Disturb soil/sediment surface: freshwater marshes
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
Background information and definitions
This action involves shallow disturbance of the top few centimetres of soil/sediment in degraded marshes (e.g. by tilling, ploughing, disking or scarifying) without permanently removing any material. Such disturbance may encourage the growth of desirable plants. It can break up any hard soil crust, or create bare patches clear of competing vegetation or litter in which new plants can grow. Marsh plants may colonize from nearby habitat patches, or germinate from propagules (e.g. seeds, spores or root/rhizome fragments) already in the soil. The first colonizing plants will typically be fast-growing, weedy species – but these may also be desirable members of target plant communities, or act as nurse plants for later desirable communities.
Supporting evidence from individual studies
A replicated, paired, controlled study in 1992–1993 in five freshwater marshes undergoing restoration in New York State, USA (Brown & Bedford 1997) found that plots with disturbed soil contained a more wetland-characteristic plant community, with more and greater cover of wetland species, after one growing season – but that these effects disappeared after two growing seasons. After one growing season, disturbed plots contained a plant community more characteristic of wetland conditions than undisturbed plots (data reported as a wetland indicator index). Disturbed plots also contained more and greater total cover of wetland plant species (3.2 species/plot; 28% cover) than undisturbed plots (2.0 species/plot; 19% cover). After two growing seasons, all metrics were statistically similar under both treatments: community composition, wetland plant cover (disturbed: 72%; undisturbed: 54%) and wetland plant richness (disturbed: 3.6; undisturbed: 2.8 species/plot). Methods: In May 1992, twenty 0.25-m2 plots were established across five recently rewetted sites (drained for ≥40 years previously). In five plots (one plot/site), the top 15 cm of soil was removed then put back in place. The other 15 plots (three plots/site) were left undisturbed. Plant species and cover were recorded in autumn 1992 and 1993.Study and other actions tested
A replicated, controlled study in 1993–1995 in five freshwater marshes undergoing restoration in New York State, USA (Brown & Bedford 1997) found that plots disturbed by ploughing typically contained more and greater cover of wetland plant species than unploughed plots after one year, and higher cover of cattails Typha spp. after two years. After one year, ploughed plots had greater total cover of wetland plants than unploughed plots in three of three comparisons (ploughed: 33–74%; unploughed: 5–15%). Ploughed plots contained more wetland plant species in two of three comparisons (for which ploughed: 5.7–6.4; unploughed: 3.0 species/plot; other comparison no significant difference). After two years, treatments did not significantly differ in either total wetland plant cover (ploughed: 114–138%; unploughed: 71–96%) or richness (ploughed: 2.4–4.9; unploughed: 3.7–4.7 species/plot). However, ploughed plots had far greater cover of cattails in three of three comparisons (ploughed: 72–148%; unploughed: 0–7%). Methods: The study used five degraded wetland sites, drained for ≥40 years. In summer 1993, areas within two sites were ploughed. In autumn 1993, all five sites were rewetted. Plant species and cover were recorded in 1994 and 1995 (precise date not reported), in 18 quadrats in the ploughed areas and 39 quadrats in nearby unploughed areas. Quadrats spanned a range of elevations.Study and other actions tested