Björn Elfving | SLU - Academia.edu (original) (raw)
Papers by Björn Elfving
Forest Ecology and Management
Scandinavian Journal of Forest Research
Canadian Journal of Forest Research
Biomass equations for cultivated lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia En... more Biomass equations for cultivated lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were developed based on data from destructive biomass sampling of 164 trees collected from 13 sites at latitudes 61.9°N–66.2°N in northern Sweden. Stand age varied between 20 and 87 years and top height varied between 8 and 32 m. Seeded and planted stands with different densities were included. Allometric biomass equations for all above-stump components were constructed, expressing dry mass of stem, bark, living and dead branch wood, foliage, and cones, as well as total mass. Equations with one to three independent variables were constructed for each component, accounting for variances within and between sites. Estimated values for trees of different sizes were compared with corresponding estimates for lodgepole pine in Canada and Scots pine (Pinus sylvestris L.) in Sweden and Finland. Residual variation of our equations was lower than that of equations from other sources. Our equ...
Scandinavian Journal of Forest Research
Lodgepole pine is native to western North America, but it is also planted as a fast-growing alter... more Lodgepole pine is native to western North America, but it is also planted as a fast-growing alternative to Scots pine in Sweden. The production of these two species, when grown as native and as exotic species, was compared in a transcontinental two-species provenance experiment. The tests were planted in 1986 on five sites in northwestern Canada and two sites in Sweden, and included full-sib families, half-sib families, seed orchard collections and natural stand seed collections of both species. After 25 years, lodgepole pine produced 48% more volume (m 3 ha −1) and had 27% higher survival than Scots pine at one Swedish site, and had similar volume production and survival at a second. In the five Canadian sites, Scots pine produced on average 22% more volume than lodgepole pine. The variation between sites was, however, large. This higher volume of Scots pine in Canada could be due to higher survival (+28%) and less frequent damage; but higher top height for lodgepole pine in Canada indicated higher potential productivity. The results indicate that an exotic species may produce more than the native species, possibly thanks to higher survival, but it is also possible to increase production with successful population selection of the native species.
Forestry, 2015
The general belief that intense regeneration measures are financially viable and essential for hi... more The general belief that intense regeneration measures are financially viable and essential for high sustained yields of commercial forest products has been inadequately tested. This field experiment evaluates effects of three different regeneration intensities 24-27 years after clear-cutting of 14 sites across Sweden. The treatments, designated high (HI), normal (NI) and low (LI), respectively, consisted of: mechanical site preparation and planting of large seedlings at 2 ×2 m spacing, with supplemental planting and pre-commercial thinning (PCT) when deemed necessary; standard local practices; and natural regeneration with no site preparation, artificial regeneration or PCT. Average crop seedling densities were highest and lowest (3359 and 1662 ha 21) under the HI and LI treatments, respectively, 4-8 growing seasons after planting. After 24-27 years, HI also resulted in higher mean stem volume (90 m 3 ha 21) than LI (36 m 3 ha 21) but was not significantly different from NI (65 m 3 ha 21) and increasing the regeneration intensity was not consistently positive. In some cases, high planted seedling mortality and generally abundant natural regeneration resulted in minor (or no) differences between the treatments. The results illustrate that current Swedish regeneration standards may need revision in order to reflect contemporary societal and commercial demands.
Forestry
The general belief that intense regeneration measures are financially viable and essential for hi... more The general belief that intense regeneration measures are financially viable and essential for high sustained yields of commercial forest products has been inadequately tested. This field experiment evaluates effects of three different regeneration intensities 24–27 years after clear-cutting of 14 sites across Sweden. The treatments, designated high (HI), normal (NI) and low (LI), respectively, consisted of: mechanical site preparation and planting of large seedlings at 2 × 2 m spacing, with supplemental planting and pre-commercial thinning (PCT) when deemed necessary; standard local practices; and natural regeneration with no site preparation, artificial regeneration or PCT. Average crop seedling densities were highest and lowest (3359 and 1662 ha−1) under the HI and LI treatments, respectively, 4–8 growing seasons after planting. After 24–27 years, HI also resulted in higher mean stem volume (90 m3 ha−1) than LI (36 m3 ha−1) but was not significantly different from NI (65 m3 ha−1)...
