Understory vegetation development six years after a wildfire in the temperate forests of Patagonia, Argentina

Abstract

Fire is a fundamental driver in many forest ecosystems, yet increasing fire severity, frequency and extent threaten recovery processes. In the Andean-Patagonian forests, early post-fire succession remains poorly understood despite its importance in shaping long-term ecosystem structure and function. We evaluated the effects of three fire severity levels (unburned, moderate, and high) and five forest types (Nothofagus pumilio, N. antarctica, N. dombeyi, mixed N. dombeyi-Austrocedrus chilensis, and A. chilensis) on the plant community developed 6 years after a large wildfire in the Cholila Lake basin (Argentina). We assessed understory species composition and traits, vertical structure, and regeneration of dominant species. Both fire severity and forest type significantly influenced understory composition. High-severity sites showed pronounced compositional differences, including higher richness and cover of exotic species, greater dominance of annual herbs, and a more developed upper stratum (1.5–3 m height) dominated by shrubs. In contrast, moderate-severity sites showed assemblages more similar to unburned forests, higher total richness, greater cover of nitrogen-fixing species, and a more developed middle stratum (0.5–1.5 m height). Differences among forest types were also detected, with the highest total and native species richness in A. chilensis forests and the highest exotic species cover in N. antarctica and N. dombeyi forests. Regeneration of foundational tree species and the bamboo Chusquea culeou was present in moderate-severity sites but strongly limited in high-severity sites. Our results highlight that fire severity acts as a filter on early post-fire dynamics, while forest type further shapes community responses, consistent with potentially divergent successional pathways that require long-term monitoring. As fire regimes intensify and early post-fire landscapes expand, understanding the structure and dynamics of understory communities will assist restoration efforts aimed at achieving desirable states while maintaining the ecological processes supported by early successional communities.