Carlos A. Peres

Primary forests are irreplaceable for sustaining tropical biodiversity

Human-driven land-use changes increasingly threaten biodiversity, particularly in tropical forests where both species diversity and human pressures on natural environments are high. The rapid conversion of tropical forests for agriculture, timber production and other uses has generated vast, human-dominated landscapes with potentially dire consequences for tropical biodiversity. Today, few truly undisturbed tropical forests exist, whereas those degraded by repeated logging and fires, as well as secondary and plantation forests, are rapidly expanding. Here we provide a global assessment of the impact of disturbance and land conversion on biodiversity in tropical forests using a meta-analysis of 138 studies. We analysed 2,220 pairwise comparisons of biodiversity values in primary forests (with little or no human disturbance) and disturbed forests. We found that biodiversity values were substantially lower in degraded forests, but that this varied considerably by geographic region, taxonomic group, ecological metric and disturbance type. Even after partly accounting for confounding colonization and succession effects due to the composition of surrounding habitats, isolation and time since disturbance, we find that most forms of forest degradation have an overwhelmingly detrimental effect on tropical biodiversity. Our results clearly indicate that when it comes to maintaining tropical biodiversity, there is no substitute for primary forests.

Quantifying the biodiversity value of tropical primary, secondary, and plantation forests

Biodiversity loss from deforestation may be partly offset by the expansion of secondary forests and plantation forestry in the tropics. However, our current knowledge of the value of these habitats for biodiversity conservation is limited to very few taxa, and many studies are severely confounded by methodological shortcomings. We examined the conservation value of tropical primary, secondary, and plantation forests for 15 taxonomic groups using a robust and replicated sample design that minimized edge effects. Different taxa varied markedly in their response to patterns of land use in terms of species richness and the percentage of species restricted to primary forest (varying from 5% to 57%), yet almost all between-forest comparisons showed marked differences in community structure and composition. Cross-taxon congruence in response patterns was very weak when evaluated using abundance or species richness data, but much stronger when using metrics based upon community similarity. Our results show that, whereas the biodiversity indicator group concept may hold some validity for several taxa that are frequently sampled (such as birds and fruit-feeding butterflies), it fails for those exhibiting highly idiosyncratic responses to tropical land-use change (including highly vagile species groups such as bats and orchid bees), highlighting the problems associated with quantifying the biodiversity value of anthropogenic habitats. Finally, although we show that areas of native regeneration and exotic tree plantations can provide complementary conservation services, we also provide clear empirical evidence demonstrating the irreplaceable value of primary forests.

The Potential for Species Conservation in Tropical Secondary Forests

In the wake of widespread loss of old-growth forests throughout the tropics, secondary forests will likely play a growing role in the conservation of forest biodiversity. We considered a complex hierarchy of factors that interact in space and time to determine the conservation potential of tropical secondary forests. Beyond the characteristics of local forest patches, spatial and temporal landscape dynamics influence the establishment, species composition, and persistence of secondary forests. Prospects for conservation of old-growth species in secondary forests are maximized in regions where the ratio of secondary to old-growth forest area is relatively low, older secondary forests have persisted, anthropogenic disturbance after abandonment is relatively low, seed-dispersing fauna are present, and old-growth forests are close to abandoned sites. The conservation value of a secondary forest is expected to increase over time, as species arriving from remaining old-growth forest patches accumulate. Many studies are poorly replicated, which limits robust assessments of the number and abundance of old-growth species present in secondary forests. Older secondary forests are not often studied and few long-term studies are conducted in secondary forests. Available data indicate that both old-growth and second-growth forests are important to the persistence of forest species in tropical, human-modified landscapes.

