Covering Bare Ground Suppresses Unwanted Willows and Aids a Fen Meadow Restoration in Switzerland

Abstract

Many calcareous fen meadows in central Europe have been destroyed in the last two centuries, but now there are several projects to restore them. Unfortunately, excessive establishment of volunteer willows (Salix spp.) can considerably inhibit the establishment of the plant species to be re-introduced, especially when the sod is not yet closed. To control willow establishment, we experimentally tested the influence of sowing times for fen species (autumn, spring), soil cover treatments (straw layers, plastic), and tilling on the establishment of goat willow (Salix caprea) and the fen species themselves.

Plastic covering or a thick layer of straw at 3.7 pounds/yd² (2.0 kg/m²) during the willows’ germination time in May almost completely inhibited the establishment of the willows. Fen species sown after removing these layers became established at intermediate levels of roughly 50 individuals/yd² (60 individuals/m²). Fen species had the highest establishment with no cover (119 individuals/yd², 142 individuals/m²); however, willows establishment was also highest in those plots (about 3 individuals/yd², 4 individuals/m²). Tilling showed intermediate results for both willows and fen species.

We suggest the use of a thick straw layer (more than 3.0 lbs/yd²) or plastic cover in May to reduce large numbers of willows. These layers have to be removed before sowing the fen species. If the presence of willow seeds is low, straw can be reduced to 1.0 lb/yd², which will be low enough to allow the establishment of fen species with the straw remaining on the soil.