The vegetative spread of Pteridium aquilinum in a hemiboreal forest – invasion or revegetation?

Abstract The purpose of this study was to determine whether Pteridium aquilinum (L. Kuhn) invades new ground or remain static under a closed forest canopy. It was also to study whether the species invades into new areas or revegetate previous occupied ground after clear-cutting in the hemiboreal zone. Two separate experiments were conducted over a six-year period: (1) The change in P. aquilinum frond density and cover under a closed tree canopy was studied on permanent plots; (2) P. aquilinum spread after clear-cutting was studied in terms of expanding fronts into new ground. The density of fronds did not change beneath the closed tree canopy during the study period. Expansion of the front of adjacent established P. aquilinum into one of two clear-cut sites was extremely rapid indicating an already present rhizome system, while expansion into the other site without rhizomes present was very slow. The results indicate that P. aquilinum does not increase its frond density or colonize new ground in the closed forest or invade new ground on clear-cut areas in the studied forest stands, but instead revegetates clear-cut areas in which it has previously been more abundant. However, forestry practices such as clear-cutting in areas in which P. aquilinum is sparsely distributed in the field layer in the closed forest prior to clear-cutting results in an increasing density of P. aquilinum which is sufficient to restrain forest regeneration.