis salicifolia (Ruiz & Pav.) Pers. B. confertifolia was recognised in the past as an independent species in the Flora of Chile (Marticorena & Quezada, 1985), and even this century in the print version of the Flora of the Southern Cone (Zuloaga et al., 2008). We are unaware of any possible subsequent taxonomic studies, but in the most recent update of the genus by Giuliano & Plos (2014), it was assumed to be synonymous within the concept of B. salicifolia. However in our study of these communities we have confirmed a phenotype that we identify with B. confertifolia, and that can be clearly distinguished by its more linear –sometimes practically acicular– leaves, which give the shrub an appearance that is more similar to the branches of a young pine than the lanceolate leaves presented by the typical Baccharis salicifolia. This clear morphological differentiation, coupled with the geographic distinction we also observed and which will be discussed in the Results section, lead us to defend the independence of the taxon Baccharis confertifolia Bert. ex Colla. For syntaxonomical purposes, we followed the guidelines in the third edition of the International Code of Phytosociological Nomenclature (Weber et al., 2000; Izco & Del Arco, 2003). Results The formations containing a predominance of Salix humboldtiana (“Humboldt’s willow”) can be interpreted as a clearly recognisable association throughout almost the entire territory in the study, whose floristic composition is shown in Table 1. We assign it the name of Otholobio glandulosi-Salicetum humboldtianae ass. nova hoc loco, (holotypus rel. 11). These are tree/shrub formations (micro-woodlands sensu Rivas-Martínez 2004), since the autochthonous willow barely exceeds 10−12 m in height; this does not prevent other taller exotic trees from occasionally appearing, either on a second front of phreatophilic tree formations or else completely mixed with Salix humboldtiana. The species most frequently encountered include Populus nigra and P. xcanadensis (described in Table 1 as a “collective” taxon), Salix babylonica and Acacia dealbata. The geomorphological features of the riverbanks where these willow stands become established are quite varied, as S. humboldtiana can tolerate very precarious conditions in terms of soil formation. Its pioneering character is probably its greatest adaptive quality, so it can be found growing on banks with a predominance of gravel and particularly sand, and even in torrential river reaches with an abundance of boulders; its broad ecological range means it is also present on completely silted banks with well-formed soil with fine sediment, although it has usually been displaced from these types of sites with more fertile soils due to their use by humans as farmlands or pastures. Table 1 includes, for each relevé, a descriptive code of the gravimetric composition of the substrate according to size: rock, gravel, sand or silt (Figure 2). Many of the main rivers in the Central Chilean province have a very broad secondary riverbed as they flow through the Central Depression on their way to the Pacific, in which large extensions of gravel or sand have accumulated intermittently along their length and breadth. Thus except in major flooding events, the river’s normal regime consists of a main flow of water, and lateral streams with shallow or stagnant water or which are in the process of drying up; these irregular streams are prone to colonisation by the Humboldt’s willow, which is therefore sometimes found at some distance from running water (Figure 3). As a result of this diversity of substrates in the sites where these willow stands become established, the main companion species are similarly versatile woody plants such as Otholobium glandulosum and Baccharis salicifolia, the second of which is substituted in northerly relevés by B. confertifolia, a phenomenon already noted by Oberdorfer (1960) in his description of Tessario-Baccharidetum marginalis. Other hygrophilous shrubs, although with a lesser presence, are Luma chequen, Tessaria absinthioides and Discaria trinervis. Maytenus boaria and Aristotelia chilensis have a higher frequency because both present a broad distribution in the Mediterranean and humid temperate territory, and both are perfectly integrated in the riparian shrublands that replace these Humboldt’s willow stands towards the river headwaters, with steeply sloping banks and narrow channels and a predominance of boulders, also extending into the supramediterranean thermotype. These are the habitat characteristics of the communities that were described and grouped into an alliance Escallonion illinito-myrtoideae, proposed as provisional by Amigo & Flores-Toro (2017) with 251Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 two associations that can be integrated in the concept of “Salicetea chilenae”; we have therefore selected Maytenus boaria and Aristotelia chilensis as territorial characteristics of this possible class. One notable feature of the floristic composition of Otholobio glandulosi-Salicetum humboldtianae is the inevitable presence of both herbaceous and woody allochthonous species, most of which have the clear denomination of invasive exotic species. They have been labelled with a specific symbology in Table 1 (in addition to the aforementioned woody species) to highlight the fact that this ecological environment continues to suffer particularly aggressively from human activities. The frequent incursions of Galega officinalis in this environment is a clear example of this (Figure 4). Two significant trends can be noted with regard to the variability of this association. One floristic peculiarity of all the northernmost relevés located between the south of Coquimbo and towards the north of the Metropolitana region, with a semi-arid ombroclimate, is the participation of Baccharis confertifolia and often also Escallonia illinita and Equisetum giganteum [although according to Rodríguez et al. (2018) this corresponds to Equisetum pyramidale Goldmann, as these authors defend the independence of this taxon from E. giganteum L.]