Causes and consequences of mother tree population decline in Fazara Natural Forest Reserve, Sudan

J. Bio. & Env. Sci. 20 23 189 | Mohammed et al. RE RERE RESEARCH SEARCHSEARCH SEARCH PAPER PAPERPAPER PAPER OPEN ACCESS OPEN ACCESSOPEN ACCESS OPEN ACCESS Causes and consequences of mother tree population decline in Fazara Natural Forest Reserve, Sudan Elmugheira M I . Mohammed *1 , Difo V . Harouna 2 , Elmamoun H . Osman 3 , Elmalih MI. Mohammed 4 , Sohad AA. Fadlelmola 5 1 Department of Forest Management Science, Faculty of Forest Sciences and Technology, University of Gezira, Wad Medani, Sudan 2Department of Forestry, College of Natural Resources and Environmental Studies, University of Bahri, Khartoum, Sudan 3Department of Biological Sciences, Genetic, Genomic and Proteomics Research Unit, Faculty of Sciences, University of Maroua, Maroua, Cameroon 4Freelance, Gedaref State, Sudan 5Department of Forestry and Environment, Faculty of Forest Sciences and Technology, University of Gezira, Wad Medani, Sudan Article published on July 16, 2023 Key words: Illegal harvesting, Seeds production, Sustainable management, Yield regulation Abstract Although recent progress has been made in exploring and understanding tree population ecology and factors that disturb its development and dynamics, other pivotal research gaps remain untouched. Causes and consequences of mother tree decline, a seed-producing source and biodiversity niche, are at the core of these gaps. We bridged this gap by analyzing the status of mother trees, dendrometric parameters, stand parameters, and factors driving changes in species composition at Fazara natural forest reserve, across 74 samples of 1000 m 2 , systematically distributed in the high and lowland sites of the forest. To run the analysis, we respectively used ANOVA, pairedsampled t-test, post hoc test, and cross-tabulation in JAMOVI, Minitab, and SPSS. Findings showed that the abundance of mother trees, saplings, and seedlings were twice and three times higher in highland sites than lowland ones, respectively (F 1,72 = 141.2 and P = 0.03; F 1,72 = 128.3 and P = 0.01; F 1,72 = 116.5 and P < 0.001, respectively). While juvenile trees displayed no significant differences between the sites (F 1,72 = 162.4 and P = 0.06). Illegal harvesting was the principal contributor to mother tree decline, where stumps and debranched trees density at lowland sites were four and three times that of highland sites, respectively. However, deterioration of species richness, regeneration, and abundance were the common consequences of mother trees decline in the reserve. Interventions through restriction of trespassing, awareness-raising, and patrolling guards are urgently needed to protect both mother and juvenile trees. * Corresponding Author: Elmugheira MI. Mohammed  [email protected] Journal of Biodiversity and Environmental Sciences (JBES) ISSN: 2220-6663 (Print) 2222-3045 (Online) Vol. 23, No. 1, p. 189-209, 2023 http://www.innspub.net J. Bio. & Env. Sci. 20 23 190 | Mohammed et al. Introduction Mother and old trees represent the key iconic biota in most terrestrial ecosystems worldwide (Lindenmayer & Laurance, 2017). They form a foundation for habitat diversity (Asbeck et al., 2021), niche complexity (Derroire et al., 2016; Gebru et al., 2019), seeds production and seedlings recruitment for most seedly regenerated tree species in tropical, subtropical and temperate forests, as well as savannas, pastures and urban environments (Domene et al., 2017; Kutnar et al., 2019). They significantly guide the spatial and temporal allocation and distribution of their newly recruited individuals and other related plant and animal species found in natural forests and rangelands (Asigbaase et al., 2019; Ghanbari et al., 2021; Mohammed et al., 2021). In addition to that, they play essential functions in nutrient cycling, weather acclimatization, recreation sites, and carbon sequestration, as well as provision of food, feed, and medicine (Adam et al., 2013; Ibrahim et al., 2018; Neya et al., 2019). However, the sustainability of these roles and functions is