HERBAGE DYNAMICS ON 2 NORTHERN GREAT-PLAINS RANGE SITES

Quantity and quality of forage produced are primary determinants of le vel of livestock production derived from grazing lands, Moreover, spec ies composition of herbage is often considered a primary determinant o f the ecological condition of rangelands, The broad objective of this study was to quantify the productivity, growth dynamics, and quality o f herbage growing on 2 Northern Great Plains range sites and to concur rently relate magnitude and composition of production to the ecologica l condition of the sites, Using frequent harvest techniques, the 2-yea r study showed herbage production on the highly productive silty range site averaged 219 g m(-2) as compared to 218 g m(-2) on the supposedl y less productive Clay pan range site. The primary reason the clay pan site proved to be as productive as the silty site was attributed to t he greater amounts of introduced annual grasses on the clay pan (148 g m(-2)) than the silty site (104 g m(-2)), The annual grass component on the clay pan was a near equal mix (71 vs 51 g m(-2)) of Japanese br ome (Bromus japonicus Thunb,) and cheatgrass (B. tectorum L,) whereas the ovenwhelming dominant on the silty site was cheatgrass (73 g m(-2) ), Western wheatgrass [Pascopyrum smithii Rydb, (Love)] was the domina nt perennial grass on both sites averaging 49 g m(-2) on the clay pan site and 57 g m(-2) on the silty site, There were minimal differences between sites in terms of nutrient quality values (i.e., crude protein , acid detergent fiber, neutral detergent fiber) with results showing clearly that age of tissue was the major factor altering seasonal fora ge quality values, Range condition analyses revealed the clay pan site was in fair ecological condition and the silty site was in good condi tion, Study results demonstrate the need for land management agencies to continue to refine productivity estimates as well as adopt new tech niques for assessing the ecological condition of rangelands.