Patterns of species change in anthropogenically disturbed forests of Madagascar

Five main conclusions arise from this review of the responses of species to anthropogenic disturbance in Madagascar: First, species’ reactions to anthropogenic disturbance are generally negative, but remain poorly known. Our knowledge is patchy among and within higher taxonomic groups; we are still largely gathering case studies. Second, taxonomic groups vary considerably in which proximate factors are most important. Third, several groups show differing responses within different ecoregions. Whether these differences are consistent across groups requires further testing. Fourth, related species often have divergent reactions to disturbance, even within lower taxonomic groupings (families or genera). Thus, we cannot rely on phylogenetic relatedness or even ecological similarity to infer similarity in responses. Finally, disturbance typically reduces species diversity (especially of native and/or endemic species), but also causes species turnover, typically with forest specialists replaced by grassland generalists, and endemics replaced by non-endemics (including invasives). Given these knowledge gaps, we stress the urgency of applied studies that assess species’ ecology, behaviour and health across disturbance gradients, including purely anthropogenic landscapes. Remaining natural vegetation and protected areas will be unable to preserve Madagascar’s biodiversity under the impact of climatic change; we must understand responses of plants and animals to disturbance in order to create buffer zones and corridors combining secondary, degraded and natural habitats.     

Tolerance of frugivorous birds to habitat disturbance in a tropical cloud forest

In view of the continued decline in tropical forest cover around the globe, forest restoration has become a key tool in tropical rainforest conservation. One of the main - and least expensive - restoration strategies is natural forest regeneration. By aiding forest seed influx both into disturbed and undisturbed habitats, frugivorous birds facilitate forest regeneration. This study focuses on the tolerance of a frugivorous bird community to anthropogenic habitat disturbance within the broader context of natural forest regeneration with conservation purposes. It was carried out in the tropical cloud forest of Costa Rica’s Talamanca Mountains. Bird community response and tolerance to habitat disturbance was assessed by comparing bird presence and densities along a disturbance gradient, ranging from open pastures to closed mature forests. Birds were censused along nine transects applying the variable width line transect procedure. Forty relevant frugivorous bird species were observed during 102 h of survey time. Densities were calculated for 33 species; nine species responded negatively to increasing level of disturbance and nine others positively. Results indicate that large frugivores are generally moderately tolerant to intermediate, but intolerant to severe habitat disturbance, and that tolerance is often higher for medium and small frugivores. It appears that moderately disturbed habitats in tropical cloud forests are highly suitable for restoration through natural regeneration aided by frugivorous birds. Due to a lack of large forest seed dispersers, severely disturbed habitats appear less suitable.     

Patch size and isolation effects on epiphytic and epiphyllous bryophytes in the fragmented Brazilian Atlantic forest

An inventory of the understory forest epiphyte and epiphyllous bryophyte floras was carried out in eight Atlantic rain forest fragments. The fragments were between 7 and 500 ha in size and belonged to two areas (lowland and submontane) of the state of Pernambuco, northeastern Brazil. The aim of this study was to investigate the effect of habitat fragmentation and changes in the natural landscape on community structure (composition, richness, diversity, and abundance). Although the influence of altitude was noted in this study by increasing richness, diversity, and abundance, it was clear that in some fragments the influence of fragment size and isolation can be more important than this positive environmental factor. Fragment size and isolation affect both communities but the last one seems to be a stronger threatening factor for the epiphylls. The least isolated and the largest fragments housed the richest floras - especially in relation to the epiphylls - and had the greatest proportion of shade species. Habitat fragmentation negatively affected epiphytic and epiphyllous bryophytes and increased the representation of species with larger niches (generalists) while decreasing the representation of species with smaller niches (typically found in shady or in sunny areas). The results suggests that the critical fragment size necessary for bryophyte preservation must be correlated with insularity levels; for epiphytes, however, it is likely that low levels of isolation cannot compensate borderline effects as with the epiphyllous bryophytes.     

