LEAF-AREA DEVELOPMENT OF 4 PLANT-COMMUNITIES IN THE COLORADO STEPPE

Leaf area index (LAI) values were periodically estimated along permanent transects to compare LAI development patterns among four shortgrass steppe plant communities in Colorado. For 2 growing seasons the point-quadrat method was used to determine the LAI of old standing dead tissue, current-year standing dead tissue and green plant tissue. Separate LAI values were determined for green tissue of C3 graminoids, C4 grasses, forbs, shrubs, cacti, Bouteloua gracilis, the dominant C4 grass, and Carex eleocharis, an abundant C3 sedge. Maximum LAI values of all green tissue ranged from 0.31 to 0.55 and occurred from late May to mid-July. In both years the sandy-loam site had the highest, the clay-loam site the lowest, and the two loam sites consistently had intermediate maximum LAI values. LAI amounts were greater for C3 than C4 graminoids in early spring, were greater for C4 than C3 graminoids during mid- and late summer, but C3 and C4 graminoids both produced the most leaf area during May. Even when May had below average rainfall amounts, the availability of soil-stored water, warmer temperatures and variable climatic conditions combined to facilitate maximum leaf area development at this time of year for plants in both photosynthetic pathways. Later in the growing season leaf area development was more closely related to the amount of precipitation.