Shrubs, Runoff and Erosion in Arctic Alaska Foothills

Authors Tape et al. (2011) 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?"

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. And what did they find?

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."

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.

Additional 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.

Forbes, B.C., Fauria, M.M. and Zetterberg, P. 2010. Russian Arctic warming and 'greening' are closely tracked by tundra shrub willows. Global Change Biology 16: 1542-1554.

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Hallinger, M., Manthey, M. and Wilmking, M. 2010. Establishing a missing link: Warm summers and winter snow cover promote shrub expansion into alpine tundra in Scandinavia. New Phytologist 186: 890-899.

Jia, G., Epstein, H.E. and Walker, D.A. 2003. Greening of arctic Alaska, 1981-2001. Geophysical Research Letters 30: 10.1029/2003GL018268.

Joly, K., Jandt, R.R., Meyers, C.R. and Cole, M.J. 2005. Changes in vegetative cover on Western Arctic Herd winter range from 1981 to 2005: Potential effects of grazing and climate change. Rangifer 27: 199-206.

Mack, M.C., Schuur, E.A.G., Bret-Harte, M.S., Shaver, G.R. and Chapin, F.S. 2004. Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization. Nature 431: 440-443.

Myneni, R.B., Keeling, C.D., Tucker, C.J., Asrar, G. and Nemani, R.R. 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature 386: 698-702.

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Shulski, M. and Wendler, G. 2007. The Climate of Alaska. University of Alaska Press, Fairbanks, Alaska, USA.

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Swann, A.L., Fung, I.Y., Levis, S., Bonan, G.B. and Doney, S.C. 2010. Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect. Proceedings of the National Academy of Sciences USA 107: 1295-1300.

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.