Bracken Versus Heather, A Study in Plant Sociology

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Abstract
The temporal and spatial relations between bracken (Pteridium aquilinum) and heather (Calluna vulgaris) are investigated in part of an area where the soil (a podzolised sand) and the microclimate are believed to be uniform. Yet in part of the area bracken invades and suppresses heather; in another part heather invades and partly suppresses bracken, leaving a reduced population incorporated in the heather community. In the successional relations between the two species evidence is presented to show that in the marginal belt of bracken the suppression of heather is the result of the social structure of the invading bracken in which there is a continuous front of fronds at their most competitive. In the bracken hinterland the fronds are shorter and patchy. Heather becomes established and spreads suppressing bracken but not completely, forming a Callunetum with scattered fronds. The fronds in this Callunetum are overdispersed; there is a greater number of fronds in the pioneer and degenerate phases and a smaller number in the building and mature phases, than if at random; there is also phasic interdigitation, pioneer fronds are found in the pioneer phase of the Callunetum, fronds of the building phase type are found in the building phase of the heather etc. The interpretation of the phenomena is based on a knowledge of the life history of the plants and of the pattern of phases in the communities they form.

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