Growth Trends in European Forests, 1996
Silva Fennica, 2014
Highlights • Growth models based on historical growth data gave reliable growth predictions up to... more Highlights • Growth models based on historical growth data gave reliable growth predictions up to the century shift. • Detailed single tree growth models had lower precision for estimation of total growth than one single stand-based model. • The prediction error was in average about 15% and did not increase with extended prediction period.
Silva Fennica, 2012
Productivity of Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) was st... more Productivity of Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) was studied in 12 paired plots in the interior of northern Sweden. Stands were established between 1928 and 1959; yield plots were established between 1974 and 1983 during precommercial thinning of the stands. Gross stem-wood production was significantly higher for Scots pine than for Norway spruce, stem-wood production by Norway spruce being 29.4% that of Scots pine. The site index for Norway spruce was lower than for Scots pine at all sites except one; the average difference in site index was 4.8 m. The simulated maximum mean annual increment (MAI max) during the rotation was 19% higher than the MAI max estimated with the site index for Scots pine, whereas simulated MAI max and MAI max estimated from the site index was about the same for Norway spruce. The simulations also indicated that MAI peaked about 50 years later for Norway spruce than for Scots pine. More small trees were included in the diameter distribution of Norway spruce than of Scots pine resulting in a lower stem-wood volume for Norway spruce when stands with the same dominant height were compared. This study shows that the difference in growth and rotation length between Scots pine and Norway spruce has implications when choosing which species to grow in the interior of northern Sweden.
Scandinavian Journal of Forest Research, 1996
... BR dbh Epl MAI N Opl ... New functions for basal area before thinning were developed in this ... more ... BR dbh Epl MAI N Opl ... New functions for basal area before thinning were developed in this study in order to relate our data to earlier investigations. The functions were also used to relate productivity on plots with different initial basal area levels and site index (MAI =/[SIH, Bal]). ...
Scandinavian Journal of Forest Research, 1996
Scandinavian Journal of Forest Research, 2008
... Ekö a , Ulf Johansson b , Nils Petersson c * , Jonas Bergqvist d , Björn Elfving e & Joha... more ... Ekö a , Ulf Johansson b , Nils Petersson c * , Jonas Bergqvist d , Björn Elfving e & Johan Frisk f pages 307-318. ... [Taylor & Francis Online], [Web of Science ®] View all references), while the other methods are only available for spruce and pine (Hägglund & Lundmark, 197719. ...
Scandinavian Journal of Forest Research, 2002
Scandinavian Journal of Forest Research, 2013
Corridor thinning can be an efficient method for extracting biomass from young stands, but its ef... more 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.
Forest Ecology and Management, 1997
Fire history and stand structure was examined in twelve virgin forest stands situated within fore... more Fire history and stand structure was examined in twelve virgin forest stands situated within forest reserves in northern Sweden. The selected stands represented fire refuges as well as different successional stages after fire. Six of the stands were dominated by Norway spruce (Piceu abies L. Karst.), three were dominated by Scats pine (Pinus sylvestris L.), and three were dominated by hairy birch (Be&a pubescens Ehrh.) or aspen (Populus tremulu L.). In 3 of the southernmost stands, the average fire interval was 34 to 65 years during the late 1600s to late 18OOs, but since 1888 no fires had occurred in any of the stands. The absence of fire disturbance since 1888 is probably caused by the fire suppression in the overall landscape. The standing volume of living trees ranged between 87 and 5 11 m3 ha-' while the volume of dead trees, including both snags and logs, ranged between 27 and 201 m3 ha-'. The volume of dead trees constituted ca. 30% of the total stem volume. In the conifer dominated stands, there was a statistically significant relationship between total stem volume, including both living and dead trees, and site productivity. A comparison between the amount of dead and living trees indicated substantial changes in tree species composition in several stands. It is suggested that data on the amount of dead trees, especially logs, and its distribution over decay classes could be used to examine the continuity of certain tree species. All stands had a multi-sized tree diameter distribution, which in most cases was similar to a reversed J-shaped distribution. In general spruce was numerous in the seedling cohort and in small diameter classes, indicating that its proportion in the stands was stable, or was increasing at the expense of pioneer tree species such as pine, aspen and silver birch (Beth pendulu Roth.). The most numerous species in the seedling cohort, rowan (Sorbus aucupuriu L.), was almost totally missing in the tree layer, indicating a high browsing pressure preventing rowan seedlings from growing into trees. The general increase of spruce and the sparse regeneration of pioneer species, in the stands previously affected by fire, are discussed in relation to natural disturbance regimes, biological diversity and nature conservation policies. It is proposed that reintroduction of fire disturbance is a necessity for future management plans of forest reserves. Other management practices to increase species diversity within forest reserves are also discussed. 0 1997 Elsevier Science B.V.
