CHANGES IN COMPETITION BETWEEN A C-4 GRASS AND A WOODY LEGUME WITH DIFFERENTIAL HERBIVORY

Effects of simulated herbivory (clipping) on the growth of bermuda gra ss, Cynodon dactylon, and huisache, Acacia smallii, was evaluated in t he greenhouse when they were grown alone, in competition with each oth er, and with or without added nutrients. Clipping reduced shoot dry-ma ss of both species, but the effect was modified by the presence of add ed nutrients. The addition of nutrients stimulated shoot dry-mass prod uction in C. dactylon, but had no stimulatory effect on A. smallii unl ess C. dactylon was clipped. Although shoot dry-mass in C. dactylon wa s reduced by clipping, that in A. smallii was reduced an order of magn itude more. One seedling of A, smallii had essentially no negative eff ect on shoot dry-mass in C. dactylon. The presence of defoliated C. da ctylon reduced shoot dry-mass in clipped A. smallii by 86% in low nutr ient soil, but with the addition of nutrients, dry mass in unclipped A . smallii was only reduced 62%. If neither C. dactylon or A. smallii w ere clipped, shoot dry-mass in A. smallii was reduced 92%, but if clip ping was applied differentially to A. smallii but not the grass, the r eduction of dry mass in A. smallii was greatest at 38% regardless of n utrient level. Results of nutrient additions suggest that reduced grow th of A. smallii in the presence of the clipped grass is at least part ially due to removal of a nutrient from the soil by the grass.