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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
A. J. Parsons, Anne Harvey and Jane Woledge
Journal of Applied Ecology
Vol. 28, No. 2 (Aug., 1991), pp. 619-634
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2404572
Page Count: 16
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(1) Several features of the physiology of leaf expansion and the turnover and fate of leaves of two contrasting forage species were studied under continuous grazing to identify the mechanisms that control the relative performance of these species in a mixture. For this, swards of perennial rye-grass and white clover were maintained at three intensities of continuous grazing by sheep (sward surface heights of 3, 6 and 9 cm) and a heavily fertilized grass sward was maintained at 6 cm. (2) 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. (3) 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. (4) 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 weight than grass when the total size of the unit was large (e.g. under lenient grazing). But clover had a greater specific leaf area than grass in all cases. (5) These findings explain how clover had an advantage over grass during summer grazing and increased its proportion in the mixture.
Journal of Applied Ecology © 1991 British Ecological Society