Pm. Drennan et Ps. Nobel, FREQUENCIES OF MAJOR C-3, C-4, AND CAM PERENNIALS ON DIFFERENT SLOPESIN THE NORTHWESTERN SONORAN DESERT, Flora, 192(3), 1997, pp. 297-304
Of the thirty-three perennial species recorded along line transects at
a site in the northwestern Sonoran Desert, nine species were succulen
ts from different families (Cactaceae, Crassulaceae, and Agavaceae) an
d a further eight were from the Asteraceae. The CAM succulent Agave de
serti, the C-3 drought-deciduous Encelia farinosa, and the C-4 bunchgr
ass Pleuraphis rigida were codominant, with 33%, 13%, and 15%, respect
ively, of the total cover. Agave deserti, which is clonal and had a cl
umped distribution, was the most abundant species on all slopes except
south-facing ones, where the randomly distributed E. farinosa was dom
inant. Encelia farinosa was infrequent on west- and north-facing slope
s, were the randomly distributed P. rigida reached its maximum cover.
Although intra- and interspecific competition was evident for all thre
e species, their frequency was dependent predominantly on microclimate
.