Forest-tundra ecotone response to climate change in the Western Sayan Mountains, Siberia

摘要

Tree response to climate trends is most likely to be observed in the forest-tundra ecotone, where mainly temperature limits tree growth. On-ground observation and multitemporal Landsat data were used in the analysis of forest-tundra ecotone dynamics (from 1976 to 2000) in the Western Sayan Mountains, Siberia. Observations showed an increase in forest stand crown closure, upward tree-line and regeneration shift and the transformation of Siberian pine and fir krummholz into arboreal forms. Closed stands were increasing in the area at a rate of 0.8% year(-1) and advancing their upper boundary at an altitudinal rate of 0.6 m year(-1); these changes were shown mainly by the transformation of sparse stands into closed stands. The altitudinal rate of regeneration propagation was estimated at 1.2 m year(-1). It was also found that these changes correlated positively with temperature trends. The response of tree vegetation to air temperature increase was dependent on topographic relief features (azimuth and slope steepness).