The 9000-year histo of vegetation development and disturbance patterns of a swamp-forest in Dalama, northern Sweden

Abstract

Analysis of pollen and charcoal in peat cores together with age-structure data of a swamp- forest site in the western part of central Sweden show the regional vegetation succession and the disturbance patterns over the last 9000 years. Five major vegetation sequences are identified: 1) Betula- Pinus period (c. 7000 to c. 6000 cal. BC); 2) wetland development (c. 6000 cal. BC to c. cal. AD 300); 3) Picea swamp-forest establishment ( c. cal. AD 300-1000); 4) human exploitation (c. cal. AD 1000-1900); and 5) cessation of human impact ( c. cal. AD 1900- present). Between c. 7000 cal. BC and c. cal. AD 1000, 17 fires were recorded in the peat. During the last 900 years, the area has been under the influence of human impact, mainly by animal grazing and trampling, together with deliberate flooding. These activities have affected the structure and dynamic of the swamp-forest by suppressing the regeneration of Picea and thereby creating an open Picea stand. During the last hundred years, a gradual cessation of human activities has led to increased Picea establishment and a denser swamp-forest. Despite these prolonged anthropogenic disturbances, the swamp-forest has qualities that make it unique in the Swedish forest landscape: 1) it has been forested for about 1700 years, during the last c. 900 years of which fire has been of little or no importance; 2) there are no visual signs of logging; and 3) dynamic processes, with trees continuously establishing, ageing and reaching senescence, have produced a forest with a high abundance of dead wood. The results show that the vegetation has been highly dynamic in response to both anthropogenic and 'natural' disturbance, and to the immigration of Picea. The present high biodiversity, and subsequent conservation interest does not result from long-term stability or absence of fire and other disturbance agencies. Conservation policies should therefore, in addition to species preservation, work to create a mosaic-like landscape where many different forest types are represented, containing structures, substrates and processes that are important for many different species. This provides the species the freedom of movement necessary for survival within the forest landscape in a longer perspective.

Early land use and centennial scale changes in lake-water organic carbon prior to contemporary monitoring

“…Apophytes are native plants indicative of a more open landscape, which are favored by human landscape disturbances such as forest grazing and cultivation. There is evidence of limited land use already during c. 500 B.C.-A.D. 1450, such as smaller increases in apophyte pollen and isolated occurrences of anthropochore pollen in Lång-Älgsjön, which are seen in other regional pollen records (40,41). During this earlier period, there is also a slight decline, ∼3 mg·L −1 , in inferred lakewater TOC relative to mid-Holocene values, but given the isolated occurrence for anthropogenic indicators and the possible transport of pollen from outside the catchment, we do not interpret this decline as such.…”

“…This evidence occurs mainly in the form of disturbance indicators, resulting from the gradual opening and alteration of the forest vegetation (40)(41)(42)(43). However, the region underwent more fundamental changes in agricultural practices after the medieval agrarian crisis.…”

“…These seasonal settlements were established at some distance from permanent settlements in areas where resources were less exploited and fodder not limited. Activities at these sites included the grazing of the livestock in the forest, production and processing of milk, haymaking on mires for fodder, and occasionally also cultivation of cereals (e.g., barley and rye) (40). To improve forest grazing, the canopy cover was opened and unwanted field-layer vegetation such as dwarf shrubs and mosses was grazed, removed, or burned, leading to an altered, more open forest composition (42).…”

Fifty years of Quaternary pollen analysis in Fennoscandia 1954–2004

“…Pollen stratigraphies from small hollows in Denmark, Sweden, and Norway have provided unique temporal insights into local forest stand continuity, cultural landscape history, vegetation dynamics, forest change, fire regimes, tree invasion, and conservation evaluation (e.g. Berglund 1962, Bradshaw 1988Bradshaw & Zackrisson 1990, Bradshaw & Hannon 1992, Lindbladh & Bradshaw 1995Bjö rkman 1996Bjö rkman , 1997aBjö rkman , b, 1999Bjö rkman & Bradshaw 1996, Segerströ m et al 1996, Hjelle 1998a, Hannon et al 2000, Niklasson et al 2002, Hellberg et al 2003, Lindbladh et al 2003. Local-scale pollen stratigraphies have been compared with hindcast simulations from a forest-gap model to test hypotheses about the role of extrinsic climate factors and intrinsic forest dynamics in influencing forest change over 1500 years (Cowling et al 2001).…”

“…Local-scale pollen stratigraphies such as those from Denmark and Sweden permit detailed analysis of the Holocene structure of north-west European temperate forest and some elucidation of the possible role of browsing animals, fire, waterlogging and soil changes, storms, and anthropogenic influence on forest dynamics and structure (Bradshaw & Hannon 2004). Palaeoecological data are now being used to test Vera's (2000) ideas about a widespread early -midHolocene 'wood pasture' in north-west Europe by Bradshaw & Mitchell (1999), Bradshaw et al (2003), and Mitchell (2005), to present new ideas about forest management in southern Sweden (Bjö rse , and to test hypotheses about the control and maintenance of landscape and biological diversity through time (Segerströ m et al 1994(Segerströ m et al , 1996Hö rnberg et al 1998). …”