In order to restore natural salt marsh in a 460-ha nature reserve established in man-made salt marsh in the Dollard estuary, The Netherlands, the artificial drainage system was neglected and cattle grazing reduced. Vegetation changes were traced through two vegetation surveys and monitoring of permanent plots over 15 yr after the management had been changed. Exclosure experiments were started to distinguish grazing effects from effects of increased soil waterlogging caused by the neglect of the drainage system.
Both vegetation Surveys and permanent plots demonstrated a dichotomy in vegetation succession. The incidence of secondary pioneer vegetation dominated by Salicornia spp. and Suaeda maritima increased from 0 to 20%, whereas the late-successional (Phragmites australis) vegetation from 10 to 15%.
Grazing intensity decreased towards the sea. The grazed area contracted landward, which allowed vegetation dominated by tall species to increase seaward. Grazing and increased waterlogging interacted in several ways. The impact of trampling increased. and in the intensively grazed parts soil salinity increased. This can probably be explained by low vegetation cover in spring.
Framework Ordination, an indirect-gradient-analysis technique, was used to infer the importance of environmental factors in influencing changes in species composition. Many changes were positively or negatively correlated with soil aeration and soil salinity, whereas elevation was of minor importance, Grazing accounted for only a few changes in species frequency, Changes in permanent plots were greater during the first than during the second half of the study period. In exclosures that were installed halfway through the study period, there was a relatively rapid recovery of previously dominant species that had decreased during the first half of the study period.
Species richness per unit area in the reserve increased. At the seaward side of the marsh. the altered management allowed succession to proceed leading to establishment of stands of Phragmites australis. whereas on the landward side. the combination of moderate grazing with neglect of the drainage system appeared an effective measure in maintaining habitats for a wider range of halophytic species.
|Number of pages||16|
|Journal||Applied Vegetation Science|
|Publication status||Published - May-2002|
- grazing gradient
- permanent plot
- repeated mapping