Morphological and physiological responses of perennial grasses to long-term grazing in the Pryor Mountains, Montana

We evaluated in situ the effects of long-term grazing (>100 y) on the morph ological (i.e., shoot height, leaf blade length, width and angle) and physi ological (i.e., gas exchange and water relations) responses of the dominant perennial grass species from arid lowlands and more mesic uplands of the P ryor Mountain Wild Worse Range (PMWHR) in Montana. Pseudoroegneria spicata, the most abundant grass in the lowland communities, had shorter vegetative shoot heights and leaf blade lengths and narrower leaves in plants from ga zed than long-term ungrazed sites. Similarly, vegetative and reproductive s hoot heights of Festuca idahoensis and Elymus lanceolatus, common upland gr ass species, were shorter in plants from grazed than ungrazed sites. Leaf l engths of these upland grasses also were shorter and less erect in plants f rom grazed sites than ungrazed sires. The physiological responses of the do minant grasses to sating were not consistent between species or sampling da tes. Overall, photosynthetic rates, stomatal conductances and xylem pressur e potentials were the same in over 65% of the comparisons between plants fr om grazed and unsated sites and were higher in grazed sites in only 11 to 2 2% of the grazed-ungrazed comparisons. Collectively our results indicate th at long-term grazing of grasses by wild horses and other herbivores in the PMWHR has resulted in morphological modification, but has not substantively altered physiological function.