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

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).