THE EFFECTS OF RECENT AND RELICT PERMAFROST DISTURBANCES ON TUNDRA VEGETATION, CAPE BOUNTY, MELVILLE ISLAND, NUNAVUT
Cassidy, Alison Elizabeth
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Permafrost disturbances, including active layer detachments (ALDs), have occurred both recently and historically at Cape Bounty, Melville Island. These recent and relict ALDs were studied to determine their short- and long-term landscape effects. Six relict detachments showed altered vegetation and site characteristics, despite 60 or more years of recovery. Of the environmental variables studied, including soil moisture, soil temperature, and active layer depth, soil moisture showed the greatest changes in disturbed zones. These were attributed to the concavity of disturbance, which allows for more snow accumulation. Two vegetation types influenced by moisture regimes, polar desert and mesic heath, were compared to determine the role of moisture in recovery. The best indicators of disturbance differed in areas of different moisture regimes, with canopy height showing increases in disturbed mesic heath zones, while Normalized Difference Vegetation Index (NDVI) values increased in polar desert disturbances. Ultimately, the comparison of vegetation in disturbed and undisturbed zones revealed differences to be highly localized and minimal. Remote sensing was utilized to compare the effects of recent and relict disturbances as seen on satellite and airborne imagery. Vegetation was classified using NDVI, and zonal separation of these values in ALDs revealed the upper scar areas and lower toe zones contained significantly different NDVI values. The upper scar values were similar to undisturbed control areas, as blocks of vegetation in these areas often contain unmodified vegetation, which later helps with revegetation. The lower toe zone displayed both elevated and lower NDVI values, as material accumulates in these areas but often in a complex with bare soil. Remote sensing techniques also allowed for site characterization of disturbances, with physiographic factors including slope and flow properties determined through satellite imagery. Slope values ranged from 3 to 13 degrees in each disturbance, but were found to be slightly lower in relict disturbances, as recovery and revegetation have reduced these slopes. Flow paths were identified in ALDs, however similar patterns were also identified in surrounding undisturbed landscapes. Given the small scale of many ALDs, it is difficult to characterize the nature of the changes associated with these events, particularly for relict ALDs.