Effects of habitat fragmentation on plant guild structure in the montane Atlantic forest of southeastern Brazil

Abstract Habitat fragmentation is a major cause of biodiversity erosion in tropical forests. The Brazilian Atlantic forest has both high species richness and a long history of anthropogenic disturbance, beginning with colonial agriculture in the sixteenth century. Here we examine the species composition and guild structure of woody plants within five montane Atlantic forest fragments of the Tiet River basin, State of Sao Paulo, southeastern Brazil, ranging from 5 to 7900 ha in area. We found a negative relationship between fragment size and the relative importance of tree and shrub species that (1) depend on abiotic modes of seed dispersal, (2) are shade-intolerant, and (3) occupy the forest canopy. As fragment size decreased, there was a marked rise in the relative importance of ruderal species, primarily in the Compositae, Euphorbiaceae, Solanaceae, and Leguminosae. There also was a 9% average decline in smaller fragments in relative importance of Myrtaceae, Lauraceae, Sapotaceae, and Rubiaceae, which are the main sources of fleshy fruits for vertebrate frugivores in these forests. Our results suggest that predictable shifts in plant guild structure occur as tropical forest fragments are reduced in size, and that small fragments may become dominated by edges and the surrounding habitat matrix. We suggest that small forest fragments will be unlikely to preserve intact plant and animal assemblages of Brazils Atlantic coastal forest

Effects of hunting on western Amazonian primate communities

Transect surveys were carried out in seven western Amazonian upland forest sites and compared with four additional sites to examine effects of hunting by humans on the structure of species-rich primate communities. Primate body mass was a strong positive correlate of its crude and metabolic population biomass in non-hunted but not in hunted sites. Primate body mass was a good negative correlate of population density in hunted but not in non-hunted sites. Group density was not clearly affected by hunting activity. Large primates had significantly lower group densities than small primates in both hunted and non-hunted sites. These trends are largely a consequence of differences in abundance of large-bodied genera (i.e.Alouatta, Ateles and Lagothrix), accounting for the bulk of the primate biomass in non-hunted sites, but being over-harvested or becoming extinct in sites hunted by man.

Conservation value of remnant riparian forest corridors of varying quality for amazonian birds and mammals.

Forest corridors are often considered the main instrument with which to offset the effects of habitat loss and fragmentation. Brazilian forestry legislation requires that all riparian zones on private landholdings be maintained as permanent reserves and sets fixed minimum widths of riparian forest buffers to be retained alongside rivers and perennial streams. We investigated the effects of corridor width and degradation status of 37 riparian forest sites (including 24 corridors connected to large source-forest patches, 8 unconnected forest corridors, and 5 control riparian zones embedded within continuous forest patches) on bird and mammal species richness in a hyper-fragmented forest landscape surrounding Alta Floresta, Mato Grosso, Brazil. We used point-count and track-sampling methodology, coupled with an intensive forest-quality assessment that combined satellite imagery and ground truthed data. Vertebrate use of corridors was highly species-specific, but broad trends emerged depending on species life histories and their sensitivity to disturbance. Narrow and/or highly disturbed riparian corridors retained only a depauperate vertebrate assemblage that was typical of deforested habitats, whereas wide, well-preserved corridors retained a nearly complete species assemblage. Restriction of livestock movement along riparian buffers and their exclusion from key areas alongside deforested streams would permit corridor regeneration and facilitate restoration of connectivity.

Primate responses to phenological changes in an Amazonian terra firme forest

The responses of saddleback tamarins Saguinus fuscicollis avilapiresi, moustached tamarins S. mystax pileatus, brown capuchins Cebus apella and gray woolly monkeys Lagothrix lagotricha cana to seasonal changes in plant phenology were examined in undisturbed terra firme forest in the upper Urucu river, Brazilian Amazonia. Primate species fed largely on ripe fruit pulp for most of the year, but shifted to alternative plant resources during the dry season, when the density of fruiting trees and the abundance of ripe fruit reached their lowest levels. The main dry season plant resource used by the two tamarin species was nectar, while those of brown capuchins and woolly monkeys are immature seeds and young foliage, respectively. Exudates of Parkia seedpods were heavily used by all species. Nondietary seasonal adaptations to lean fruit supplies are described for these and other sympatric primate species mainly in terms of pronounced shifts in habitat use and ranging behavior. -from Author

Density compensation in neotropical primate communities: evidence from 56 hunted and nonhunted Amazonian forests of varying productivity

