Impacts of large herbivores on plant community structure and dynamics

Abstract

INTRODUCTION How do large herbivores affect plant community structure and dynamics? Here we review the main direct impacts of herbivores on plant communities. We briefly review effects on individual plants (or ramets) and the range of responses of individual plants to herbivory, as a basis from which to explore the complexities of processes operating at the plant community level. Large herbivores make foraging decisions at a range of spatial (from bite to landscape) and temporal (from seconds to years) scales, and plants also respond to herbivore impacts at a similar ranges of scales (plant part to community) (Bailey et al . 1996, Hodgson & Illius 1996, Crawley 1997). This provides a challenge for the identification of key processes affecting plant‐herbivore interactions and the mechanisms driving plant community responses to herbivore damage under different conditions. Scale issues (both temporal and spatial) are paramount to the study of herbivore impacts on plant community dynamics (Crawley 1997, Olff & Ritchie 1998), and scale is implicitly or explicitly brought into many of the sections in this review. Scale issues can also underlie apparent controversies in the literature about herbivore influences on vegetation, and an awareness of their implications is fundamental. The impacts of large herbivores on vegetation have been particularly widely studied in relation to range management and pasture plants, primarily grasses (Rosenthal & Kotanen 1994, Hodgson & Illius 1996, Crawley 1997, Olff & Ritchie 1998). In this chapter, we focus on shrub and woodland systems where possible to complement earlier reviews.