Effects of prescribed burning on distribution and abundance of birds in a closed-canopy oak-dominated forest, Missouri, USA

Prescribed, biennial burning in forest understory started in Cuivre River State Park, Missouri, USA, in the late 1980s to help restore the forest to conditions that existed prior to European settlement. Bird surveys were started in 1996 on two burned and two unburned sections of the park to determine what effects the burning and subsequent changes in vegetation were having on bird populations. Birds were sampled at 17 60-m radius point counts on each study area; each point was sampled twice per year during the main breeding period from 1996 through 2002. Total abundance and species richness differed among the four areas but no differences could be attributed to burning. Some individual species, however, differed in abundance and frequency of occurrence between burned and unburned areas. For example, Indigo Bunting (Passerina cyanea), Kentucky Warbler (Oporornis formosus), and several species of woodpeckers were more abundant on burned areas; Ovenbird (Seiurus aurocapillus), Worm-eating Warbler (Helmitheros vermivorous), Wood Thrush (Hylocicla mustelina) and Acadian Flycatcher (Empidonax virescens) were among the species more abundant on unburned areas. As a consequence, overall community composition differed significantly between burned and unburned areas of the park, but did not differ between burned areas or between unburned areas. Prescribed burning was instituted to restore vegetation to presettlement conditions and has started to achieve that objective. Restoration also has affected and likely will continue to affect bird populations. Future maintenance of a full complement of bird species, including a number of neotropical migrants, will be dependent on presence of both burned and unburned forest habitat.     

The responses of understorey birds to forest fragmentation, logging and wildfires: An Amazonian synthesis

We combine mist-net data from 24 disturbance treatments taken from seven studies on the responses of understorey Amazonian birds to selective logging, single and recurrent wildfires, and habitat fragmentation. The different disturbance treatments had distinct effects on avian guild structure, and fire disturbance and the isolation of forest patches resulted in bird communities that were most divergent from those in continuous, undisturbed forest in terms of their species composition. Although low-intensity logging treatments had the least noticeable effects, the composition of understorey birds was still markedly different from the composition in undisturbed forest. This analysis demonstrates the importance of preventing habitat fragmentation and the spread of fires in humid tropical forests, and highlights the need for more research to determine the long-term suitability of large areas of degraded forest for forest birds.     

Thresholds in the long-term responses of breeding birds to forest cover and fragmentation

Mitigating the effects of habitat loss requires estimating the minimum amount of habitat necessary for the persistence of wildlife populations in a changing landscape. Assessing minimum habitat amounts, however, relies on identifying ecological thresholds in species’ responses to landscape change. Using two repeated state-wide atlases, our objective was to investigate the responses of 25 forest birds to a range of forest cover and fragmentation. Repeat atlases allow for the analysis of four population dynamics including: (1) colonization, (2) persistence, (3) extinction, and (4) absence. Our objective was to test the hypothesis that forest birds demonstrated thresholds in these four basic dynamics to varying amounts of forest cover and fragmentation.We found thresholds to be a common, though not pervasive, characteristic of how forest birds respond to forest cover and pattern. We found that the probability of persistence was positively correlated with forest cover and 22 species demonstrated threshold responses. In addition, 15 of 25 birds demonstrated discrete thresholds in extinction dynamics. The existence of a colonization threshold has received significantly less attention in ecology. We also found that 17 out of 25 species demonstrated thresholds in their colonization response to a greater amount of forest cover. The effects of forest fragmentation, independent of forest amount, were less clear. We found support for incorporating the effects of fragmentation, but this fragmentation effect was found both below and above threshold points. We conclude that incorporating ecological thresholds in environmental planning should be species-specific and focus on populations on the verge of rapid ecological change.     

Effects of structural and functional connectivity and patch size on the abundance of seven Atlantic Forest bird species

We studied the importance of fragment size and structural and functional connectivity on the occurrence and abundance of seven Atlantic Forest bird species in 13 patches (13-275 ha) and three sites within a continuous forest (10,000 ha). We sampled birds with point counts and evaluated structural connectivity considering the presence of corridors and the degree of isolation. We defined functional connectivity by analyzing species movements using playbacks in forest corridors between fragments and in the surrounding matrix. Species differed in their responses to fragmentation. For the frugivorous species, Trogon surrucura, Carpornis cucullatus and Triclaria malachitacea, patch size was the main factor determining abundance. Two understory insectivorous species, Basileuterus leucoblepharus and Pyriglena leucoptera, were more affected by the degree of patch connectivity, the former by the presence of corridors and the latter by the distance between patches. The capacity of P. leucoptera to use corridors and open areas (i.e. functional connectivity) shaped its abundance pattern. Fragmentation had no effect on the abundance of Chiroxiphia caudata and had a positive effect on Batara cinerea. This study emphasizes the importance of considering species’ perceptions of landscape, especially functional connectivity, in understanding the effects of habitat fragmentation.     

