Impacts of changing permafrost conditions on vegetation productivity in the northern boreal forest

• Main Author: Ogden, Emily
• Format: Text
• Language: English
• Published: Scholars Commons @ Laurier 2022
• Subjects: Climate change; remote sensing; Northwest Territories; NDVI; Biology; Integrative Biology; Terrestrial and Aquatic Ecology; Browning; Canada; Active layer thickness; permafrost
• Online Access: https://scholars.wlu.ca/etd/2447; https://scholars.wlu.ca/cgi/viewcontent.cgi?article=3590&context=etd

Vegetation productivity across the boreal forest has increased over the past several decades. However, at a regional scale there is large variation from increased (greening) to decreased (browning) productivity and large areas with no measured change. Some of this variation can be explained by disturbances, such as wildfire, or by increased climate variability. In northern regions underlain by permafrost, the interactions between climate, disturbance, and vegetation productivity may be more complex. For my thesis, I used a time-series of ground thermal data from permafrost monitoring sites established by the Geological Survey of Canada along a latitudinal transect of the Northwest Territories, Canada, paired with a Landsat-derived time-series of vegetation productivity from 1984-2019 to quantify the impacts of changing permafrost conditions on vegetation productivity. My thesis had four research objectives: 1) Quantify recent (1984-2019) changes in vegetation productivity along a latitudinal transect of the Northwest Territories; 2) Determine if permafrost conditions are associated with observed differences in vegetation productivity; 3) Determine if rates of permafrost thaw can explain differences in vegetation productivity trends; and 4) Compare the relative influence of rate of permafrost thaw, time since fire, and climate moisture index on vegetation productivity trends. My results showed that changes in active layer thickness can explain some of the variation in vegetation productivity that has been observed in the northern boreal forest over the past several decades. Specifically, I found that some active layer thickening promotes increases in productivity, which could be caused by an influx of new soil nutrients, increased room for root growth, and/or increased mineralization rates in warming soils. However, increased greening was not sustained, but rather rates of greening began to slow with continued active layer thickening. It is likely that once the thaw front extends outside the plants’ rooting zone, they can no longer access the new soil nutrients or benefit further from the increased rooting space. The results from this study highlight the importance of permafrost conditions on vegetation productivity and emphasize the need for more paired time-series analyses to better understand the complex effects of climate change on the northern boreal forest.