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

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Prepared by Antonio J. Perea, Jose L. Garrido & Julio M. Alcántara

Mixed Pine-Oak forest of “Sierra Sur de Jaén” (the sampling site), Jaén, Spain. Photo credit: Antonio J. Perea.

Interactions between established individuals and recruiting plants (canopy-recruit interactions) are key drivers of plant community dynamics. Thus, disentangling what mechanisms are involved in these interactions deserve particular attention. Among the possible mechanisms that have been proposed, in this study, we focus on plant functional traits to determine which of them contribute to explain higher or lower recruitment of a given plant species in the vicinity of established individuals of another species.

To do that, we conducted a study in three Mediterranean forest systems. Here we registered the abundance of each species and located sapling of each species recruiting under the canopy of adult individuals of each species. We monitored the canopy-recruit interactions between 37 woody-plant species, for which we took measures of 18 traits that potentially affect recruitment.

Processing of samples in the lab to obtain leaf traits. Canopy plant number 8 of Quercus pyrenaica in Sierra de Segura (Jaén, Spain). Photo credit: Antonio J. Perea.

From the recruits’ perspective, we found that those species with higher recruitment grow slowly and have larger seeds. This suggests that the persistence of species in the community may be influenced by how fast the species use the resources. Species whose recruits grow fast consume a lot of resources quickly, which may not be the best strategy when they have to compete against larger established plants. In this case, whereas fast-growing increases the chances of dying (due to resource depletion), slow-growing increases the chances of replacing the adult when it dies. From the perspective of established canopy plants, several traits influenced how good is the microhabitat for recruitment in their proximity. Here we found that those traits related to the leaf and canopy structure (branch density) improve or depress other species’ recruitment. For example, species with evergreen leaves provide a better microhabitat for recruitment than those with deciduous leaves, possibly due to amelioration of cold-related stress, to which recruits are highly sensitive.

Finally, even though some canopy and recruit traits were related to recruitment, we found limited evidence of traits’ complementarity. Thus we conclude that these interactions are primarily driven by traits of canopy and recruits playing independently during the assembly.

Mediterranean Pine-Oak mixed forest of Sierra de Jaén in the Southeastern part of the Iberian Peninsula, Spain. Transect used to measure recruitment and functional traits of woody plant species. Photo credit: Antonio J. Perea.

This is a plain language summary for the paper of Perea et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12991).