Forest Ecology and Management, 2010
Natural mortality in a 30-year period was examined in thinning and fertilisation experiments with... more Natural mortality in a 30-year period was examined in thinning and fertilisation experiments with 48 blocks in Scots pine (Pinus sylvstris L.) and 23 blocks in Norway spruce (Picea abies (L.) Karst.) with up to 12 different treatments. Of about 90,000 living trees at start of the experiments 18.7% were registered as dead by natural mortality in the 30-year observation period. In non-thinned stands about 20% of the volume growth disappeared by natural mortality, in thinned stands about 10%. In normally thinned pine stands (repeated thinning from below with moderate intensity) the annual mortality of the basal area at start of an average 7-year period was 0.34%. In spruce stands, on more fertile sites, the corresponding figure was about 0.6%. In an effort to model the mortality, severe damage not leading to final felling was identified in 1.7% of the observation periods. It was assumed that this part of the mortality, representing 24% of the total volume mortality, could be recovered by active thinning. The probability for severe damage increased sharply with stand top height, as shown in a logistic regression. The more sparse mortality was expressed as a function of site fertility, stand density, disturbance by thinning and form of treatment (thinned from above or below or non-thinned). The naturally dead trees were approximately of mean size in normally thinned stands while the self-thinning in non-thinned stands tended to occur amongst smaller than average trees. Diagrams were presented for basal area development and stem number reduction in the non-thinned stands.
Forest Ecology and Management, 1999
Results from two yield optimisation experiments in young stands of Norway spruce in northern and ... more Results from two yield optimisation experiments in young stands of Norway spruce in northern and southeastern Sweden are presented after 10 and 9 years' treatment, respectively. The aim of the experiments was to demonstrate the potential yield of Norway spruce, under given climatic conditions and non-limiting soil water, by optimising the nutritional status of the stands, at the same time as leaching of nutrients to the groundwater was avoided. A complete mix of nutrients was supplied either once a year or daily during the growing season, in combination with irrigation. On the basis of repeated foliar analysis and predicted growth response the proportions and amounts of nutrients applied were adjusted annually. After 10 years' treatment at the northern site, fertilisation had increased the annual stem volume production from 3 m 3 ha À1 a À1 in unfertilised stands to 14 m 3 ha À1 a À1. Although site quality initially was high at the southern site, nutrient optimisation increased annual stem volume yield from 12 in control stands to 29 m 3 ha À1 a À1 in irrigated±fertilised stands. Water had a positive effect on stem growth in southern experiment, but no effect in the north. In all stands in which the availability of nutrients and soil water was optimised by combined fertilisation and irrigation, the yield of stemwood was similar to or surpassed the best yields obtained by conventional silvicultural means.
