Long-term dynamics of vegetation and disturbance of a southern boreal spruce swamp forest

Analysis of pollen, charcoal and loss-on-ignition in peat cores from a Picea abies-dominated swamp forest in central Sweden show the vegetation changes and disturbance patterns over 9500 yr. Six major sequences of local vegetation development are identified: (A) Pinus period, ca. 9500 - 7000 cal. BP; (B) Open mire period (ca. 7000 - 4500 cal. BP; (C) Betula period, ca. 4500 - 2300 cal. BP; (D) Picea period (ca. 2300 - 1000 cal. BP; (E) Human impact period (ca. 1000 - 100 cal. BP); and (F) Period of human abandonment during the last ca. 100 yr. The swamp forest has been highly dynamic in response to various natural and anthropogenic disturbance agencies. Several fires have heavily influenced the vegetation development. During the last ca. 900 yr human influence has been important, initially from grazing and trampling by domesticated animals (ca. 1000 - 500 cal. BP), and subsequently small-scale cereal growing (ca. 400 - 100 BP). Cutting, burning and animal browsing influenced the structure and dynamics of the swamp forest by creating a more open stand and suppressing tree regeneration. Recent cessation of human impact has led to increased tree regeneration and a denser swamp forest stand. The present high biodiversity, and subsequent conservation interest does not result from long-term stability or absence of fire and human impact. However, in spite of repeated disturbances, a continuity of old and senescent trees produced a forest type with abundant dead wood. With the relatively minor importance of fire over long periods of time, the swamp forest developed a structure maintaining a high biological diversity. An important issue for maintaining long-term biodiversity in the boreal landscape must be to create a mosaic where different forest types are present, with a variety of structures, substrates and processes, to provide a certain degree of freedom for species to move around in the landscape.