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Habitat destruction and overhunting are two major drivers of mammal population declines and extinctions in tropical forests. The construction of roads can be a catalyst for these two threats. In Southeast Asia, the impacts of roads on mammals have not been well-documented at a regional scale. Before evidence-based conservation strategies can be developed to minimize the threat of roads to endangered mammals within this region, we first need to locate where and how roads are contributing to the conversion of their habitats and illegal hunting in each country. We interviewed 36 experts involved in mammal research from seven Southeast Asian countries to identify roads that are contributing the most, in their opinion, to habitat conversion and illegal hunting. Our experts highlighted 16 existing and eight planned roads - these potentially threaten 21% of the 117 endangered terrestrial mammals in those countries. Apart from gathering qualitative evidence from the literature to assess their claims, we demonstrate how species-distribution models, satellite imagery and animal-sign surveys can be used to provide quantitative evidence of roads causing impacts by (1) cutting through habitats where endangered mammals are likely to occur, (2) intensifying forest conversion, and (3) contributing to illegal hunting and wildlife trade. To our knowledge, ours is the first study to identify specific roads threatening endangered mammals in Southeast Asia. Further through highlighting the impacts of roads, we propose 10 measures to limit road impacts in the region.

The need to proactively manage landscapes and species to aid their adaptation to climate change is widely acknowledged. Current approaches to prioritizing investment in species conservation generally rely on correlative models, which predict the likely fate of species under different climate change scenarios. Yet, while model statistics can be improved by refining modeling techniques, gaps remain in understanding the relationship between model performance and ecological reality. To investigate this, we compared standard correlative species distribution models to highly accurate, fine-scale, distribution models. We critically assessed the ecological realism of each species’ model, using expert knowledge of the geography and habitat in the study area and the biology of the study species. Using interactive software and an iterative vetting with experts, we identified seven general principles that explain why the distribution modeling under- or overestimated habitat suitability, under both current and predicted future climates. Importantly, we found that, while temperature estimates can be dramatically improved through better climate downscaling, many models still inaccurately reflected moisture availability. Furthermore, the correlative models did not account for biotic factors, such as disease or competitor species, and were unable to account for the likely presence of micro refugia. Under-performing current models resulted in widely divergent future projections of species’ distributions. Expert vetting identified regions that were likely to contain micro refugia, even where the fine-scale future projections of species distributions predicted population losses. Based on the results, we identify four priority conservation actions required for more effective climate change adaptation responses. This approach to improving the ecological realism of correlative models to understand climate change impacts on species can be applied broadly to improve the evidence base underpinning management responses.

QUESTIONS: Which factors affect the diversity and species composition of tropical secondary rain forests in a region with little information regarding their contribution to global biodiversity? Can older secondary forests approach the diversity and composition of mature forests following 100 yr of pasture use? LOCATION: Tropical secondary rain forest, northeast Australia. METHODS: We identified trees, shrubs and vines ≥2.5 cm DBH in a chronosequence comprising 33 sites, aged 3–60 yr since the formation of closed canopy (9–69 yr since pasture abandonment) and compared them with eight sites in nearby mature forest remnants. RESULTS: Species richness and community composition were strongly influenced by secondary forest age but did not attain values of mature forest. Sites in close proximity to mature forests had higher plant richness, whereas low soil fertility appeared to depress species recruitment. Thus, multiple factors operated in secondary forest community assembly. Unusual tree community patterns that suggest accelerated or slowed successional trajectories were observed at several sites. CONCLUSIONS: Secondary forests in our study region contained important plant diversity for conservation, particularly in older sites, however, even the oldest secondary forests (60 yr) did not converge with the species composition and diversity of mature forests. The protection of mature forest tracts and remnants must be a priority if we are to maintain high levels of plant diversity in tropical landscapes, conserve rare species and facilitate the recruitment of plant species in recovering forests.