Forest Ecology and Management, 2004
Woody growth at five sites, covering a range of precipitation (620-785 mm) and soil conditions in... more Woody growth at five sites, covering a range of precipitation (620-785 mm) and soil conditions in North Sudan zone in Burkina Faso was investigated 5-14 years after clear-cutting. Woody growth ranged from 0.7 to 1.7 Mg ha À1 per year, corresponding to 1.0-2.4 m 3 ha À1 per year in terms of green volume when species-specific basic densities were applied. Trunks (girth more than 10 cm), branches and stemlets made up about a third each of the yield and about one-third of the trunk was bark. Thus, the actual trunk wood production ranged from 0.2 to 0.7 Mg ha À1 per year corresponding to 0.3-0.9 m 3 ha À1 per year. Woodfuel yield was reduced to about a fourth of the total yield, when excluding small dimensions and trunk-bark, species with low calorific value or multiple use, e.g. fruit bearing or forage. Each site was dominated by some few species in terms of percentage of dry mass: Sclerocarya birrea (13%), Anogeissus leiocarpus (57%), Acacia seyal (38%), Combretum glutinosum (17%) and Combretum nigricans (37%). Mean stool growth per site ranged from 0.5 to 1.7 kg per year. Largest stool growth was recorded for S. birrea and A. leiocarpus with 4.1 and 3.6 kg per stool per year, respectively.
Forest Ecology and Management, 2004
Retention of live and dead trees in harvested stands has become a common practice in Scandinavian... more Retention of live and dead trees in harvested stands has become a common practice in Scandinavian forestry. We examined how retained Scots pines (Pinus sylvestris L.) grow and to what extent they compete with the new generation. In a mixed stand of about 5 ha in Northern Sweden, 44 retained pines and adjacent growth of the new stand was measured for the last 90 years. After liberation in 1912, the pines, then with a mean age of 180 years, doubled their annual ring width to a culmination after about 30 years. The trees below mean height showed the biggest response to liberation. The lower part of the stem (0.5-1.3 m) showed the largest growth relative to the decade before release during the first two decades after release. In the last decade the relative growth was largest at 6 m height. Growth of the new generation was measured on 9.5 m radius plots, centred on the retained pines. The growth of the new stand was reduced by 20% in the inner third of the plot area. With 10 evenly dispersed retained pines per hectare the production loss in the new generation was estimated at 2.5% over one rotation. The growth of retained trees more than compensated for this loss. The volume of the new stand was positively correlated with retained tree size and negatively correlated with retained tree growth. Of 17 species and species groups identified in the forest floor vegetation, only lichen occurrence correlated with distance to retained trees. Lichen was more common close to small and fast-growing retained trees.
Forest Ecology and Management
Scandinavian Journal of Forest Research
Canadian Journal of Forest Research
Biomass equations for cultivated lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia En... more Biomass equations for cultivated lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were developed based on data from destructive biomass sampling of 164 trees collected from 13 sites at latitudes 61.9°N–66.2°N in northern Sweden. Stand age varied between 20 and 87 years and top height varied between 8 and 32 m. Seeded and planted stands with different densities were included. Allometric biomass equations for all above-stump components were constructed, expressing dry mass of stem, bark, living and dead branch wood, foliage, and cones, as well as total mass. Equations with one to three independent variables were constructed for each component, accounting for variances within and between sites. Estimated values for trees of different sizes were compared with corresponding estimates for lodgepole pine in Canada and Scots pine (Pinus sylvestris L.) in Sweden and Finland. Residual variation of our equations was lower than that of equations from other sources. Our equ...
Scandinavian Journal of Forest Research
Lodgepole pine is native to western North America, but it is also planted as a fast-growing alter... more Lodgepole pine is native to western North America, but it is also planted as a fast-growing alternative to Scots pine in Sweden. The production of these two species, when grown as native and as exotic species, was compared in a transcontinental two-species provenance experiment. The tests were planted in 1986 on five sites in northwestern Canada and two sites in Sweden, and included full-sib families, half-sib families, seed orchard collections and natural stand seed collections of both species. After 25 years, lodgepole pine produced 48% more volume (m 3 ha −1) and had 27% higher survival than Scots pine at one Swedish site, and had similar volume production and survival at a second. In the five Canadian sites, Scots pine produced on average 22% more volume than lodgepole pine. The variation between sites was, however, large. This higher volume of Scots pine in Canada could be due to higher survival (+28%) and less frequent damage; but higher top height for lodgepole pine in Canada indicated higher potential productivity. The results indicate that an exotic species may produce more than the native species, possibly thanks to higher survival, but it is also possible to increase production with successful population selection of the native species.
