SIZE DECLINE IN LARREA TRIDENTATA (CREOSOTEBUSH)

This study documents a dramatic decline in size of individuals within a Larrea triden- tata population in southern New Mexico over a decade long period. It is most likely that the decline in size represents individual plants shrinking in size resulting from the death of shoot systems, especially the larger branches within these multi-stemmed shrubs. We suggest that the decline in size observed in our study area may be the initial stages of a more widespread phenomenon, driven by the desertifica- tion process that accompanies the conversion of grasslands into shrublands. In the northern Chihuahuan desert of New Mexico and west Texas, shrublands dominated by Prosopis glandulosa (mesquite) and Larrea tridentata (creosotebush) have replaced former perennial grasslands over the last century. The importance of this conversion of shrublands into grasslands is now widely recognized (Schlesinger et al., 1990). However, less atten- tion has been directed towards the possibility that these shrub dominated communities may be a temporary stage in this dramatic transfor- mation process. One approach toward understanding plant community dynamics is to focus on the popula- tion dynamics of a dominant species within the community. Larrea tridentata is a dominant spe- cies and forms the basic structure of ecosystems in many areas in the desert southwest. This study