Remote sensing reveals long-term effects of caribou on tundra vegetation |
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Authors: | Erica J Newton Bruce A Pond Glen S Brown Kenneth F Abraham James A Schaefer |
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Institution: | 1. Environmental and Life Sciences Graduate Program, Trent University, Peterborough, ON, K9J 7B8, Canada 2. Ontario Ministry of Natural Resources, Second Floor DNA Building, Block B, 2140 East Bank Drive, Peterborough, ON, K9J 7B8, Canada 3. Ontario Ministry of Natural Resources, 1235 Queen Street East, Sault Ste. Marie, ON, P6A 2E5, Canada 4. Department of Biology, Trent University, Peterborough, ON, K9J 7B8, Canada
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Abstract: | Declining use and abandonment of traditional ranges by migratory caribou (Rangifer tarandus) have often been related to density-dependent depletion of summer forage. The Pen Islands caribou herd (R. t. caribou), Ontario and Manitoba, Canada, numbered in the thousands on its traditional summer tundra range during the 1980s, but then declined in that region. We postulated that increased caribou abundance over three decades negatively affected phytomass, given that under the exploitation ecosystem hypothesis (EEH), grazers limit the amount of primary production if few predators are present. We tested this prediction using the Normalized Difference Vegetation Index (NDVI), as a proxy for phytomass available to caribou. We lagged caribou abundance in the explanatory model by the number of years (4–7) between peak caribou abundance and minimum NDVI. NDVI was negatively related to caribou abundance lagged by 6 years, and growing degree days explained much of the annual variation in NDVI. Precipitation was not an important predictor in the model. Our study is the first to apply NDVI to support the EEH for caribou. We propose that this method could be used over broad scales to shed light on limiting factors for migratory caribou across the circumpolar North. |
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