BIOTIC INTERACTIVITY BETWEEN GRAZERS AND PLANTS - RELATIONSHIPS CONTRIBUTING TO ATMOSPHERIC BOUNDARY-LAYER DYNAMICS

During 1987 and 1988 First ISLSCP (International Satellite Land Surfac e Climatology Project) Field Experiment (FIFE) studies conducted in th e tallgrass prairie of central Kansas, variations in ungulate grazing intensity produced a patchy spatial and temporal distribution of remai ning vegetation. Equally variable plant regrowth patterns contributed further to a broad array of total primary production that resulted in a pronounced mosaic of grazing impacts. This regrowth potential, deriv ed from a relative growth rate (RGR) equation comparing ungrazed and g razed plants, determines much of the ecosystem dynamics within and amo ng the grazed pastures and between years. Rates of change in new plant growth (Delta RGR(g)) ranged from -100% to +40%; however, 78% of the time in 1987 and 71% in 1988, productivity increased as a function of grazing intensity. Since plant growth potential in ungrazed (RGR(g)) a nd grazed systems (RGR(g)) have inherently different attributes, inter actions with the abiotic environment may develop many uncertainties. T hus, changes in growth rates in grazed areas compared to ungrazed area s (Delta RGR(g)) may impose major controls over system productivity an d associated biological processes currently not accounted for in ecosy stem models. Because FIFE microsite atmospheric boundary layer (ABL) s tudies aid not directly incorporate grazing intensity into their desig n, Type I and Type II statistical errors may introduce significant unc ertainties for understanding cause and effect in surface flux dynamics . As a consequence these uncertainties compromise the ability to extra polate microsite ABL biophysical findings to other spatial and tempora l scales.