Dispersal, recruitment and establishment limitations are crucial processes shaping forest composition. In secondary forests these mechanisms may operate differently than in mature forests, because young and isolated secondary forests may suffer stronger limitations due to a lack of suitable dispersers and harsh environmental conditions—such as the elevated competition of exotic grasses. To assess establishment limitations in these forests, we undertook transplant experiments involving seeds and seedlings along a chronosequence of secondary forests in tropical Australia. The experiments included six species that varied in seed size (6–50 mm in length) and successional status (early to late successional). Seeds of five species were placed in one of three treatments: (1) exposed seeds, (2) fenced seeds, and (3) buried seeds, and multiple seedlings of six species were transplanted in block treatments. After 14–17 months, seed from all plant species germinated across all ages of secondary forests. However, in young secondary forest sites (4–12 years) fewer germinated seeds survived. The highest survival rates were observed for buried seeds (27.2%) compared to the low survival of exposed seeds (6.0%). Planted seedlings (6 spp) had the greatest overall survival (63.1%) and the highest growth rates in older secondary forests. We found that species identity was important for growth and survival in both experiments, but detected no effect of successional status or seed size. A crucial finding of this study was that the buried seeds of all species germinated and had relatively high survival irrespective of variation in site conditions or successional status, suggesting that seed availability may be a greater barrier to recovery of secondary forests in the region than the establishment limitations imposed by environmental conditions.

Fragmentation is a severe threat to tropical rainforests. However the habitat loss and less extensive fragmentation caused by roads can also be a threat, not only through allowing access to remote areas, but also through a suite of insidious associated impacts. These include abiotic and biotic edge effects adjacent to road clearings, the disturbance impacts caused by vehicle operation, invasions by weeds, feral and alien fauna and disease, and faunal mortality from vehicle collisions. In combination, these can create a significant barrier to movements of rainforest biota. Impacts can be ameliorated through clever road design and sustainable vehicle operation.

Frogs are potentially sensitive indicators of road impacts, with studies indicating particular susceptibility to road mortality. Calling, i.e., breeding, behavior could also be affected by traffic noise. We investigated effects on frog abundance and calling behavior where a busy highway crosses rainforest stream breeding habitat in northeast Australia. Frog abundance was repeatedly surveyed along five stream transects during a summer breeding season. Abundance of two species,Litoria rheocolaandAustrochaperina pluvialis, increased significantly with perpendicular distance from the road along two transects. No trends in abundance were detected forA. pluvialison two other transects where it was common, or forLitoria serrataon one transect where abundance was sufficient for analysis. Both species with lowered abundance near the road,L. rheocolaandA. pluvialis, are rare in road kill statistics along this highway, suggesting road mortality is not the cause of reduced frog abundance near the road. We postulate that lowered abundance may reflect traffic noise effects. We analyzed calls of the International Union for Conservation of Nature endangered speciesL. rheocolaalong the one stream transect on which it was common. We found significant trends in two call traits over a very fine scale: both call rate and dominant frequency were significantly higher closer to the road. Furthermore, males were significantly smaller closer to the road. These call and body size trends most likely reflect road impacts, but resolving these is complicated by correlations between traits. Potential mechanisms, effects on fitness, and management recommendations to mitigate the impacts of roads on frogs are outlined.

A global zoning scheme is proposed to limit the environmental costs of road building while maximizing its benefits for human development, by discriminating among areas where road building would have high environmental costs but relatively low agricultural advantage, areas where strategic road improvements could promote agricultural production with relatively modest environmental costs, and ‘conflict areas’ where road building may have large agricultural benefits but also high environmental costs. The number and extent of roads will expand dramatically this century 1 . Globally, at least 25 million kilometres of new roads are anticipated by 2050; a 60% increase in the total length of roads over that in 2010. Nine-tenths of all road construction is expected to occur in developing nations 1 , including many regions that sustain exceptional biodiversity and vital ecosystem services. Roads penetrating into wilderness or frontier areas are a major proximate driver of habitat loss and fragmentation, wildfires, overhunting and other environmental degradation, often with irreversible impacts on ecosystems 2 , 3 , 4 , 5 . Unfortunately, much road proliferation is chaotic or poorly planned 3 , 4 , 6 , and the rate of expansion is so great that it often overwhelms the capacity of environmental planners and managers 2 , 3 , 4 , 5 , 6 , 7 . Here we present a global scheme for prioritizing road building. This large-scale zoning plan seeks to limit the environmental costs of road expansion while maximizing its benefits for human development, by helping to increase agricultural production, which is an urgent priority given that global food demand could double by mid-century 8 , 9 . Our analysis identifies areas with high environmental values where future road building should be avoided if possible, areas where strategic road improvements could promote agricultural development with relatively modest environmental costs, and ‘conflict areas’ where road building could have sizeable benefits for agriculture but with serious environmental damage. Our plan provides a template for proactively zoning and prioritizing roads during the most explosive era of road expansion in human history.