Effect of forest fragmentation on fruit and seed predation of the tropical dry forest tree Ceiba aesculifolia

Forests fragmentation reduces the density of natural plant populations forming patches of the remaining individuals. One of the biotic interactions that can be affected by forest fragmentation and is poorly studied is seed predation. We determined the effects of forest fragmentation on seed and fruit predation in Ceiba aesculifolia by comparing trees in continuous forest with trees in fragmented forest. We compared the following variables: (a) frequency of fruit predation by Collie’s squirrel (Sciurus colliaei) in each habitat; (b) frequency of the cotton-staining bug seed predator (Dysdercus, Orden Hemiptera) in each habitat; (c) the effect of seed predation on germination frequency and time; and (d) the effect of different life stages of Dysdercus on seed viability. In continuous habitat, 100% of the trees presented fruits with squirrel predation while only 34% of trees in fragmented habitats presented fruit predation. In continuous forest 27% of the trees contained fruits with the seed predator Dysdercus, while only 2% of the trees in fragmented forest presented Dysdercus. The initial weight of damaged seeds was greater than seeds that were not damaged indicating that seed predators select heavier seeds to feed upon. Frequency of seed germination was affected by different life stages; pre-adults decreased germination significantly more than nymphs and adults. Seed predation significantly increased the time it took for germination to occur. Our study shows that forest fragmentation significantly affects predation patterns of squirrels and cotton-staining bugs. Reduction of natural seed predators in forest fragments may have long-term consequences on forest structure and diversity.     

The importance of gallery forests in the tropical lowlands of Costa Rica for understorey forest birds

Rivers and streams lined by narrow forest strips are common in the lowland countryside of south-western Costa Rica. We studied the importance of these gallery forests for understorey birds, especially forest species. Using mist-nets, we captured 1110 birds belonging to 90 species between June and September 2007 at 16 sites spread equally over four habitat types: forest interior, forest margin, gallery forest connected to closed forest, and isolated gallery forest. Though isolated gallery forests had the greatest number of expected species in total, they supported the lowest number of forest-specialist species, lower even than connected gallery forests. Granivorous birds showed an increase from forest to isolated gallery forest, all other feeding guilds however showed no change. The studied habitats differed from each other in their faunal composition. Assemblages of three species groups categorised by their habitat preferences (forest specialists, forest generalists, non-forest species) showed nested distribution patterns across the four habitats. There was no significant difference in the proportion of birds with brood patches or of recaptures across the studied habitat types, leading to the assumption that birds not only use gallery forests for movement and foraging but also for reproduction. Though of limited conservation value for most forest understorey birds, at least for a small fraction of forest species gallery forests constitute an important secondary habitat. More significantly, they can form corridors or stepping stones that allow movements within the matrix of human-dominated habitats, and represent an important landscape component benefiting total bird species richness in the Costa Rican countryside.     

The impacts of forest clearance on lizard, small mammal and bird communities in the arid spiny forest, southern Madagascar

Madagascar is a global biodiversity hotspot threatened by forest loss, degradation and fragmentation, all of which are detrimental to the future survival of forest-dwelling organisms. For conservation purposes it is essential to determine how species respond to habitat disturbance, specifically deforestation. In this study we investigated the impacts of deforestation on three vertebrate communities, lizards, small mammals and birds, in an area of spiny forest subjected to anthropogenic forest clearance. Spiny forest has high levels of endemism, but conservation in this unique ecosystem is hindered by the lack of research. We undertook standardised trapping, time-constrained and timed species searches to assess species richness, species abundance and community composition of lizards, small mammals and birds in six areas of ‘forest’ and six ‘cleared’ areas. From surveys and opportunistic sightings we recorded a total of 70 species of birds, 14 species of mammals and 38 species of reptiles and amphibians. We found forest clearing to have a negative effect on species richness and community structure of all groups and identified loss of canopy cover as a driving factor behind this. However, the response and sensitivity to clearing varied between groups and species. Lizards (50%) and small mammals (40%) had the greatest decline in species richness in response to clearing as compared to birds (26%), although birds showed the greatest shift in community structure. The community in cleared areas contained more generalist and introduced species that have wider geographic ranges and habitat preferences, than those unique to the spiny forest. We found the first suite of species to suffer from forest clearance were those of high conservation priority due to their restricted geographic range. Our findings are discussed in relation to future spiny forest conservation and management.     

