Physical rather than chemical soil properties influence tree community structure and functional composition in forests and savannas

Abstract

Background and Aims Understanding how edaphic gradients influence trait composition is key to interpreting vegetation dynamics across contrasting ecosystems such as seasonal forests and savannas. We evaluated how gradients in soil clay content and acidity affect woody plant abundance and community-level trait composition in forests and savannas. We hypothesized that conservative traits are associated with sandy, more acidic soils, and acquisitive traits with clayey, less acidic soils.

Methods We sampled 286 woody species across 120 plots distributed among six forest and six savanna sites throughout the Cerrado, Brazil. At each site, we recorded tree and shrub species and collected soil samples from ten 100-m2 plots. We measured plant height (Hmax), leaf area (LA), specific leaf area (SLA), leaf phosphorous concentration (LPC), stem-specific density (SSD), leaf thickness (LT) and leaf carbon–nitrogen ratio (C:N). These traits were used to calculate community-weighted means (CWMs) for each plot. Linear regression was used to assess how CWMs and woody plant abundance varied along soil clay and acidity gradients.

Key Results Woody plant abundance declined with increasing soil acidity and clay content in forests, and with clay content in savannas. In forests, trait patterns reflected acquisitive strategies (greater Hmax and LA in clay-rich soils; lower SLA and LPC in acidic soils) and conservative strategies (higher SSD and C:N ratios in acidic soils). In savannas, fewer traits responded to soil gradients (higher LA in clayey soils and increased LT in acidic soils).

Conclusions Our findings demonstrate that edaphic gradients influence woody plant abundance and functional composition in forests and savannas, especially in the former, where species in less acidic and clayish soils tend to adopt acquisitive strategies, whereas those in acidic and sandy soils are conservative. Importantly, physical soil properties, rather than chemical, were the primary drivers of tree community structure and functional composition across vegetation types.