of high significance to Africa particularly, the natives of sub-Sahara countries and Sahel region (Marone et al., 2017; Ouédraogo et al., 2019). In Africa, the contribution of forest trees to rural communities livelihood is high, especially in marginalized areas and conflicted sites (Deafalla et al., 2014; Suleiman et al., 2017). This contribution clearly observed in the eastern and southern parts of Sudan, where trees and their by-products support more than 60% of the local community’s needs and represent the main source of income regeneration (Adam et al., 2013; Mahgoub, 2014; Mohammed et al., 2021). However, such utilization needs to be regulated and properly managed to avoid the decline and depletion of these valuable resources (Gebrehiwot & Hundera, 2014; Ibrahim & Hassan, 2015; Tsegu, 2019). Moreover, for a good yield regulation plan, restoration program, or sustainable management of forest and tree resources, up-to-date information on its juvenile and adult trees population, species composition, as well as seeds production, dispersal, and seedlings establishment, is indispensably required (Gustafsson et al., 2012; Masuku & Xaba, 2013; Owusu et al., 2021). Different studies had filled the gaps associated with growth and development of herbaceous plants in Sudan and other savannas environments (Dayamba et al., 2008; Gebrehiwot & Hundera, 2014; Hassan & Tag, 2017), the status of seedlings and saplings of woody plants in their natural forests and rangelands (Ali et al., 2015; Hanief et al., 2016; Hasoba et al., 2020; Maua et al., 2020), as well as the species richness, abundance, and uses (Kikoti &mLigo, 2015; Nacoulma et al., 2016). However, information on the status of mother trees and how the observed dramatic human population growth can affect its population is lacking. The current study addressed this gap by assessing the status of mother trees in Fazara natural forest reserve towards the sustainable management of tree resources in the area. Fazara Natural Forest Reserve (FNFR) is among the largest forest reserves in the eastern part of the Gedaref State at Basunda locality (Mahgoub, 2014; Mohammed, 2019). It is located close to Fazara and Karima villages and forms the only source for wood, edible fruits, medicinal products, grazing areas, and recreation sites for these villages’ residents (Hassan, 2019; Mohammed, 2019). The usual income generation activities of the people around FNFR are agriculture, livestock keeping, nontimber forest products trade, and charcoal production (Ahmed, 2005; Elmekki, 2008; Hassan, 2015). While local community is mainly depending on this reserve (Mahgoub, 2014; Mohammed, 2019), information on its growing stock, adult to juvenile ratio, species richness, and the change driving factors are limited. Additionally, data on the status of the mother tree population, the main source of seeds and new seedlings, and whether it is stable or declining is unknown. Therefore, exploration of the tree population structure in FNFR is a core process to achieve the sustainable management of the forest, which will conserve its multiuse and vulnerable tree species and fulfills the local community needs. J. Bio. & Env. Sci. 20 23 191 | Mohammed et al. The study hypothesized that areas close to the villagers’ settlements (lowland sites) had fewer mother trees and new regeneration compared to remote and mountainous areas (highland sites). Moreover, as most locals are agro-pastoralists and charcoal producers, we predicted that livestock grazing and illegal harvesting are the main drivers of species composition change in FNFR. Furthermore, we expected that the population of native broadleaved tree species had been severely affected by illegal harvesting and limited individuals remain alive. Besides that, as information on mother and seedproducing trees are scarce, the findings of this study will form a baseline and guide for the decision-maker and natural reserves management to formulate a comprehensive management plan that ensures the regular provision of goods and services, as well as natural restoration and stands