On the Spatial Organization of Plant Species in a Limestone Grassland Community

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Abstract
(1) studies of the spatial organization of plant communities have been based on samples of the physical space occupied by communities. To determine the spatial organization of a community as the plant species themselves experience it (the ''plant''s-eye-view''), it is necessary to use a sampling method in which the individual plant is the sample unit. The method of cluster sampling makes this possible in the absence of a census list from which to sample. (2) Cluster sampling is used to estimate the structure of a limestone grassland community as it "appears'' to seven common plant species (''target species'') in the community. (3) The mean distances from the target species to the nearest neighbour of each target species indicate that, qualitatively, each experiences the other species in proportion to their abundance in the community, although there is evidence of within-species aggregation in several cases. (4) A similar picture emerges from the mean densities of species in the immediate neighbourhood of each target species. Although spatial patterns within certain species are highly non-random, the spatial patterns of different species are interlocked in such a way that there is little indication of interspecific associations. (5) The amount of neighbour-free space differs between targets species. In most cases, this is not correlated with plant size. (6) Spatial organization of the community as exemplified by this study is most likely to be a result of the patterns of clonal growth, although the possibility of fine-scale niche differentiation is not excluded. Such organization could play an important role in shaping future interactions in the community, causing interspecific interactions to be weaker than intraspecific ones.