Contrasting understorey species responses to the canopy and root effects of a dominant shrub drive community composition

Abstract

AbstractQuestionsContrasting understorey species responses to the effects of dominant species might occur within a single community even with neutral community‐level interactions. However, no studies have assessed the contribution of below‐ and above‐ground effects for all species of a community and their consequences for community composition. We tested the following hypotheses: (i) there are contrasting responses of understorey species to the canopy and root effects of a dominant shrub; (ii) the contrasting understorey responses to the canopy and root effects of the shrub are related to community composition.LocationSpecies‐rich sub‐alpine community, eastern Tibet Plateau, China, dominated by Dasiphora fruticosa.MethodsWe used a removal procedure and shade cloth treatment to separate root from canopy effects and quantified the biomass responses of 41 species of the understorey community. Species‐level responses to the root and canopy effects were quantified with the relative interaction index. We conducted multivariate analyses to assess the relative contribution of root and canopy effects to community composition.ResultsWe found contrasting species‐level responses to the canopy and root effects of D. fruticosa that could be grouped into six cluster groups. Dominant effects were positive for the roots and negative for the canopy, with a tendency for a trade‐off between the two. Community‐level effects were less strong and weakly significant, in particular for species richness. Root and canopy effects strongly explained understorey species composition but net shrub effects did not.ConclusionsThis study highlights that communities include species having contrasting responses to both the canopy and root effects of dominant species that importantly explain species composition.