Woody plant encroachment into grasslands within the Red Deer River drainage, Alberta

Abstract

Montane grasslands play a key role in supporting wintering elk in the Rocky Mountains of Alberta. To document change in grassland extent and patch sizes, I analyzed repeat aerial photography at 4 sites in the upper Red Deer River drainage between 1952 and 2003. Excluding the Ya Ha Tinda, grassland extent declined 52 + 20%, shrubland 39 + 41%, with an increase in mixedwood forest of 32%, and coniferous forest of 39 + 10%. The rate of grassland loss differed among sites: West Lakes > Tyrrell Flats ~ Scotch Camp. Grassland area at Ya Ha Tinda was the same in 1952 and 2003 due to shrub mowing. Grassland patch size increased on average, but decreased in WL as larger patches of fragmented with woody plant encroachment. From 100-m transects along grassland-shrub-forest ecotones, differences in herbaceous biomass and species richness existed within cover types, but no pattern in edge effects on herbaceous biomass could be detected between ecotone type or among sites, except at the Ya Ha Tinda.