Erik Hellberg

Changes in mixed deciduous forests of boreal Sweden 1866-1999 based on interpretation of historical records

Current knowledge of patterns and abundance of deciduous trees in thepre-industrial landscape of boreal Sweden is limited. This is due to a dramatictransformation of the forest landscape during the last 100 years and the lackofrepresentative forest reserves. We used historical records to study change infive mixed deciduous forests between 1866 and 1999. The results show that largechanges occurred due to complex interactions between fire disturbance, firesuppression, logging and silviculture. Before fire suppression, the presence ofdeciduous trees was mainly determined by earlier fire influence. Laterselectivelogging disturbed natural succession and favoured regeneration of deciduoustrees. During the 20th century deciduous trees were removed bygirdling, thinning and herbicide spraying. Much of the mixed deciduous standschanged to coniferous stands between 1906–15 and 1969–70, and thendeciduous trees were totally removed from these stands between late 1960s and1999. Today mixed deciduous forest occurs mainly in young stands and on othersites than previously. Our results also show that large coniferous trees andmulti-aged forest occurred in all sites in the early 1900s. Most sites weredominated by coniferous species and forest dominated by deciduous treesoccurredonly in smaller areas. These results are not consistent with the current viewthat deciduous-dominated forest occupied substantial areas in boreal Swedenbefore fire suppression. Appropriate changes in forest management arediscussed,as is the value of historical data in interpreting changes in forestlandscapes.

Influence of habitat history on the distribution of Usnea longissima in boreal Scandinavia: a methodological case study

Changes in habitat affect the distribution of species at different spatial and temporal scales. Our aim was to assess the use of several retrospective methods when determining habitat history and its influence on species distribution, using the pendent lichen Usnea longissima Ach. as a model organism. The study was carried out in a Norway spruce dominated forest, located in the middle boreal zone of northern Sweden. Historical sources (including forest inventories and maps) and dendrochronology were combined with field surveys to determine past stand characteristics with a high spatial precision. Also, present stand characteristics were thoroughly surveyed and the relationship between distribution of U. longissima and past and present habitat characteristics were evaluated. Our results showed that, despite the fact that historical logging was unevenly distributed within the study area, similarities in stand structure exist today. Several essential factors affecting the distribution of U. longissima could be related to changes in past stand structure, especially the extent and intensity of previous logging operations and the subsequent stand development during the last c . 150 years. Our results also showed that U. longissima was favoured by a continuous old age structure with canopy openness preserved. The importance of detailed reconstructions of specific habitat components is highlighted when relating species presence to habitat change. It is suggested that the use of retrospective methods presented in this study can be helpful in clarifying possible causes for the complex distribution of certain organisms.

Isostatic land uplift and Mesolithic landscapes: lake-tilting, a key to the discovery of Mesolithic sites in the interior of Northern Sweden

Until recently only a few Mesolithic sites were known from the interior of N. Sweden, although extensive archaeological surveys have been carried out since the 1950s. The lack of archaeological data made every attempt to interpret the process of pioneer colonization quite fruitless. In this paper we present a model of non-uniform glacio-isostatic uplift and lake-tilting used to identify potential areas of Mesolithic habitation. By reconstructing shoreline displacement of ancient lakes, archaeological, palaeoecological and geological studies have resulted in the discovery of a significant number of Mesolithic sites and of an early post-glacial landscape previously unknown.

Vegetation dynamics and disturbance history in three deciduous forests in boreal Sweden

Abstract Remaining deciduous forests in the Fennoscandian boreal landscape have high ecological value, and are considered as key components of the forest landscape as well as remnants of a former natural forest type. To improve our understanding of the formation of deciduous forests, we studied past disturbance regimes and vegetation dynamics in three deciduous forests in boreal Sweden using dendro-ecology, pollen analysis and charcoal analysis. We identified three stages in the development of the studied stands. Firstly, the coniferous period (pre 1800), a long-lasting period characterized by frequent fires, livestock grazing and extensive agriculture during which Pinus sylvestris was dominant. Secondly, the transformation period (1800 - 1900), when logging removed most pines from the sites while fire and grazing continued. At the time of the last fire, the sites lacked a local seed source of pines, resulting in a post-fire succession dominated by deciduous species with the capacity to disperse over long distances. Thirdly, the deciduous period (1900 - present), with little or no disturbance from fire, grazing or logging. Thus, the present deciduous stands have their origins in a complex interaction between changes in fire regime, extensive land use patterns and logging, contrary to earlier simplified explanations. We conclude that the complexity of historical patterns of land use, vegetation dynamics and disturbance should be acknowledged in the future when selecting areas for nature conservation and developing models for ecologically oriented forestry. Nomenclature: Lid (1985).

Wood anatomy of West European Betula: Quantitative descriptions and applications for routine identification in paleoecological studies

Abstract In paleoecological and archaeological studies the species present in wood and charcoal samples are often identified to obtain information about past climatic conditions and vegetation. The main references for identification of Betula at the species level are qualitative descriptions of wood anatomy. The aim of the study presented here was to characterize the wood anatomy of West European Betula species more fully, and quantitatively. For this, the size, abundance, and organization of vessels and rays were quantitatively estimated in carbonized wood samples of four Betula taxa: B. pendula, B. pubescens, B. pubescens ssp. tortuosa, and B. nana. Principal components analyses were used to detect statistical differences among species and to identify characters useful for distinguishing species. An anatomical gradient between B. pendula and B. nana was found, in which B. nana was clearly distinct from the three tree species of Betula. Differences were also observed between the tree species, but with less statistical significance. Our quantitative results support earlier, qualitative descriptions in some respects and conflict with them in others. We highlight the occurrence of narrow vessels in the wood that have not been described previously. This feature accounts for both a major portion of the variance in the data and the discrepancies with earlier qualitative studies. We suggest that B. nana and B. pubescens ssp. tortuosa can be distinguished from one another and from B. pendula and B. pubescens. Based on our results, it is not possible to distinguish between B. pendula and B. pubescens, at least in the routine identification of wood charcoal.