Abstract
Widespread increases in Arctic tundra productivity have been documented for decades using coarse-scale satellite observations, but finer-scale observations indicate that changes have been very uneven, with a high degree of landscape- and regional-scale heterogeneity. Here we analyze time-series of the Normalized Difference Vegetation Index (NDVI) observed by Landsat (1984–2012), to assess landscape- and regional-scale variability of tundra vegetation dynamics in the northwest Siberian Low Arctic, a little-studied region with varied soils, landscape histories, and permafrost attributes. We also estimate spatio-temporal rates of land-cover change associated with expansion of tall alder (Alnus) shrublands, by integrating Landsat time-series with very-high-resolution imagery dating to the mid-1960s. We compiled Landsat time-series for eleven widely-distributed landscapes, and performed linear regression of NDVI values on a per-pixel basis. We found positive net NDVI trends (‘greening’) in nine of eleven landscapes. Net greening occurred in alder shrublands in all landscapes, and strong greening tended to correspond to shrublands that developed since the 1960s. Much of the spatial variability of greening within landscapes was linked to landscape physiography and permafrost attributes, while between-landscape variability largely corresponded to differences in surficial geology. We conclude that continued increases in tundra productivity in the region are likely in upland tundra landscapes with fine-textured, cryoturbated soils; these areas currently tend to support discontinuous vegetation cover, but are highly susceptible to rapid increases in vegetation cover, as well as land-cover changes associated with the development of tall shrublands.
Highlights
The climate of the Arctic is changing, and there is strong interest in understanding how vegetation will respond to and contribute to this change
Satellite observations of vegetation dynamics have shown that this warming leads to increased vegetation growth and a marked ‘greening’ trend in non-forested tundra (Walker et al 2009)
normalized difference vegetation index (NDVI) data In this study we examine changes in vegetation productivity in northern West Siberia (NWS) (2000–14) using variations in NDVI, which is a well-established proxy for gross photosynthesis at different spatial scales (Goetz et al 2005) and an index of vegetation greening, density and development
Summary
The climate of the Arctic is changing, and there is strong interest in understanding how vegetation will respond to and contribute to this change. The direct impact of the climate warming factors on boreal and arctic vegetation cannot be established unambiguously. Satellite observations of vegetation dynamics have shown that this warming leads to increased vegetation growth and a marked ‘greening’ trend in non-forested tundra (Walker et al 2009). Reflecting temperature change, a widespread ‘greening’ indicated by the increasing growing-season maxima of normalized difference vegetation index (NDVI) has been reported north of 64°N (e.g., Walker et al 2009, Epstein et al 2012). Since 2003, the greening in tundra has slowed down (Bhatt et al 2013) and the surface temperature trends have become negative or at least more spatially fragmented in the tundra zone (Comiso and Hall 2014)
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