Morphological dynamics and seedling recruitment in young swards of three contrasting cultivars of white clover (Trifolium repens) under continuous stocking with sheep

Abstract

Although there has been some recent interest in the morphology of individual white clover plants within established mixed swards under sheep grazing, there is little information available on the morphological changes taking place during the critical first 3 years of sward development. Undamaged white clover plants were sampled from an experiment at Plas Gogerddan, Ceredigion, comparing three contrasting white clover cultivars, sown with a common companion ryegrass cultivar, under continuous stocking with sheep. Turves (250 × 250 mm), from which individual plants were carefully extracted, were taken every month during 1990–91 (years 2 and 3 after sowing). Each plant was described in detail by assessing a range of morphological characters. Information was also gathered from each quadrat on the degree of flowering and seedling recruitment. There were clear seasonal variations in plant size and complexity with an increase in the number of simple, unbranched plants over the winter/spring period, which became the dominant plant type by June. During the later part of each year, the reverse was true. Characters associated with plant size also decreased over the winter period, followed by recovery during the ensuing summer. However the recovery was not complete and there was a strong general trend towards an increased proportion of less complex plants of reduced size over the 2 years. As plant size fell, plant number increased and morphological differences between cultivars diminished. By autumn of the second year (third year after sowing) the mean plant size reached a critical level with further stolon loss resulting in large scale plant death. Over the 2-month period August–October 1991, plant number fell by 60% and resulted in a reduction in stolon abundance of 76%; a true clover crash. The seedling data also suggest that under these conditions seedling recruitment can be up to one twentieth of that expected from a conventional sowing and can play a substantial role in the regeneration of the sward.