Felipe P. L. Melo

On the hope for biodiversity-friendly tropical landscapes

With the decreasing affordability of protecting large blocks of pristine tropical forests, ecologists have staked their hopes on the management of human-modified landscapes (HMLs) to conserve tropical biodiversity. Here, we examine key forces affecting the dynamics of HMLs, and propose a framework connecting human disturbances, land use, and prospects for both tropical biodiversity and ecosystem services. We question the forest transition as a worldwide source of new secondary forest; the role played by regenerating (secondary) forest for biodiversity conservation, and the resilience of HMLs. We then offer a conceptual model describing potential successional trajectories among four major landscape types (natural, conservation, functional, and degraded) and highlight the potential implications of our model in terms of research agendas and conservation planning.

Multiple successional pathways in human-modified tropical landscapes : New insights from forest succession, forest fragmentation and landscape ecology research

Old‐growth tropical forests are being extensively deforested and fragmented worldwide. Yet forest recovery through succession has led to an expansion of secondary forests in human‐modified tropical landscapes (HMTLs). Secondary forests thus emerge as a potential repository for tropical biodiversity, and also as a source of essential ecosystem functions and services in HMTLs. Such critical roles are controversial, however, as they depend on successional, landscape and socio‐economic dynamics, which can vary widely within and across landscapes and regions. Understanding the main drivers of successional pathways of disturbed tropical forests is critically needed for improving management, conservation, and restoration strategies. Here, we combine emerging knowledge from tropical forest succession, forest fragmentation and landscape ecology research to identify the main driving forces shaping successional pathways at different spatial scales. We also explore causal connections between land‐use dynamics and the level of predictability of successional pathways, and examine potential implications of such connections to determine the importance of secondary forests for biodiversity conservation in HMTLs. We show that secondary succession (SS) in tropical landscapes is a multifactorial phenomenon affected by a myriad of forces operating at multiple spatio‐temporal scales. SS is relatively fast and more predictable in recently modified landscapes and where well‐preserved biodiversity‐rich native forests are still present in the landscape. Yet the increasing variation in landscape spatial configuration and matrix heterogeneity in landscapes with intermediate levels of disturbance increases the uncertainty of successional pathways. In landscapes that have suffered extensive and intensive human disturbances, however, succession can be slow or arrested, with impoverished assemblages and reduced potential to deliver ecosystem functions and services. We conclude that: (i) succession must be examined using more comprehensive explanatory models, providing information about the forces affecting not only the presence but also the persistence of species and ecological groups, particularly of those taxa expected to be extirpated from HMTLs; (ii) SS research should integrate new aspects from forest fragmentation and landscape ecology research to address accurately the potential of secondary forests to serve as biodiversity repositories; and (iii) secondary forest stands, as a dynamic component of HMTLs, must be incorporated as key elements of conservation planning; i.e. secondary forest stands must be actively managed (e.g. using assisted forest restoration) according to conservation goals at broad spatial scales.

Plant β‐diversity in fragmented rain forests: testing floristic homogenization and differentiation hypotheses

Summary Land-use change is the main driver of global biodiversity loss, but its relative impact on species turnover (β-diversity) across multiple spatial scales remains unclear. Plant communities in fragmented rain forests can undergo declines (floristic homogenization) or increases (floristic differentiation) in β-diversity. We tested these alternative hypotheses analysing a large vegetation data base from a hierarchically nested sampling design (450 plots in 45 forest patches in 3 landscapes with different deforestation levels) at Los Tuxtlas rain forest, Mexico. Differences in β-diversity across spatial scales (i.e. among plots, among patches, and among landscapes) were analysed using multiplicative diversity decompositions of Hill numbers. Plant β-diversity among plots within forest patches decreased in landscapes with higher deforestation levels, leading to floristic homogenization within patches. This homogenization process can be explained by the loss of rare and shade-tolerant plant species, and the recruitment and dominance of disturbance-adapted species, and can limit the accumulation of species (γ-diversity) in landscapes with higher deforestation. Nevertheless, the landscape with the highest deforestation level showed the highest floristic differentiation among patches. This landscape showed the greatest isolation distances between patches; a landscape spatial pattern that can limit the interchange of seeds (and species) between patches. Because the study patches are undergoing secondary succession following disturbances (e.g. logging, edge effects), different disturbance regimes and increased distance among patches could lead to higher β-diversity. Synthesis. These findings indicate that patterns of floristic homogenization and differentiation depend on the landscape configuration and on the spatial scale of analysis. At the landscape scale, our results suggest that, in accordance with non-equilibrium dynamics and the landscape-divergence hypothesis, patches located in landscapes with different forest cover and different connectivity can experience contrasting successional pathways due to increasing levels of compositional differentiation between patches. These novel findings add further uncertainties to the maintenance of biodiversity in severely deforested tropical landscapes and have key ecological implications for biodiversity conservation planning.

