The Gran Chaco harbors high biodiversity, including many endemic species (3, 6, 7). This region is also a global deforestation hotspot (8) due to the recently accelerated expansion of cattle ranching and soybean cultivation there (9, 10). Given the agricultural potential of the region and the growing global demands for agricultural products, the pressure to convert additional natural ecosystems into agricultural land remains very high. Yet, only 9% of the Gran Chaco is currently protected (6). For these reasons, the Gran Chaco is one of the most threatened ecoregions worldwide. Various definitions of dry forests exist, but the Gran Chaco should not be neglected when raising awareness to the urgent conservation needs in the often forgotten neotropical dry forests.

Habitat loss is the primary cause of local extinctions. Yet, there is considerable uncertainty regarding how fast species respond to habitat loss, and how time‐delayed responses vary in space. We focused on the Argentine Dry Chaco (c. 32 million ha), a global deforestation hotspot, and tested for time‐delayed response of bird and mammal communities to landscape transformation. We quantified the magnitude of extinction debt by modelling contemporary species richness as a function of either contemporary or past (2000 and 1985) landscape patterns. We then used these models to map communities' extinction debt. We found strong evidence for an extinction debt: landscape structure from 2000 explained contemporary species richness of birds and mammals better than contemporary and 1985 landscapes. This suggests time‐delayed responses between 10 and 25 years. Extinction debt was especially strong for forest specialists. Projecting our models across the Chaco highlighted areas where future local extinctions due to unpaid extinction debt are likely. Areas recently converted to agriculture had highest extinction debt, regardless of the post‐conversion land use. Few local extinctions were predicted in areas with remaining larger forest patches. Synthesis and applications. The evidence for an unpaid extinction debt in the Argentine Dry Chaco provides a substantial window of opportunity for averting local biodiversity losses. However, this window may close rapidly if conservation activities such as habitat restoration are not implemented swiftly. Our extinction debt maps highlight areas where such conservation activities should be implemented.

1. Understanding how biodiversity responds to intensifying agriculture is critical to mitigating the trade-offs between them. These trade-offs are particularly strong in tropical and subtropical deforestation frontiers, yet it remains unclear how changing landscape context in such frontiers alters agriculture-biodiversity trade-offs. 2. We focus on the Argentinean Chaco, a global deforestation hotspot, to explore how landscape context shapes trade-off curves between agricultural intensity and avian biodiversity. We use a space-for-time approach and integrate a large field dataset of bird communities (197 species, 234 survey plots), three agricultural intensity metrics (meat yield, energy yield and profit) and a range of environmental covariates in a hierarchical Bayesian occupancy framework. 3. Woodland extent in the landscape consistently determines how individual bird species, and the bird community as a whole, respond to agricultural intensity. Many species switch in their fundamental response, from decreasing occupancy with increased agricultural intensity when woodland extent in the landscape is low (loser species), to increasing occupancy with increased agricultural intensity when woodland extent is high (winner species). 4. This suggests that landscape context strongly mediates who wins and loses along agricultural intensity gradients. Likewise, where landscapes change, such as in deforestation frontiers, the very nature of the agriculture-biodiversity trade-offs can change as landscapes transformation progresses. 5. Synthesis and applications. Schemes to mitigate agriculture-biodiversity trade-offs, such as land sparing or sharing, must consider landscape context. Strategies that are identified based on a snapshot of data risk failure in dynamic landscapes, particularly where agricultural expansion continues to reduce natural habitats. Rather than a single, fixed strategy, adaptive management of agriculture-biodiversity | 2055 Journal of Applied Ecology MACCHI et Al.

Land-use change is a root cause of the extinction crisis, but links between habitat change and biodiversity loss are not fully understood. While there is evidence that habitat loss is an important extinction driver, the relevance of habitat fragmentation remains debated. Moreover, while time delays of biodiversity responses to habitat transformation are well-documented, time-delayed effects have been ignored in the habitat loss versus fragmentation debate. Here, using a hierarchical Bayesian multi-species occupancy framework, we systematically tested for time-delayed responses of bird and mammal communities to habitat loss and to habitat fragmentation. We focused on the Argentine Chaco, where deforestation has been widespread recently. We used an extensive field dataset on birds and mammals, along with a time series of annual woodland maps from 1985 to 2016 covering recent and historical habitat transformations. Contemporary habitat amount explained bird and mammal occupancy better than past habitat amount. However, occupancy was affected more by the past rather than recent fragmentation, indicating a time-delayed response to fragmentation. Considering past landscape patterns is therefore crucial for understanding current biodiversity patterns. Not accounting for land-use history ignores the possibility of extinction debt and can thus obscure impacts of fragmentation, potentially explaining contrasting findings of habitat loss versus fragmentation studies.