maintenance. Materials and methods Study area Fazara natural forest reserve is located at 12º 41ʹ 00ʺ N, 12º 48ʹ 00ʺ N, 35º 37ʹ 00ʺ E, and 35º 44ʹ 00ʺ E (Fig. 1), and covers an area of 7,095.9 ha (Hassan, 2015; Mohammed, 2019). It hosts more than 15 tree and shrub species with various perennial plants and grasses, distributed randomly across the mountainous and flatland sites of the reserve (Hassan, 2019; Mohammed, 2019). While the mountainous sites are dominated by Anogeissus leiocarpus, Terminalia brownii, Terminalia laxiflora, Lannea fruticosa, Sterculia africana, Ziziphus spina-christi, and Pterocarpus lucens tree species, the flatland sites are dominated by Acacia seyal, Acacia senegal, Balanites aegyptiaca, and Combretum hartmannianum (Hassan, 2019). Moreover, based on the analyzed meteorological data received from Sudan Meteorological Authority (SMA), the average minimum and maximum temperatures, as well as rainfall, were 26 ⁰C, 41 ⁰C, and 700mm, respectively (Figs. 2 and 3). The flat and semi-flat lands of FNFR are characterized by cracky clay and sandy-clay soil types, while the mountainous areas were dominated by sandy soil and rocks (Hassan & Tag, 2017; Mohammed & Hashim, 2015). Data collection To inventory the growing stock, population composition, and richness of tree species in FNFR, the study used a systematic sampling technique to establish eleven survey lines across the stratified sites of the reserve (Fig. 1). We stratified the study area into high and lowland sites based on their topographical characteristics (Plates 1 and 2). While the high land sites of FNFR cover its mountainous and hilly areas, the lowland ones encompass its flat and semi-flat lands (Gebru et al., 2019; Mohammed et al., 2021). The seventy-four (74) rectangular sample plots of 25 m x 40 m (1000 m 2 ) were laid across the high and lowland sites of the forest to assess their dendrometric and stand parameters. After marking the sample plot boundary and identifying its hosted tree species, we classified them into mature trees, saplings, and seedlings as recommended by (Derroire et al., 2016; Lindenmayer & Laurance, 2017). We further divided the mature trees into mature and over-mature ones (mother trees) based on their diameter at breast height (diameter measured at 1.3 m above ground level). We considered seedlings and saplings as woody plants with diameters of < 3 cm and 3 to < 7cm, while mature and mother trees are of ≥ 7 to 30 cm and > 30 cm diameters, respectively (Gebrehiwot & Hundera, 2014; Kikoti et al., 2015; Ligate et al., 2019). Plate 1. The lowland sites of FNFR; (A) dominated by Acacia seyal, and (B) dominated by Combretum hartmannianum tree species. J. Bio. & Env. Sci. 20 23 192 | Mohammed et al. Plate 2. The highland sites of FNFR; (A) dominated by Terminalia brownii and Sterculia africana, and (B) rocky area. Fig. 1. The map of Fazara natural forest reserve showing the geographic location of the study area and the inventoried sample plots. While tree diameter at breast height (DBH) was measured using an Ordinary caliper for small trees and diameter tape for large ones (Endale et al., 2017; Tetemke et al., 2019), Vernier caliper was used for seedling and sapling diameters measurements in high and lowland sites of the study area (Hanief et al., 2016; Ligate et al., 2019; Maua et al., 2020; Mohammed et al., 2021). Moreover, a hypsometer was used for total tree height measurements as recommended by other researchers (Ghanbari et al., 2021; Hassan et al., 2022; Mohammed et al., 2021). Additionally, we measured tree crown width using measuring tape at eight directions radiating from the tree base towards its crown edge perpendicular to the surveyor (Ibrahim et al., 2015; Mohammed et al., 2021). In each 1000 m 2 sample plot, we gathered information on anthropogenic activities like livestock grazing and browsing, stem debarking and crown debranching, tree logging and charcoal production, and intensive seeds (fruits) collection (Chaudhary et al., 2016; Guedje et al., 2016; Nndwammbi et al., 2018; Paulo & Tomé, 2017). All monitored animals were recorded, as well