Defoliation-induced enhancement of total aboveground nitrogen yield of grasses

We conducted an experiment in a northern mixed-grass prairie at Wind Cave N ational Park. South Dakota, USA to evaluate the effect of defoliation frequ ency on aboveground net primary production (ANPP), shoot nitrogen concentra tion, and aboveground N yield of graminoids. ANPP was significantly reduced at weekly and biweekly defoliation frequencies, but unaffected relative to unclipped controls at monthly and bimonthly frequencies. By contrast, clip ping at all frequencies increased shoot N concentration above that of contr ols, and this increase was greatest at monthly or more frequent defoliation s. Total aboveground N yield and potential N yield to grazers were greatest at intermediate (bimonthly to biweekly) frequencies. We suggest that graze rs may maximize their nutritional status in this system by periodically reg razing areas at Frequencies dear the approximately monthly optimum that we observed.