Björn Elfving

Construction of site index equations for Pinus sylvestris L. using permanent plot data in Sweden

Abstract Three general methods for construction of site index equations (the guide curve method, the parameter prediction method and the difference equation method) and 13 growth functions were tested on data from permanent plots in 156 Scots pine ( Pinus sylvestris ) stands. Most stands were of cultivated origin with known year of establishment. Data consisted of measured top height and total age at the start and at the end of observation periods of different lengths. Functions and construction methods were compared with respect to residual variation (root mean square error (RMSE), meter) from original data. The guide curve method gave RMSE ∼ 0.56 while the difference equation method with the anamorphic formulation gave RMSE ∼ 0.46, with appropriate functions. The difference equation method gave a higher RMSE with polymorphic than with anamorphic formulation. The special formulation of the Hossfeld function for the difference equation method proposed by Cieszewski and Bella [Cieszewski, C.J., Bella, I.E., 1989. Polymorphic height and site index curves for lodgepole pine in Alberta. Can. J. Res. 19, 1151–1160] gave a simple and straigtforward, polymorphic solution with RMSE = 0.40. The parameter prediction method, in combination with the deviation method proposed by Tveite [Tveite, B., 1969. A method for construction of site-index curves. Meddelelser fra Det Norske skogforsoksvesen 27, 134–159] and a four-parameter growth model, gave the lowest RMSE, but this solution had patterns of overfitting. Parameter prediction with the Mitscherlich function gave an equation with almost the same accuracy as the polymorphic difference equation with the Hossfeld function. These functions deviate much at higher ages, but too few observations in old stands in primary data prevented their separation. Published data from yield plots in old, natural stands supported the Hossfeld function. But, indications of a changed growth pattern in later decades still leave open the question of height growth pattern in old pine stands of cultivated origin. The presented Hossfeld equation can only be recommended for use in 10–80-year-old pine stands of cultivated origin.

Ecological effects and management aspects of an exotic tree species: the case of lodgepole pine in Sweden.

The North American tree Pinus contorta var, latifolia was experimentally introduced in Sweden already in the 1920s, and has been used in Swedish forestry on a large scale since the 1970s. These pla ...

Trends of tree growth in Swedish forests 1953–1992: An analysis based on sample trees from the national forest inventory

Average tree height and basal area growth for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) in Sweden were studied as functions of species, age, stand density, location and year of inventory in the period 1953–1992, on the basis of sample tree data from the National Forest Inventory. A highly significant annual increase of both height and basal area growth was found, of the magnitude 0.5–0.8%, during the 40 yr period. Possible reasons for the trend are discussed. The altered way of cutting in the early 1950s, from selective cutting to clear felling and thinning from below, has had a large impact. Also, improved regeneration methods, nitrogen fertilization and ditching have increased growth. The increasing atmospheric deposition of nitrogen is another possible factor.

Twelve-year growth response of Scots pine to thinning and nitrogen fertilisation

Effects of thinning and nitrogen fertilisation, singly and in combination, on growth of 56-year-old Scots pine (Pinus sylvestris L.) trees in northern Sweden were examined for the 12 years after treatment. The response to treatments was measured as dry weight biomass change in above and below ground components over the 12 years and as four-year period changes in relative radial, height, and volume growth under bark. Results were expressed in terms of average tree and as a stand total. During the 12-year period following treatment, biomass production per tree was increased in all fractions by thinning, but only for shoot axes and crown biomass by fertilisation. In the first four-year period after treatment both thinning and fertilisation gave a positive response in radial and volume growth. The response to fertilisation in radial and volume growth faded out after eight years, although a positive effect after thinning could still be seen after 12 years. Height growth was not affected by treatments. In comparison to the control, volume production per hectare decreased by 37% after thinning singly, 10% after the combined treatment, and increased by 20% after fertilisation. The results are discussed in terms of nitrogen availability, light competition, and needle efficiency.

Studies on Growth Trends of Forests in Sweden and Norway

In the Swedish National Forest Inventory (NFI), a steady increase in the estimated productivity of forest land has been noticed since inventory was begun in 1923. Young stands generally indicate higher site indices than old stands at equal site conditions. For spruce, this rise of site index has been estimated at 0.05–0.11 m.year−1, with the highest value in the south. In a study based on sample tree data from the NFI, a highly significant annual increase of both height and basal area growth of the magnitude 0.5–0.8% was found for the period 1953–1992. At the same time, top height seems to develop according to the site curves on permanent plots both in Sweden and Norway.

