Effects of stand structure on natural regeneration in uneven-aged mixed forest : a case study from Tranemåla, Blekinge

Sammanfattning

The growing conditions in southern Sweden can support a wide range of native broadleaf and coniferous tree species, which all are important for biodiversity and provision of ecosystem services. However, forest management in southern Sweden has for the last century been dominated by planted even-aged stands of Norway spruce or Scots pine, with a main focus on production of pulp and timber. Ecosystem resilience and biodiversity are often low in even-aged monocultures and there is an increasing interest in developing the management of uneven-aged mixed forest. Tranemåla forest in Blekinge is one of relatively few areas that during the last century have been managed with less focus on the traditional rotational forestry that is dominating in Sweden. Due to this, more heterogeneous forest and structures have developed, offering a unique possibility to do research within the field of continuous cover forestry that can provide insight with regard to both challenges and opportunities for future forest management in Sweden. The purpose of this case study was to examine how stand structure influences natural regeneration in Tranemåla forest. Two spruce (Picea abies) dominated, uneven aged mixed stands were selected and 24 circular sample plots of 10-meter radius were established systematically and examined for tree species composition, stem density, basal area and natural regeneration. The results show that the current diameter distribution provides a good potential for uneven-aged mixed forest management, although there is still a relatively low stem density in the smallest diameter classes. The results also indicate that natural regeneration is increasing with decreasing basal area, regardless of tree species. Other factors than overstory density, such as nutrient and water availability, may also affect regeneration outcomes, and further research is needed to include more aspects. The understory development of the two selected stands is recommended to follow up in the future.