Forestry, 2015
The general belief that intense regeneration measures are financially viable and essential for hi... more The general belief that intense regeneration measures are financially viable and essential for high sustained yields of commercial forest products has been inadequately tested. This field experiment evaluates effects of three different regeneration intensities 24-27 years after clear-cutting of 14 sites across Sweden. The treatments, designated high (HI), normal (NI) and low (LI), respectively, consisted of: mechanical site preparation and planting of large seedlings at 2 ×2 m spacing, with supplemental planting and pre-commercial thinning (PCT) when deemed necessary; standard local practices; and natural regeneration with no site preparation, artificial regeneration or PCT. Average crop seedling densities were highest and lowest (3359 and 1662 ha 21) under the HI and LI treatments, respectively, 4-8 growing seasons after planting. After 24-27 years, HI also resulted in higher mean stem volume (90 m 3 ha 21) than LI (36 m 3 ha 21) but was not significantly different from NI (65 m 3 ha 21) and increasing the regeneration intensity was not consistently positive. In some cases, high planted seedling mortality and generally abundant natural regeneration resulted in minor (or no) differences between the treatments. The results illustrate that current Swedish regeneration standards may need revision in order to reflect contemporary societal and commercial demands.
Forestry
The general belief that intense regeneration measures are financially viable and essential for hi... more The general belief that intense regeneration measures are financially viable and essential for high sustained yields of commercial forest products has been inadequately tested. This field experiment evaluates effects of three different regeneration intensities 24–27 years after clear-cutting of 14 sites across Sweden. The treatments, designated high (HI), normal (NI) and low (LI), respectively, consisted of: mechanical site preparation and planting of large seedlings at 2 × 2 m spacing, with supplemental planting and pre-commercial thinning (PCT) when deemed necessary; standard local practices; and natural regeneration with no site preparation, artificial regeneration or PCT. Average crop seedling densities were highest and lowest (3359 and 1662 ha−1) under the HI and LI treatments, respectively, 4–8 growing seasons after planting. After 24–27 years, HI also resulted in higher mean stem volume (90 m3 ha−1) than LI (36 m3 ha−1) but was not significantly different from NI (65 m3 ha−1)...
Growth Trends in European Forests, 1996
Silva Fennica, 2014
Highlights • Growth models based on historical growth data gave reliable growth predictions up to... more Highlights • Growth models based on historical growth data gave reliable growth predictions up to the century shift. • Detailed single tree growth models had lower precision for estimation of total growth than one single stand-based model. • The prediction error was in average about 15% and did not increase with extended prediction period.
Silva Fennica, 2012
Productivity of Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) was st... more Productivity of Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) was studied in 12 paired plots in the interior of northern Sweden. Stands were established between 1928 and 1959; yield plots were established between 1974 and 1983 during precommercial thinning of the stands. Gross stem-wood production was significantly higher for Scots pine than for Norway spruce, stem-wood production by Norway spruce being 29.4% that of Scots pine. The site index for Norway spruce was lower than for Scots pine at all sites except one; the average difference in site index was 4.8 m. The simulated maximum mean annual increment (MAI max) during the rotation was 19% higher than the MAI max estimated with the site index for Scots pine, whereas simulated MAI max and MAI max estimated from the site index was about the same for Norway spruce. The simulations also indicated that MAI peaked about 50 years later for Norway spruce than for Scots pine. More small trees were included in the diameter distribution of Norway spruce than of Scots pine resulting in a lower stem-wood volume for Norway spruce when stands with the same dominant height were compared. This study shows that the difference in growth and rotation length between Scots pine and Norway spruce has implications when choosing which species to grow in the interior of northern Sweden.
Scandinavian Journal of Forest Research, 1996
... BR dbh Epl MAI N Opl ... New functions for basal area before thinning were developed in this ... more ... BR dbh Epl MAI N Opl ... New functions for basal area before thinning were developed in this study in order to relate our data to earlier investigations. The functions were also used to relate productivity on plots with different initial basal area levels and site index (MAI =/[SIH, Bal]). ...