Development of Pinus sylvestris Main Stems Following Three Different Precommercial Thinning Methods in a Mixed Stand

Reducing competition by point cleaning may be an attractive alternative to conventional precommercial thinning in forestry. In this study, survival and development of main stems of Scots pine (Pinus sylvestris L.) following point cleaning were examined in a mixed stand of mainly Scots pine and birch (Betula pendula Roth and Betula pubescens Ehrh.) in northern Sweden. Treatments studied were: no precommercial thinning, conventional precommercial thinning, point cleaning of all secondary stems, and point cleaning of only the secondary stems that were higher than the main stem, within a radius of 0.8 m from the main stem, respectively. A randomised complete block design with three replicates was used. Measurements taken 13 growing seasons after these treatments showed that conventional precommercial thinning was the best treatment for retaining Scots pines as main stems. However, conventional precommercial thinning resulted in the poorest timber quality of the remaining Scots pines in terms of stem taper, thickest branch diameter and relative live crown height. In conclusion, point cleaning has to be followed by a complementary cleaning operation if the objective is to retain Scots pines as main stems in such mixed stands.

Performance of Improved Pinus sylvestris in Northern Sweden

Genetic gain from utilization of improved planting stock of Scots pine (Pinus sylvestris L.) in northern Sweden is presented. A total of 36 genetic field tests, comprising more than 177 000 individual trees, was analysed with respect to tree height and survival at the age of 9–13 yrs. The field tests included control pollinated progenies from 434 phenotypically selected parent trees constituting the clones of 11 commercial seed orchards, and 16 natural stand control lots. The field test covered a wide geographical and climatic gradient (latitude 62.3–67.8° N, temperature sum 496–1056 day-degrees). covering the area used for commercial forestry in northern Sweden. Progenies of selected trees had 10% superior height growth, whereas differences in survival were small and non-significant. Thus, selection of individual trees within a stand did not result in the strong negative relationship between growth and survival normally observed among provenances of different latitudinal origin. The height superiority did not show any significant dependency on the growth conditions of the site (temperature climate), the transfer distance of the seedlings or the age of trees. The effect of improved regeneration stock on volume production during an entire rotation period was discussed using growth and yield functions, and indicated substantial volume gain at the time of both first thinning and final harvest.

Needle size and nitrogen concentration of Pinus sylvestris and Pinus contorta

Needle mass, length, and nitrogen concentration, and their relation to site index were studied for lodgepole pine (Pinus contorta Dougl.) and Scots pine (Pinus sylvestris L.). Needles were collected at 53 locations throughout Sweden where the two species, of the same age, were growing on adjacent, comparable sites. Sampling was done throughout the growing season, with a pause during the period of most active growth. Needles of lodgepole pine had a higher mass, were longer, and had a lower nitrogen concentration than those of Scots pine. Site index was positively correlated to needle length and weight for both species, and to nitrogen concentration for lodgepole pine. For the characteristics studied, the relative differences between needles of the two species decreased with increasing site index.

Long-term effects on growth and yield of corridor thinning in young Pinus sylvestris stands

Abstract Corridor thinning can be an efficient method for extracting biomass from young stands, but its effects on subsequent productivity are uncertain. Therefore, its long-term effects were studied, using data obtained from two pre-commercial thinning (PCT) experiments (over 28 years) and nine thinning experiments (over 22 years). In the PCT experiments, thinning with total corridor areas of 0 (control), 57, 65, 73, 79 and 82% were compared to selective PCT leaving 1000 and 1400 stems/ha. In the thinning experiments corridor thinning (50% corridor area) and selective thinning from below (50% of basal area) were compared. No significant differences in diameter at breast height (DBH) were found between the corridor PCT and control treatments, but the control resulted in approximately 28–83% higher standing volumes/ha than the PCT treatments. Corridor PCT and thinning treatments resulted in higher stand stem density and lower mean DBH than selective treatments. No significant differences in volume growth, standing volume, mortality volume or height growth were detected between selective and corridor thinning or between most of the PCT treatments. The findings indicate that relatively large amounts of biomass could be extracted schematically, by early thinning instead of PCT, in young Scots pine stands without significant future yield losses.

Yield capacity of planted Picea abies in northern Sweden

Norway spruce (Picea abies (L.) Karst.) is the dominant species in the older forests of central northern Sweden. However, spruce has seldom been planted in the area, partly because existing tools for site classification have indicated a low yield capacity for the species. The aim of this study was to examine the yield capacity of spruce on the basis of existing plantations. In total, 91 operational and experimental plantations in the age interval 27–46 yrs were sampled. Stands were located between 62° and 65° N at altitudes 130–620 m a.s.l. Site index was estimated by height growth and site‐factor equations previously developed from old‐growth stand data. Height developments in the plantations indicate that site index for these stands is on average 4.6 m higher than predicted by site‐factor equations. The differences between the two methods are larger on poor sites than on rich sites. No systematic deviations of top height development from the site index curves could be detected on remeasured sample plots...