Effect of mowing to replace black locust plantation with grassland
The first restoration project of the Group started in 1995 with the aim to replace non-native black locust (Robinia pseudoacacia) plantations with open sand grasslands. Black locust was introduced to Hungary in the 1750s to stabilize wind-blown sand in the region between the Danube and Tisza rivers and is now frequently grown in plantations and planted along roadsides. Unfortunately, it often escapes from plantations and establishes on nearby lands and native vegetation. We wanted to explore strategies for replacing unprofitable black locust plantations with open sand grassland, which is the characteristic community type of historical landscapes in the sand dune region of the Hungarian lowlands. With this in mind, we designed a study to determine the response of sand grassland vegetation to a combination of tree cutting, chemical application, mowing, and hay removal.
Our study sites were located on sand dune summits within three different landscape types: a closed forest, a grassland-forest mosaic, and a predominantly open area. All sites were relatively small (1 ha) and had stands of black locust that were old enough for timber harvest. We clear-cut black locust during the winter of 1994-1995. To avoid resprouting, we applied a 1:1 mixture of triclopyr (Garlon® 4E) and engine-oil on the tree trunks shortly after cutting. Chemical application was repeated when necessary in the initial year. on the clear-cut area, mowing with hay removal treatment was applied twice a year (early June and early September) in 1995-2001 to assist grassland recovery. A block of 12 adjacent plots of 10 m by 10 m was assigned for the experiment at each site, with six control (unmowed) and six treatment (mowed) plots randomly selected. Vegetation was sampled in June and August yearly in 1995-1999 during the experiment, followed by occasional re-sampling until 2019.
Herbicide application with repeated mowing successfully eliminated R. pseudo-acacia. In the unmowed plots, dense woody cover developed at all sites. Vegetation of mowed plots approached the reference grasslands in sites with better propagule availability of target species according to trajectory analyses. In these sites, higher cover of target species was found in mowed compared to unmowed plots, though still significantly lower than in the reference. Mowed plots were more prone to secondary invasion than the unmowed. The long-term monitoring revealed that initial mowing assisted the restoration of Pannonian sand grassland, but further management is needed to control secondary invasion and increase target species cover.
Reis, B.P., Kövendi-Jakó A., Szitár K., Török K., Halassy M. (2021): Long-term effect of mowing on the restoration of Pannonian sand grassland to replace invasive black locust plantation. Restoration Ecology, 29: e13152.