ASSESSMENT OF INTERSPECIFIC INTERACTIONS IN PLANT-COMMUNITIES - AN ILLUSTRATION FROM THE COLD DESERT SALTBUSH GRASSLANDS OF NORTH-AMERICA

Interspecific interactions influence both the productivity and composi tion of plant communities. Here, we propose new field procedures and a nalytical approaches for assessing interspecific interactions in natur e and apply these procedures to the salt desert shrub grasslands of we stern Utah. Data were collected from two grazing treatments over a per iod of 2 years. The proposed equations were fairly consistent across b oth treatments and years. In addition to illustrating how to assess in terspecific interactions within a community, we also develop a new app roach for projecting the community composition as a result of some alt eration, i.e. increase or decrease in the abundance of one or more spe cies. Results demonstrate competition both within and between plant li fe-form groups. While introduced annuals were found to depress profoun dly the likelihood of perennial plants replacing themselves, perennial s had little influence on annuals. Thus, as native perennials die, the y are more likely to be replaced by perennials than for the reverse to occur. Our results suggest that unless conditions change, these commu nities will become increasingly dominated by introduced annuals. (C) 1 995 Academic Press Limited