Drastic erosion in functional attributes of tree assemblages in Atlantic forest fragments of northeastern Brazil

The long-term dynamics of plant communities remain poorly understood in isolated tropical forest fragments. Here we test the hypothesis that tropical tree assemblages in both small forest fragments and along forest edges of very large fragments are functionally much more similar to stands of secondary growth (5-65-yr old) than to core primary forest patches. The study was carried out in a severely fragmented landscape of the Brazilian Atlantic forest. Nine functional attributes of tree assemblages were quantified by sampling all trees (DBH ? 10 cm) within 75 plots of 0.1 ha distributed in four forest habitats: small forest fragments (3.4-79.6 ha), forest edges, second-growth patches, and primary forest interior areas within a large forest fragment (3500 ha). These habitats were markedly different in terms of tree species richness, and in the proportion of pioneer, large-seeded, and emergent species. Age of second-growth stands explained between 31.4% and 88.2% of the variation in the functional attributes of tree assemblages in this habitat. As expected, most traits associated with forest edges and small forest fragments fell within the range shown by early (<25-yr old) and intermediate-aged secondary forest stands (25-45-yr old). In contrast to habitat type, tree assemblage attributes were not affected by vegetation type, soil type and the spatial location of plots. An ordination analysis documented a striking floristic drift in edge-affected habitats. Our results suggest that conservation policy guidelines will fail to protect aging, hyper-fragmented landscapes from drastic impoverishment if the remaining forest patches are heavily dominated by edge habitat.     

The challenge of maintaining Atlantic forest biodiversity: A multi-taxa conservation assessment of specialist and generalist species in an agro-forestry mosaic in southern Bahia

Recent developments have highlighted the importance of forest amount at large spatial scales and of matrix quality for ecological processes in remnants. These developments, in turn, suggest the potential for reducing biodiversity loss through the maintenance of a high percentage of forest combined with sensitive management of anthropogenic areas. We conducted a multi-taxa survey to evaluate the potential for biodiversity maintenance in an Atlantic forest landscape that presented a favorable context from a theoretical perspective (high proportion of mature forest partly surrounded by structurally complex matrices). We sampled ferns, butterflies, frogs, lizards, bats, small mammals and birds in interiors and edges of large and small mature forest remnants and two matrices (second-growth forests and shade cacao plantations), as well as trees in interiors of small and large remnants. By considering richness, abundance and composition of forest specialists and generalists, we investigated the biodiversity value of matrix habitats (comparing them with interiors of large remnants for all groups except tree), and evaluated area (for all groups) and edge effects (for all groups except trees) in mature forest remnants. Our results suggest that in landscapes comprising high amounts of mature forest and low contrasting matrices: (1) shade cacao plantations and second-growth forests harbor an appreciable number of forest specialists; (2) most forest specialist assemblages are not affected by area or edge effects, while most generalist assemblages proliferate at edges of small remnants. Nevertheless, differences in tree assemblages, especially among smaller trees, suggest that observed patterns are unlikely to be stable over time.     

Conservation value of forest fragments to Palaeotropical bats

Forested landscapes in Southeast Asia are becoming increasingly fragmented, making this region a conservation and research priority. Despite its importance, few empirical studies of effects of fragmentation on biodiversity have been undertaken in the region, limiting our ability to inform land-use regimes at a time of increased pressure on forests. We estimated the biodiversity value of forest fragments in peninsular Malaysia by studying fragmentation impacts on insectivorous bat species that vary in dependence of forest. We sampled bats at seven continuous forest sites and 27 forest fragments, and tested the influence of fragment isolation and area on the abundance, species richness, diversity, composition and nestedness of assemblages, and the abundance of the ten most common species. Overall, isolation was a poor predictor of these variables. Conversely, forest area was positively related with abundance and species richness of cavity/foliage-roosting bats, but not for that of cave-roosting or edge/open space foraging species. The smallest of fragments (<150 ha) were more variable in species composition than larger fragments or continuous forest, and larger fragments retained substantial bat diversity, comparable to continuous forest. Some fragments exhibited higher bat abundance and species richness than continuous forest, though declines might occur in the future because of time lags in the manifestation of fragmentation effects. Our findings suggest that fragments >300 ha contribute substantially to landscape-level bat diversity, and that small fragments also have some value. However, large tracts are needed to support rare, forest specialist species and should be the conservation priority in landscape-level planning. Species that roost in tree cavities or foliage may be more vulnerable to habitat fragmentation than those that roost in caves.     

