SEASONAL GRAZING IMPACT ON CRYPTOGAMIC CRUSTS IN A COLD DESERT ECOSYSTEM

Since settlement, cattle grazing has been a major cause of soil distur bance in cold desert ecosystems. The objective of this study was to de termine the impact of cattle grazing in different seasons on cryptogam ic soil crusts. This study was conducted adjacent to the Brigham Young University Skaggs Research Ranch, near Malta, Ida. Five areas of a cr ested wheatgrass pasture each interplanted with shrubs were evaluated. Each of the 5 areas was subdivided into 4 paddocks; a control paddock remained ungrazed, while the other 3 paddocks were grazed in either s pring, summer, or winter. Each of the 1.2-ha grazed paddocks was graze d annually in the same season for 2 consecutive years by 10 cows for 4 consecutive days. Percent of the soil surface covered by litter, vasc ular plant bases, and cryptogams was measured using a 10-pin, point sa mpling frame. Mosses were the main component of the cryptogamic soil c rusts under all grazing treatments. Winter grazing had no effect on th e moss component of the crusts while spring and summer grazing reduced mosses. While winter grazing had significantly less impact on the lic hen component of crusts relative to spring and summer grazing, there w as a 50% reduction relative to the control plots. Total cryptogamic co ver in the control paddocks averaged 27.6%; winter grazed paddocks 27. 4%; summer grazed paddocks 14.4%; and spring grazed paddocks 10.6%. Co ntrolled winter grazing has minimal impact on the total cryptogamic pl ant cover that protect soil surfaces on cold desert range ecosystems.