Effects of disturbance intensity on species and functional diversity in a tropical forest

Abstract

Summary Disturbances are widespread and may affect community assembly, species composition, (functional) diversity and hence ecosystem processes. It remains still unclear to what extent disturbance‐mediated species changes scale‐up to changes in community functional properties, especially for species‐rich tropical forests. A large‐scale field experiment was performed in which the dynamics of 15 000 stems >10 cm in diameter was monitored for 8 years in 44 one‐ha forest plots. Twelve functional effect and response traits were measured for the most dominant tree species. The effects of different intensities of disturbance caused by logging and silvicultural treatments on the species and functional diversity of a Bolivian tropical forest community were evaluated, along with how these changes were driven by underlying demographic processes. Disturbance treatments did not affect species diversity or functional diversity indices based on multiple traits related to primary productivity and decomposition rate. This result suggests that species richness is conserved, and trait variation is maintained, which can buffer the community against environmental change. In contrast, disturbance intensity affected the average plant trait values in the community (the community‐weighted mean) for seven of 12 traits evaluated. At high disturbance intensity, the community had a lower wood density of stem and branches, lower leaf toughness and dry matter content, but higher specific leaf area and leaf N‐ and P concentration, with the value of these traits changing on average 6% over the 8‐year period. The functional spectrum of the community changed, therefore, from ‘slow’, conservative, shade‐tolerant species towards ‘fast’, acquisitive, light‐demanding species. These functional changes in mean trait values may enhance primary productivity and decomposition rate in the short term. Temporal changes in community functional properties were mainly driven by recruitment, and little by mortality or survival. Synthesis . Moderate levels of (logging) disturbance neither affected species diversity nor functional diversity per se in the 8‐year period after logging. Disturbance did, however, change the functional community composition towards ‘fast’ species with more acquisitive traits, thus potentially fuelling primary productivity and nutrient and carbon cycling. In conclusion, tropical forest management may contribute to conserving functional biodiversity of trees while providing forest resources.