Decoupling of trait and species turnover in fire-prone Mediterranean plant communities

Abstract

Plant taxa and traits do not necessarily show synchronous responses to ecological disturbance. Based on the observation that taxonomically over-diversified communities might be phenotypically redundant, we speculated that taxonomic and phenotypic community reassembly might be decoupled after fire in Mediterranean ecosystems. We applied a multi-trait approach to describe plant community re-assembly after fire across three 20-year chronosequences based on 117 species and 23 traits, including whole-plant, above-ground and below-ground traits. We quantified the post-fire trajectories of different plant traits by analysing their community-weighted means individually. We estimated the short- and long-term phenotypic diversity of burned plots based on sets of traits. We also tested if trait and species turnover are decoupled across post-fire trajectories. Finally, we calculated phenotypic redundancy, and assessed if above- and below-ground traits have contrasted responses during post-fire community reassembly. Individually, 16 out of 23 traits were affected by fire in the short term. Plant phenotypic diversity (stdMPD) decreased immediately after fire, driven by changes in whole- and above-ground traits. Both whole- and above-ground stdMPD in burned plots described positive trajectories across the chronosequences tending to converge with long-unburned plots, whereas below-ground stdMPD remained unaltered through time. Taxonomic and phenotypic beta diversity showed decoupled trajectories due to a larger species than trait replacement across time since fire. Finally, overall phenotypic redundancy of the studied plant communities described a regressive trajectory, similarly to above-ground traits, whereas root traits kept a steady phenotypic redundancy through time. Synthesis. We provide evidence that above- and below-ground traits describe different recovery trajectories after fire, with significant effects on the phenotypic redundancy of plant communities. Our results encourage the use of multi-trait approaches to understand how the plant reassembly operates after disturbance, in order to refine ecological theory. This strategy might improve the efficacy of restoration programs through a functional approach to species selection.