Plant functional traits involved in the assembly of canopy–recruit interactions

Questions: The assembly of plant communities depends strongly on mechanisms that determine the recruitment of different plant species. Studying recruitment using a trait-based approach may help in the search for general or dominant mechanisms involved in this process. Here, we try to disentangle what traits of saplings and established (canopy) plants can be considered as functional for recruitment, and whether the complementarity of these functional traits may be a driver of the plant community assembly. Location: Regional. Two pine–oak forest communities in Sierra Sur de Jaén and one in Sierra de Segura, southeast of the Iberian peninsula. Methods: In each forest community, we established three 50 m × 50 m plots, where we identified the saplings of each species recruiting under the canopy of each species or in open interspaces. The study focuses on 37 woody species. Measures of 18 traits were conducted for 30 saplings and 10 adults of each species. Results: Seed mass and the ratio height:basal diameter of saplings were positively associated with species abundance in the sapling bank under vegetation, while abundance in the sapling bank in open interspaces was only related to the type of mycorrhizal association. On the other hand, some traits of adult plants (leaf mass per unit area [LMA], seed dispersal mechanism, leaf habit and branch density) favour the recruitment of other species in their close proximity. However, we found only circumstantial evidence of canopy/recruit trait complementarity affecting recruitment. Conclusions: Our results suggest that the assembly of canopy–recruit interactions is primarily driven by the filtering effect of canopy species on recruitment, through traits that affect both seed arrival and soil properties. Species abundance in the sapling bank was related to resource acquisition traits. We did not find any clear evidence supporting that trait complementarity is involved in the interaction between canopy and recruit species.This study was conducted under the projects COEXMED (CGL2012-36776) and COEXMED II (CGL2015-69118-C2-1-P) of the Spanish Ministerio de Economía y Competitividad (MEC) and FEDER funds from the EU. AJP was supported by a FPI grant from the Spanish Ministerio de Ciencia, Innovación y Universidades (MCIU/BES-2016-077688) associated to the COEXMED II projec