A comparison of the history and present state of an Alnus glutinosa and a Betula pubescens dominated patch of wetland forest in the nature reserve ‘Het Molenven’, The Netherlands

The species composition, the above-ground biomass of woody plants, herbs and mosses, and the age-structure of trees and shrubs were studied in an Alnus glutinosa and a Betula pubescens dominated patch of wetland forest in the nature reserve ‘Het Molenven’, The Netherlands. These patches were more or less similar in stand age and height of the water table, but differed in nutrient content of the substrate. Insight into the vegetational history of these sites was obtained by analysing the micro-fossils and macro-remains embedded in the peat. Man’s impact on the hydrology of the reserve triggered the observed changes in vegetation in both woodland patches. The different routes in vegetation succession and the differences in above-ground phytomass observed between the two sites can be explained, at least in part, by the differences in chemistry of the substrate. Betula pubescens seems to be more sensitive to a rise in water table than Alnus glutinosa, Frangula alnus and Salix cinerea, particularly because of its poorly developed ability to rejuvenate under water-logged conditions.