| Walter D. Willms, Johan F. Dormaar, Barry W. Adams, and Harriet E. Douwes |
| Walter D. Willms, Johan F. Dormaar, and Harriet E. Douwes are Range Ecologist, Soil Scientist (emeritus), and Range Technician, respectively, Agriculture and AgriFood Canada, PO Box 3000, Lethbridge, Alberta, Canada T1J 4B1; Barry W. Adams is Range Specialist, Alberta Agriculture, Food and Rural Development, #100, 5401 - 1ST Ave. S., Lethbridge, Alberta, Canada T1J 4V6. |
Abstract |
| The Mixed Prairie plant communities developed with the influences of fire and grazing. Available evidence suggests that removal of these disturbances could cause succession toward a more mesic type with the accumulation of litter or loss in productivity as nutrient turnover is delayed. Exclosures constructed in 1927 in a semiarid Mixed Prairie community provided an opportunity to examine the effects that protection had on vegetation and soils. Fifteen exclosures were selected for detailed examination; of these, 11 were located on Chernozemic soil and 4 on Solonetzic soil. We measured plant and soil variables both inside and outside the exclosures in a test of the hypothesis that protection from grazing will lead to a loss of production potential of the semi-arid. Mixed Prairie communities in the Northern Great Plains of southeastern Alberta. We found little evidence that 70 years of protection from large animal disturbance reduced the production potential of the plant communities. Conversely, most evidence suggested a neutral effect or an improvement as reflected in an increased cover of Pascopyrum smithii Rydb. (Löve) (P = 0.049) and increased annual net primary production (P = 0.047). The effect of protection appeared largely driven by the accumulation of litter mass that primarily benefits soil and plant indices of quality on the Chernozemic soil type. Although protection tended to reduce species diversity (P = 0.097) among native plants on the Chernozemic soil type, evenness and richness were not affected (P > 0.10). The potential effect that reduced diversity might have on reducing production stability appears more than compensated for by increased litter mass. |
| Key Words: Soil nitrogen, soil depth, botanical composition, plant biomass, plant nitrogen |