Long-term vegetation dynamics and land-use history: Providing a baseline for conservation strategies in protected Alnus glutinosa swamp woodlands

Abstract

Alnus glutinosa (alder) swamp woodlands are in danger of disappearing in Europe and, in Norway, several habitats with alder are threatened. Knowledge about the dynamics of alder swamp woodlands is crucial for the conservation and management of this vegetation. Our studied site, Rambjøra, in western Norway encompasses the Rambjøra Landscape Protected Area. We combined information from three sources—recent alder swamp woodland ecology, vegetation history, and agricultural history—to reveal the long-term vegetation dynamics of Rambjøra in relation to land-use. Dynamic changes in the predominance of forest or semi-natural grassland over 2800 years, concurrent with varying anthropogenic disturbances are inferred. At the investigated site, alder swamp woodland developed after forest clearance and changes in the water balance. The abundance of alder swamp woodlands have varied through time, increasing with low-impact land-use and declining with intensified use or abandonment. The highest biodiversity is found in periods with grazing, hay mowing, and probably fodder and fire wood collection. This indicates that agricultural practices of moderate intensity (grazing and hay cutting) should be part of the future management in order to maintain the biodiversity and meet the objective of the protection of Rambjøra. The study demonstrates the advantages of combining vegetation surveys, pollen records, and land-use history to provide a long-term perspective on vegetation development, and in our case also as an aid when establishing conservation strategies. Our findings need to be considered in future conservation and restoration of ecosystems with alder swamp woodlands.