SPATIAL PATTERNS OF MORTALITY IN A COLORADO DESERT PLANT COMMUNITY

Spatial pattern and patterns of mortality were analyzed from a five ye ar re-census of over 7 000 mapped perennial shrubs within a one hectar e study plot in Joshua Tree National Park. A five year interval reveal ed evidence for negative intraspecific interactions which was not evid ent after a one year evaluation of the same plants within the study ar ea. Juvenile mortality was a positive function of conspecific density for Ambrosia dumosa, Eriogonum fasciculatum and Sphaeralcea ambigua. I n addition,juvenile E. fasciculatum that died occurred closer to consp ecific adults than would be expected by chance. The two censuses are s imilar in that uniform patterns of distribution among conspecifics are rare, particularly for non-succulent species. These results emphasize the value of mapped study sites in allowing dynamic inferences from o therwise static analyses. Herbivory and nurse effects are implicated a s potential factors influencing the dispersion of perennial plants wit hin deserts.