as, the debarked, debranched, and logged trees. Furthermore, we calculated the severity of debarking, debranching, and logging activity as the number of damaged stem to the total number of stems in the plot (Brodie et al., 2015; Ji et al., 2017; Mohammed et al., 2021). To gather socio-economic data about the reserve, we distributed 240 questionnaires on the residents of Fazara and Karima villages and interviewed 50 key informants (Angelsen, 2012; Fahmi et al., 2018). The key informant interviews covered local leaders, forest officers, rangeland officers, mechanized-farming management officers and the directors of active nongovernmental organizations in the area (Hassan, 2019; Mohammed, 2019). Data analysis Mother trees, juvenile trees, saplings, and seedlings abundance were assessed as the number of stems per sample, as recommended by (Endale et al., 2017; Fakhry et al., 2020; Ghanbari et al., 2021). To compute the basal area, volume, relative abundance, relative dominance, relative frequency, and importance value index of various tree species in the high and lowland sites of the reserve, we used the formulae listed in table 1 (Abdou et al., 2016; Gebeyehu et al., 2019; Idrissa et al., 2018; Mohammed et al., 2021). The species dominance and frequency were expressed as species coverage per area and as the presence or absence of the species per area, respectively (Hasoba et al., 2020; Lempesi et al., 2017; Mohammed et al., 2021). Further, we calculated the species richness as the total number of species reported at each site (Asigbaase et al., 2019; Kutnar et al., 2019; Mohammed et al., 2021). To compare the species richness, dendrometric and stand parameters between sites, we used a pairedsampled t-test in Minitab and ANOVA in JAMOVI, respectively (Kingazi et al., 2020; Mohammed, 2019; Mohammed et al., 2021). J. Bio. & Env. Sci. 20 23 193 | Mohammed et al. A similar procedure was applied to compare the change driving factors across the sites, including the debarking, debranching, logging, and root damages. Table 1. The equations used to compute basal area, volume and importance value index of the tree species assessed in the high and lowland sites of Fazara natural forest reserve. Equation Reference Basal area (g) =  ∗            (Ghanbari et al., 2021) Volume (Vol) = Ba sal area*Height*Form Factor (Ligate et al ., 2019) Relative abundance (RA) =          ∗ 100 (Mohammed et al., 2021) Relative dominance (RD) =   "  "     ∗ 100 (Assogbadjo et al., 2010) Relative frequency (RF) =   #$  #$       ∗ 100 (Idrissa et al., 2018) Importance value index (IVI) = RA + RD + RF (Maua et al ., 2020) All descriptive statistics, normality and homogeneity tests have been respectively performed in SPSS (version 26) and JAMOVI (version 1.1.17), as recommended by (Gessesse et al., 2016; Missanjo et al., 2015; Suleiman et al., 2017). Moreover, questionnaires and interview data were sorted, coded, and analyzed in SSPS using one-way ANOVA and cross-tabulations (Burman et al., 2018; Jayakumar & Nair, 2013; Sukhbaatar et al., 2019). To trace the significant differences between various variables and parameters within and across the sites, we applied Tukey’s post hoc test with α = 0.05 (Burman et al., 2018; Mohammed et al., 2022). Furthermore, we classified the regeneration status into good, fair, poor, and none, as guided by (Arosa et al., 2017; Dibaba et al., 2020; Gebeyehu et al., 2019; Mohammed et al., 2021). Good if seedlings > saplings > adults, fair if seedlings > saplings ≤ adult, poor if no seedlings, and none if no seedlings and saplings. Results Mother trees abundance and adult to juvenile ratio Mother trees abundance in highland sites was double that of lowland ones, with significant differences between the sites (F 1,72 = 141.2 and P = 0.03, Fig. 4). While juvenile trees illustrated no significant differences between the sites (F 1,72 = 162.4 and P = 0.06, Fig. 4), saplings and seedlings were twice and three times higher in highland sites than lowland sites, respectively (F 1,72 = 128.3 and P = 0.01; F 1,72 = 116.5 and P < 0.001, respectively, Fig. 