Population dynamics of grass-forb complexes on a semidesert range and some demographic aspects of James rushpea (<i>Hoffmanseggia jamesii</i> Torr. and Gray)

Dynamics of forbs and important grass species from 1915 to 1974 were investigated utilizing records from long-term charted quadrats on the Jornada Experimental Range, USDA, SEA-AR, in southern New Mexico. A short-term demographic study focusing on longevity and age-structure of the perennial forb, James rushpea (<i>Hoffmanseggia jamesii</i>), was also conducted using a technique for counting growth increments. Interesting results were obtained by the study of some demographic aspects of James rushpea. A maximum number of 9 growth increments was found for this species. A highly significant correlation (P<.001) was found between the number of growth increments and the cormlike base circumference (cm.). Age-structure of this species was described by two patterns: A J-shaped pattern on protected and highly disturbed sites, and an inverse J-shaped pattern on lightly grazed sites.