TREE AND SHRUB COMMUNITIES OF WOODED DRAWS NEAR THE MATADOR RESEARCH STATION IN SOUTHERN SASKATCHEWAN

Composition of tree and shrub communities in wooded draws near the Mat ador Research Station in southern Saskatchewan featured three tree and 11 shrub community types identified by dominant cover: Acer negundo, Populus x jackii (Populus deltoides x Populus balsamifera), Populus tr emuloides, Salix bebbiana, Prunus virginiana, Crataegus chrysocarpa, S ymphoricarpos occidentalis, Rosa spp. (R. woodsii x R. acicularis), El aeagnus commutata, Juniperus horizontalis, Shepherdia argentea, Rhus a romatica var. trilobata, Artemisia cana and a Mixed Shrub type co-domi nated by Symphoricarpos occidentalis, Prunus virginiana, Rosa spp. and Amelanchier alnifolia. A total of 133 species of vascular plants were present in the 136 stands sampled; species richness ranged from 27 in the Rosa spp. community to 59 in the Elaeagnus commutata community. I n all communities the number of forb and graminoid species (22 to 49) exceeded that of trees (0 to 3) and shrubs (5 to 11). A diversity inde x based on total canopy cover revealed that diversity in tree and shru b communities was similar; in all communities the diversity index for the herbaceous stratum was generally greater than the tree or shrub st rata. A similarity index based on species frequency ranged from 0.11 t o 0.83 whereas a cover-based similarity index ranged from 0.01 to 0.62 indicating the canopy cover and its uniformity was very different amo ng communities. Ordination of frequency data suggests that Elaeagnus c ommutata was a distinct community whereas Juniperus horizontalis and A rtemisia cana were similar as were Rhus aromatica var. trilobata and S hepherdia argentea. The remaining communities formed another cluster o f similar communities. Ordination using total canopy cover suggests th at Populus tremuloides, Crataegus chrysocarpa, and Salix bebbiana comm unities were distinct from the others. The communities of Shepherdia a rgentea, Artemisia cana, Rhus aromatica var. trilobata and Juniperus h orizontalis were clustered, and the remaining tree and shrub communiti es tended to form another group. Less similarity in canopy coverage am ong communities probably reflects constraints imposed on plant growth by the environment within communities. Plant communities dominated by woody species are more numerous and diverse than acknowledged in earli er ecological studies.