A Case Study: The Implementation of a Nature-Based Engineering Solution to Restore a Fallopia japonica-Dominated Brook Embankment

Abstract

Considering the high abundance of knotweeds along river courses, the expected increase of invasion and the consequent negative impacts on riparian ecosystems, there is a high demand for innovative approaches and management strategies. While a primary aim of weed management is to reduce the population of an invasive plant species, the goal of the pre-sented nature-based engineering solution (NABES) is to reinstall native riparian forests and to restore ecosystem functioning. The concept of NABES is to support the implemented species by frequent removal of the knotweed shoots until the native vegetation represses the knotweeds by root competition and shadow pressure. In order to be able to develop adaptive knotweed management strategies, knowledge concerning sea-sonal biomass development and the most effective maintenance intervals must be improved. Additionally, greater understanding of the interaction between invasive and native species is essential. In the present study, the effectiveness of a willow brush mattress (a frequent technique for controlling riverbank erosion) in combination with adapted management strategies was tested on a Fallopia japonica-dominated brook embankment. Due to its high ecological amplitude and excellent soil bioengineering properties the species S. purpurea was used. In the upper part of the embankment, F. japonica shoot production was by far the strongest, while it was low in the sections next to the water. The strongest biomass production was observed in the months April and May. Even though the temporal interval between shoot removal was increased, shoot production decreased strongly and nearly ceased in August. Branches of S. purpurea with contact to the water of the brook showed good development. In contrast to F. japonica, which suffered a rapid decrease in biomass production after the third survey, the coverage ratio of S. purpurea decreased gradually over the vegetation period.