Woody lianas increase in dominance and maintain compositional integrity across an Amazonian dam-induced fragmented landscape

Tropical forest fragmentation creates insular biological communities that undergo species loss and changes in community composition over time, due to area- and edge-effects. Woody lianas thrive in degraded and secondary forests, due to their competitive advantage over trees in these habitats. Lianas compete both directly and indirectly with trees, increasing tree mortality and turnover. Despite our growing understanding of liana-tree dynamics, we lack detailed knowledge of the assemblage-level responses of lianas themselves to fragmentation, particularly in evergreen tropical forests. We examine the responses of both sapling and mature liana communities to landscape-scale forest insularization induced by a mega hydroelectric dam in the Brazilian Amazon. Detailed field inventories were conducted on islands created during reservoir filling, and in nearby mainland continuous forest. We assess the relative importance of variables associated with habitat fragmentation such as area, isolation, surrounding forest cover, fire and wind disturbance, on liana community attributes including abundance, basal area, diversity, and composition. We also explore patterns of liana dominance relative to tree saplings and adults ≥10 cm diameter at breast height. We find that 1) liana community composition remains remarkably similar across mainland continuous forest and islands, regardless of extreme area- and edge- effects and the loss of vertebrate dispersers in the latter; and 2) lianas are increasing in dominance relative to trees in the sapling layer in the most degraded islands, with both the amount of forest cover surrounding islands and fire disturbance history predicting liana dominance. Our data suggest that liana communities persist intact in isolated forests, regardless of extreme area- and edge-effects; while in contrast, tree communities simultaneously show evidence of increased turnover and supressed recruitment. These processes may lead to lianas becoming a dominant component of this dam-induced fragmented landscape in the future, due to their competitive advantage over trees in degraded forest habitats. Additional loss of tree biomass and diversity brought about through competition with lianas, and the concurrent loss of carbon storage, should be accounted for in impact assessments of future dam development

Carbon-focused conservation may fail to protect the most biodiverse tropical forests

As one of Earth’s most carbon-dense regions, tropical forests are central to climate change mitigation efforts. Their unparalleled species richness also makes them vital for safeguarding biodiversity. However, because research has not been conducted at management-relevant scales and has often not accounted for forest disturbance, the biodiversity implications of carbon conservation strategies remain poorly understood. We investigated tropical carbon–biodiversity relationships and trade-offs along a forest-disturbance gradient, using detailed and extensive carbon and biodiversity datasets. Biodiversity was positively associated with carbon in secondary and highly disturbed primary forests. Positive carbon–biodiversity relationships dissipated at around 100 MgC ha–1, meaning that in less disturbed forests more carbon did not equal more biodiversity. Simulated carbon conservation schemes therefore failed to protect many species in the most species-rich forests. These biodiversity shortfalls were sensitive to opportunity costs and could be decreased for small carbon penalties. To ensure that the most ecologically valuable forests are protected, biodiversity needs to be incorporated into carbon conservation planning

Sampling method drives differing detection of responses to land-use change in small mammals

Tropical land-use change is the key driver of the global extinction crisis. Understanding of the effects of land-use change on biodiversity depends on using a method that can accurately detect impacts. Studies evaluating conservation questions using small mammals in the tropics are mostly conducted using live-trap or pitfall, yet those that use both methods revealed substantial variation in the range and number of species sampled. A key question is whether variation between trapping methods alters the interpretation of the impacts of land-use change on small mammals. Focusing on the fragmented Brazilian Atlantic Forest, we sampled across five landscape units: interior and edge of contiguous forest; riparian forest remnant connected near or far from the contiguous forest; and unconnected riparian remnant. We found contrasting results from live-trap and pitfall regarding species composition, community structure, and functional abundance of small mammals. We then show that interpretations of land-use change impacts on small mammal communities differ significantly when using live-trap versus pitfalls. Using live-traps, riparian forest closely connected to contiguous forest supported similar composition and structure as the contiguous forest, but similarity decreased with distance from contiguous forest sinks. With pitfalls, the estimated small mammal community did not differ among habitats. Methodological variation could result in key impacts of land-use change on small mammals going undetected and in erroneous conservation planning within fragmented landscapes, indicating either a necessity to use live-traps or a combination of both methods

Seed-dispersal mode and habitat connectivity underpin variation in carbon stocking between Brazilian biomes

In tropical forests, about 60%–80% of woody plant species depend on animal–plant interactions for dispersal. The dependence on animal species for dispersal makes this interaction very fragile in the face of anthropogenic changes in land use. Disrupting seed-dispersal processes, principally zoochoric dispersal, could significantly alter the long-term carbon storage potential of tropical forests. An important question is how landscape structure changes tree carbon stocks in different types of tropical vegetation and how variation is mediated by the dispersal mode of animal (zoochoric) or abiotic (non-zoochoric) seeds. We focused on tree plots at 126 sites in Brazil spanning four types of forest and savanna vegetation, and calculated carbon stored in zoochoric, non-zoochoric, and large frugivore-dispersed species. Our results showed that carbon stocks in zoochoric species and non-zoochoric species differ significantly among vegetation types, with rainforests having higher stocks in zoochoric species and deciduous seasonally dry tropical forests having higher values in non-zoochoric species. A greater area of native vegetation promotes higher proportions of carbon stocks dispersed by large frugivore species, whereas a higher mean shape index reduces this proportion. Synthesis. This study highlights that seed-dispersal type underpins the variation in carbon stocks between vegetation types and that the maintenance of habitat of large dispersers and connectivity are key for retaining carbon stocks in zoochoric species, particularly in rainforest and cerrado sensu stricto