4). Moreover, the study results displayed that the proportion of the five top tree species significantly differed for mother trees (F 1,72 = 91.3 and P = 0.04), juvenile trees (F 1,72 = 101.2 and P = 0.01), saplings (F 1,72 = 87.4 and P = 0.01), and seedlings (F 1,72 = 131.3 and P = 0.001) between the high and lowland sites, with a low frequency of seedlings, saplings, and mother trees in lowland sites compared to highland ones (Fig. 5). Acacia senegal and Acacia seyal have the highest juvenile trees percent compared to Combretum hartmannianum and Ziziphus spina-christi, which have better seedlings and saplings percentages (Fig. 5). Fig. 2. Mean maximum and minimum temperatures for FNFR (2012 – 2021) that computed based on the data acquired from Sudan Meteorological Authority. J. Bio. & Env. Sci. 20 23 194 | Mohammed et al. Fig. 3. Mean rainfall for FNFR (2012 – 2021) that computed based the data acquired from Sudan Meteorological Authority. Fig. 4. Mean (±SE) abundance per plot for mother trees, juveniles, saplings, and seedlings inventoried in the low and highland sites of Fazara natural forest reserve. Asterisks on the bars display the significant differences between the sites based on Tuckey Post Hoc test as * = P ≤ 0.05, ** = P ≤ 0.01, and *** = P ≤ 0.001. Characteristics of dendrometric parameters and regeneration status The highland sites showed the highest values of tree crown width (m) with significant differences across the sites especially for Combretum hartmannianum, Balanites aegyptiaca, Lonchocarpus laxiflorus, and Ziziphus spina-christi (Fig. 6). Moreover, the diameter at breast height (cm) and basal area (m 2 ) of Balanites aegyptiaca and Ziziphus spina-christi in highland sites were double that of lowland sites (F 1,72 = 118.7 and P < 0.01; F 1,72 = 81.3 and P < 0.01; F 1,72 = 128.1 and P = 0.01; F 1,72 = 101.3 and P = 0.01, respectively), as well as that of Acacia senegal (Fig. 7). However, Combretum hartmannianum exhibited the highest tree height and volume values throughout the forest, with significant differences between the high and lowland sites (F 1,72 = 78.9 and P < 0.01; F 1,72 = 86.7 and P = 0.01, respectively, Fig. 7). Fig. 5. The proportions (%) of tree development stages of the five top common tree species inventoried in the low and highland sites of Fazara natural forest reserve. (A) mother trees, (B) juvenile trees, (C) saplings, and (D) seedlings. Asterisks on the bars display the significant differences between the sites based on Tuckey Post Hoc test as * = P ≤ 0.05, ** = P ≤ 0.01, and *** = P ≤ 0.001. Additionally, the top five common tree species showed a good regeneration status in highland sites with a frequency percent ≥ 60% compared to their fair status in lowland sites (Tables 2 & 3). The tree species of Fabaceae family dominate both sites with percentages of 43% and 62% for high and lowland sites respectively (Tables 2 & 3). Fig. 6. Mean (±SE) crown width (m) of all tree species inventoried in the low and highland sites of Fazara natural forest reserve. J. Bio. & Env. Sci. 20 23 195 | Mohammed et al. Fig. 7. Mean (±SE) dendrometric parameters of the five top common tree species inventoried in the low and highland sites of Fazara natural forest reserve. (A) diameter at breast height, (B) basal area, (C) height, and (D) volume. Asterisks on the bars display the significant differences between the sites based on Tuckey Post Hoc test as * = P ≤ 0.05, and ** = P ≤ 0.01. Factors driving the changes in species composition and mother tree decline We found that illegal harvesting is the main contributor to mother tree decline and tree species composition changes. The density of tree stumps and debranched trees at lowland sites were respectively four and three times equal to that of highland sites, with significant differences between sites (F 1,72 = 152.3 and P < 0.001; F 1,72 = 128.4 and P < 0.01, respectively, Fig. 8). However, the density of debarked trees and root damages were high in highland sites compared to lowland ones (F 1,72 = 102.8 and P = 0.03; F 1,72 = 112.2 and P = 0.04, respectively, Fig. 8). Moreover, the