The role of forest structure, fragment size and corridors in maintaining small mammal abundance and diversity in an Atlantic forest landscape

Using the abundance and distribution of small mammals at 26 sites in an Atlantic forest landscape, we investigated how species abundance and alpha and beta diversity are affected by fragment size and the presence of corridors. To account for the variability in forest structure among fragments, we described and minimized the influence of foliage density and stratification on small mammal data. Sites were distributed among three categories of fragment size and in continuous forest. For small and medium-sized categories, we considered isolated fragments and fragments connected by corridors to larger remnants. Small mammal abundance and alpha and beta diversity were regressed against site scores from the first axis of a Principal Component Analysis on forest structure variables. Residuals were used in analyses of variance to compare fragment size and connectivity categories. Forest structure influenced total abundance and abundance of some species individually, but not the diversity of small mammal communities. Total abundance and alpha diversity were lower in small and medium-sized fragments than in large fragments and continuous forest, and in isolated compared to connected fragments. Three species were less common, but none was more abundant in smaller fragments. At least one species was more abundant in connected compared to isolated fragments. Beta diversity showed an opposite relationship to fragment size and corridors, increasing in small and isolated fragments. Results highlight the importance of secondary forest for the conservation of tropical fauna, the hyper-dynamism of small isolated fragments and the potential of corridors to buffer habitat fragmentation effects in tropical landscapes.     

Hollow selection by vertebrate fauna in forests of southeastern Australia and implications for forest management

We examined the types of hollows, and types of hollow-bearing trees, occupied by vertebrate fauna in temperate eucalypt forests in southeastern Australia. Hollow-bearing trees are selected for retention in wood production forests to mitigate the effects of logging on hole-nesting fauna. A total of 471 hollows was examined in 228 trees felled as part of routine logging operations. Fauna had occupied 43% of all hollows (?2cm minimum entrance width; ?5cm depth). Hollows with small (2-5cm), medium (6-10cm) and large (>10cm) minimum entrance widths had occupancy rates of 29, 44 and 62%, respectively. The internal dimensions of hollows, especially hollow depth, were the best predictors of hollow occupancy, even when variables measured at the tree and site levels were considered. Fauna occupied 57% of all hollow-bearing trees. In a Poisson regression model, the number of hollows in trees that contained evidence of occupancy was positively associated with: (1) the total number of hollows visible in the tree; (2) the proportion of the tree's crown that contained dead branches; and (3) tree diameter. The number of different vertebrate species that occupied trees was positively associated with the same explanatory variables except tree diameter. Thus, our results suggest that trees with multiple hollows and dead branches in the crown should be preferentially selected for occupancy by hollow-using fauna. Our results suggest that trees with the largest diameter are not the most suitable for retention. Possibly because they contain proportionally fewer hollows with small entrances, which are favoured by some vertebrate species.     

Tree species composition and similarity in semideciduous forest fragments of southeastern Brazil

This study investigates the influence of fragment size on tree species composition, species richness and on individual groups of species within 11 semideciduous forest fragments in southeastern Brazil. We compared same-sized samples of 500 trees from 10 fragments <100 ha, allocated to three size categories, with three 500-tree samples collected in different areas within a large forest, used as a reference forest. The variation in species richness, in the proportion of species/individuals in dispersal modes, and in the proportion of rare species was not related to fragment size. Nonetheless, comparisons between the mean values of these variables of each fragment size categories, using 95% confidence intervals, showed a wider range of variation within the category of small-sized fragments than in the other size categories. NMS ordination plot also suggested the absence of a relationship between fragment area and tree species composition. However, multiple regressions using the scores from the NMS ordination as response variables, and area and disturbance intensities as predictor variables, suggested that the interaction of area and disturbance might be a good predictor of species composition. Pre-existing environmental heterogeneity and geographical proximity also appeared to play a role in the variations of forest composition among the fragments studied. Our results demonstrated the high conservation value of small forest fragments.     

From genetic diversity and structure to conservation: Genetic signature of recent population declines in three mouse lemur species (Microcebus spp.)

