The workings of grazed pastures : sward structure and biodiversity.

摘要

Studies of plant populations help to conceive and to assess management rules adapted to the various types of present-day grazing practices. Sward structure influences both the growth and quality of the available herbage. The residual leaf index after grazing depends on the growth and senescence rate. Sheath length influences both the blade length and blade digestibility. Grazing management consists of finding a compromise between heights i.e. tall for maximum ingestion or short for improved digestibility. The phenotypic plasticity of the forage grasses is both morphogenetical and physiological. It is reversible, within limits, which may vary according to species. There is a strong genetic variability within natural population and within cultivars,the fittest individuals dominate those less well-adapted to an extent that depends on the environment. Defoliation interacts with mineral nutrition on the biological diversity of the natural and semi-natural pastures. The diversity of species increaseswhen the availability of mineral nutrients decreases and it decreases when there is overgrazing or marked undergrazing. A functional approach based on the grouping of species sharing common biological features makes it possible to set up predictive models for the evolution of sward population.