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Report, 2012

Stand structure and future development of a managed multi-layered forest in southern Sweden

Drössler, Lars; Fahlvik, Nils; Ekö, Per-Magnus


A heterogeneously structured forest stand with pine overstory and naturally regenerated spruce and oak trees in different size classes was documented. The effect of target diameter cutting on stand structure and growth was analyzed as a case-study. Both, systematic sample plots and forest gaps were used to describe the stand structure after cutting. Target diameter cutting in different treatments reduced the standing volume from ca. 320 to 180 m³/ha. Forest canopy gaps were created on more than 15% of the stand area. The seedling number of advanced natural regeneration was low (less than 500-1000 individuals per ha). Based on the advanced regeneration in gaps, three different scenarios for future ingrowth into the tree layer were defined. The extreme minimum ingrowth scenario assumed about 10 cm annual height growth and rather high mortality reported in literature from other experiments (resulting in one tree annually reaching 5 cm DBH during the next 50 years). Two other scenarios assumed 20 and 30 cm annual height growth. While no mortality was presumed within the latter scenario, moderate mortality rates (reported in literature) were chosen for the intermediate scenario. The maximum scenario postulates ten trees per year and ha reaching 5 cm DBH (equal to ingrowth reported from boreal single-tree selection forests). The moderate scenario assumes four new trees per year and he. Additional scenarios after soil preparation in gaps were used, defined on the base of shelterwood experiments. To describe the future basal area growth and continued target diameter cutting in the next 50 years, a single-tree growth model was applied, using stand age-independent estimations of the age of single trees. Thereby, a mean annual increment of 0.53-0.64 m2/ha was projected, similar to 5.6-6.8 m³/ha volume. Some errors to estimate the standing volume in multi-layered stands were detected during the simulation process. Compared to an evenaged spruce stand planted on the same site, the expected growth of the study stand during the next 50 years was one third lower. In average, about 120 m3/ha standing volume was removed in 20-25 years-cutting cycles. To continue without longer harvest intervals after the 50 years-simulation period, soil preparation seems necessary to achieve a sustainable number of small trees. Beside timber production, profitability was also lower by selective cutting. But, the important advantage of target diameter cutting can be more equally distributed income over time, with investments costs that can be covered by profit from timber harvest at the same time. A regular income of 17000-28000 SEK per ha every 20-25 years seems possible from today´s perspective. An additional treatment with alternative target diameters to promote particular tree species did not affect the amount of removals and the length of cutting intervals substantially. But simulations with 5 cm reduced target diameters caused very heavy removals and 35-40 years to reach 300 m³/ha standing volume again. The study includes discussions of tree species composition and development as well as a sensitivity analysis of the applied growth model.


Continuous cover forestry; kontinuitetsskogsbruk; måldiameterhuggning

Published in

Arbetsrapport - Sveriges lantbruksuniversitet, Institutionen för sydsvensk skogsvetenskap
2012, Volume: 46, number: 46
ISBN: 978-91-576-9110-1
Publisher: Institutionen för sydsvensk skogsvetenskap, Sveriges lantbruksuniversitet