Canadian Forest Service Publications
Changing northern vegetation conditions are influencing barren ground caribou (Rangifer tarandus groenlandicus) postcalving movement rates. 2018. Rickbeil, G.J.M.; Hermosilla, T.; Coops, N.C.; White, J.C.; Wulder, M.A.; Lantz, T.C. Journal of Biogeography, 45:702–712.
Issued by: Pacific Forestry Centre
Catalog ID: 39000
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Aim: To quantify changes in vegetation productivity over the past three decades across five barren ground caribou (Rangifer tarandus groenlandicus) herd ranges and assess how these changes are influencing caribou movement rates. Location: Northwest Territories and Nunavut, Canada. Methods: As an indicator of vegetation productivity, the enhanced vegetation index (EVI) was calculated on newly developed cloud-free, gap-free, Landsat surface reflectance image composites representing 1984–2012. Changes in EVI were assessed on a pixel basis using Theil-Sen’s nonparametric regression and compared across herd ranges and land cover types using generalized least squares regression. Animal movement velocity was calculated from caribou telemetry data and generalized additive mixed models were used to link movement rates with vegetation productivity during the post-calving phase of the year (July and August). Results: Vegetation productivity increased across the five caribou herd ranges examined. The largest productivity increase occurred over the ranges of the most western herds, with the largest observed changes in grassland or shrub habitats. Caribou tended to move more slowly through tundra habitats with elevated levels of productivity to a point, while grasslands movement rates decreased linearly with increasing productivity. Movement velocities peaked at intermediate productivity levels in shrub habitats. Main conclusions: Over the three decades of collected data, barren ground caribou habitats have become more productive, which is consistent with other studies that have documented increases in Arctic vegetation productivity. The more western herds, whose ranges are also closest to the Arctic Ocean, experienced the largest increases in productivity. Finally, we demonstrate that barren ground caribou movement patterns will likely change as a result of changing vegetation productivity in complex manners depending on herd, habitat type and the magnitude of change in vegetation productivity.
Plain Language Summary
The objective of this study is to document changes in barren ground caribou habitat, specifically vegetation productivity, and assess how these changes are affecting caribou behavior using a vegetation productivity index generated from comprehensive, annual, Landsat-derived 30 m data. Recent work has demonstrated that at a broad scale (i.e. using MODIS 1 km pixels), the lower Arctic and Boreal forests are increasing in productivity. However, this has been difficult to assess at finer scales (i.e. 30 m Landsat pixels) owing to data acquisition challenges. Here, we apply a newly developed Landsat compositing and proxy infilling technique to estimate vegetation productivity changes across 700 000 km2 of barren ground caribou habitat from 1984 to 2012. Additionally, we relate how these changes are influencing caribou behavior by incorporating these data with behavioral metrics derived from GPS telemetry data collected on 258 individual barren ground caribou from 2006 to present.