TO GRAZE OR NOT TO GRAZE: THAT IS THE QUESTION

Abstract

Changing land use in both natural and artificial salt marshes shifted the focus from coastal protection and agricultural exploitation towards nature conservation interest. Transformation of large areas into nature reserves or national parks included abandoning of livestock grazing by some authorities in charge of management. Succession in natural salt marshes that have never been grazed by livestock, shows a climax of the shrub Atriplex portulacoides at the lower marsh and the tall grass Elymus athericus at the higher marsh of Schiermonnikoog. As this salt marsh has an age of about 40 years, the long-term climax of natural succession is not known. Exclosure experiments at the always cattle-grazed marsh of Schiermonnikoog, reveals an increase of Atriplex portulacoides at the lower and of Elymus athericus at the higher marsh. The species richness in permanent plots (4 m2) decreases in abandoned areas on the marshes at Schiermonnikoog, Terschelling and Skallingen. The species richness is always higher in grazed plots ranging from 0.01-2500 m2 in artificial marshes in the Netherlands. Long-term (over 20 years) experiments with exclosures and different stocking rates of cattle and sheep in the Netherlands and Germany, show that the Elymus athericus community can get dominant in both natural and artificial marshes. Subsequently, the number of plants communities decreases. Exceptions seem to be related to low rates of sedimentation or influence of fresh water. Experiments lasting less than 10 years show no dominance of the Elymus athericus community. Changes in canopy structure towards a taller vegetation after abandoning or decreasing stocking rate, has negative effects on winter and spring staging geese, and positive effects on some breeding birds. As with natural succession, further changes may take place at the longer term. Continuation of these experiments and monitoring are of vital importance to draw further conclusions. As results of abandoning or reduction of stocking rate may affect various organisms in different ways, the task for salt-marsh management is to define the management goal. After that the means to reach the target can be decided upon, and the question 'to graze or not to graze' can be answered. Nomenclature of plant species follows Van Der Meijden 1990