Climate-driven variation in dispersal ability predicts responses to forest fragmentation in birds.

Species sensitivity to forest fragmentation varies latitudinally, peaking in the tropics. A prominent explanation for this pattern is that historical landscape disturbance at higher latitudes has removed fragmentation-sensitive species or promoted the evolution of more resilient survivors. However, it is unclear whether this so-called extinction filter is the dominant driver of geographic variation in fragmentation sensitivity, particularly because climatic factors may also cause latitudinal gradients in dispersal ability, a key trait mediating sensitivity to habitat fragmentation. Here we combine field survey data with a morphological proxy for avian dispersal ability (hand-wing index) to assess responses to forest fragmentation in 1,034 bird species worldwide. We find that fragmentation sensitivity is strongly predicted by dispersal limitation and that other factors-latitude, body mass and historical disturbance events-have relatively limited explanatory power after accounting for species differences in dispersal. We also show that variation in dispersal ability is only weakly predicted by historical disturbance and more strongly associated with intra-annual temperature fluctuations (seasonality). Our results suggest that climatic factors play a dominant role in driving global variation in the impacts of forest fragmentation, emphasizing the need for more nuanced environmental policies that take into account local context and associated species traits.

Producing wood at least cost to biodiversity: integrating Triad and sharing-sparing approaches to inform forest landscape management.

Forest loss and degradation are the greatest threats to biodiversity worldwide. Rising global wood demand threatens further damage to remaining native forests. Contrasting solutions across a continuum of options have been proposed, yet which of these offers most promise remains unresolved. Expansion of high-yielding tree plantations could free up forest land for conservation provided this is implemented in tandem with stronger policies for conserving native forests. Because plantations and other intensively managed forests often support far less biodiversity than native forests, a second approach argues for widespread adoption of extensive management, or 'ecological forestry', which better simulates natural forest structure and disturbance regimes - albeit with compromised wood yields and hence a need to harvest over a larger area. A third, hybrid suggestion involves 'Triad' zoning where the landscape is divided into three sorts of management (reserve, ecological/extensive management, and intensive plantation). Progress towards resolving which of these approaches holds the most promise has been hampered by the absence of a conceptual framework and of sufficient empirical data formally to identify the most appropriate landscape-scale proportions of reserves, extensive, and intensive management to minimize biodiversity impacts while meeting a given level of demand for wood. In this review, we argue that this central challenge for sustainable forestry is analogous to that facing food-production systems, and that the land sharing-sparing framework devised to establish which approach to farming could meet food demand at least cost to wild species can be readily adapted to assess contrasting forest management regimes. We develop this argument in four ways: (i) we set out the relevance of the sharing-sparing framework for forestry and explore the degree to which concepts from agriculture can translate to a forest management context; (ii) we make design recommendations for empirical research on sustainable forestry to enable application of the sharing-sparing framework; (iii) we present overarching hypotheses which such studies could test; and (iv) we discuss potential pitfalls and opportunities in conceptualizing landscape management through a sharing-sparing lens. The framework we propose will enable forest managers worldwide to assess trade-offs directly between conservation and wood production and to determine the mix of management approaches that best balances these (and other) competing objectives. The results will inform ecologically sustainable forest policy and management, reduce risks of local and global extinctions from forestry, and potentially improve a valuable sector's social license to operate.

Characterising the spatial distribution of opportunities and constraints for land sparing in Brazil.

Brazil is a megadiversity country with more tropical forest than any other, and is a leading agricultural producer. The technical potential to reconcile these roles by concentrating agriculture on existing farmland and sparing land for nature is well-established, but the spatial overlap of this potential with conservation priorities and institutional constraints remains poorly understood. We mapped conservation priorities, food production potential and socio-economic variables likely to influence the success of land sparing. Pasture occupies 70% of agricultural land but contributes ≤11% of the domestic food supply. Increasing yields on pasture would add little to Brazil's food supply but - if combined with concerted conservation and restoration policies - provides the greatest opportunities for reducing land demand. Our study illustrates a method for identifying municipalities where land-sparing policies are most likely to succeed, and those where further effort is needed to overcome constraints such as land tenure insecurity, lack of access to technical advice, labour constraints, and non-compliance with environmental law.

Extinction filters mediate the global effects of habitat fragmentation on animals.

Habitat loss is the primary driver of biodiversity decline worldwide, but the effects of fragmentation (the spatial arrangement of remaining habitat) are debated. We tested the hypothesis that forest fragmentation sensitivity-affected by avoidance of habitat edges-should be driven by historical exposure to, and therefore species' evolutionary responses to disturbance. Using a database containing 73 datasets collected worldwide (encompassing 4489 animal species), we found that the proportion of fragmentation-sensitive species was nearly three times as high in regions with low rates of historical disturbance compared with regions with high rates of disturbance (i.e., fires, glaciation, hurricanes, and deforestation). These disturbances coincide with a latitudinal gradient in which sensitivity increases sixfold at low versus high latitudes. We conclude that conservation efforts to limit edges created by fragmentation will be most important in the world's tropical forests.

Impacts of the Northwest Forest Plan on forest composition and bird populations.

The Northwest Forest Plan (NWFP) initiated one of the most sweeping changes to forest management in the world, affecting 10 million hectares of federal land. The NWFP is a science-based plan incorporating monitoring and adaptive management and provides a unique opportunity to evaluate the influence of policy. We used >25 years of region-wide bird surveys, forest data, and land-ownership maps to test this policy's effect on biodiversity. Clearcutting decreased rapidly, and we expected populations of older-forest-associated birds to stabilize on federal land, but to continue declining on private industrial lands where clearcutting continued. In contrast, we expected declines in early-seral-associated species on federal land because of reduced anthropogenic disturbance since the NWFP. Bayesian hierarchical models revealed that bird species' population trends tracked changes in forest composition. However, against our expectations, declines of birds associated with older forests accelerated. These declines are partly explained by losses of older forests due to fire on federal land and continued clearcutting elsewhere. Indeed, the NWFP anticipated that reversing declines of older forests would take time. Overall, the early-seral ecosystem area was stable, but declined in two ecoregions-the Coast Range and Cascades-along with early-seral bird populations. Although the NWFP halted clearcutting on federal land, this has so far been insufficient to reverse declines in older-forest-associated bird populations. These findings underscore the importance of continuing to prioritize older forests under the NWFP and ensuring that the recently proposed creation of early-seral ecosystems does not impede the conservation and development of older-forest structure.