Enjoying tranquility – Development of ground vegetation after cessation of management in forests on loamy soils in Flanders (Belgium)

Prepared by Kris Vandekerkhove, Arno Thomaes, Luc De Keersmaeker, Peter Van de Kerckhove, Thierry Onkelinx, Hans Van Calster & Kris Verheyen

A view on one of the investigated set-asides: an old mixed oak forest in Meerdaalwoud (close to Leuven, Belgium). Notice the dense layer of spring flowers. (Photo credit: Kris Vandekerkhove)

Managed forests are often more uniform than natural forests, but with frequent canopy gaps and soil disturbances due to harvest operations. When these stands are abandoned or set aside, they can go through a transitional phase with dense canopy and less disturbance. There is debate whether this is, in the end, positive or negative for the ground flora. Does the species richness increase or decrease, and is the species composition changing?

In this study, we investigated the vegetation in four forest sites that were set aside in the 1990’s in a fertile lowland area in Belgium. We studied the ground flora in 183 permanent plots in the years 2003-2005 and repeated this ten years later.

Anemone nemorosa, a typical spring flower in European forests on richer soils. This species became much more abundant in the set-aside forests. (Photo credit: Kris Vandekerkhove)

The results show that the species richness indeed decreased, both at site and plot level. This decline was not random. We saw strong declines for light-demanding species that are mainly found in gaps and also for species that need bare soil to germ. These species may recover in the longer run, when natural disturbances (like trees being blown over) gradually will take the place of disturbances related to tree harvests.

The typical forest spring flowers and species that can grow in the shade under dense tree canopies, however, did not decline but became much more abundant.

The outcome is a ground flora that may (at least temporarily) contain fewer species, but the species that remain and thrive are the characteristic species of shady forest undergrowth.

This is a plain language summary for the paper of Vandekerkhove et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12593).