Terrestrial ecosystems

On the basis of satellite and aircraft-based remote sensing as well as direct field observations, a number of studies have documented changes in vegetation, which seem to be linked to recent warming. Mynemi et al. (1997) presented evidence that photosyn-thetic activity of terrestrial vegetation in northern high latitudes increased from 1981 to 1991, indicative of increased plant growth and lengthening of the active growing season. This assessment was based on two independent records of the normalized difference vegetation index (NDVI) derived from AVHRR satellite records. Subsequent studies including more recent data (e.g., Sturm et al., 2001; Zhou et al., 2001; Nemani et al., 2003) lend further support to a "greening" of the Arctic. Hinzman et al. (2005) give a comprehensive summary of ecosystem changes with a focus on Alaska. Among many other changes, they note a widespread advance of trees and shrubs into tundra ecosystems.

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