Areas of boreal forest in the Clay Belt of northern Ontario, burned at a range of times from 0 to 57 years before the present, were examined. The range of vegetation present was sampled by means of a number of plots in each area. A simple test of heterogeneity, based on the number of significant correlations between species, was applied to the data from each area. Vegetation samples and species were each classified into nonexclusive groups, and the properties of the groups explored. Maturity weightings, based on the age of the site at which each species was first detected, were calculated for each sample.The results of analyses indicated the presence of four stages in the succession: (a) initial heterogeneity; (b) early phase; (c) heterogeneous phase; and (d) late phase. Initial heterogeneity, attributable to burning intensity, persists for a year, but is succeeded by a more homogeneous phase dominated by species which survive the fire in various ways. The heterogeneous phase is dominated by environmentally differentiated mosaic elements; it is succeeded by the late phase as a canopy develops and as ephemeral species, which colonized the disturbed area, disappear. The late phase is dominated by jack pine in sandy areas and by black spruce in peaty areas.There is evidence that the changes from one phase to the next are spatially heterogeneous because some sites mature more rapidly than others. The paths of succession at different sites within an area may differ, but there is convergence to one of the two main vegetation types in the late phase. The late phase types are differentiated at a much larger scale than the seral mosaic elements.
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