Ecosystem engineers in the subarctic

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The growth and distribution of organisms are primarily determined by abiotic conditions. However, some organisms modify their environment, uncoupling growth, distribution and ecosystem processes from site conditions. In addition to our traditional understanding of how trophic interactions affect communities and ecosystems, the concept of ecosystem engineering offers a set of mechanisms whereby some species modify habitats and resource availability. My work will be unique, examining two opposing ecosystem engineering processes in the detrital and consumer food chains in the subarctic. First, I will determine the degree to which plants and their mycorrhizae engineer low productivity soils near the tree line, inhibiting the ability of many plant species to exist in these habitats and reducing food availability for the consumer food chain. Second, I will examine how carnivores disrupt these habitats via fecal and urine deposition. They will therefore have a positive feedback on the consumer food chain, creating unique plant communities on the tundra and woodlands, and increase the growth and survival of tree islands on the tundra. Recent research shows that some mycorrhizal associations allow plants access to nutrients from soil organic matter. Ericaceous plants, which dominate upland subarctic habitats, have mycorrhizal fungi that may be particularly effective at breaking down organic matter since they retain the cellulose-degrading enzymes of their saprophytic ancestors. By accessing nutrients in organic matter, these fungi may slow decomposition by reducing soil nutrient availability. I will determine if this short-circuiting of the nutrient cycling occurs in the subarctic, which would explain the massive buildup of soil organic matter in these systems and the absence of plants that rely on conventional inorganic sources of nutrients. I will use stable isotope analysis to measure organic element uptake. Fertilization experiments using root and fungal exclusion, and monitoring soil development after wildfires, will allow us to discover the mechanisms controlling soil nutrient cycling and carbon retention. I will also build on my previous work on how fox denning activity creates patches of nutrient enrichment, allowing unique plant communities to establish in what would typically be nutrient-poor habitat. The concept of soil enrichment by carnivores will be extended to studying trees at the treeline and tree islands on the subarctic tundra where large carnivores (wolves and eagles) preferentially use certain tree islands for shelter and perching. Modification of plant productivity will then be linked to herbivore population dynamics. Given the rapid rate of climate change occurring in the subarctic and large pools of soil organic matter found there, these studies will provide essential training to students becoming researchers and natural resources managers working in these fragile systems, and give them tools to predict and manage their fate.