Functional traits as indicators of ecological strategies of savanna woody species under contrasting substrate conditions

Abstract

Environmental filters and functional adjustments of species to local conditions are major determinants of plant communities in stressing habitats. We set out to understand the role of different substrates in functional trait variation in wood plants by investigating key functional traits at the community and intraspecific levels in different types of Brazilian savanna: two sites of alluvial savannas (lowland savannas that occur in old alluvial deposits in riverbeds with sandy soils and low water-holding capacity), and two sites of typical savannas (upland savannas that occur in interfluvial zones, far from the influence of rivers, in which clay soils with higher fertility and water-holding capacity predominate). We conducted this study in four sites with savanna vegetation in the northeast region of the Cerrado Biome, nearby the transition with the Amazon. In each site we sampled six functional traits for each tree species: leaf area, leaf thickness, specific leaf area (SLA), stem-specific density, relative bark thickness and maximum plant height. We sampled 101 wood species, ranging from 26 to 62 species within each site. In both community and intraspecific levels, alluvial savanna plants showed higher SLA and specific-stem density, and lower leaf area, leaf thickness, bark thickness, and plant height compared with the typical savanna. We also found that, at a given leaf thickness, species from typical savanna exhibited ∼20% higher SLA. In addition, at a given plant height, typical species showed ∼56% higher bark thickness and ∼20% lower specific-stem density. Our findings suggest that savanna tree species growing on alluvial savannas tend to adopt strategies related to water acquisition while species growing on typical savannas invest in both water conservation strategies and protection against high-intensity fires. We conclude that water deficit and fire, both related to substrate properties, play a key role in determining the woody plant communities functioning in savannas.