9306499 Wallace The aim of this proposal is to provide new data on individualistic competitive interactions among dominant grass species that do versus do not have compensatory responses to being grazed by large ungulates. An exixting model of plant growth and competition will be modifed to increase the handling of spatial and temporal variablity for individualistic competitive interactions. The data will be used to parameterize the model as well as increase our mechanistic understanding of competitive interactions and plant compensatory response to removal of aboveground biomass under competitive circumstances. The question is an important one for the structuring of grasslands. And few studies focus on actually documenting and then incorporating differential plant response to herbivory into mechanistic, predictive models. The proposed work builds on the expertise of productive PIs and the collaboration is likely to continue to be a productive one. The experimental approach proposed is carefully thoughtout and intensive. I like the intensive physiological compenent, the data from which should complement and verify work being done on other labs. For the experiment, I had one question which I did not find addressed: What are the proposed extent, timing and persistence of the clipping treatments proposed? Also, a quibble perhaps, it seems to me that the experiment measures response of clipped vs unclipped plants to (potential) resource limitation rather than directly measuring competition as claimed. For the model, the one question I had was whether the rule, to distribute resources in proportion to demand ba sed on root biomass, was really an appropriate rule (even though I know that it is often the rule used)? It seems to me to build in a couple pf assumptions that are probably not warranted, especially in this study: that rate of uptake is proportional to root biomass and that it is equal among compensating and noncompensating species. Overall, a very strong proposal (though perhaps a somewhat disproportionaltely large investment, even on an annual basis, especially since the offcampus overhead rate was allowed. ! F v v 7 Times New Roman Symbol & Arial 5 Courier New " h E+ e 8 K abstract for Linda Wallace Deborah Johnson Deborah Johnson
