资源环境科技发展态势分析平台

In open woodlands and savannas, fire is often the dominant disturbance that shapes and maintains their structure and dynamics. Numerous studies have explored tree-grass coexistence under different fire regimes in these ecosystems; however, there is a lack of research on the tree-tree relationship in the presence or absence of fire. In the present study, we explored the effects of fire regime on tree spatial pattern, mortality and regeneration in the Argentine Caldenal, which is one of the most endangered and least studied open woodlands in the Neotropics. While there was no significant difference in the overall tree density between frequently burned and fire-excluded regimes, we found clear divergences between fire regimes in the within-stand spacing of not only all trees, but also of large and small trees in addition to their spatial interactions. In contrast with previous results from other frequently burned open forests, trees in the Caldenal were randomly distributed in burned plots whereas both mid-and long-term fire exclusion lead to the strong short-scale aggregation of trees. In the absence of fire, both large and small trees were significantly clumped, but in the frequently burned woodlands, large and small trees had a tendency to repulsion and aggregation, respectively. Fire regime also significantly affected tree mortality and regeneration mechanisms in the Caldenal. Our mortality analysis indicated that fire suppression led to the shift from fire-induced to competition-driven mortality of trees. When analysing tree regeneration, we found a lack of seedlings in any of the fire regimes but the presence of vigorous sprouting only in frequently burned plots. The present study thus revealed the key role of frequent fires in the Caldenal open woodlands because recurrent burning not only shaped the spatial arrangement of trees, but fire-induced mortality also triggered an essential tree recruitment mechanism in these ecosystems.