Spatial patterns of mortality in a Colorado desert plant community

Spatial pattern and patterns of mortality were analyzed from a five year re-census of over 7 000 mapped perennial shrubs within a one hectare study plot in Joshua Tree National Park. A five year interval revealed evidence for negative intraspecific interactions which was not evident after a one year evaluation of the same plants within the study area. Juvenile mortality was a positive function of conspecific density for Ambrosia dumosa, Eriogonum fasciculatum and Sphaeralcea ambigua. In addition,juvenile E. fasciculatum that died occurred closer to conspecific adults than would be expected by chance. The two censuses are similar 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 otherwise static analyses. Herbivory and nurse effects are implicated as potential factors influencing the dispersion of perennial plants within deserts.