Relationships between aspect and plant distribution on calcareous soils near Missoula, Montana
Aspect and depth to the CaCO3 horizon explain most of the variation in the plant communities on calcareous soils near Missoula, Montana, USA. Linear regression and the Mann Whitney U test were used to evaluate trends in soil properties and plant communities. The CaCO3 horizon (a proxy for leaching) ranges from 2 to 48 cm deep on the south aspect and ridge top and 46 to 125 cm deep on the north aspect. The forb-grass community dominates the south-facing slopes and the ridge top, providing more than 90% coverage, whereas on the forested north-facing slope, tree coverage ranges from 9-56% and forbs/grasses from 23-69%. Considerable difference in species composition occurs on each aspect. Differences in leaching are exemplified by higher [H+] on the north aspect (pH 6.6-7.0) than on the south aspect and ridge top (pH 7.1-8.3), partly as a result of twice the moisture content on the north slope (17 to 24% versus 10 to 12%).