The structural dynamics of Suserup Skov, a near-natural temperate deciduous forest in Denmark

Abstract

Nature-based silviculture is a promising approach to meet the criteria for sustainable forestry. This brings the natural forest into focus as a basic reference for forest management. The present study focuses on the structural dynamics of a near-natural temperate deciduous forest in Denmark as a reference for forestry. The study was conducted in Suserup Skov (55° 22′N, 11° 34′E, 19.2 ha), an ancient woodland with a long history of low human impact. It is a mixed deciduous forest dominated by Fagus sylvatica L. and Fraxinus excelsior L. with some Quercus robur L. and Ulmus glabra Huds. The dynamics and structures of Suserup Skov can be described in time and space according to the mosaic-cycle concept. A specific model of the forest cycle in Suserup Skov was developed, including five sequential phases. The typical duration of each phase was determined: innovation (14 years), aggradation (56 years), early biostatic (96 years), late biostatic (108 years) and degradation (10 years) phases, equalling some 284 years for the full cycle. In principle, the forest cycle takes place at any given patch of the forest, asynchronous from patch to patch, resulting in a shifting mosaic of the constituent phases. The mosaic, mapped in a 10.65-ha plot in 1992, had an average patch size of 839 m 2, ranging from 100 to 12 730 m 2. The patches of the shorter phases (innovation, degradation) were on average considerably smaller than the patches of the longer phases, which can be explained partly by fusion of neighbouring patches. The aggregate areas of each phase were almost directly proportional to their respective duration, suggesting that the shifting mosaic was close to the steady state. The disturbance regime and disturbance history of Suserup Skov is discussed. It is concluded that several disturbances of smaller scale had occurred during the past centuries and that the most influencing recent disturbance has been the long period of human influence by rural, woodland management (pannage, pasture and coppicing) before the enclosure of the forest in 1807. The Suserup Skov example shows that a temperate deciduous forest under a relatively calm disturbance regime can develop into a very fine-grained mosaic, apparently approaching the shifting mosaic steady state within a rather small area. The structural steady state in Suserup Skov occurs, even though the overall species composition is still under successional change. Further, `climax microsuccession' from Fraxinus to Fagus occurs as an integral part of the forest cycle in Suserup Skov. Cyclic and directional processes are intermingled in Suserup Skov, highlighting the complex relationships between the concepts of succession and climax. The paper finally exemplifies how natural forests can be used as a reference for silviculture, nature conservation and landscape planning.