Plant-animal interactions in a continuously grazed mixture. I. Differences in the physiology of leaf expansion and the fate of leaves of grass and clover.
In grazing trials at Hurley in Mar.-Oct. 1984, mixed Trifolium repens cv. Huia/Lolium perenne cv. S23 swards were continuously grazed by sheep to maintain sward height of 3, 6 or 9 cm; a pure L. perenne sward given 30 kg N every 2 weeks was also maintained at 6 cm. Mixed swards received no N fertilizer. Grass and clover leaves appeared on average at a similar rate, but grass leaves appeared more slowly in the tall swards than in the short ones. In clover, leaf appearance was unaffected by grazing intensity but in the tall swards the leaves took longer to complete their expansion. Growing clover leaves escaped grazing by appearing and expanding close to the soil surface, but once expanded near the top of the canopy, they were soon grazed, often in their entirety. Grass leaves were grazed earlier, often while they were still growing, but defoliation was only partial. This, and a difference in the pattern of leaf unfolding, led to differences between grass and clover in the age structure of the leaf area in the canopy. Grass and clover also differed in their degree of investment in lamina. Ungrazed youngest expanded units of clover had a smaller proportion of lamina to total wt than grass when the total size of the unit was large (e.g. under lenient grazing). However, clover always had a greater specific leaf area than grass.