Department of Biology
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Browsing Department of Biology by Author "93b32e76dfcef4321a89cb8babc494ce"
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Item Open Access Grazing impacts of White-tailed Deer or "Culling Bambi to save the forest"(Heritage Resources Centre, University of Waterloo, 2000) Koh, Saewan; Bazely, Dawn; Timciska, M.Large herbivores, such as white-tailed deer, can significantly determine the structure and composition of forest plant communities. In several National and Provincial Parks located on southwestern Ontario shorelines, deer overgrazing has been a major cause of habitat degradation. Few studies of herbivory have examined the link between herbivory-induced or mediated changes in environmental variables, and vegetation change. In this study we used ordination analyses (DCA, CCA) to examine the effect of changes in understorey light levels on plant communities in Rondeau Provinical Park and other Carolinian forests. In 1996, plant communities in forest stands with a past history of high deer densities (50 deer/km2) were compared with deer exclosures and other long-term ungrazed sites. Ordinations showed that older exclosures were similar to ungrazed sites and dominated by native plant species. Both differed significantly from grazed sites, which were dominated by non-native species. Newer exclosures and stands where deer densities were reduced differed from both grazed and long-term ungrazed sites, suggesting that these plant communities are following an intermediate or alternate recovery trajectory. Interestingly, despite the differences in plant community composition there were no significant differences in species diversity among treatments. Thus, measurements of diversity or species richness alone are inadequate descriptors of plant community change. From 1987-91 over 50% of trees were lost from permanent plots in Rondeau. The main reason is that deer overgrazing has prevented tree regeneration, causing increased understorey light levels. We suggest that in this more open forest, the normal recovery of native plant species is prevented, and the trajectory of some plant communities over time, may have been significantly altered. The major implication for park managers is that sustained deer herd reductions alone are not enough to ensure the recovery of vegetation - management for accelerated canopy closure may also be desirable.Item Open Access Shedding Light on the Problem of Deer Overgrazing in Carolinian Forests(Centre for Wildlife and Conservation Biology, Acadia University, 2002) Hynes, Kim E.; Koh, Saewan; McLachlan, S.M.; Timciska, M.; Bazely, DawnIn nearly a decade of research we have carried out a multi-faceted study of the impact of deer grazing in three major Carolinian parks: Point Pelee National Park, and Rondeau and Pinery Provincial Parks. This research has had a direct impact on management policy. We will review key findings of the research program and highlight what we consider to be our most general research finding, namely that the state of the overhead canopy in Carolinian forests appears to have a major impact on the composition of understorey plant communities. We suggest that deer overgrazing has initiated a process that has signiticantly altered understorey light conditions. Our hypothesis is that increased canopy gaps, initially caused by deer preventing forest regeneration, have led to trees being more susceptible to wind throw. This further opens the canopy, leading to increased light levels in the understorey, which in turn drive changes in the vegetation. Non-native, invasive species can take advantage of the increased light conditions and appear to replace and suppress native woodland species, which are adapted to shade. The forest may then switch to some alternative stable state. Currently, analysis of long-term data sets is aimed at evaluating this hypothesis. Our current research aims to quantify the relationship between understorey light levels and the plant community, and it will establish whether there is some threshold light level beyond which many vulnerable native understorey species cannot survive, and are suppressed by exotics. In this respect it is of general interest to anyone working in a degraded, highly disturbed forest, with an interest in habitat restoration.