The effects of cutting intensity and neighbour species on plants of Lolium perenne, Poa annua, Poa trivialis and Trifolium repens

The species composition of grass swards can be altered by differences in defoliation intensity. Differences in the response of plants of different species to defoliation intensity could be responsible, in part, for such differences in species composition. Our objective was to characterise the effects of defoliation intensity, in interaction with neighbour species, on the numbers of tillers per plant and plant mass of Lolium perenne, Trifolium repens, Poa annua and Poa trivialis. We compared the effects of high and low intensities of defoliation on single target plants grown in 1 m(2) plots of neighbour species. There were all possible combinations of target species and monocultures of neighbour species, with the same list of species used as targets and neighbours. Relative to L. perenne, P. annua had more tillers per plant and greater mass under the high than the low intensity cutting treatment. Thus, the effects of defoliation on plants can partly explain differences in the proportion of P. annua in short and tall swards dominated by L. perenne. There was no evidence that this was also true for P. trivialis. However, the results did predict that a low herbage height or biomass around mid-May might lead to a reduction in the proportion of P. trivialis in a pasture. As a neighbour, L. perenne reduced the number of tillers, or growing points, on target plants. T. repens as a neighbour increased the height of the target plants and it increased the plant mass of P. trivialis (perhaps as a result of a temporal niche separation). The Poa species as neighbours only affected the heights of the target plants. Neighbour species did not significantly affect the mass per tiller of the target plants. ((C) Inra/Elsevier, Paris.).