Habitat filtering and niche specialization of termite mound herbaceous flora in tropical dry woodlands

Abstract

Termite mounds (TMs) are characteristic micro‐ecosystems of tropical dry woodland landscapes. Although their effects on woody plant functional diversity and ecosystem functioning have been relatively well studied, herbaceous communities have received much less attention. We inventoried herbaceous species within 336 4‐m ² quadrats marked along transects spanning 16 TM (base‐slope‐top) and their surrounding habitats, across three sites. Species' habitat affinities were assessed using the IndVal index, based on 52,808 individuals from 74 species. Thirty‐two topographic and edaphic variables, as well as canopy openness, were measured within each quadrat. We also collected eight functional traits for all 74 species from databases and measured nine traits including six leaf traits and three root traits on a subset of 15 species. Additionally, Competitive (C), Stress‐tolerant (S), and Ruderal (R) life strategies were determined based on three leaf traits. We found that 30% of the species were significantly associated with TM (19 “TM species”), 35% with the non‐termite‐mound (NTM) environment (22 “NTM species”), and 35% did not show any significant IndVal (22 “indifferent species”, IND). On TM, clay and exchangeable cation content decreased from the top to the base, whereas water content and aluminum concentration followed an opposite trend. There was a clear functional specialization among species with a significant IndVal. NTM species exhibit resource conservation syndromes (high leaf and root dry mass, high root to shoot dry mass ratio). In contrast, TM species favor rapid resource acquisition traits (high specific root length, specific leaf area, leaf cation concentrations). Three groups of TM species were identified, significantly associated with the three TM microhabitats: nine species at the base, three on the slope, and seven at the top. TM species showed both ruderal strategies, driven by disturbances from termites and large herbivores at the base, and stress tolerance traits (high leaf succulence index) at the top. In contrast, NTM species exhibited a strategy linked to competition. Our study emphasizes the key role of TM habitats in enhancing biodiversity and contributing to the ecological uniqueness of tropical dry woodland landscapes, a vast biome whose ecological complexity remains to be fully explored, with important implications for plant conservation.