Studies on the Population Biology of the Genus Viola: IV. Spatial Pattern of Ramets and Seedlings in Three Stoloniferous Species

Abstract

(1) The spatial pattern of demographic variables of ramets and seedlings in sixteen populations of Viola blanda, V. pallens and V. incognita were analysed using a variety of approaches (area and distance methods, G-tests of heterogeneity based on area counts, neighbourhood analysis, spatial autocorrelation). The variables considered were the position of ramets in space and time, emergence and mortality of ramets and seedlings. (2) Emergence of new seedlings is clumped in space. The seedlings tend to be more numerous in areas where the overall ramet density is low, indicating that seed germination or seedling emergence or both are inversely correlated with overall density of ramets. Seedling survival is affected by density. (3) Ramets one-year-old or older appear to be aggregated or randomly distributed in space. (4) The pattern of emergence of new ramets from stolons and the pattern of ramet death is random in space and not density dependent. (5) It is proposed that seedling germination or survival or both are density dependent, but that the pattern of adult ramet distribution, vegetative production of new ramets and ramet mortality is more sensitive to environmental variables such as light, water and nutrients which are known to be unevenly distributed on the forest floor. (6) The concept of 'safe site' for seed germination has little predictive value in these populations of Viola.