Background
The authors write that "recent changes in the climate of Arctic Alaska, including warmer temperatures and a lengthened growing season (Chapin et al., 2005; Serreze and Francis, 2006; Shulski and Wendler, 2007), are linked with ... increased vegetation productivity, as measured using time series of satellite vegetation indices such as Normalized Difference Vegetation Index (NDVI)," as documented by Myneni et al. (1997), Jia et al. (2003), Goetz et al. (2005) and Bhatt et al., 2010); and they say that this phenomenon "has been partly attributed to the expansion of shrubs, which has been documented using time series of aerial photography (Sturm et al., 2001; Tape et al., 2006), plot studies (Joly et al., 2007), and shrub growth ring chronologies (Forbes et al., 2010; Hallinger et al., 2010)." And in light of these observations they ask themselves the question: "Is the current warming and concurrent shrub expansion on older Arctic landscapes associated with increased or decreased erosion?"

What was done
Working with time series imagery obtained from Landsat thematic mapper data covering the period 1986-2009, Tape et al. examined the landscape pattern of tall shrub distribution and expansion in the Arctic foothills, located on the north side of the Brooks Range, Alaska, while they studied sediments obtained from cores of four lakes near the Chandler River on the central North Slope of Alaska (where shrub expansion is occurring), in order to compare relationships among shrub cover, erosion and runoff over the past quarter-century.

What was learned
The three researchers say their results reveal "a background decline in erosion (collectively, in 3 cores) since 1980, superimposed by episodic erosional events (in 1 core)," and they state that "the background decline in erosion is associated with trends of increasing shrubs and declining peak runoff events."

What it means
Tape et al. conclude that "in contrast to the positive feedbacks associated with shrub expansion and climate (Chapin et al., 2005; Mack et al., 2004; Sturm et al., 2005; Swann et al., 2010)" - which tend to enhance local warming - their results "suggest a negative feedback from shrubs stabilizing soil (including carbon)," which is a very positive result.

References
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Chapin III, F.S., Sturm, M., Serreze, M.C., McFadden, J.P., Key, J.R., Lloyd, A.H., McGuire, A.D., Rupp, T.S., Lynch, A.H., Schimel, J.P., Beringer, J., Chapman, W.L., Epstein, H.E., Euskirchen, E.S., Hinzman, L.D., Jia, G., Ping, C.-L., Tape, K.D., Thompson, C.D.C., Walker, D.A. and Welker, J.M. 2005. Role of land-surface changes in Arctic summer warming. Science 310: 657-660.

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Tape, K.D., Sturm, M. and Racine, C. 2006. The evidence for shrub expansion in Northern Alaska and the Pan-Arctic. Global Change Biology 12: 686-702.