Scandinavian Journal of Forest Research, 1996
Scandinavian Journal of Forest Research, 2008
... Ekö a , Ulf Johansson b , Nils Petersson c * , Jonas Bergqvist d , Björn Elfving e & Joha... more ... Ekö a , Ulf Johansson b , Nils Petersson c * , Jonas Bergqvist d , Björn Elfving e & Johan Frisk f pages 307-318. ... [Taylor & Francis Online], [Web of Science ®] View all references), while the other methods are only available for spruce and pine (Hägglund & Lundmark, 197719. ...
Scandinavian Journal of Forest Research, 2002
Scandinavian Journal of Forest Research, 2013
Corridor thinning can be an efficient method for extracting biomass from young stands, but its ef... more 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.
Forest Ecology and Management, 1997
Fire history and stand structure was examined in twelve virgin forest stands situated within fore... more Fire history and stand structure was examined in twelve virgin forest stands situated within forest reserves in northern Sweden. The selected stands represented fire refuges as well as different successional stages after fire. Six of the stands were dominated by Norway spruce (Piceu abies L. Karst.), three were dominated by Scats pine (Pinus sylvestris L.), and three were dominated by hairy birch (Be&a pubescens Ehrh.) or aspen (Populus tremulu L.). In 3 of the southernmost stands, the average fire interval was 34 to 65 years during the late 1600s to late 18OOs, but since 1888 no fires had occurred in any of the stands. The absence of fire disturbance since 1888 is probably caused by the fire suppression in the overall landscape. The standing volume of living trees ranged between 87 and 5 11 m3 ha-' while the volume of dead trees, including both snags and logs, ranged between 27 and 201 m3 ha-'. The volume of dead trees constituted ca. 30% of the total stem volume. In the conifer dominated stands, there was a statistically significant relationship between total stem volume, including both living and dead trees, and site productivity. A comparison between the amount of dead and living trees indicated substantial changes in tree species composition in several stands. It is suggested that data on the amount of dead trees, especially logs, and its distribution over decay classes could be used to examine the continuity of certain tree species. All stands had a multi-sized tree diameter distribution, which in most cases was similar to a reversed J-shaped distribution. In general spruce was numerous in the seedling cohort and in small diameter classes, indicating that its proportion in the stands was stable, or was increasing at the expense of pioneer tree species such as pine, aspen and silver birch (Beth pendulu Roth.). The most numerous species in the seedling cohort, rowan (Sorbus aucupuriu L.), was almost totally missing in the tree layer, indicating a high browsing pressure preventing rowan seedlings from growing into trees. The general increase of spruce and the sparse regeneration of pioneer species, in the stands previously affected by fire, are discussed in relation to natural disturbance regimes, biological diversity and nature conservation policies. It is proposed that reintroduction of fire disturbance is a necessity for future management plans of forest reserves. Other management practices to increase species diversity within forest reserves are also discussed. 0 1997 Elsevier Science B.V.
Forest Ecology and Management, 2010
Natural mortality in a 30-year period was examined in thinning and fertilisation experiments with... more Natural mortality in a 30-year period was examined in thinning and fertilisation experiments with 48 blocks in Scots pine (Pinus sylvstris L.) and 23 blocks in Norway spruce (Picea abies (L.) Karst.) with up to 12 different treatments. Of about 90,000 living trees at start of the experiments 18.7% were registered as dead by natural mortality in the 30-year observation period. In non-thinned stands about 20% of the volume growth disappeared by natural mortality, in thinned stands about 10%. In normally thinned pine stands (repeated thinning from below with moderate intensity) the annual mortality of the basal area at start of an average 7-year period was 0.34%. In spruce stands, on more fertile sites, the corresponding figure was about 0.6%. In an effort to model the mortality, severe damage not leading to final felling was identified in 1.7% of the observation periods. It was assumed that this part of the mortality, representing 24% of the total volume mortality, could be recovered by active thinning. The probability for severe damage increased sharply with stand top height, as shown in a logistic regression. The more sparse mortality was expressed as a function of site fertility, stand density, disturbance by thinning and form of treatment (thinned from above or below or non-thinned). The naturally dead trees were approximately of mean size in normally thinned stands while the self-thinning in non-thinned stands tended to occur amongst smaller than average trees. Diagrams were presented for basal area development and stem number reduction in the non-thinned stands.
