Biocomplexity of arctic patterned-ground ecosystems.

TitleBiocomplexity of arctic patterned-ground ecosystems.
Publication TypeConference Paper
Year of Publication2006
AuthorsWalker, LA, Daanen, R, Epstein, H, Gould, WA, González, G, Kade, A, Kelley, A, Krantz, W, Kuss, P, Michaelson, G, Munger, C, Nickolsky, D, Peterson, R, Ping, CL, Raynolds, M, Romanovsky, V, Tarnocai, C, Vonlanthan, C
Date Published12/2006
PublisherAmerican Geophysical Union, Fall Meeting
Accession NumberLUQ.1125

Small-scale patterned-ground features, including non-sorted circles and small non-sorted polygons, are important features of most arctic landscapes. The size, abundance and morphology of these features are affected by complex interactions between cryological processes, soil properties, and biological processes. We examined the interactions between frost-heave, contraction cracking, soil properties, and vegetation along an 1800-km transect through 10 degrees of latitude and approximately 11 degrees C of mean July temperature. We established permanent monitoring sites at 11 locations in the 5 bioclimate subzones of the Arctic (Subzone A is the coldest; E is warmest). Patterned-ground morphology on zonal sites changes in predictable ways with differences in climate, soil-moisture, soil-texture, and the structure of the vegetation. Large well- vegetated earth hummocks 2-3 m in diameter are prevalent in forested areas and in tussock tundra areas of Subzone E. Partially vegetated and barren 1-2-m diameter non-sorted circles are dominant in the more open vegetation of subzones D and southern parts of subzone C, and small barren non-sorted polygons and turf hummocks 10-30 cm in diameter are related to small-scale contraction cracking in subzones C, B and A. Strong thermal, physical, and chemical gradients develop within frost-heave features that help to maintain the position of these features in the same locality over long time periods. Many of these gradients are related to the contrast in the vegetation mat on and between these features. This results in much warmer soil conditions within the heave features in summer and much colder conditions during the winter. Strong thermal differences drive the movement of water and the development of frost heave. Cryoturbation of organic material from the margins of frost-heave features to the permafrost table, combined with aggrading permafrost tables, acts to sequester large amounts of carbon within the permafrost of these ecosystems. Using a model (WIT3D/ArcVeg) that includes interactions between geophysical and biological processes, we were able to replicate common patterned ground forms involving differential frost heave. So far, the models have replicated the patterns in the Low Arctic where differential frost heave is the dominant process. Contraction cracking is the dominant process in the High Arctic and new models will be needed to elucidate this process. The presence of non- sorted circles affects active-layer depths, carbon storage and flux rates, and is likely to affect the rate at which Arctic systems will adjust to climate change. Analysis of a 14-yr record of greening near Toolik Lake, Alaska indicate that areas with abundant non-sorted circles experience more rapid change than stable areas without circles, suggesting that landscapes with a significant amount of disturbance, whether caused by natural or anthropogenic forces, will change most rapidly under a warming climate