The exceptional biodiversity of Madagascar is threatened by anthropogenic landscape changes that took place during the 2000 years of human colonization. This study focuses on the influence of geographic distance and forest fragmentation on genetic diversity and population differentiation of three rare, nocturnal, arboreal lemur species in northwestern Madagascar. Historic declines in population sizes as a consequence of forest fragmentation are quantified and dated. Eighteen sites were visited, and a total of 205 Microcebus ravelobensis, 45 M. bongolavensis and 78 M. danfossi were genotyped with eight microsatellite loci. Genetic differentiation among the sites, as measured by F_ST, ranged from 0.01 to 0.19. These values were significant in almost all cases and indicated genetic structure in the samples. Isolation-by-distance was detected in one species and a STRUCTURE analysis indicated that fragmentation further promoted genetic differentiation. Bayesian methods revealed that populations from all three species underwent a major demographic collapse of around two orders of magnitude. This decrease probably began after the arrival of humans, most likely within the last 500 years. This result suggests that anthropogenic changes may have been limited during the first 1500 years of human colonization in all three ranges. Two of the study species (M. danfossi, M. bongolavensis) lack effectively protected areas in their ranges. Consequently, quick conservation actions are now needed in order to secure the remaining genetic diversity of these species.     

Bird conservation in fragmented Mediterranean forests of Spain: effects of geographical location, habitat and landscape degradation

The effects of habitat fragmentation on forest bird assemblages were analysed in 214 holm oak (Quercus ilex) remnants spread across the northern and southern plateaux of central Spain. Bird richness was highly dependent on fragment area for all species regardless of isolation, and barely affected by habitat traits. Geographical location was associated with high differences in richness of bird assemblages, which included 17 species exclusive to northern remnants and one exclusive to southern remnants. This supports the hypothesis that habitat suitability deteriorates sharply from north to south for forest birds in Spain. The species-area relationships of bird assemblages sampled in fragmented forests along a broad continental gradient (from Norway to southern Spain) showed that true forest birds only nest in woodlands >100 ha in southern Spain, whereas the full complement of forest species occurs in much smaller fragments in central-western Europe. Loss of species that are particularly sensitive to habitat fragmentation accounts for these differences between dry Spanish and mesic European woodlands. These results are explained by the low habitat suitability of Spanish woodlands, associated with the restrictive conditions for plant regeneration in the Mediterranean climate and long-standing human usage. There is, therefore, a particular need to develop management strategies that conserve birds, and probably other forest organisms, in Mediterranean regions by preventing habitat deterioration and decreases in fragment size, and by conserving all woods >100 ha.     

Birds in eucalypt and pine forests: landscape alteration and its implications for research models of faunal habitat use

Most studies of faunal habitat fragmentation are based on a human perspective of the landscape in which landscape elements are classified as habitat and non-habitat. Moreover, many landscape models that define “habitat patches” assume that the same set of patches will be suitable for all taxa or a broad range of taxa. McIntyre and Hobbs [Conservation Biology 13 (1999) 1282] recently proposed a model in which landscapes can be classified according to the amount of habitat remaining and in which the remaining habitat can correspond to a continuum or gradient of modification. The perception of a landscape as being intact, variegated, fragmented or relictual [sensu Conservation Biology 13 (1999)] will depend on the capacity of individual species to utilise modified habitat. We suggest that although the continuum concept of habitat use is reasonably well established for plants, faunal studies have often ignored the notion of a gradient of habitat use and have classified landscape areas simplistically and inappropriately as either habitat or non-habitat. Data on birds in southeastern Australia are used to illustrate how the binary view of habitat can be incorrect. Birds were sampled in landscapes that ranged from intact to relictual as defined from an anthropocentric perspective. Our data: (1) illustrated a wide range of bird responses to habitat modification including many that might have been overlooked using a simple binomial approach to habitat classification, and (2) highlighted the fact that the way in which humans perceive landscapes may not correspond to how some elements of the biota perceive the same landscape. Viewing landscapes as a species-specific gradient of states of remaining habitat and condition has important implications for undertaking studies of human impacts on biodiversity and also integrating conservation considerations in production environments. It also challenges the effectiveness of “quick fixes” such as species-based biodiversity surrogates schemes and the uncritical use of generic landscape indices to save “habitat” because the assumption that all species will conform to the same landscape pattern will not hold.     

