Restoration of wet dune slacks on the Dutch Wadden Sea islands: recolonization after large-scale sod cutting

Published source details Grootjans A.P., Everts H., Bruin K. & Fresco L. (2001) Restoration of wet dune slacks on the Dutch Wadden Sea islands: recolonization after large-scale sod cutting. Restoration Ecology, 9, 137-146.
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This study is summarised as evidence for the following.

	Action	Category
	Remove surface soil/sediment: freshwater marshes Action Link
	Use grazing to maintain or restore disturbance: freshwater marshes Action Link
	Raise water level to restore degraded freshwater marshes Action Link

Remove surface soil/sediment: freshwater marshes

A replicated, site comparison study in 1993–1998 involving 12 dune slacks in the Netherlands (Grootjans et al. 2001) reported that slacks where topsoil was removed (along with stopping groundwater extraction and reintroducing grazers) developed plant communities with characteristic wetland species and more plant species than mature, unmanaged slacks. Statistical significance was not assessed. Restored slacks developed plant communities, the overall composition of which changed over time (data reported as a graphical analysis). After five years, restored slacks contained 76–108 plant species overall and 48–86 species/100 m². This included species characteristic of dune slacks (5–11 species/100 m²) and nutrient-rich marshes (2–11 species/100 m²) alongside other wetland and upland species. In each slack, total vegetation cover was always <50% and only two individual species – creeping willow Salix repens and bushgrass Calamagrostis epigejos – ever had cover >1%. For comparison, during the second year of the study, mature slacks contained 12–39 plant species/m² (data not reported for other outcomes). Methods: Dune slacks are low-lying areas amongst dunes. Eight degraded slacks (stabilized and covered with undesirable, mature vegetation) were restored. In summer 1993, vegetation and topsoil were removed (10–40 cm depth, across all or part of each slack). Earlier that year, groundwater extraction had been stopped. In 1995, grazers (a “small herd” of cattle and ponies) were reintroduced to seven slacks. The study does not distinguish between the effects of these interventions. Vegetation was surveyed in at least five of the restored slacks (spring or summer 1994–1998) and four mature slacks (spring 1994): species across the whole of each slack; species and cover in five comparable 100-m² plots/slack.

(Summarised by: Nigel Taylor)
Use grazing to maintain or restore disturbance: freshwater marshes

A replicated study in 1993–1998 of four dune slacks in the Netherlands (Grootjans et al. 2001) reported that slacks where grazing was reintroduced (after stopping groundwater extraction and removing topsoil) developed plant communities with habitat-characteristic species. Restored slacks developed plant communities, the overall composition of which changed through time (data reported as a graphical analysis; statistical significance of changes not assessed). After three years of grazing, restored slacks contained 84–108 plant species overall and 48–86 species/100 m². This included species characteristic of dune slacks (5–11 species/100 m²) and nutrient-rich marshes (2–11 species/100 m²) alongside other wetland and upland species. In each slack, total vegetation cover was always <50% and only two individual species – creeping willow Salix repens and bushgrass Calamagrostis epigejos – ever had cover >1%. Methods: In 1995, traditional grazing (by a “small herd” of cattle and ponies) was resumed in four degraded dune slacks (stabilized and covered with undesirable, mature vegetation). Dune slacks are wetter, low-lying areas between dune ridges. In 1993, groundwater extraction had been stopped. Vegetation and topsoil were also stripped, completely or partially, from each slack. The study does not distinguish between the effects of these interventions. Each spring or summer between 1994 and 1998, seed-plants were surveyed: species across the whole of each slack; species and cover in five comparable 100-m² plots/slack.

(Summarised by: Nigel Taylor)
Raise water level to restore degraded freshwater marshes

A replicated, site comparison study in 1993–1998 involving 12 dune slacks in the Netherlands (Grootjans et al. 2001) reported that after stopping groundwater extraction (along with removing topsoil and resuming grazing), the slacks developed plant communities with habitat-characteristic species, and more species than mature, unmanaged slacks. Statistical significance was not assessed. Restored slacks developed plant communities, the overall composition of which changed over time (data reported as a graphical analysis). After five years, restored slacks contained 76–108 plant species overall and 48–86 species/100 m². This included species characteristic of dune slacks (5–11 species/100 m²) and nutrient-rich marshes (2–11 species/100 m²) alongside other wetland and upland species. In each slack, total vegetation cover was always <50% and only two individual species – creeping willow Salix repens and bushgrass Calamagrostis epigejos – ever had cover >1%. For comparison, during the second year of the study, mature slacks contained 12–39 plant species/m² (data not reported for other outcomes). Methods: Dune slacks are low-lying areas amongst dunes. Eight degraded slacks (stabilized and covered with undesirable, mature vegetation) were restored. In 1993, groundwater extraction was stopped. Vegetation and topsoil were also stripped, completely or partially, from each slack. In 1995, grazers (a “small herd” of cattle and ponies) were reintroduced to seven slacks. The study does not distinguish between the effects of these interventions. Vegetation was surveyed in at least five of the restored slacks (spring or summer 1994–1998) and four mature slacks (spring 1994): species across the whole of each slack; species and cover in five comparable 100-m² plots/slack.

(Summarised by: Nigel Taylor)