Forest fragment size and microhabitat effects on palm seed predation

The establishment of plant species depends crucially on where the seeds are deposited. However, since most studies have been conducted in continuous forests, not much is known about the effects of forest fragmentation on the maintenance of abiotic and biotic characteristics in microhabitats and their effects on seed survival. In this study, we evaluated the effects of forest fragmentation on the predation upon the seeds of the palm Syagrus romanzoffiana in three microhabitats (interior forest, forest edge and gaps) in eight fragments of semi-deciduous Atlantic forest ranging in size from 9.5 ha to 33,845 ha in southeastern Brazil. Specifically, we examined the influence of the microhabitat structure, fauna and fragment size on the pattern of seed predation. Fragments <100 ha showed similar abiotic and biotic characteristics to those of the forest edge, with no seed predation in these areas. Forest fragments 230-380 ha in size did not present “safe sites” for S. romanzoffiana seed survival and showed high seed predation intensity in all microhabitats evaluated. In fragments larger than 1000 ha, the seed predation was lower, with abiotic and biotic differences among gaps, interior forests and forest edges. In these fragments, the survival of S. romanzoffiana seeds was related to squirrel abundance and interior forest maintenance. Based on these results, we concluded that there are no safe sites for S. romanzoffiana seed establishment in medium- and small-sized fragments as result of the biotic and abiotic pressure, respectively. We suggest that on these forest fragments, management plans are needed for the establishment of S. romanzoffiana, such as interior forest improvement and development in small-sized sites in order to minimize the edge effects, and on medium-sized fragments, we suggest post-dispersal seed protection in order to avoid seed predation by vertebrates. Our findings also stress the importance of assessing the influence of forest fragmentation on angiosperm reproductive biology as part of the effective planning for the management of fragmented areas.     

Effects of fragmentation on pollinator abundance and fruit set of an abundant understory palm in a Mexican tropical forest

Tropical forest fragmentation affects both biodiversity and plant reproductive success when small, isolated fragments sustain a reduced diversity or abundance of pollinators. Fragmentation-related effects have been poorly investigated in the case of palms, an important structural and functional component of tropical forests. We examined the relationships between fragment size and diversity and abundance of flower visitors, and palm reproduction, by quantifying the arthropod fauna associated to inflorescences of the palm Astrocaryum mexicanum, and its fruit set, in fragments of different size. The sample yielded a total of 228,772 arthropods (10 orders, 60 species). Coleoptera was the predominant group (?50% of the species), followed by Hymenoptera (20%), while the remaining (30%) was distributed among the other eight orders. We found a predominance of pollinating insects (Coleoptera-Nitidulidae), representing 85% of all visitors. Pollinator abundance was negatively affected by fragmentation, with a 4.2-fold average difference between small (<35 ha) and large (114-700 ha) fragments. However, fruit set was relatively high (?0.7) and not affected by fragmentation during three reproductive seasons. This could be explained because small fragments retained remarkably high numbers of pollinators (1191.4/inflorescence) and by the high abundance of palms (and flowers) in fragments. Further research is needed, however, to assess if fragmentation restricts pollinator movements to plants within the fragments, leading to a reduction in genetic variation of the progeny present in forest remnants.     

