Stability of boreal forest stands during recent climate change: evidence from Landsat satellite imagery

Aim To detect possible expansion of boreal forest stands in response to rec ent warming. Previous modelling studies have concluded that major shifts in vegetation patterns, including changes in boreal forest extent, could aris e during the next two centuries under global warming scenarios. However, fi eld investigations of tree stands at ecotones have so far revealed little i ndication of stand response to warming during the last 100 years. This stud y uses a c. 25-year record of Landsat satellite observations to quantify ch anges in forest stand extent in two areas of northern Canada. Location Two regions of northern Canada, near Richmond Gulf, Quebec, and Gr eat Slave Lake, north-west Territories. Methods Normalized-difference vegetation index (NDVI) plots across forest-t undra boundaries were obtained from radiometrically corrected Landsat image ry acquired during the 1970s and 1990s. These curves were evaluated to look for changes over the c. 25-year period related to forest stand expansion. Results Although forest-tundra boundaries could be clearly mapped from the satellite data, no obvious change in forest boundaries was apparent during the duration of the image time series, constraining recent geographical exp ansion rates to <200-300 m per century. Also, no evidence for local expansi on of forest stands (e.g. within sheltered valleys) was found. Main conclusions The results are consistent with field observations, and su ggest that, at the moment, boreal forest extents remain basically stable. T his may reflect inherent lags between forest response and climate change, o r competitive pressures between tree stands and surrounding tundra and herb aceous vegetation.