Effect of defoliation on grass growth. A quantitative review.

DIEGO OMAR FERRARO; OESTERHELD, M.

Oikos

Año: 2002 vol. 98 p. 125 - 133

0030-1299

The diversity of responses of individual grasses to defoliation created a controversyabout 15 years ago, which still needs clarification. We quantitatively assessed theevidence of defoliation effects on individual grass growth, addressing two mainquestions: 1) what is the average and variability of the effect of defoliation on plantgrowth? and 2) what are the associated conditions accounting for the diversity ofeffects? Regarding the first question, the results showed a negative overall effect ofdefoliation on plant growth and substantial variability in the defoliation responses ofdifferent plant components. There was an intermediate negative effect on totalproduction (which included clipped-off biomass), a large negative effect on final livebiomass at harvest, and a minimal effect on root biomass. Regarding the secondquestion (conditions accounting for the diversity of effects), defoliation intensity hadno effect on the response to defoliation, but both time for recovery from the lastdefoliation and the period of time between defoliation events significantly decreasedthe negative effect of defoliation. Nitrogen availability also altered the effect ofdefoliation, as plants grown at highest nitrogen levels were more negatively affectedby clipping than plants with no supplementary addition of nitrogen. These resultsindicate that the magnitude of defoliation response by an individual plant differsamong plant compartments and this response is modulated by other factors, such astime for recovery after defoliation, and nutrient availability. In general, the effect ofdefoliation on individual plant production was more negative than reported effects ofgrazing on ecosystem primary production.