Forest Ecology and Management, 1999
Results from two yield optimisation experiments in young stands of Norway spruce in northern and ... more Results from two yield optimisation experiments in young stands of Norway spruce in northern and southeastern Sweden are presented after 10 and 9 years' treatment, respectively. The aim of the experiments was to demonstrate the potential yield of Norway spruce, under given climatic conditions and non-limiting soil water, by optimising the nutritional status of the stands, at the same time as leaching of nutrients to the groundwater was avoided. A complete mix of nutrients was supplied either once a year or daily during the growing season, in combination with irrigation. On the basis of repeated foliar analysis and predicted growth response the proportions and amounts of nutrients applied were adjusted annually. After 10 years' treatment at the northern site, fertilisation had increased the annual stem volume production from 3 m 3 ha À1 a À1 in unfertilised stands to 14 m 3 ha À1 a À1. Although site quality initially was high at the southern site, nutrient optimisation increased annual stem volume yield from 12 in control stands to 29 m 3 ha À1 a À1 in irrigated±fertilised stands. Water had a positive effect on stem growth in southern experiment, but no effect in the north. In all stands in which the availability of nutrients and soil water was optimised by combined fertilisation and irrigation, the yield of stemwood was similar to or surpassed the best yields obtained by conventional silvicultural means.
Forest Ecology and Management, 2004
Woody growth at five sites, covering a range of precipitation (620-785 mm) and soil conditions in... more Woody growth at five sites, covering a range of precipitation (620-785 mm) and soil conditions in North Sudan zone in Burkina Faso was investigated 5-14 years after clear-cutting. Woody growth ranged from 0.7 to 1.7 Mg ha À1 per year, corresponding to 1.0-2.4 m 3 ha À1 per year in terms of green volume when species-specific basic densities were applied. Trunks (girth more than 10 cm), branches and stemlets made up about a third each of the yield and about one-third of the trunk was bark. Thus, the actual trunk wood production ranged from 0.2 to 0.7 Mg ha À1 per year corresponding to 0.3-0.9 m 3 ha À1 per year. Woodfuel yield was reduced to about a fourth of the total yield, when excluding small dimensions and trunk-bark, species with low calorific value or multiple use, e.g. fruit bearing or forage. Each site was dominated by some few species in terms of percentage of dry mass: Sclerocarya birrea (13%), Anogeissus leiocarpus (57%), Acacia seyal (38%), Combretum glutinosum (17%) and Combretum nigricans (37%). Mean stool growth per site ranged from 0.5 to 1.7 kg per year. Largest stool growth was recorded for S. birrea and A. leiocarpus with 4.1 and 3.6 kg per stool per year, respectively.
Forest Ecology and Management, 2004
Retention of live and dead trees in harvested stands has become a common practice in Scandinavian... more Retention of live and dead trees in harvested stands has become a common practice in Scandinavian forestry. We examined how retained Scots pines (Pinus sylvestris L.) grow and to what extent they compete with the new generation. In a mixed stand of about 5 ha in Northern Sweden, 44 retained pines and adjacent growth of the new stand was measured for the last 90 years. After liberation in 1912, the pines, then with a mean age of 180 years, doubled their annual ring width to a culmination after about 30 years. The trees below mean height showed the biggest response to liberation. The lower part of the stem (0.5-1.3 m) showed the largest growth relative to the decade before release during the first two decades after release. In the last decade the relative growth was largest at 6 m height. Growth of the new generation was measured on 9.5 m radius plots, centred on the retained pines. The growth of the new stand was reduced by 20% in the inner third of the plot area. With 10 evenly dispersed retained pines per hectare the production loss in the new generation was estimated at 2.5% over one rotation. The growth of retained trees more than compensated for this loss. The volume of the new stand was positively correlated with retained tree size and negatively correlated with retained tree growth. Of 17 species and species groups identified in the forest floor vegetation, only lichen occurrence correlated with distance to retained trees. Lichen was more common close to small and fast-growing retained trees.