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The influence of plant functional groups on ecosystem function in a grassland in northern Canada

McLaren, J.R. 2010. PhD Dissertation, University of British Columbia, Vancouver, BC

Abstract

Human development, climate change, diseases and habitat degradation and loss are resulting in species extinction rates up to a thousand times faster than pre-human levels. Biodiversity-ecosystem functioning research examines how this loss of species and changes in the composition of plant communities are likely to influence numerous ecosystem functions. The effects of biodiversity loss on ecosystem properties may also be highly dependent on the identity of the organisms lost. I investigated the influence of plant functional group identity in determining ecosystem properties. I established a removal experiment in a grassland in northern Canada in 2003 with four treatments: a no removal control and independent removal of forbs, graminoids and legumes. As biodiversity loss is occurring in concert with environmental change, I crossed removals with a fertilizer and a mycorrhizal reduction (fungicide) treatment to determine the context dependency of effects. I showed that graminoids have the largest influence on ecosystem properties in this community, despite not being the most abundant group. Short-term (4 years) biomass compensation for the removals showed no compensation for graminoid removal, but after 7 years there was full biomass compensation for this treatment. Light interception, soil moisture, and soil nutrients were all largely determined by the presence of graminoids in the plant community, and surprisingly legumes had very few effects on any ecosystem property. Graminoids also showed plant-driven environmental effects on leaf decomposition, although no removal treatment resulted in changes in the decomposition of roots. Graminoids promoted decomposition of leaf litter through 2 mechanisms: influence on the decomposition microenvironment and changes in the litter composition. Finally, I have demonstrated that very few of the effects of functional group identity were context dependent on either fertilization or fungicide treatments. These results highlight the importance of considering plant functional group identity when predicting the effects of species loss, and indicate that plant identity, more so than dominance, determines effects on ecosystem properties.