Tree-ring based growth modelling to aid timber management of congeneric Aspidosperma and Handroanthus species along a seasonal tropical forest gradient

Abstract

Tropical dry forests (TDF) are vital carbon sinks, yet they are increasingly threatened by the effects of climate and land-use activities. In Brazil, law-based management practices in these forests do not ensure the sustainable use of these ecosystems, leaving them highly vulnerable. Here we use tree-ring widths to calculate cumulative diameter growth and estimate the ages at which trees congeneric species of Aspidosperma and Handroanthus reach the minimum logging diameter (MLD) across a gradient TDF types in northeastern Brazil (evergreen forest, savanna, and dry forests). Using the Growth-Oriented Logging (GOL) approach, we estimated the optimized MLD and logging-cycle length for each species from the current and mean annual increment curves for each species. Finally, we modeled tree-growth trajectories of each species and simulated timber yields at the next logging cycle under different scenarios (by law, by GOL, and in more stringent scenarios). Our results demonstrate that species from dry forests exhibit the slowest growth rates and the longest recovery times compared to species in other forest types. Only Aspidosperma castroanum from the evergreen forest approached sustainable yield levels under our simulations (∼80 %), while yields for the other species were much lower (10–30 %). These findings emphasize the need for forest management practices that account for tree growth variations between species and forest types. The prospects for sustainably extracting timber in the dry forests are bleak and a combination of increased logging cycle lengths and lower logging intensities are needed to ensure that timber stocks in these forests are not overexploited.