interviewed participants reported that illegal harvesting, overgrazing, and agricultural activities are the main reasons behind the decline of mother trees within and around the reserve with a frequency of 48%, 24%, and 17%, respectively (Fig. 9). Table 2. The family, frequency, and regeneration status of tree species inventoried in the highland sites of Fazara natural forest reserve No Species Family Habit Frequency (%) Regeneration status 1 Acacia polyacantha Willd. Fabaceae Tree 9.6 None 2 Acacia senegal (L.) Willd. Fabaceae Tree 59.6 Good 3 Acacia seyal Del. Fabaceae Tree 59.8 Good 4 Anogeissus leiocarpus (DC.) Guill . & Perr. Combretaceae Tree 11.3 None 5 Balanites aegyptiaca (L.) Del. Balanitaceae Tree 68.2 Good 6 Combretum hartmannianum Schweinf. Combretaceae Tree 43.4 Fair 7 Dichrostachys cinerea (L.) Wight et Arn. Fabaceae Shrub 42.1 Fair 8 Lannea fruticosa (Hochst. ex. A. Rich.) Engl. Anacardiaceae Tree 16.6 None 9 Lonchocarpus laxiflorus (Guill. & Perr.) Fabaceae Tree 27.8 Poor 10 Maerua angolensis DC. Capparaceae Shrub 8.7 None 11 Pterocarpus lucens Lepr. ex Guill. et Perr. Fabaceae Tree 13.1 None 12 Sterculia africana (Lour.) Fiori. Malvaceae Tree 26.4 Poor 13 Terminalia brownii Fresen. Combretaceae Tree 25.2 Poor 14 Ziziphus spina - christi (L.) Desf. Rhamnaceae Tree 63.1 Good Table 3. The family, frequency, and regeneration status of tree species inventoried in the lowland sites of Fazara natural forest reserve. No Species Family Habit Frequency (%) Regeneration status 1 Acacia polyacantha Willd. Fabaceae Tree 28.6 Poor 2 Acacia senegal (L.) Willd. Fabaceae Tree 51.3 Fair 3 Acacia seyal Del. Fabaceae Tree 57.6 Fair 4 Balanites aegyptiaca (L.) Del. Balanitaceae Tree 62.2 Good 5 Combretum hartmannianum Schweinf. Combretaceae Tree 41.4 Fair 6 Dichrostachys cinerea (L.) Wight et Arn. Fabaceae Shrub 62.5 Good 7 Lonchocarpus laxiflorus (Guill. & Perr.) Fabaceae Tree 6.5 None 8 Ziziphus spina - christi (L.) Desf. Rhamnaceae Tree 46.5 Fair J. Bio. & Env. Sci. 20 23 196 | Mohammed et al. Fig. 8. Mean (±SE) density (stem/ha) of debarked trees, debranched trees, tree stumps, and root damage reported in the high and lowland sites of Fazara natural forest reserve. Asterisks on the bars show the significant differences between the sites based on Tuckey Post Hoc test as * = P ≤ 0.05, ** = P ≤ 0.01, and *** = P ≤ 0.001. Fig. 9. The six common stated factors driving the changes of species composition and mother trees population decline in Fazara natural forest reserve based on the interviewees responses. Consequences of mother tree decline Low species richness and tree density in the lowland sites The species richness in lowland sites was half of that in highland sites, with a significant difference between sites (T = 39.4 and P < 0.01, Table 4). While the overall density displayed a low value in the lowland sites (T = 22.1 and P = 0.01, Table 4), the density of Acacia seyal and Acacia senegal in the same sites was twice that of highland sites (F 1,72 = 75.9 and P < 0.001; F 1,72 = 98.3 and P = 0.04, respectively, Fig. 10). However, Balanites aegyptiaca, Combretum hartmannianum, and Ziziphus spina-christi exhibited an inverse pattern (Fig. 10). Fig. 10. Mean (±SE) species density per ha for the common top five tree species assessed in the low and highland sites of Fazara natural forest reserve. Asterisks on the bars illustrate significant differences between the stratified sites for each species based on Tuckey Post Hoc test as * = P ≤ 0.05, ** = P ≤ 0.01, and *** = P ≤ 0.001. Table 4. Species richness and mean tree density (stem/ha) assessed in Fazara natural forest reserve. Parameter Highland sites Lowland sites T P Species richness 14 8 39.4 < 0.01 Density (stem/ha) 93.2 64.3 22.1 0.01 T = paired-sampled t-test, and P = probability value High dominance, frequency, and importance value index (IVI) in lowland sites Findings show that lowland sites have high values of relative abundance, dominance, frequency, and importance value index (IVI) compared to highland sites (Tables 5 & 6). Acacia seyal and Balanites aegyptiaca in lowland sites