Diversity Patterns of Tree Communities Across Multiple Flood Gradients With Separate Fire Histories: Unveiling Patterns in a Wetland Ecosystem

Abstract

Question

How do fire and flooding, acting as ecological filters separately and in combination, influence species richness, taxonomic diversity, functional diversity, and phylogenetic diversity in tree communities along a flood gradient with varying fire histories?

Location

Pantanal, Mato Grosso do Sul, Brazil.

Methods

We sampled trees in 45 forest patches along a flood gradient, assessing species richness, alpha and beta taxonomic diversity, functional diversity, and phylogenetic diversity. Fire histories were categorized as 25, 13, and 2 years without fire (1997, 2009, 2020, respectively). Alpha diversity was estimated using Hill numbers, beta diversity via the Sørensen Index, and functional and phylogenetic diversity through the standardized effect size of mean pairwise distance (SES-MPD). A total of 321 plots were analyzed.

Results

Functional diversity increased along the flood gradient, promoting environmental heterogeneity. However, in recently burned areas, species richness, alpha taxonomic diversity, and functional diversity declined. The positive effect of flooding on functional diversity was reduced in recently burned areas, suggesting fire selectively removes flood-adapted but fire-sensitive species. Beta diversity analysis revealed a nested pattern, with species in recently burned areas forming subsets of older communities, indicating strong environmental filtering. Phylogenetic diversity remained stable across fire and flood gradients, suggesting fire filters species within lineages rather than altering evolutionary relationships.

Conclusions

Fire and flooding shape species richness, taxonomic diversity, and functional diversity in the Pantanal. Flooding enhances functional diversity, while fire reduces alpha and functional diversity, leading to species loss and functional homogenization. Strong adaptive trade-offs limit species' tolerance to both disturbances. Recently burned areas contain subsets of older communities, emphasizing the role of fire-free intervals in biodiversity recovery. As fire frequency increases due to climate change and human activity, conservation strategies should prioritize fire management and integrate hydrological dynamics into conservation planning to maintain wetland resilience.