Studies on the dynamic structure of persistent and productive pasture ecosystems

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(1) Analyses of biological factors of persistency : In order to clarify biological factors responsible for persistency of grasslands, adaptive strategy of major temperate grass species was investigated in relation to tradeoff between growth performance and stress tolerance. The extent of intraspecific genetic variation in adaptive strategy was also examined and discussed in relation to grassland managements. To know the reason for instability of pasture vegetation we conducted some manipulations on some pastures. Selective grazing was the main reason for instability of pasture vegetalion.(2) Ecology of grassland species : Ecological aspects of reproduction were studied for some pasture plants. Some properties of clonal reproduction in Trifolium repens and the condition for consistence of wind pollination and extended flowering in Anthoxanthum odoratum were shown. The leaf dynamics of bracken in semi-natural grassland was investigated. The pattern of leaf emergence was associated with cumulative air temperatures and seasonal change of photosynthetic activity.(3) Modeling of the vegetation dynamics and distribution pattern : A model of canopy dynamics of a bahia grass sward was constructed, dealing with a tiller as a basic unit. This model enables us to examine the effects of sward management and meteorology on the dynamics of tiller density, herbage mass, sward height and leaf area index. In semi-natural grasslands in Tochigi Prefecture, small-scale spatial heterogeneity in plant species community was measured based on a new method. The relationship between the spatial heterogeneity and the species diversity was expressed by a model.