Navigating the biogeography of wide-spread short-forests in global drylands

Abstract

Canopy height is pivotal in sustaining carbon cycling and upholding ecological functions, especially in dryland forests where massive short-forests exist primarily due to insufficient water supply. Here, we divided global dryland forests into the tall-forests (36%) and short-forests (64%) and mapped their distributions separately for plantations and natural forests. Short-forests are ubiquitously distributed in global drylands, constituting 54% planted forests and 65% natural forests, with broader distribution thresholds across environmental gradients compared to tall-forests. Notably, the key ecological determinants of canopy height for both planted and natural short-forests are similar, involving topography (elevation), soil (soil moisture content), climate (mean temperature of warmest quarter and aridity index), and anthropogenic (population density) factors, but divergent between planted and natural tall-forests. The canopy height of planted tall-forests is predominantly influenced by precipitation, while natural tall-forests additionally depend on temperature, disturbance, and soil. Under all climate change scenarios, we projected that some dryland forests (more than 70%) cannot sustain current forest canopy heights, with a more pronounced decline in harsher climates, and some dryland tall forests may even degrade into short-forests or non-forests. With many dryland regions being marked as potential areas for forestation, our study offers critical insights for preserving dryland forests' carbon sequestration potential and guiding decision-making in dryland forestation initiatives.