Abstract Density compensation is a community-level phenomenon in which increases in the abundance of some species may offset the population decline, extirpation, or absence of other potentially interacting competitors. In this paper we examine the evidence for density compensation in neotropical primate assemblages using data from 56 hunted and nonhunted, but otherwise undisturbed, forest sites of Amazonia and the Guianan shields from which population density estimates are available for all diurnal primate species. We found good evidence of density compensation of the residual assemblage of nonhunted mid-sized species where the large-bodied (ateline) species had been severely reduced in numbers or driven to local extinction by subsistence hunters. Only weak evidence for density compensation, however, was detected in small-bodied species. These conclusions are based on the effects of ordinal measures of hunting pressure on the aggregate primate biomass across different size classes after controlling for the effects of forest type and productivity. These results are interpreted primarily in relation to patterns of niche partitioning between different primate functional groups or ecospecies. This study suggests that while overhunting drastically reduces the average body size in multi-species assemblages of forest vertebrates, depletion of large-bodied species is only partially offset (i.e. undercompensated) by smaller taxa.

Fire-mediated dieback and compositional cascade in an Amazonian forest

The only fully coupled land–atmosphere global climate model predicts a widespread dieback of Amazonian forest cover through reduced precipitation. Although these predictions are controversial, the structural and compositional resilience of Amazonian forests may also have been overestimated, as current vegetation models fail to consider the potential role of fire in the degradation of forest ecosystems. We examine forest structure and composition in the Arapiuns River basin in the central Brazilian Amazon, evaluating post-fire forest recovery and the consequences of recurrent fires for the patterns of dominance of tree species. We surveyed tree plots in unburned and once-burned forests examined 1, 3 and 9 years after an unprecedented fire event, in twice-burned forests examined 3 and 9 years after fire and in thrice-burned forests examined 5 years after the most recent fire event. The number of trees recorded in unburned primary forest control plots was stable over time. However, in both once- and twice-burned forest plots, there was a marked recruitment into the 10–20 cm diameter at breast height tree size classes between 3 and 9 years post-fire. Considering tree assemblage composition 9 years after the first fire contact, we observed (i) a clear pattern of community turnover among small trees and the most abundant shrubs and saplings, and (ii) that species that were common in any of the four burn treatments (unburned, once-, twice- and thrice-burned) were often rare or entirely absent in other burn treatments. We conclude that episodic wildfires can lead to drastic changes in forest structure and composition, with cascading shifts in forest composition following each additional fire event. Finally, we use these results to evaluate the validity of the savannization paradigm.

Abiotic and vertebrate seed dispersal in the Brazilian Atlantic forest: implications for forest regeneration

This study documents the proportion of woody plant species having different modes of seed dispersal, and classes of seed and fruit size at 16 Atlantic montane forest plots of southeastern Brazil (23–24 � S). These plots represent six chronosequences (from 5year-old to old-growth forest) of forest regeneration following small-scale shifting agriculture. Our results indicate that there is a gradual but predictable increase in the number of woody plant species relying on vertebrate-mediated seed dispersal in increasingly older plots. Moreover, the percentage of plant species bearing small seeds and fruits ( < 0.6 cm in length) was more than halved from earlier to older forest plots, while the percentage of plant species producing middle-sized seeds and fruits at least doubled. Plant species belonging to the Melastomataceae, Myrsinaceae, Rubiaceae and Flacourtiaceae comprised a large proportion of the small-seeded and fruit species (33–53%), and largely occurred in early successional forest plots (5–30 years old). In contrast, species belonging to the Myrtaceae and Lauraceae represented most of the species (51–72%) bearing medium-sized seeds and fruits (0.6–1.5 cm in length), and occurred primarily in the old-growth forests. Shifts in the relative importance of dispersal strategies during the regeneration process of Atlantic montane forest, as well as in diaspore size appear to be related to the balance between early successional and shade-tolerant species associated with particular life forms and plant families. Finally, we discuss the relationships between the species richness of Myrtaceae and Lauraceae trees, seed dispersal by medium to large vertebrates, and possible regeneration scenarios for the Atlantic forest. # 2002 Elsevier Science Ltd. All rights reserved.