Forest fragmentation reduces recruitment of large-seeded tree species in a semi-deciduous tropical forest of southern Mexico

This study tested whether the reduction in the number of large-bodied seed dispersers is correlated with shiftsinthetaxonomicandfunctional(e.g.dispersalmodeandseedsize)traitsoftheseedingcommunitieswithinsmall fragmentsofsemi-deciduousforest,southernMexico.Infivefragments(2.3-640ha)andonecontinuousforestsitewe sampled tree and seedling species in 40 (20 × 20 m) and 120 (3 × 3 m) plots respectively, and recorded the incidence (presence/absence)ofthedisperserfauna(threecommonlarge-birdsand >500-gmammals).Treeandseedlingspecies were categorized according to dispersal mode, seed size and whether they originated from local (i.e. from dropped) or immigrant (i.e. from actively dispersed) seeds. Fragment size negatively correlated with number of species of medium to large vertebrate seed-dispersers and number of seedlings of large-seeded species, but had no influence on functional traits of the adult-tree community. Between 41% and 61% of all seedlings were considered as immigrants and the proportion of immigrant seedlings of large-seeded tree species was negatively correlated with forest size. The results suggestthatbiaseddefaunationinsmallforestfragmentsmayseriouslyreducerecruitmentoflarge-seededtreespecies (>1.4 cm length) dispersed by vertebrates, negatively affecting successional trajectories of small forest fragments.

Conserving Tropical Tree Diversity and Forest Structure: The Value of Small Rainforest Patches in Moderately-Managed Landscapes

Rainforests are undergoing severe deforestation and fragmentation worldwide. A huge amount of small forest patches are being created, but their value in conserving biodiversity and forest structure is still controversial. Here, we demonstrate that in a species-rich and moderately-managed Mexican tropical landscape small rainforest patches (<100 ha) can be highly valuable for the conservation of tree diversity and forest structure. These patches showed diverse communities of native plants, including endangered species, and a new record for the country. Although the number of logged trees increased in smaller patches, patch size was a poor indicator of basal area, stem density, number of species, genera and families, and community evenness. Cumulative species-area curves indicated that all patches had a similar contribution to the regional species diversity. This idea also was supported by the fact that patches strongly differed in floristic composition (high β-diversity), independently of patch size. Thus, in agreement with the land-sharing approach, our findings support that small forest patches in moderately-managed landscapes should be included in conservation initiatives to maintain landscape heterogeneity, species diversity, and ecosystem services.

Extirpation of large-seeded seedlings from the edge of a large Brazilian Atlantic forest fragment

ABSTRACT In this study we assessed the seedling assemblages of a large fragment of the Atlantic forest to test 2 hypotheses: (1) seedling abundance and richness are lower in the forest edge (0–200 m) than in the forest interior (>250 m); and (2) large-seeded seedlings (seeds >1.5 cm) are the main group affected by edge creation. The study was car ried out at the Coimbra forest, an old, 3500-ha fragment surrounded by sugar cane plantations in northeast Brazil. The seedling survey was based on 200-m-long transects along which 420 plots of 1-m2 were set up per habitat and per season (dry and rainy). Within the plots, all shrub, tree, palm, and liana species seedlings ≤ 50 cm tall were counted and classified to morphospecies level. A total of 13 208 seedlings were recorded in the whole survey. At plot level, forest edge and interior showed similar scores for both average seedling density (4.7–11.2 seedlings·m−2) and richness (2.8–5.1 species·m−2) irrespective of season. At community level, however, scores for total species richness were 4.8–17.9% lower in forest edge plots than in those of the forest interior, depending on the estimator used. Moreover, large-seeded species accounted for 2.3–2.7% of all species recorded in forest edge plots, yet this group reached 13.1–14.9% in forest interior plots. As a consequence, the forest edge housed between 166 and 262 large-seeded seedlings·ha−1, whereas the forest interior housed 5 952–6 047 large-seeded seedlings·ha−1. Our results suggest that old forest edges hold biased and impoverished assemblages of seedlings, particularly in terms of large-seeded trees.

Landscape Attributes Drive Complex Spatial Microclimate Configuration of Brazilian Atlantic Forest Fragments

Habitat fragmentation imposes profound impacts on the tropical forest microclimate, but the microclimatic configuration of isolated forest patches and its implications for biodiversity persistence and habitat management are not clear. In this study we assessed a set of 10 aged (> 80 years) fragments (3.0 – 3,500 ha in size) of the Atlantic forest to examine to what extent fragment microclimatic attributes are correlated with distance to the nearest edge as frequently proposed in the literature. We used 129 sampling points and took a total of 516 measures of air temperature and humidity, vapor pressure deficit and light incidence to characterize the microclimate of forest fragments in terms of their relative deviation from the surrounding matrix. Fragments as a whole presented strong internal variation and strongly differed from the microclimate exhibited by the open matrix of sugar-cane fields. Distance to nearest edge, percentage of forest cover around the measurement point, percentage of edge-affected area, and geographical orientation of the nearest edge all proved to have minor effects on the microclimate of forest fragments. Conversely, we identified percentage of forest cover and fragment area as the most significant explanatory variables driving their microclimatic configuration: as forest cover increases at landscape scale, forest microclimate deviates less from the open matrix (a forest-mediated matrix buffering). Our results suggest that microclimatic conditions are spatially complex, as they do not correlate with the distance to the nearest forest edges; rather, they are driven by a forest-mediated buffering of the surrounding matrix that minimizes heat and humidity exchanges between forest and non-forest habitats, thus shaping the microclimatic signature of isolated forest fragments.

