Mammalian herbivory alters structure, composition and edaphic conditions of a grey-dune community

Abstract

Question Mammalian herbivory affects the structure and composition of plant communities, soil characteristics and intraspecific leaf traits. Understanding the effects of this type of herbivory is particularly relevant in grey dunes, a priority habitat type of the European Union Habitats Directive.

Location Sálvora island (NW Spain).

Methods Vegetation surveys and sampling were carried out in a coastal grey-dune community, comparing the structure and composition of plant communities and soil characteristics in plots with herbivory exclusion and plots with herbivore activity, in autumn and spring. Changes in the specific leaf area (SLA), C/N ratio, δ13C and δ15N of two main plant species were also analysed.

Results The differentiation between treatments was low in autumn, in contrast to spring results, which demonstrated seasonal variation in the plant community and herbivore behaviour. Spring results showed lower above-ground dry mass in plots with herbivory due to defoliation, but greater richness and diversity, indicating that intermediate levels of disturbance reduced competition from dominant species. Herbivory treatments were different in terms of species composition, highlighting the positive effects of herbivory on the development of the threatened species Linaria arenaria. Soil temperature and moisture content were higher in herbivory plots because of the suppression of vegetation cover and the effect of trampling, respectively. No differences were detected in the chemical composition of the soil or the SLA, although the variability of these traits was greater in herbivory plots, indicating spatial heterogeneity generated by the activity of herbivores. No differences between treatments were obtained for % C and δ13C, whereas herbivory plots showed lower values of N content and δ15N as an adaptive response to herbivory pressure at the leaf and root level.

Conclusion Our findings show that herbivory effects on plant communities vary by season — stronger in spring and weaker in autumn — emphasising the need for seasonal analysis and highlighting disturbance as a driver of spatial heterogeneity.