Invasion of Alnus glutinosa (L.) Gaertn. in a former grazed meadow in relation to different grazing intensities

Abstract

The invasion of Alnus glutinosa in a former grazed meadow in Hørret Wood near Århus (Eastern Jutland, Denmark) has been investigated. A dense Filipendula ulmaria vegetation, which has been developing since the grazing stopped, seems to prevent the establishment of seedlings of Alnus glutinosa, although the seeds are able to germinate in the spring, before the growth of Filipendula ulmaria starts. By reconstructing the development of four Alnus glutinosa thickets, it was concluded that moderate grazing favours the spread of Alnus glutinosa, whereas intensive grazing or cessation of grazing inhibits further invasion. The optimal grazing intensity for establishment of trees and bushes in meadows is discussed and related to the ‘floristic optimum’. Two situations in the management of meadows with grazing animals are proposed.