Phylogenetic Impoverishment of Amazonian Tree Communities in an Experimentally Fragmented Forest Landscape

Amazonian rainforests sustain some of the richest tree communities on Earth, but their ecological and evolutionary responses to human threats remain poorly known. We used one of the largest experimental datasets currently available on tree dynamics in fragmented tropical forests and a recent phylogeny of angiosperms to test whether tree communities have lost phylogenetic diversity since their isolation about two decades previously. Our findings revealed an overall trend toward phylogenetic impoverishment across the experimentally fragmented landscape, irrespective of whether tree communities were in 1-ha, 10-ha, or 100-ha forest fragments, near forest edges, or in continuous forest. The magnitude of the phylogenetic diversity loss was low (<2% relative to before-fragmentation values) but widespread throughout the study landscape, occurring in 32 of 40 1-ha plots. Consistent with this loss in phylogenetic diversity, we observed a significant decrease of 50% in phylogenetic dispersion since forest isolation, irrespective of plot location. Analyses based on tree genera that have significantly increased (28 genera) or declined (31 genera) in abundance and basal area in the landscape revealed that increasing genera are more phylogenetically related than decreasing ones. Also, the loss of phylogenetic diversity was greater in tree communities where increasing genera proliferated and decreasing genera reduced their importance values, suggesting that this taxonomic replacement is partially underlying the phylogenetic impoverishment at the landscape scale. This finding has clear implications for the current debate about the role human-modified landscapes play in sustaining biodiversity persistence and key ecosystem services, such as carbon storage. Although the generalization of our findings to other fragmented tropical forests is uncertain, it could negatively affect ecosystem productivity and stability and have broader impacts on coevolved organisms.

Leaf-cutting ants alter seedling assemblages across second-growth stands of Brazilian Atlantic forest

Secondary forests promote an increased abundance of leaf-cutting ants (LCA) but the consequences on forest dynamics have been poorly addressed. Here we examine seedling assemblage attributes, seed germination and seedling survival across foraging zones of Atta cephalotes colonies inhabiting 15 second-growth patches (25–47 y old) of Atlantic forest. Seeds and seedlings were monitored within foraging zones and control sites over 1 y, including spots around ant nests. Overall, 1862 seedlings from 108 plant species were recorded. Seedling density decreased by 53% in foraging-zone plots (3.31 ± 0.23 seedlings m −2 ) when compared with control plots (7.02 ± 0.44 seedlings m −2 ) and a similar decrease was observed for species richness. Ant-induced alterations in the seedling assemblage were further indicated by segregation between foraging-zone and control plots (NMDS), habitat effects on species similarity (ANOSIM), and indicator tree species associated with control plots. While seed germination and seedling survivorship were uncorrelated to either nest distance or age of second-growth stands (with the exception of Tapirira guianensis ), defoliation by LCAs was a significant cause of seedling mortality. Our results suggest that LCAs interfere with successional trajectories of Atlantic forest as foraging zones filter seedling establishment, supporting less-dense, impoverished and convergent seedling assemblages.

Challenges and opportunities for biodiversity conservation in the Atlantic Forest in face of bioethanol expansion

Brazil is the world largest producer of sugarcane ethanol, an alternative to gasoline. Large players, including international oil companies, are aware of the potential of Brazilian ethanol and are investing in the production and expansion of sugarcane plantations in the country. The growing ethanol market imposes some conservation challenges on Brazil to meet the increasing demand. The market points out to an expansion of sugarcane crops, but this can be extremely harmful to the remaining biodiversity of the Brazilian Atlantic Forest. The impact of such expansion will be more severe in the states of Alagoas, Pernambuco, Paraíba and Rio Grande do Norte, the second largest sugar-ethanol production region, and one of the most globally threatened areas of tropical forest (only 12% left, ∼ 1% legally protected). There, most forest fragments are smaller than 100 ha and several endemic species are on the verge of extinction. Here we advocate that instead of expanding plantations, increasing crop productivity should be the more logical and environment-friendly solution for that region. Further, we indicate that the current challenge is to increase the number of sugar and ethanol companies following best management practices and to turn these programs into a real opportunity to restore the biodiversity and environmental services of an ecosystems in eminent collapse. We urge that companies should move one step further and, at least, guarantee the protection of the habitats that go beyond the protection area imposed by the current environmental law.