CONTEXT: Tropical forest regeneration is increasingly prominent as agro-pastoral lands are abandoned. Regeneration is characterised as favouring ‘marginal’ lands; however, observations of its drivers are often coarse or simple, leaving doubt as to spatial dynamics and causation. OBJECTIVES: We quantified the spatial dynamics of forest regeneration relative to marginality and remnant forest cover in a 3000 km² pastoral region in northern tropical Australia. METHODS: Classification and regression trees related the extent and distribution of regeneration to soil agricultural potential, land-cover history, terrain slope, distance to primary forest, and primary forest fragment size, as defined by aerial photography. RESULTS: Secondary forest extent and distribution overwhelmingly reflect the proximity and size of primary forest fragments. Some 85 % of secondary forest area occurs <1 km of primary forest, and 86 % of secondary forest patches >50 ha are <400 m from primary forest and coincident with historic primary forest fragments. Where primary forest fragments are >8.5 ha, secondary forest area declines less rapidly with increasing distance from primary forest up to 1.5 km. Marginality inferred by soil potential and slope had no bearing on regeneration, except at the coarsest of spatial scales where regeneration is a proxy for primary forest cover. CONCLUSION: Findings underline the need to conserve even modest rainforest patches as propagule reservoirs enabling regeneration. Marginality per se may have a limited role in regeneration. As most secondary forest was an extension of primary forest, its unique conservation value relative to that of primary forest may likewise merit reconsideration.

Road development in the tropics is fraught with economic, socio-political, and environmental risks (Alamgir et al. 2017). Roads have helped alleviate rural poverty to some extent(Jones 2006), but have also caused tremendous collateral environmental damage (e.g., Singleton et al. 2004). In Southeast Asia, for example, roads have been shown to have detrimental environmental impacts on threatened biodiversity (Clements et al. 2014). It is therefore important that road development projects strive to balance social benefits and environmentalcosts (Laurance and Arrea 2017). The social impacts of roads, particularly on indigenous people, have not been adequately quantified. In reality, indigenous people are rarely consulted in the planning phase of road projects despite the fact that they have rights to self-determination and consultation involving the development of indigenous lands and resources, including road construction, according to the United Nations Declaration on the Rights of Indigenous Peoples (Wiessner 2008). Studies have shown that roads can provide indigenous people greater access to markets, increased social mobility, migration, and greater economic opportunities (Adam et al. 2011). Roads can also facilitate access to traditional hunting grounds; however, forest loss and degradation over time (e.g., Clements et al. 2014) may negatively affect their livelihoods and cultural traditions in the long term. Given these trade-offs, it is important to understand indigenous people’s level of support for road development, and to examine motivations behind their attitudes towards road development. In Peninsular Malaysia, we conducted a questionnaire survey of indigenous groups residing in a globally important tiger landscape, in order to identify factors (i.e., demography, livelihood activities, and perceived impacts of the road on their livelihoods) affecting their support for the presence of an existing road, and the construction of additional roads to their village. We also assessed their perceptions concerning the state of wildlife near the existing road. Our findings have important implications for conservation practitioners working in biologically important areas, with indigenous communities that are or will be affected by road construction.

We investigated microclimatic edge gradients associated with grassy powerlines, paved highways and perennial creeks in wet tropical forest in northeastern Australia during wet and dry seasons. Photosynthetically active radiation, air temperature and vapor pressure deficit, soil temperature, canopy temperature, soil moisture, and air speed in the rain forest understory were measured during traverses perpendicular to the forest edge. Light intensity was elevated near the edges of powerlines, highways, and creeks, but this effect was strongest for creek edges. Air temperature and vapor pressure deficit were elevated near powerline edges in the dry season and highway edges in both wet and dry seasons but were not elevated near creek edges in either season. In contrast, soil moisture was lowered near creek edges but not near either powerline or highway edges. No edge gradients were detected for air speed. Canopy temperature was elevated near highway edges and lowered near powerline edges in the wet season but no edge gradients in canopy temperature were detected near creek edges in either the wet or the dry season. We suggest that these different edge gradients may be largely the result of differences in the fluxes of latent and sensible heat within each type of linear canopy opening, with periodic flood disturbance assisting by maintaining a more open canopy near creek edges. Our data indicate that the nature of the linear canopy opening is at least as important as the width in determining the nature and severity of microclimatic edge effects, analogous to the \"matrix effect\" of traditional fragmentation studies.