Red foxes engineer the boreal forest: impacts of denning on vegetation near the Arctic treeline
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Date
2019-12-19
Authors
Lang, Jessica Ashley
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Abstract
Terrestrial predators are known for their role in controlling herbivore populations, but they can also influence vegetation by altering soil nutrients through excretions and redistributing prey remains. Added nutrients, specifically nitrogen and phosphorus, can modify plant assemblages by alleviating nutrient limitations in soils, thereby altering plant diversity and growth. Red foxes (Vulpes vulpes L.) are a top predator in the Subarctic, and their dens, which are reused over many years, could serve as biogeochemical hotspots for soil nutrients. If nutrient additions by red foxes alter the availability of resources for other organisms, such as plants, then red foxes can be considered ecosystem engineers. My thesis examined the impacts of denning on soils, plant assemblages and tree growth in the Subarctic boreal forest, near Churchill, Manitoba, Canada. I quantified and compared soil characteristics (inorganic nitrogen, extractable phosphorus, soil pH and respiration), understory vegetation composition (diversity and abundance) and the growth of white spruce (Picea glauca (Moench) Voss) between red fox dens and paired control sites. Red fox denning increased soil nutrients, pH and respiration (microbial activity), which could indicate higher rates of nutrient mineralization. By increasing soil nutrients and disturbance, red fox denning increased the cover of woody shrubs (Salix L. spp.), grasses (Leymus mollis (Trinius) Pilger) and weedy ephemerals on dens compared to control sites. Increased nutrients also promoted long-term radial growth of white spruce trees on dens, despite having stand characteristics otherwise similar to control sites. Denning by red foxes therefore creates distinct microhabitats near the Arctic treeline. Predators that engineer ecosystems can play critical roles in the structure of ecological food webs by modifying habitat resources in addition to trophic interactions, and can therefore influence a broad suite of other organisms.
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Keywords
Red fox, Ecosystem engineer, Tree growth, Subarctic vegetation, Soil nutrients, Vulpes vulpes