Thinning Pine Plantations for Ecological Restoration of Oak Savannah

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In the Carolinian Life Zone, St. Williams CR is a standout with 1000 ha of forest. Originally conceived as a reserve for timber production, the area was planted with the typical uniform density of rows and rows of trees.  By 2011, colleagues at OMNRF decided that given the changes to our knowledge of forest management and new goals of win-win for both timber and ecosystem services, new methods were needed.

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A variable density thinning treatment was planned and then implemented. This emulates the more natural conditions that exist when succession occurs and produces a heterogeneous and diverse ecosystem.  Modest in scope, the VDT experiment underway will show us how much timber production can result when the smaller trees are not only thinned to allow for larger, more economically desirable trees to remain but also how much ecological complexity results.  Shelley Hunt at U Guelph is working on the vegetation on this project; CaRE is working on the below-ground portion of the ecosystem – an oft-neglected angle.  CaRE is especially  interested in how the mycorrhizal community will respond to VDT disturbances.

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Using the stratified design OMNR already has implemented, we are using a BACI experimental design (before-after-control-impact) to assess how each thinning treatment affects the soil fauna, soil fungi, duff layer, and nutrient dynamics. Thirty small 5 cubic cm bore hole size samples will be taken from each replicate treatment plot 6 times a year (April, May, June, August, September, October) for at least 3 years to assess dynamic changes. Repeated measures, autocorrelation, and multivariate analysis will allow us to test the impacts of the thinning treatments. Year 1 and Year 2 work is complete.

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So far, we’ve found there to be no significant differences in any of the key variables of nitrogen, phosphate, potassium, mycorrhizal hyphal density or mycorrhizal spore density.  We have detected significant declines in the duff layer in the VDT treatments vs. controls.  Soil fauna is trending towards a shift away from collembola dominated systems and this is beginning to show up in fungal response – this is not a surprise as collembola have been shown to directly or indirectly affect fungal biomass in other studies of pine and other types of forest ecosystems. We’re detecting more beetles in the VDT treatments but their diversity and numbers are not yet significantly greater than the controls.

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