Prospects for biodiversity conservation in the Atlantic Forest: Lessons from aging human-modified landscapes

Recent global assessments have shown the limited coverage of protected areas across tropical biotas, fuelling a growing interest in the potential conservation services provided by anthropogenic landscapes. Here we examine the geographic distribution of biological diversity in the Atlantic Forest of South America, synthesize the most conspicuous forest biodiversity responses to human disturbances, propose further conservation initiatives for this biota, and offer a range of general insights into the prospects of forest species persistence in human-modified tropical forest landscapes worldwide. At the biome scale, the most extensive pre-Columbian habitats across the Atlantic Forest ranged across elevations below 800 masl, which still concentrate most areas within the major centers of species endemism. Unfortunately, up to 88% of the original forest habitat has been lost, mainly across these low to intermediate elevations, whereas protected areas are clearly skewed towards high elevations above 1200 masl. At the landscape scale, most remaining Atlantic Forest cover is embedded within dynamic agro-mosaics including elements such as small forest fragments, early-to-late secondary forest patches and exotic tree monocultures. In this sort of aging or long-term modified landscapes, habitat fragmentation appears to effectively drive edge-dominated portions of forest fragments towards an early-successional system, greatly limiting the long-term persistence of forest-obligate and forest-dependent species. However, the extent to which forest habitats approach early-successional systems, thereby threatening the bulk of the Atlantic Forest biodiversity, depends on both past and present landscape configuration. Many elements of human-modified landscapes (e.g. patches of early-secondary forests and tree monocultures) may offer excellent conservation opportunities, but they cannot replace the conservation value of protected areas and hitherto unprotected large patches of old-growth forests. Finally, the biodiversity conservation services provided by anthropogenic landscapes across Atlantic Forest and other tropical forest regions can be significantly augmented by coupling biodiversity corridor initiatives with biota-scale attempts to plug existing gaps in the representativeness of protected areas.     

The effects of forest patch size and matrix type on changes in carabid beetle assemblages in an urbanized landscape

In this study we compared ground beetles (Carabidae) from a range of different forest fragments along an urbanization gradient in Brussels, Belgium. We address the following questions: (i) How does the degree of urbanization in the surrounding habitat affect forest beetles, and does it interact with the effects of patch size and distance to forest edge? (ii) Do these factors have a different effect at the level of individual species, habitat affinity groups or total community? During 2002 we sampled 13 forest plots in 10 forest patches, ranging in size from 5.27 to 4383 ha. The beetles were captured using transects of pitfall traps from the edge to a distance of 100 m into each woodland and identified to species level. Effects of urbanization, forest size and forest edge were evaluated on total species number, abundance and habitat affinity groups and ten abundant, widespread model carabid species. Overall, the effects of urbanization, forest size and edge effects slightly influenced total species richness and abundance but appeared to have a major effect on ground beetle assemblages through species specific responses. More urbanized sites had significantly fewer forest specialists and more generalist species. Large forest fragments were favoured by forest specialist species while generalist species and species frequently associated with forest (forest generalists) dominated the smaller forests. Forest edges mainly harboured generalist species while forest specialist species were more frequent into the forests if the forest patches were large enough, otherwise they disappeared due to the destruction or impoverishment of their habitat. Our results show the importance of differentiating between habitat affinity, especially habitat generalists versus specialists, the latter having a higher value in nature conservation, and merely the quantity of species represented in human-dominated areas.     

Abundance, body size and movement patterns of a tropical treefrog in continuous and fragmented forests in the Brazilian Amazon

Phyllomedusa tarsius is a hylid frog that breeds in ponds located in a range of habitats from continuous forests to severely disturbed matrix habitats in Central Amazon. During three reproductive seasons, we followed the movement patterns, measured body size and registered abundance and residency time of this species in five habitats: pasture, Vismia regrowth, Cecropia regrowth, 1 and 10 ha forest fragments, and continuous forest. The frog captures were strongly correlated with rainfall in all disturbed habitats, but not in continuous forest, probably because individuals respond more directly to rainfall patterns in more open habitats. Males in disturbed habitats were smaller than those found in continuous forest, perhaps as a result of differences in habitat quality. Males remained at sites for longer periods in fragments and continuous forest compared to matrix habitats. Here again, the quality and suitability of breeding sites in matrix habitats may be lower than in continuous forest resulting in the need for more movement. We found bigger subpopulations in matrix habitat ponds and a higher percentage of individuals moving among them when compared to continuous forest ponds. Constant movement of individuals among disturbed subpopulations decreases population isolation and increases interbreeding among different subpopulations. No movement between individuals from continuous forest ponds and disturbed habitats was observed. This suggests that the disturbed habitat subpopulations are not acting as sink subpopulations for continuous forest populations. The maintenance of individuals in fragments is more dependent on local conditions for reproduction and on subpopulations in the matrix habitat than on recruitment of individuals from populations in continuous forest.     

