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.