Implications of galling herbivory on ground thaw in Canada’s northern boreal forest

• Main Author: McManus, Allison
• Format: Text
• Language: English
• Published: Scholars Commons @ Laurier 2016
• Subjects: galling herbivory; Eriophyoid mites; permafrost thaw; Betula; climate change; compensatory response; Integrative Biology; Active layer thickness; permafrost; Mite
• Online Access: https://scholars.wlu.ca/etd/1801; https://scholars.wlu.ca/context/etd/article/2906/viewcontent/Allison_McManus___MSc._Thesis.pdf

Canada’s northern boreal forest has faced significant climate warming over the past century. This change can have direct and indirect effects on forest dynamics, including altering the disturbance patterns of herbivores and changing the abundance of natural enemies. Warmer air temperatures can impact the distribution and survival of arthropods, both novel species and resident natural enemies. Gall-inducing mites are a resident natural enemy in high latitude forests and have been shown to drive dramatic reductions in gas-exchange rates in infested plants. Physiological reductions in plants can directly affect the shrub energy balance and underlying soil processes. This can have major implications in permafrost-dominated environments. This study examines the potential impacts of a gall-inducing Eriophyoid mite, Vasates oldfieldi, on Betula shrub energy inputs to the ground surface. This study will 1) quantify how shrubs are physiologically and morphologically responding to galling herbivory; 2) determine if galling on shrubs influences the shrub-soil energy balance; and 3) quantify the implications of this for active layer thickness, and consequently the potential for this biotic process to impact localized permafrost thaw. I hypothesize that as the shrubs’ physiology changes in response to herbivory, so too will the energy balance, driving unexpected changes in ground thaw conditions. To test this, the following variables were measured during two consecutive field seasons (2013-14): soil moisture, soil surface temperature, frost table depth, gas exchange, leaf area index and shortwave radiation. The results from both seasons indicate a compensatory response in the galled shrubs resulting in increased stomatal conductance, altering available soil moisture below galled shrubs, and changes in aboveground canopy structure, resulting in decreased amounts of incident solar radiation below the infested shrub, cooling the soil surface. As a result, there is a decrease in active layer thickness under galled shrubs.