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Silva Fennica 1926-1997
Acta Forestalia Fennica

Articles by Ulf Sikström

Category: Research article

article id 139, category Research article
Ulf Sikström, Curt Almqvist, Gunnar Jansson. (2010). Growth of Pinus sylvestris after the application of wood ash or P and K fertilizer to a peatland in southern Sweden. Silva Fennica vol. 44 no. 3 article id 139.
The effects of the application of wood ash and of fertilizer regimes including phosphorus (P) and potassium (K), with and without simultaneous addition of nitrogen (N), were investigated on a stand of Scots pine (Pinus sylvestris L.) saplings growing on a drained oligotrophic peatland site in southern Sweden. A randomized block design was used. Tree growth and concentrations of various elements in the needles were measured. The addition of similar doses of P (approx. 40 kg P ha–1) from different sources resulted in similar growth responses, amounting to 1.6–1.9 m3 ha–1 yr–1 of stem wood over the 26-year study. The P source was either wood ash (2500 kg d.w. ha–1) or PK-fertilizer (raw phosphate and potassium chloride). In response to several treatments there were both increased numbers of trees and increased growth of individual trees. The high PK-dose (40 kg P ha–1 and 80 kg K ha–1) appeared to result in a larger growth increase than the low dose (20 kg P ha–1 and 40 kg K ha–1). The N treatment had no additional effect on growth. In the control plots, tree growth was more or less negligible (0.04 m3 ha–1 yr–1). After almost 26 years, concentrations of P and K in the needles of treated plants were still higher than in the untreated control plants. Nevertheless, in spite of the elevated P concentration, P appears to limit the growth of Scots pine. In conclusion, after sufficient drainage of this type of peatland site, it is possible for a forest stand to develop to the pole stage if wood ash or PK-fertilizer is applied.
  • Sikström, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID:E-mail: (email)
  • Almqvist, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID:E-mail:
  • Jansson, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID:E-mail:
article id 372, category Research article
Ulf Sikström. (2005). Pre-harvest soil acidification, liming or N fertilization did not significantly affect the survival and growth of young Norway spruce. Silva Fennica vol. 39 no. 3 article id 372.
Acidification, liming, and N fertilization affect a number of soil properties. Such changes may have an impact on forest regeneration and yield. The aim of this study was to investigate the survival and growth of Picea abies (L.) Karst. planted on plots that had been acidified (in 12 annual treatments totalling 600 or 1200 kg S ha–1 in the form of elemental sulphur), limed (12 x 500 = 6000 kg lime ha–1 in the form of CaCO3) or N-fertilized (3 x 200 = 600 kg N ha–1 in the form of urea) prior to harvest. Trees growing on plots treated with a combination of the N plus the lower S application were also tested. None of the treatments, applied in three replicate stands, significantly influenced either survival or growth of Picea abies trees during the first 11 growing seasons after planting.
  • Sikström, SkogForsk, Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID:E-mail: (email)
article id 604, category Research article
Dan Glöde, Ulf Sikström. (2001). Two felling methods in final cutting of shelterwood, single-grip harvester productivity and damage to the regeneration. Silva Fennica vol. 35 no. 1 article id 604.
In order to find an efficient and careful way of final-cutting shelterwoods, two felling methods, in a single-grip harvester system, were compared with respect to productivity and damage caused to the regeneration. The shelterwood (140–165 m3/ha) consisted of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) and the natural regeneration (9530–11 780 seedlings/ha) mostly of Norway spruce. Treatments were: (i) conventional felling on both sides of the harvester striproad, preferably in blanks of the regeneration; (ii) felling of the trees top-end first into the striproad using a method named “tossing the caber”. Both treatments included forwarding after felling. Conventional felling had a non-significantly higher productivity (27.4 m3/E15–h) and lower cost (25.9 SEK/m3) than tossing the caber (26.1 m3/E15–h and 27.2 SEK/m3). However, tossing the caber was significantly more efficient in the felling and processing of pine trees compared with conventional felling. The mean proportions of the disappeared and damaged seedlings were approximately 40% after both treatments. The logging-related damage to the regeneration decreased with increased distance to the striproad in the tossing the caber treatment but not in conventional felling. The conclusions were that there were no differences between the treatments regarding productivity, cost and total damage to the regeneration in mixed conifer shelterwoods but that tossing the caber could be a more productive method than conventional felling in pine dominated stands. Tossing the caber could also be beneficial at a regeneration height of 2–3 m since at this height the damage to the regeneration seems less than at conventional felling.
  • Glöde, SkogForsk, Uppsala Science Park, S-751 83 Uppsala, Sweden ORCID ID:E-mail: (email)
  • Sikström, SkogForsk, Uppsala Science Park, S-751 83 Uppsala, Sweden ORCID ID:E-mail:

Category: Review article

article id 1416, category Review article
Ulf Sikström, Hannu Hökkä. (2016). Interactions between soil water conditions and forest stands in boreal forests with implications for ditch network maintenance. Silva Fennica vol. 50 no. 1 article id 1416.
Highlights: Ditch network maintenance (DNM) may influence soil water conditions less than initial ditching due to reduced hydraulic conductivity of the peat; Stand stocking and management substantially influence soil-water conditions; DNM can lower the GWL and increase tree growth; DNM growth responses of 0.5–1.8 m3 ha–1 yr–1 during 15–20-years in Scots pine peatland stands reported; Greatest need for DNM in the early phase of a stand rotation; Need for better understanding of the link between soil water and tree growth.

At sites with either peat or mineral soils in large areas of boreal forests, high soil-water contents hamper tree growth and drainage can significantly increase growth. Hence, areas covering about 15 × 106 ha of northern peatlands and wet mineral soils have been drained for forestry purposes. Usually ditches gradually deteriorate, thus reducing their functionality as drains, and ditch-network maintenance (DNM) might be needed to maintain stand growth rates enabled by the original ditching. This article reviews current knowledge on establishing the need for DNM in boreal forest stands, subsequent growth responses, and the financial outcome of the activity. The issues covered in the review are: (i) ditching, changes in ditches over time and the need for DNM; (ii) interactions between soil water and both stand properties and stand management; (iii) ground-water level (GWL) and tree growth responses to DNM; and (iv) financial viability of DNM. Conclusions about the current understanding of issues related to DNM are drawn and implications for DNM in practice are summarized. Finally, gaps in knowledge are identified and research needs are suggested.

  • Sikström, The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID:E-mail: (email)
  • Hökkä, Natural Resources Institute Finland (Luke), Management and Production of Renewable Resources, P.O. Box 16, FI-96301 Rovaniemi, Finland ORCID ID:E-mail:

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