The Growth, Distribution and Neighbour Relationships of Trifolium Repens in a Permanent Pasture: III. The Establishment and Growth of Trifolium Repens in Natural and Perturbed Sites

(1) The establishment and growth of Trifolium repens was studied in natural and perturbed sites in an area of permanent pasture in North Wales. (2) The density of buried viable seeds of T. repens in the pasture was estimated at 218 seeds per m2. Seedlings were rare, and no established plants formed from the seedlings except on molehills or deliberately disturbed areas. (3) Clones of T. repens from different parts of the field differed in aggressiveness towards a standard clone, and often showed evidence of 'ecological combining ability', i.e. were capable of yielding more in mixture than in a pure stand. (4) Transplants (phytometers) of T. repens (cuttings each with c. 2.5 cm of stolon, one trifoliate leaf and one axillary bud) made least growth in swards dominated by Holcus lanatus (yield per plant 0-09 g), followed by Agrostis tenuis (0.17 g), Lolium perenne (0.21 g) and Cynosurus cristatus (0.41 g). (5) The survivorship curves of transplants were linear, showing that the risk of death was relatively independent of season. Survivorship was greatest in swards dominated by Cynosurus cristatus (51% after 1 year), followed by Agrostis tenuis (41 %), Holcus lanatus (31%) and Lolium perenne (25%). (6) If the natural vegetation was killed by herbicide, the growth of transplants was increased sixty-five-fold. Removal of dicotyledonous species from the sward usually increased the number of leaves produced by naturally-occurring clover. (7) It is argued that part of the fundamental niche of Trifolium repens is occupied by grasses and dicotyledonous herbs, and that the distribution and activity of clover in the community is determined by interactions with these species.