Supply of tree-holes limits nest density of cavity-nesting birds in primary and logged subtropical Atlantic forest

Tree cavities are proposed to limit populations and structure communities of cavity-nesting birds. Although the greatest diversity of cavity-nesting birds is found in tropical and subtropical moist forests, little is known about how tropical logging affects the abundance of cavities or cavity-nesting birds. We compared the abundance of cavities and cavity nests between primary and selectively-logged subtropical moist Atlantic forest in Argentina, and conducted the first before-after controlled nest-box addition experiment to determine whether nest sites limit the breeding density of cavity-nesting birds in tropical or subtropical moist forest. Visual inspection of 86 cavities identified through ground-surveys revealed that only 19% were suitable for nesting birds, suggesting that cavity abundance may be overestimated in the literature on tropical forests. Suitable cavities were found in fewer than 1% of 1156 trees <60 cm dbh but 20% of 20 trees >100 cm dbh. Logged forest had half the basal area of primary forest, one third the density of large trees, nine times fewer cavities suitable for nesting birds, and 17 times fewer active nests. When we added nest boxes, nesting density increased on treatment plots but not on control plots in both logged and primary forest, suggesting that cavity supply can limit nest density even in relatively undisturbed forest. This is the first experiment to show how reduced cavity supply in logged tropical forest can limit breeding density of cavity-nesting birds. International initiatives such as forest certification should promote tropical timber management strategies that conserve large live cavity-bearing trees.     

Does the matrix matter? A forest primate in a complex agricultural landscape

Many threatened primates now exist in fragmented forest habitats. The survival of these populations may depend on their ability to utilise agricultural or other matrix habitats between forest fragments, but this is poorly known. Here, we systematically investigate an arboreal primate’s use of a heterogeneous matrix in a fragmented forest landscape: the Angola black-and-white colobus (Colobus angolensis palliatus) in southern Kenya. We used a novel technique, based on semi-structured interviews with local informants, to address the difficulty of sampling relatively rare but important events, such as dispersal between fragments. We found that colobus frequently travelled and foraged in indigenous matrix vegetation (such as mangrove, wooded shrubland and shrubland) up to 4 km from the nearest forest fragments. Agricultural habitats, such as perennial plantation (coconut, mango and cashew nut) were also used by colobus for travelling and foraging (in remnant indigenous trees). The probability of sighting colobus in the matrix increased with the proportion of both tall (>6 m) vegetation cover and food tree cover, but declined with distance from forest habitat. Our findings suggest that certain matrix habitats are important for C. a. palliatus, and that future primate conservation initiatives might benefit from adopting a ‘landscape-level’ approach to habitat management, particularly in fragmented forest systems.     

Matrix effects on bird assemblages in fragmented Afromontane forests in South Africa

We examine the effects of matrix type on forest bird species richness in historically fragmented forests of the KwaZulu-Natal midlands, South Africa. Bird species-area relationships for forest fragments within natural grassland were compared with those surrounded by plantation forestry (Pinus spp.). While fragments in grasslands displayed a species-area effect, no such effect (slope ∼0) was detected for fragments in plantations. The critical fragment size to avoid an island effect on species richness was 302 ha for fragments in grasslands, and contained 51 of the 61 forest bird species encountered. Small forest fragments (<50 ha) within grasslands were less species-rich than those surrounded by plantation, while the reverse was true for forests larger than 50 ha. Bird density was significantly lower in larger forest patches within plantation when compared to those in grassland. However, a slight decline in species density with increasing species richness in a patch (i.e. weak density compensation) characterised only those bird assemblages surrounded by a grassland matrix, suggesting these are approaching species saturation. Commercial plantations may increase the likelihood of colonisation of, and immigration from, small forest fragments by birds, reducing the incidence of area-dependent extinction in small fragments, but may also result in lower species richness in larger fragments. The latter is likely a consequence of the promotion by plantations of a wider distribution of generalist species in, and the loss of some specialised or rare species from, large patches. Management options are to avoid planting plantations near large forest patches and to increase the size of small patches where possible. Where afforestation is unavoidable, placing plantations in the vicinity of small forest patches rather than large forest patches may be preferable.     

