QUADRAT VARIANCE ANALYSIS AND PATTERN DEVELOPMENT DURING PRIMARY SUCCESSION

Abstract. The interpretation of Hill's ‘Two Term Local Quadrat Variance’ analysis to detect the scale of spatial pattern in vegetation is improved by an equation that relates the block size of a variance peak to the scale of the pattern that gave rise to it. (Contrary to previous belief, the two are not the same, especially for large block sizes.) Deviations of pattern from a perfectly regular alternation of equally sized gaps and patches of uniform density cause changes in the variance. To aid in the interpretation of these changes, two indices of pattern regularity are proposed, one based on density and one based onpresence/absence, in orderte distinguish the effects of irregularities of patch density from irregularities of patch size and position. These methods are applied to a study of primary succession on glacial moraines near Mt. Robson, British Columbia, Canada, in order to evaluate certain hypotheses about the development of pattern. Other researchers have proposed that during succession, the pattern at first intensifies at the scales initially observed, then as succession proceeds some scales of pattern are lost due to coalescence of patches and eventually the intensity of those that remain decreases as the patterns become more and more irregular. The vegetation on the Mt. Robson moraines confirms this sequence of changes in vegetation pattern, only to the extent that patterns intensify initially in the chronosequence; the number of scales of pattern in the vegetation remains about the same throughout and there is no evidence that the patterns become more irregular. The variance‐block size graphs derived from presence / absence data matched those from density data well, indicating that the simpler data, in this case, are almost as informative about pattern as the more detailed data. 1990 IAVS ‐ the International Association of Vegetation Science