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Pattern in the Plant Community
Journal of Ecology
Vol. 45, No. 2 (Jul., 1957), pp. 451-463
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2256928
Page Count: 13
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(1) A method of determining groups of positively associated species (basic units) within a plant community is described. The method is based on the analysis of data from numerous small quadrats by a 2 × 2 contingency table and testing by a χ2 test. (2) The quadrats used to determine these basic units are allotted to one or more such units and an estimate is made of the proportion of the community area occupied by each basic unit. (3) A suggested method for determining the order of mean size of these basic units is described. The proportion of quadrats belonging to each basic unit is plotted against the quadrat area; the mean size of the basic unit occurs somewhere in the region where this proportion falls to zero. (4) The criticisms of the method are discussed. (5) Three widely different types of British vegetation have been studied. The results show that the basic units can be picked out by the method described. The communities were found to consist of three or more basic units one of which occupied over 60 per cent of the community area, forming a matrix within which the other basic units were distributed. (6) It is suggested that the concept of minimal area should be replaced by the concept of basic units. The field work required to characterize basic units is quite quick to carry out although the computation is rather more laborious. Once characterized, basic units are of great ecological use for analysing vegetation pattern and showing up ecological problems.
Journal of Ecology © 1957 British Ecological Society