The Brazilian Atlantic Forest: How much is left, and how is the remaining forest distributed? Implications for conservation

The neotropical Atlantic Forest supports one of the highest degrees of species richness and rates of endemism on the planet, but has also undergone a huge forest loss. However, there exists no broad-scale information about the spatial distribution of its remnants that could guide conservation actions, especially when systematic biodiversity data are not available. In this context, our objectives were to quantify how much of the forest still remains, and analyze its spatial distribution. We considered the entire Brazilian Atlantic Forest, and eight sub-regions, defined according to species distribution. The results revealed a serious situation: more than 80% of the fragments are <50 ha, almost half the remaining forest is <100 m from its edges, the average distance between fragments is large (1440 m), and nature reserves protect only 9% of the remaining forest and 1% of the original forest. On the other hand, our estimates of existing Atlantic Forest cover were higher than previous ones (7-8%), ranging from 11.4% to 16%. The differences among estimates are mainly related to our inclusion of intermediate secondary forests and small fragments (<100 ha), which correspond to approximately 32-40% of what remains. We suggest some guidelines for conservation: (i) large mature forest fragments should be a conservation priority; (ii) smaller fragments can be managed in order to maintain functionally linked mosaics; (iii) the matrix surrounding fragments should be managed so as to minimize edge effects and improve connectivity; and (iv) restoration actions should be taken, particularly in certain key areas. The clear differences in the amount remaining and its spatial distribution within each sub-region must be considered when planning for biodiversity conservation.     

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 forest fragmentation on two sister genera of Amazonian rodents (Myoprocta acouchy and Dasyprocta leporina)

Because agoutis (Dasyprocta sp.) and acouchies (Myoprocta sp.) are the most important dispersers of several large-seeded Amazonian trees, knowing their responses to forest fragmentation is essential and urgent. But until now, there was no study showing their population trends in Amazonian land forest fragments. The present study was conducted at the Biological Dynamics of Forest Fragments Project, Central Amazon, Brazil. Eleven sites (three fragments of 1 ha, three of 10 ha, two of 100 ha and three sites of continuous forest) were surveyed between 2003 and 2005. Agoutis and acouchies were systematically counted at each site through standard transect censuses and their densities were estimated with DISTANCE 4.1. Overall, I walked 100 km, and encountered 136 acouchies and 35 agoutis. Fragmentation had a significant negative effect on acouchies and a significant positive effect on agouti densities. Acouchy density was 0.64 ± 0.09 inds./ha in continuous forests and 0.07 ± 0.07 inds./ha in 1-ha fragments. On the other hand, agouti density was 0.16 ± 0.05 inds./ha in continuous forests and 0.71 ± 0.24 inds./ha in 1-ha fragments. This study is consistent with the idea that in fragments, larger species of mammals are initially less affected by forest fragmentation than smaller ones. More critical to conservation is the fact that acouchies, which were negatively affected by fragmentation, are restricted to the core region of the Amazonian rainforests. Continued fragmentation of Amazonian forests should have vast negative consequences for the genus.     

Polypore diversity in the herb-rich woodland key habitats of Koli National Park in eastern Finland

Species diversity of polypores (Basidiomycetes) was compared between woodland key habitats (WKHs) and old-growth forest controls in boreal forests in eastern Finland. WKHs, which were set aside for their rich vascular plant flora, turned out not to be hot spots for the species richness of polypores, nor did their species composition represent the overall species richness of the area. Differences in the total volume of CWD, tree species composition and several CWD qualities were reflected as differences in the species assemblages between the groups. The results indicated that only a fraction of the overall polypore diversity was represented in the small-size WKHs (<0.5 ha), and the protection of red-listed and indicator polypores in WKHs was random. However, rare old-growth forest indicators were found even in small-size WKHs, if the CWD quality was appropriate for them. Nevertheless, our study does not answer the question whether the occurrences of rare and red-listed species will survive in small-size WKHs surrounded by altered environments such as clear-cuts, because our study sites were located in undisturbed areas. The results stress the importance to protect typical old-growth forest patches with high CWD volume and quality in boreal forests.     

