Insect herbivory on snow gum (Eucalyptus pauciflora, Myrtaceae) saplings near the alpine treeline: the influence of local- and landscape-scale processes

Abstract

The distribution and abundance of plant species in high mountain ecosystems are thought to depend largely on abiotic factors that play out at both landscape scales (e.g. steep environmental gradients affected by increasing elevation) and local scales (e.g. changes in topography, aspect and canopy cover). However, relatively little attention has been paid to biotic interactions, and how these might also change with landscape-wide and local factors. Ecological interactions between plants and insect herbivores are likely to alter species performance and affect local abundance, but their role in the Australian Alps remains largely unexplored. Here, we examine the prediction that the amount of herbivory on saplings of the dominant high elevation tree, snow gum Eucalyptus pauciflora Sieb. ex Spreng. (Myrtaceae), are lower at higher elevation because of increasing environmental stress. Using a reciprocal transplant experiment, we tested the prediction that origin of seed (low, mid, high elevation) has less effect on insect herbivory than environmentally-driven changes in plant morphology (height, leaf thickness, specific leaf area). Across all mountains studied, herbivory was best explained by a combination of plant height, canopy openness, leaf thickness and elevation, but not seed origin. This study highlights the individuality of each mountain environment, at landscape and local scales, as well as the complexity of relationships between environmental change, plants and insects. Given the factors that best explain herbivory across mountains, herbivory may decrease with decreasing productivity associated with increasing elevation, a trend in broad agreement with hypotheses associating leaf area loss to the availability of resources and plant vigour.