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Food web dynamics of flying squirrels, red squirrels and voles along a 100 year gradient of stand age following clearcut logging and wildfire
Sidlar, Kate
Identifying thresholds for maintaining ecological resilience has been approached by focusing on indicators associated with landscape patterns, biodiversity and stand structure. The use of less-visible components of ecosystems, such as trophic structure and food web dynamics may be an equally valid approach to develop sensitive indicators. This approach, as compared with the traditional approach, may be more sensitive to perturbations as well as having sensitivity to the recovery from perturbations. Ectomycorrhizas are a mutualistic symbiosis between fungi and fine roots of higher plants, including most of our commercially important trees within British Columbia. They play an essential role in forested ecosystems affecting nutrient and water uptake, reduction of root pathogens, as well as providing a food source to above and belowground consumers (Smith and Read 1997). Many ectomycorrhizal fungi produce fruit bodies that are eaten by small mammals, which are in turn, fed upon by carnivores. In Oregon, truffles can constitute up to 90% of a squirrels diet. Recently, ectomycorrhizal (ECM) fungi have been studied as possible indicators for monitoring effects of biodiversity and sustainability of past and new forestry practices (Durall et al. 2006; Twieg 2006). Information gathered from the proposed study will help to augment these earlier findings. Both red squirrels and northern flying squirrels are well-known mycophagists (Carey et al. 1999, Claridge et al. 1999) . The latter and its diet of fungi has been particularly well-studied through the Pacific Northwest coastal forests, but relatively little information has been collected from the interior of British Columbia. Red squirrels also are known to forage on and/or cache large quantities of fungi. Previous work (Currah et al. 2000) suggests that the two species may compete for certain types of fungi. The red-backed vole is a smaller rodent that has also been shown to feed heavily on mycorrhizal and epigeous fungi (Claridge et al. 1999). Together, these three animals likely play an important role in vectoring fungal spores via their feces, which can be deposited at a substantial distance from where the animals fed. Understanding the relationship between these three animals and mycorrhizal communities will provide important insight into how food web dynamics change as forests mature. We recently established a chronosequence of sites to study possible thresholds of ectomycorrhizal fungal diversity and community structure. Within this chronosequence, a gradient of ages were selected, i.e., 5-, 25-, 65- and 100 year-old sites, with each age category replicated 4 times. In the 5- and 25-year-old categories, stands were selected either from fire or from clear-cut logging, constituting an additional 8 sites for a total of 24 sites. Using this chronosequence design, we found the age threshold for ECM fungal diversity was approximately 25 years and for community structure it was 65 years (Twieg 2006). To develop a sensitive indicator of ecological resilience, we will build on an existing inventory of ectomycorrhizal fungi to determine the relationship between those organisms and the vertebrates known to use the fungi as a source of food. We will use the chronosequence sites described above to compare these processes along an age gradient as well as between blocks initiated by fire or clearcutting. This work will not only reveal the trophic interactions and implications of fungal communities, but it will examine how small-mammals transport fungal spores between undisturbed and disturbed blocks, thereby helping in the generation of mycorrhizal fungi and their associated tree hosts. Red squirrels, flying squirrels, and red-backed voles (all known mycophagists) will be systematically live-trapped across the chronosequence sites, providing fecal samples for analysis . Epigeous fruit bodies will also be collected during the peak fruiting season from all sites. Hypogeous fru ...
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