Land use and conservation value for forest birds in Central Sulawesi (Indonesia)

Unprecedented deforestation is currently underway in Southeast Asia. Since this trend is likely to continue, it is critical to determine the value of human-modified habitats (e.g., mixed-rural habitat) for conserving the regional native forest avifauna. The impacts of ongoing deforestation on the highly endemic avifauna (33%) of Sulawesi (Indonesia) are poorly understood. We sampled birds in primary and secondary forests in the Lore Lindu National Park in central Sulawesi, as well as the surrounding plantation and mixed-rural habitats. Species richness, species density and population density of forest birds showed a consistent decreasing trend in the following order: primary forests > secondary forests > mixed-rural habitat > plantations. Although primary forests contained the highest proportion (85%) of a total of 34 forest species recorded from our point count surveys, 40-yr old secondary forests and the mixed-rural habitat showed high conservation potential, containing 82% and 76% of the forest species, respectively. Plantations recorded only 32% of the forest bird species. Fifteen forest species had the highest abundance in primary forests, while two species had higher abundance outside primary forests. Our simulations revealed that all forest birds that were sensitive to native tree cover could be found in areas with at least 20% continuous native tree cover. Our study shows that although primary forests have the highest conservation value for forest avifauna, the potential of degraded habitats, such as secondary forests and the mixed-rural habitat, for conserving forest species can be enhanced with appropriate land use and management decisions.     

Habitat fragmentation alters the structure of dung beetle communities in the Atlantic Forest

Habitat loss and fragmentation have turned into the most important threats to biodiversity and ecosystem function worldwide. Here we investigate the effects of habitat fragmentation and drastic changes in tree communities on dung beetle richness and community structure. This study was carried out in a severely fragmented 670-km² forest landscape of the Atlantic Forest of north-eastern Brazil. Sampling was carried out in 19 forest fragments between September 2007 and March 2008 with the use of pitfall traps and flight interception traps. A total of 5893 individuals and 30 species of dung beetle were collected. Fragment area and isolation were the most significant explanatory variables for predictable and conspicuous changes in dung beetle species richness. Smaller and isolated fragments presented lower number of species, but fragments with lower tree species richness and lower proportion of shade-tolerant species were also considerably impoverished in terms of dung beetle species richness. The body mass of dung beetles were explained by fragment area and the percentage of emergent trees with smaller and less stratified fragments being dominated by small-bodied dung beetles. An ordination analysis segregated dung beetle communities between small fragments (<100 ha) and the control area. Seventy-seven percent of the species were recorded in the control area and 22% of all species were unique to this habitat. Our findings indicate that large fragments in the Atlantic Forest appear to consist in a sort of irreplaceable habitats for particular groups of dung beetle species, as well as for the integrity of their communities.     

Methods for conservation outside of formal reserve systems: The case of ants in the seasonally dry tropics of Veracruz, Mexico

