Invasive herbivores can alter the composition of forest communities, and in doing so may impact emergent ecosystem properties. New Zealand—having no native mammalian herbivores—provides a unique opportunity to determine if selective feeding by introduced deer translates into changes in forest community composition and ecosystem carbon (C) storage. We assessed deer herbivory impacts in New Zealand mixed conifer-hardwood forests using a nation-wide network of c. 400 m2 deer exclosures that had been established 20–60 ya.
Results/Conclusions
There was no detectable influence of deer on total ecosystem C including soil to 30-cm depth; however, they did reduce the pool of C in small trees. Deer had marked effects on the species composition of forest vegetation including reduced species richness and diversity of browse layer vegetation and increased tree heterogeneity nationally (beta diversity). Deer also selected certain tree species, but promoted none, suggesting broad diet choice. We conclude that there was tremendous resistance of ecosystem C to invasive deer despite their clear effect on altering forest community composition. This resistance appears to be driven by deer primarily impacting only relatively small pools of C (forest floor vegetation and small trees) and having little influence on the functional trait composition (e.g. wood density) making up forest communities.