Recent paraglacial dynamics impact on plant colonization: a study case on Midre Lovénbreen foreland, Spitsbergen (79°N).
Résumé
Climatic changes since the end of the Little Ice Age have considerably disturbed environmental balances of plant colonization in high latitudes. Within one century on Spitsbergen, valley glaciers have retreated up to one kilometre from their original terminus as of 1918, affecting several hundred hectares of two types of landscape processes: plant colonization and paraglacial morphogenesis. Since these processes are limited to the chronological position of the old ice-front it is possible to know the rate of plant colonization by both qualitative and quantitative means, as well as speculate on the processes involved, such as the effects of runoff. The present study is limited to the Midtre Lovénbreen forefield (latitude 79°N, longitude 12°E), where geomorphologic and floristic samples were collected in 2003. On stable deposits in this area, the settlement and the evolution of floristic groups have been documented. During this time period of colonization, the plain areas are reworked by runoff at a kilometric scale, and are characterized as similar to their surrounding biogeographic landscapes. Thus, a relationship can be observed between the paraglacial process occurring in the proglacial forelands and surrounding stable surfaces on till deposits. These features that occur as spatial discontinuities across the landscape are perceptible through either plant colonization or disturbance to vegetation caused by hydrological processes. Ultimately, however, runoff dynamics maintain pioneer vegetation groups which are superimposed on plant colonization that are driven by temporal periods of deglaciation. Differences in the rates and the nature of plant colonization are biomarkers of paraglacial dynamics.