. Relevés 1−8 in Table 1 are only differentiated as a variant of Baccharis confertifolia, whose biogeographical and ecological significance is interpreted as being linked to the character of semi-arid ombroclimate. There is a further group of relevés that mark another biogeographical differentiation: the presence of an additional hygrophilous shrubland can be seen towards the southern section of the territory in the study (south of Maule, Ñuble and Bío-Bío), which could be presented as dominant, although its height never exceeds that of Humboldt’s willow: Myrceugenia lanceolata. We considered it particularly interesting to find formations of riparian shrublands with a dominance of this Myrtaceae species in relevés from more torrential reaches of rivers with headwaters within the Temperate macrobioclimate; as mentioned earlier, some of these relevés may even fall within this bioclimatic territory. It is our opinion that with more information it will be possible to confirm this community as a different association, for which we propose a provisional name: Baccharido salicifoliae- Myrceugenietum lanceolatae. We have only assigned it relevés 23−26 in Table 1 due to the absence of Salix humboldtiana, although obviously there are some transitional situations in which Salix humboldtiana and Myrceugenia lanceolata (rels. 21 and 22) coexist. Some species that may be significant in differentiating this other association are Sophora cassioides, Azara celastrina, Buddleja globosa or Colliguaja dombeyana; the presence of Rosa rubiginosa is only due to the type of substrate with a predominance of coarse materials (rocks and gravels) frequently found on riverbanks with this community. In our search for riverbanks with shrub formations containing willows, we found a range of situations with a floristically impoverished version of the Otholobio glandulosi-Salicetum humboldtianae in more open formations with not very dense cover and where, apart from the inevitable xenophytes, there are no more than half a dozen autochthonous species that are typical of the hygrophilous environment. These situations are physiognomically defined as phreatophilic scrublands (as they are less than 2−3 m in height, and their root stratum is not always in contact with flowing water) and are more similar to the community designated by Oberdorfer (op. cit.) as Tessario-Baccharidetum marginalis; we show a sample of this community in Table 2. Although most of the species in this community in Table 2 are also integrated in the relevés in Table 1, the dynamic relation between both has led us to consider them separately, as described in the following section. Discussion From the data provided so far we can argue in favour of recognising an association Otholobio glandulosi- Salicetum humboldtianae, widely distributed throughout the thermo– and mesomediterranean thermotypes in ombroclimates ranging from semiarid (at its limit with the arid) to the humid ombroclimate in the Central Chilean province. Once in the humid ombroclimate and penetrating slightly into the territory of the Temperate macrobioclimate there is a riparian community where Salix humboldtiana has already failed and the presence of the myrtaceae Myrceugenia lanceolata has gained predominance. We consider that this last, which we have called Baccharido salicifoliae-Myrceugenietum lanceolatae, represents a transition between the Mediterranean phreatophilic and riparian formations on highly fluctuating flows and the formations that appear when the rivers or streams have a more stable flow and when the ombroclimate becomes more humid. San Martín et al. (2001) described an important example of this type of riparian shrublands in the mesomediterranean territory in the Maule region, in which the most notable components are several myrtaceae species; it was assigned the name of Myrceugenio-Tepualietum stipularis, which is in fact an invalid name (due to the ambiguity caused by the lack of precision in the species of Myrceugenia used for the name, according to art. 3g of the ICPN), but which is a good example of how different “myrtles” (Tepualia stipularis, Myrceugenia pinifolia, M. lanceolata, Luma apiculata) colonise the riverbanks along with the typical temperate woodland species (Nothofagus dombeyi, Drimys winteri, Podocarpus saligna, etc.) when the river regime becomes more constant and moves away from the prevailing model in the Mediterranean macrobioclimate. This is a constant phenomenon in the Temperate and pluviseasonal Mediterranean territories in situations of stagnant waters that generate the swampy myrtle woodlands which are designated by the order Myrceugenietalia exsuccae (Palud-Myrceugenietalia sensu Oberd. 1960) in the class Wintero-Nothofagetea. 258 Amigo Vázquez, J.; Flores-Toro, L. & Caballero-Serrano, V. Mediterranean Botany 40(2) 2019: 243-258 (holotypus: Mayteno boariae-Escallonietum illinitae Amigo & Flores-Toro 2017, Int. J. Geobot. Res.7: 120). Characteristic species: Escallonia illinita, Escallonia myrtoidea, Buddleja globosa, Equisetum bogotense, Tropaeolum tricolor, Azara dentata. Mayteno boariae-Escallonietum illinitae Amigo & Flores-Toro 2017 ass. nova hoc loco (holotypus Amigo & Flores-Toro 2017, Int. J. Geobot. Res.7: 116s; Tab. 5, rel. 1). Buddlejo globosae-Escallonietum myrtoideae Amigo & Flores-Toro 2017 ass. nova hoc loco (holotypus Amigo & Flores-Toro 2017, Int. J. Geobot. Res.7: 118s; Tab. 6, rel. 5). salicetea PurPureae Moor 1958 lithraeo causticae-cryPtocaryetea albae Oberd. 1960 PhragMito-Magno-caricetea Klika in Klika & Novák 1941 nom. inv. salici huMboldtianae-ProsoPidetea albae Riv.-Mart. & Navarro in Navarro & Maldonado 2002 acacio Macracanthae-ProsoPidetea Pallidae Galán de Mera 1999 tessario integrifoliae-baccharidetea salicifoliae Riv.-Mart. & Navarro in Navarro & Maldonado 2002 Wintero-nothofagetea Oberd. 1960 Myrceugenietalia exsuccae Oberd. 1960 corr. Amigo & Rodríguez Guitián 2011 Myrceugenion exsuccae Oberd. 1960 Myrceugenio pinifoliae-Tepualietum stipularidis (San Martín J, San Martín C & Ramírez 2001) ass. nova (lectotypus: Myrceugenio-Tepualietum stipularidis San Martín J, San Martín C & Ramírez 2001, Rev. Geogr. Chile Terra Australis 46: 18s; Tab. 5, rel. 7).