Altitudinal zonation of plants is often due to climatic constraints; trees and shrubs for example, have higher energy requirements in order to produce woody tissue, and they therefore exist at lower altitudes where growing seasons are longer and plants are less constrained by the environment. Whereas high alpine specialists can survive harsh conditions and shorter growing seasons and can often only be found on windy ridgelines or mountain summits. But the distribution of those alpine specialists is probably not wholly determined by climate. There is growing evidence to show that plant interactions such as competition and facilitation are perhaps just as important for species distributions as climate in alpine regions. Under harsh conditions that constrain plant growth, facilitative (positive) interactions between plants can provide shelter from frost or wind; whereas under favourable conditions, competitive (negative) interactions can lead to reduced biomass and growth among competing individuals. But the question remains, where is facilitation or completion occurring? Is there a particular place along the altitudinal/environmental/climatic gradient where a threshold is passed that causes a switch in plant interactions? Do taller, woody plants such as alpine shrubs provide any clues?
In this project, we will use high altitude shrubs to tease apart the interacting effects of plant interactions across a climatic gradient. Some shrubs are much taller than surrounding vegetation and can produce large amounts of leaf litter that smothers other plants; essentially leading to the exclusion of other vegetation types under shrub canopies. The research questions will test the effect of leaf litter and canopy on the distribution of some well-known high alpine specialist species. A large component of this project will involve field experiments and hiking up and down mountains. We may also complement the field experiments in the glasshouse, testing the ideas of competition, facilitation and the role of leaf litter. Project start will be mid-year to make best use of the alpine growing season.