Seasonal changes in multi-scale spatial structure of soil pH and related parameters along a tropical dry evergreen forest slope

Seasonal changes in multi-scale spatial variation in soil chemical properties, which may be controlled simultaneously by biotic and abiotic factors, have not been studied in tropical dry forests. We evaluated the spatial variation of physico-chemical soil properties, plant litter and terrain attributes at multiple scales in a tropical dry evergreen forest using multivariate geostatistics. Soil samples were collected at different depths using nested interval sampling during 1- and 10-m intervals in both the wet and dry seasons. We measured pH, exchangeable cations (Ex-K⁺ and Ex-Ca²⁺), acidity (Ex-H⁺ and Ex-Al³⁺), particle size (clay and sand contents), and forest floor mass (O_i and O_a). Pronounced spatial variation in pH was observed in surface soil (0-5 cm) but not in deeper soil (5-55 cm). Multi-scale spatial structures with short (20 m) and long (86 m) ranges were observed in the auto- and cross-variograms of soil, litter and slope gradient. Pronounced multi-scale structures were observed simultaneously in pH and Ex-Ca²⁺ both in the wet and dry seasons. Only a short-range structure was observed in Ex-K⁺ and O_a, whereas a long-range structure was pronounced in sand contents and slope gradients. Although the variograms had similar shapes between wet and dry seasons for almost all variables, the short-range structure of the cross-variogram between O_a with pH and base cations was more pronouncedly developed in the wet season than in the dry season. Scale-dependent correlation coefficients suggest that a small-scale spatial variation in pH was connected to heterogeneous litter accumulation via base-cation input, whereas long-range spatial variation was simultaneously linked to particle size and slope gradient. This multivariate geostatistical approach applied within a stand detected biotic and abiotic factors controlling spatial variation in soil properties at both short and long distances.     

Forest fragmentation and the distribution, abundance and conservation of the Tana river red colobus (Procolobus rufomitratus)

Evidence suggests that habitat heterogeneity, disturbance, disease, predation and food resources influence primate population abundance. However, few studies have focused on what habitat factors determine the probability that a primate species will occur in a habitat fragment. We analysed forest habitat and colobus population attributes to determine factors that influenced occurrence and abundance of the critically endangered Tana River red colobus. The probability of colobus inhabiting forests was positively related to the relative amount of habitat edge and canopy tree species composition. Most of the variance in the density of colobus monkeys was explained by basal area of food trees (per ha), basal area per food tree, density of food trees, and basal area per tree for all trees. We conclude that effective conservation of primates in fragmented habitats may require strategies that consider factors that influence both the occurrence of a species and its relative abundance.     

Habitat fragmentation and the desiccation of forest canopies: A case study from eastern Amazonia

Across the deforestation frontier in eastern Amazonia, we examined the relationship between edge-related forest desiccation and deforestation patterns using remote-sensing techniques. Canopy-moisture levels were estimated over an eight-year period in three study sites that encompassed ∼100,000 km² in area. We found four main effects of deforestation on dry-season canopy desiccation. First, intact forests showed no detectable change in canopy water content whereas forests adjacent to clearings showed significant water loss. Second, the distance to which edge-related desiccation penetrated into forest interiors varied among landscapes with differing forest loss and fragmentation. In moderately fragmented landscapes (with 65% and 51% remaining forest cover), canopy desiccation extended 1-1.5 km into forest interiors, whereas in heavily fragmented landscapes (20% forest cover) desiccation penetrated up to 2.7 km into forests. Third, the magnitude of edge-related desiccation varied among landscapes with differing fragmentation. Moderately fragmented landscapes exhibited a greater magnitude of change in canopy-water loss over the first 1 km from an edge than did heavily fragmented landscapes. Finally, forest desiccation penetrated further into forests over time in the moderately fragmented landscapes, but not in the heavily fragmented landscape, where edge-related desiccation had evidently ‘saturated’ remaining forests. We conclude that protracted dry seasons will have far more serious effects on fragmented than intact rainforests, with the former becoming highly vulnerable to destructive fires. With ∼30,000 km of new forest edge being created annually in Brazilian Amazonia, these finding have serious implications for forest conservation.     

Structure of the advanced regeneration community in tropical rain forest fragments of Los Tuxtlas, Mexico

We characterized the tree seedling community within seven forest fragments of different size (3-640 ha) at Los Tuxtlas, Mexico. We considered individual density, species richness, diversity, composition and functional group (shade tolerant, non-pioneer-light demander and pioneer species). We recorded 8038 individuals, belonging to 128 species and 40 morphospecies. Overall, shade-tolerant species had the highest density and diversity followed by non-pioneer-light demanders and pioneer species. Mean individual density per plot was not related to fragment size, but mean species richness per plot, total observed species richness and diversity were inversely related to fragment size, with the smallest fragments having the highest values. Species composition comparisons highlighted low similarity among fragments. Furthermore, larger fragments shared more species with the smallest fragments than between each other. Our results show that the largest fragments do not always hold the highest species richness; that small fragments comprise of high seedling species diversity, and represent a high regeneration potential for tree native species in the study landscape.