Like most ecosystems of the world, tropical dry forests of the central coast of the Gulf of Mexico are inadequately preserved. Given that reserve expansion is unlikely, it is imperative that the conservation capacity of the matrix surrounding reserves is enhanced. Here, we examine the habitat value of isolated pasture trees and patches of secondary regrowth in terms of their terrestrial and arboreal ant assemblages in both a wet and dry season. These simplified wooded systems increase species densities within the agricultural matrix and provide habitat for some forest ant species. Estimated species richness of arboreal ants was particularly low on isolated trees, highlighting an important limitation. This was not the case for terrestrial ants, which were particularly species rich under isolated trees. We also found that the inter-site variations in species densities and similarity to the forest ant assemblage for terrestrial and arboreal strata were not correlated, suggesting that responses to restoration may not be as uniform as often thought. This has important implications for the use of indicator taxa in suggesting the response of other taxa. In terms of species composition, neither secondary regrowth nor isolated trees were appropriate replacements for forest fragments, even though the studied forest fragments were small (13-32 ha). The ant assemblages did not exhibit a seasonal change in composition. However, season influenced the contrast between habitats, with isolated trees being more distinct from pasture, and regrowth more closely resembling forests, during the wet season. Microclimatic variables indicate that the forests were least affected by the tropical dry season, and this may contribute to their characteristic fauna. We conclude that even small forest patches make a unique contribution to landscape conservation and that, where reserves are limited, conscientious management of the landscape matrix may provide some species with sufficient new habitat to survive outside of reserve systems. These conclusions are influenced by both season and strata studied.     

Long-term consequences of habitat fragmentation—highland birds in Oaxaca, Mexico

Studies of habitat fragmentation have been restricted primarily to anthropogenically-altered habitats, with most research conducted 60-90 years post-fragmentation. It is unclear whether patterns in older systems concur with results from these dynamic landscapes, and hence the long-term viability of populations inhabiting habitat fragments remains largely unexplored. I focused on resident birds in fragments of humid pine-oak forest in Oaxaca, southern Mexico, isolated over 5000 years ago by climate-change. Seventeen fragments, ranging from 2 ha to over 150,000 ha were sampled in 1997 and 1998 yielding 141 species, of which 60 residents were used for analysis. Avian assemblages exhibited a highly nested structure and, with several notable exceptions, assemblages of birds in low-richness fragments were predictable subsets of those in more diverse fragments. Patch-scale factors—area, shape, elevation, habitat diversity and fractal dimension of edge—all exerted strong univariate influence on avian richness but were so closely inter-related that none had a significant independent effect. Thus, larger fragments were more complex in shape, included higher peaks, supported more diverse forests, and contained higher diversities of resident species. In contrast, the landscape-scale index used—distance from nearest large fragment (>50,000 ha)—had little effect on richness. This was reinforced by species-level analyses—one species was significantly influenced by isolation, compared with 31 species that displayed significant minimum-area distributions, restricted to patches larger than a particular threshold value. In terms of autecology, vagility, relative abundance and elevational breadth were closely related to distribution—those species with greater mobility, higher abundances and broader elevational tolerances were consistently more widespread. I suggest that more abundant species were less prone to extinction initially, more vagile species were better dispersers and species with broader elevational tolerances more likely to be successful colonists. As with previous research from older landscapes, patch-scale factors were consistently found to be influential, with high quality fragments supporting diverse communities regardless of landscape context. This suggests that the influence of landscape-scale factors noted in younger, anthropogenically fragmented systems may be transitory, overwhelmed by patch-scale factors with time. Which patch attributes are most influential could not be resolved, however, indicating that even thousands of years after fragmentation, they affect diversity patterns in concert. Rather than differentiating effects of area from habitat heterogeneity and other patch-level factors, I advocate resource-based approaches to understand and manage diversity in habitat fragments.     

Composition and abundance of birds in Andean alder (Alnus acuminata) patches with past and present harvest in Bolivia

We compared species richness and abundance of birds between five patches under selective Alnus exploitation and five patches that have not been harvested for at least 10 years prior to our study, during the early dry season (April-July 2001), in Cotapata National Park. Using “point counts” we recorded birds and their distribution in two (<1.5 m and >1.5 m) forest layers. Simultaneously we evaluated the floristic structure (size [dbh] distribution, basal area, tree density, tree height, and vegetation cover) and composition (diversity) on three transects placed within each Alnus patch. Both bird diversity and vegetation cover were significantly higher in not presently used patches but only for the higher layer of the forest, whereas plant diversity was higher in presently used patches. Lack of differences between the two types of Alnus patches in any of the vegetation parameters measured in the lower layer was coupled with an indistinct avifauna. Small changes in habitat characteristics following a perturbation like selective logging have the potential to affect richness and abundance of birds, at least within the habitats directly affected by the perturbation.