Satellite-based Tracking of Resilience Change in South American Tropical Dry Forests

Tropical dry forests are important for biodiversity and people, yet also exposed to high pressure from agricultural expansion and climate change, raising concerns about declining forest resilience. Global analyses of forest resilience have revealed a widespread loss of resilience in tropical and arid forests, as well as declining and increasingly more variable rainfall in many tropical regions. However, tropical dry forests have so far not been explicitly focused on in assessments of resilience under climate and land-use change. A key limitation of existing studies, which have predominantly relied on MODIS-based proxies such as the Normalised Difference Vegetation Index or VODCA-based vegetation optical depth, is that the comparatively coarse spatial resolution of these sensors cannot adequately resolve and analyse small-scale resilience changes in tropical dry forests, which are characterised by high compositional and structural heterogeneity.

Here, we address these gaps and track changes in the resilience of South American tropical dry forests using the high-resolution Landsat archive since 1999. We derive vegetation resilience trends using robust regression based on temporal and spatial indicators of critical slowing down of kNDVI time series. Additionally, we explore how local resilience trends are associated with accessibility and land use gradients, such as distances to roads, cities, and agricultural areas, as well as the hydrological context, such as distances to water surfaces. Our results show distinct patterns of resilience change in South American tropical dry forests. Nonetheless, substantial uncertainties in resilience tracking using the Landsat archive remain due to sensor inconsistencies and missing data.