Interactive impacts of climate change and land-use change on the demography of montane birds

Climate change and habitat degradation are amongst the two greatest threats to biodiversity. Together, they can interact to imperil species. However, how climate change and land-use change jointly affect the demographic vital rates that underpin population viability remains unknown. Here, using long-term data on birds from the increasingly degraded and rapidly warming Himalayas, we show that survival trends over time are linked to species’ elevational ranges in primary, but not in selectively logged forest. In primary forest, populations at their cold-edge elevational range limit show increases in survival rates over time, whereas those at their warm-edge elevational range limit suffer survival declines. This pattern is consistent with species tracking favorable climatic conditions over time, leading to improved demographic outcomes at progressively higher elevations with climate change, which in turn lead to upslope range shifts. In logged forest, however, survival rates remain relatively constant over time. This suggests that, in response to climate change in the long term, individuals of the same species can maintain demographic vital rates in higher-elevation primary forest, but not in logged forest. This is the first demonstration of how two of the most disruptive anthropogenic influences on biodiversity interact to threaten survivorship in natural populations. Ignoring interactions between climate change and land-use change can potentially undermine accurate forecasting of the future of species in an increasingly warm and degraded world. Importantly, large tracts of well-protected primary forests across Earth’s tropical elevational gradients may be essential to enable tropical montane species to persist in the face of climate change.