The colonisation of woodland gaps by ferns and horsetails

In the Voorsterbos, a planted woodland on a former sea-floor (the Netherlands), artificial gaps within stands of Fagus sylvatica on boulder clay were monitored for five or six years after cutting. Ten fern species and three species of horsetail established in these gaps, with Dryopteris cristata, Thelypteris palustris, Matteuccia struthiopteris and Equisetum telmateia not previously known from the Voorsterbos. Athyrium filix-femina was most successful and formed dense stands in some gaps. Two species (Gymnocarpium dryopteris, Dryopteris cristata) established but have since disappeared. Thelypteris palustris has built up a sustainable population. It seems plausible that the germination of ferns and horsetails took place during the first season following cutting of the gaps and was derived from a spore bank with an optimal microclimate with constant high moisture and humidity in the shaded part of the gaps. Competition from recruiting trees and shrubs was suppressed in some of the gaps for a period of five year through herbivory by Roe deer