We simulated 25-mm precipitation events and used stable isotope tracers ([H.sup.2] and [N.sup.15]) to follow water and N uptake patterns in six dominant perennials (Artemisia filifolia, Coleogyne ramosissima, Cryptantha flava, Ephedra viridis, Quercus havardii, and Vanclevea stylosa) at different times of the growing season.
The experiments were conducted in July 1996 and May, July, and September 1997 on five dominant perennial shrub species (Quercus havardii Rydb., Ephedra viridis Cov., Artemisia filifolia Ton., Coleogyne ramosissima Torr., and Vanclevea stylosa (Eastw.) Greene) and the most dominant herbaceous perennial species (Cryptantha flava (A.
Species Growth form Leaf longevity Flowering Coleogyne ramosissima shrub drought deciduous April-August Artemisia filifolia shrub winter deciduous August-October Quercus havardii shrub winter deciduous April-June Ephedra viridis shrub evergreen [+] July-August Vanclevea stylosa shrub winter deciduous July-August Cryptantha flava perennial forb evergreen May-July (+.)Carbon gain in photosynthetic stems.
The shortgrass region of the western Great Plains is a semiarid environment of sparse grasslands dominated by shortgrasses (Bouteloua gracilis and Buchloe dactyloides) on loamy soils, and a mixture of sagebrush (Artemisia filifolia
), soapweed (Yucca glauca), midheight grasses (e.g., Sporobolus cryptandrus), and shortgrasses on sandy soils (Lauenroth et al., 1999).