Assessing land-use effects on woody species? seed rain and soil seed bank in dry forests of central Argentina

Abstract

Land-use change threatens forests worldwide, and South American dry forests are no exception. In central Argentina, the Chaco and Espinal dry forest regions have been affected by intensified livestock grazing and logging, leading to structural degradation that may alter key processes such as seed-based regeneration. This study evaluates how varying degrees of structural degradation caused by combined livestock and logging use affect woody plant seed sources in these two contrasting dry forest regions.We surveyed eight forest sites per region, measuring vegetation structure and developing a Structural Degradation Index based on a reference site with no livestock or logging. At each site, we sampled the seed rain and soil seed bank, and analysed the density, richness, and compositional similarity of these two seed sources relative to preserved forest vegetation along the degradation gradient.In Espinal forests, seed rain density, richness, and compositional similarity declined significantly with increasing degradation, reaching near-zero values at highly degraded sites. In contrast, Chaco forests showed an increase in seed rain density under higher degradation, largely due to the dominance of a disturbance-adapted shrub Larrea divaricate, and maintained seed rain richness and similarity. Soil seed banks were consistently poor in both regions, confirming their limited role in woody species regeneration.These contrasting patterns reflect differences in environmental conditions and land-use history between Chaco and Espinal forests. Our results suggest that the persistence of seed rain diversity in degraded Chaco forests could allow for effective passive restoration, whereas the severely reduced regeneration potential in Espinal forests may require active restoration to recover woody species recruitment and forest regeneration.