Vegetation response to experimental and natural disturbance in two salt-marsh plant communities in the southwest Netherlands

Abstract

The present study reports on a long-term (1971–1985) experiment at the Stroodorpepolder marsh in the southwest Netherlands to investigate the response of salt-marsh vegetation to disturbance. The experiment was executed in two plant communities, one located at a creek bank dominated by Halimione portulacoides and the other situated in a depression where the vegetation was dominated by Puccinellia maritima and Limonium vulgare. The treatments entailed destruction of the vegetation either by applying herbicides or digging up the soil. Species composition in control and treated plots was recorded annually from 1971 until 1985. In three of the four treatments, species composition in these disturbed plots returned to that of the controls. In the fourth case, viz. the digging treatment at the depression site, the vegetation did not revert to its control. By the end of the experiment, it was dominated by Halimione. It is suggested that this irreversible change in species composition must be attributed to increased soil aeration caused by digging. The strong tendency to revert was further demonstrated by the response of the vegetation to frost damage, which severely affected Halimione in the winter of 1979. The average time between successive winters with temperatures low enough for frost damage to occur was estimated to be five to seven years, which is sufficiently long for the vegetation to recover. This implies that the vegetation remains close to equilibrium most of the time, and therefore, it is argued that equilibrium models can be successfully applied to describe the spatial patterns of salt-marsh vegetation.