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

The species composition of grass swards can be altered by differences in de foliation intensity. Differences in the response of plants of different spe cies to defoliation intensity could be responsible, in part, for such diffe rences in species composition. Our objective was to characterise the effect s of defoliation intensity, in interaction with neighbour species, on the n umbers of tillers per plant and plant mass of Lolium perenne, Trifolium rep ens, Poa annua and Poa trivialis. We compared the effects of high and low i ntensities of defoliation on single target plants grown in 1 m(2) plots of neighbour species. There were all possible combinations of target species a nd 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 tr eatment. Thus, the effects of defoliation on plants can partly explain diff erences 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 aro und 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 gro wing points, on target plants. T. repens as a neighbour increased the heigh t of the target plants and it increased the plant mass of P. trivialis (per haps as a result of a temporal niche separation). The Poa species as neighb ours only affected the heights of the target plants. Neighbour species did not significantly affect the mass per tiller of the target plants. ((C) Inr a/Elsevier, Paris.).