The diversity of responses of individual grasses to defoliation created a controversy years ago, which still needs clarification. Ferraro and Oesterheld quantitatively assessed the evidence of defoliation effects on individual grass growth, addressing two main questions: 1) what is the average and variability of the effect of defoliation on plant growth? and 2) what are the associated conditions accounting for the diversity of effects? They analyzed responses in the literature on defoliation effects using two complementary approaches: linear regressions and meta-analysis. Results showed a negative overall effect of defoliation on plant growth and substantial variability in the defoliation responses of different plant components. There was an intermediate negative effect on total production, a large negative effect on final live biomass at harvest, and a minimal effect on root biomass. As for the second question, defoliation intensity had no effect on the response to defoliation, but both time for recovery from the last defoliation and the period of time between defoliation events significantly decreased the negative effect of defoliation. Ferraro and Oesterheld's study indicated that the magnitude of defoliation response by an individual plant is different for the various plant components. The magnitude of defoliation impact is modulated by a number of factors. Longer time for recuperation after defoliation favors the occurrence of compensatory responses. Nutrient availability also showed an influence on defoliation responses.
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