Wildfires and the secondarization of a social forest in the eastern Amazon region

Abstract

Wildfires represent a powerful driver of tropical forest degradation across human-modified landscapes. Here, we investigated the impacts of wildfires on the functional and taxonomic dimensions of tree assemblages into old-growth, once-burned and twice-burned forest stands, covering 6 ha in the eastern Amazon. Tree assemblages were examined via a large set of functional attributes relative to wood density, bark thickness, vertical structure, forest habitat, regeneration strategy and seed dispersal mode. Overall, wildfires are positively associated with soft-woody, pioneer, canopy and those species with seed dispersal by generalist vertebrates, while shade-tolerant individuals, particularly understory species, decline. Changes become more evident as fire events accumulate, with burned forests becoming increasingly distinct from unburned old-growth forests functionally and taxonomically. Finally, wildfire was positively correlated with increasing within-habitat species dissimilarity in the adult assemblages, but with a clear trend of decreasing dissimilarity in sapling assemblages across burned forests as fire frequency increases. Our results suggest that old-growth forests are not only vulnerable to wildfires but are greatly impacted in terms of forest physical structure as well as several community-level attributes of tree assemblages. As fire events increase in frequency, forest responses, damage or degradation intensifies, leading to forest secondarization as a collection of forest patches dominated by pioneer or successional species from the local forest flora. Damage from wildfire result from tree mortality and pioneer species recruitment during fire-induced regeneration, suggesting effects may be temporary, but this will depend on forest resilience and fire regime.

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