showed the highest values of IVI, which was double that of highland ones (Tables 5 & 6). Additionally, Acacia polyacantha and Lonchocarpus laxiflorus tree species displayed the lowest values of relative dominance and abundance throughout the study area, with slight variations across sites (Tables 5 & 6). J. Bio. & Env. Sci. 20 23 197 | Mohammed et al. Table 5. Species, relative abundance, dominance, frequency and importance value index (IVI) for the inventoried tree species in the highland sites of Fazara natural forest reserve. No Species Family Relative Abundance Relative Dominance Relative Frequency IVI 1 Acacia polyacantha Fabaceae 1.48 1.84 3.92 7.24 2 Acacia senegal Fabaceae 1.57 2.49 5.88 9.94 3 Acacia seyal Fabaceae 36.11 19.19 12.42 67.72 4 Anogeissus leiocarpus Combretaceae 8.86 7.65 9.8 26.31 5 Balanites aegyptiaca Balanitaceae 16.71 20.24 14.38 51.33 6 Combretum hartmannianum Combretaceae 5.36 10.56 6.54 22.46 7 Dichrostachys cinerea Fabaceae 3.32 3.33 6.54 13.19 8 Lannea fruticosa Anacardiaceae 5.72 1.04 9.15 15.91 9 Lonchocarpus laxiflorus Fabaceae 2.59 3.31 5.88 11.78 10 Maerua angolensis Capparaceae 2.22 9.91 3.92 16.05 11 Pterocarpus lucens Fabaceae 5.17 6.85 2.61 14.63 12 Sterculia africana Malvaceae 3.51 5.25 5.23 13.99 13 Terminalia brownii Combretaceae 4.43 6.23 6.54 17.2 14 Ziziphus spina - christi Rhamnaceae 2.95 2.11 7.19 12.25 Table 6. Species, relative abundance, dominance, frequency and importance value index (IVI) for the inventoried tree species in the highland sites of Fazara natural forest reserve. No Species Family Relative Abundance Relative Dominance Relative Frequency IVI 1 Acacia polyacantha Fabaceae 2.78 4.25 7.77 14.8 2 Acacia senegal Fabaceae 2.67 3.35 11.65 17.67 3 Acacia seyal Fabaceae 63.23 44.26 25.25 132.74 4 Balanites aegyptiaca Balanitaceae 10.79 24.29 13.59 48.67 5 Combretum hartmannianum Combretaceae 8.58 14.22 11.65 34.45 6 Dichrostachys cinerea Fabaceae 5.45 3.65 12.62 21.72 7 Lonchocarpus laxiflorus Combretaceae 1.05 2.13 3.88 7.06 8 Ziziphus spina - christi Rhamnaceae 5.45 3.85 13.59 22.89 Discussion Mother trees abundance and adult to juvenile ratio The study findings of high mother trees, saplings, and seedlings abundance in highland sites compared to lowland ones are consistent with (Gebrehiwot & Hundera, 2014; Hanief et al., 2016; Hassan et al., 2022). Various studies have related the low population of adult and juvenile trees in forests and rangelands to over-utilization (Githae et al., 2011; Maleko et al., 2018; Mohammed et al., 2021), landuse change (Aleza et al., 2018; Alzubair & Hamdan, 2020; Owusu et al., 2021), and management regime changes (Bergeron et al., 2002; Chaudhary et al., 2016; Cheng et al., 2017; Sukhbaatar et al., 2019). However, for the Fazara case, the low seedlings, saplings, and mother trees abundance in lowland sites can be directly associated with high browsing by livestock and unauthorized logging activities. Literature proved that sites close to human settlements are usually subject to high anthropogenic pressure compared to remote areas (Assogbadjo et al., 2010; Cantarello et al., 2014; Gebeyehu et al., 2019; Mohammed et al., 2021). Further, the high juveniles of Acacia senegal and Acacia seyal to other broadleaves tree species reflect the impacts of selective logging practiced by the locals due to their preference of using broadleaved species for timber production rather than Acacias (Mahgoub, 2014; Mohammed et al., 2021). In addition, the invasive nature of A. senegal and A. seyal (Belsky, 1994; Kingazi et al., 2020; Maua et al., 2020), and their vigorous natural regeneration compared to other tree species like Balanites aegyptiaca (Ahmed & Desougi, 2014; Gebru et al., 2019; Hasoba et al., 2020), can potentially contribute to the current regeneration stock. Though Ziziphus spina-christi has a good mother tree abundance in the lowland, it shows a low seedling and sapling abundances resulting from its high J. Bio. & Env. Sci. 20 23 204 | Mohammed et al. Ghanbari S, Sefidi K, Kern CC, ÁlvarezÁlvarez P. 2021. 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