UBC Theses and Dissertations
Interacting effects of climate change and disturbance on grassland plants and plant communities Carlyle, Cameron Norman
Grasslands are threatened by urbanization, agricultural conversion, over-grazing, tree-encroachment, and invasive plants. Simultaneously, climate change acts on all levels of biological organization, from entire communities to the physiology of individuals. The environmental stresses induced by climate change have the potential to interact with human-caused disturbance, but the response of plants to these stresses and disturbances, and how they may interact, are not well known. To conserve grasslands it is critical to know which types of grassland and which plant species will be most affected. To understand the mechanisms of change at the ecosystem level it is necessary to study the response at lower levels of biological organization. Using a variety of approaches I studied the potentially interacting effects of stress (primarily reduced water availability) and disturbance (plant biomass removal) on different levels of biological organization. I ran a 4-year field experiment in which I manipulated water availability, temperature and clipping in three different grassland types. I found complex plant community structure and biomass response; treatments often interacted but the different grassland types had their own particular responses. As part of this experiment I monitored the effects of treatments on soil moisture and temperature and found that the effects are generally consistent with expectations, but treatments do not act exclusively or independently on target variables. In addition to stress and disturbance, competition is a key process structuring grasslands. In the greenhouse, I examined how plant competition is affected by stress and disturbance. I found that the interpretation of how competition is affected is dependent on the way competition is measured. Some measures of competition showed reduced competition across stress and disturbance gradients, but other measures showed no change. Finally, I examined the root traits of 18 species of grass in the greenhouse in response to reduced water availability. I found significant variation in traits among species, maintenance of trait hierarchies across environments and little evidence of plasticity, except for root: shoot ratio. Overall, stress, disturbance and their interactions are important in influencing individual plant performance, competition, structuring plant communities, and ecosystem function.
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