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Abstract: Johansson, T. 2011. Biomass equations for hybrid larch growing on farmland. Data were collected from 20 stands of hybrid larch (Larix x eurolepis) growing on abandoned farmland in southern and central Sweden (Lat. 55–60° N.). The mean stand age was 19 years (range 18–23). The mean number of stems per hectare was 1150 (range 364–2374) and the mean breast height diameter (over bark) was 15.6 cm (6.8–24.2). Soil types in the stands were light and medium clay and tills (sandy-silty and light clay). Mean dry weight above stump level (20 cm) for a hybrid larch tree in this study was 117 kg (range 36–245) and the standing dry weight for hybrid larch stands was 120 t ha−1 (42–350). Mean annual increment (MAI) for the tree was 6.09 kg y−1 (1.89–13.61) corresponding to production of 90–120 t ha−1 after 15–20 years growth and a stem number of 1000–1500, if the stand is mainly used for biomass. Alternatively, for pulp wood and timber production a rotation period of 30–40 years can be used, with thinnings being exploited for biomass. [Copyright &y& Elsevier]

Abstract: Growth data were collected from 41 stands of poplar (Populus sp.) growing on former farmland in Sweden, situated between latitudes 55 and 63° N. The mean age of the poplar was 20 years (range 4–73), the mean stand density 1327 stems ha−1 (range 155–4690), and the mean diameter at breast height (over bark) 210 mm (range 49–447 mm). Soil types in the poplar stands were mainly clay (25 stands), other sediments (six stands) and sandy-silty till (10 stands). The mean total standing dry weight above stump level (≈200 mm) for poplar was 141.9 ± 13.9 ton ha−1 with a range of 19–438 ton ha−1. In addition to estimating conventional dry weights of trees and tree components, SLA, PLA and LAI, among other measures, were estimated and were in agreement with published figures. The results indicate that poplar stands could produce 70–105 ton ha−1 after 10–15 years growth mainly used for biofuel. Otherwise, the stands could be thinned for pulpwood and timber production with a rotation period of 25–30 years and the thinnings used for biofuel. [Copyright &y& Elsevier]

Abstract: The aim of this study was to compare the sprouting ability of stumps of different diameters of downy (Betula pubescens Ehrh.) and silver (Betula pendula Roth) birch. The number of living stumps, and the number and height of sprouts were recorded annually and the biomass of the sprouts was calculated. Two hundred naturally regenerated downy and silver birches were examined. These were part of a commercial cleaning in late August 1983, which left 20-cm-high stumps. The experimental site was located on forest land in central Sweden (latitude 60°15′N, longitude 16°01′E). The stumps were categorised into four diameter classes: 10–19, 20–29, 30–39 and 40–50mm. The site was examined in September of the year after cutting and on a number of occasions up to 9 years after cutting. The number of living stumps of each species was recorded. When the sprouts were 9 years old, their diameter at breast height was recorded. Then, the sprouts were cut and stems and branches were dried and weighted. After 1 and 9 years, the percentage of surviving downy birch stumps was 90% and 61%, respectively. The equivalent figures for silver birch were 82% and 55%. The number of sprouts per stump differed significantly between the species and the stump diameter classes. The greatest mean number of downy birch sprouts per stump (2.8±0.3) was for the diameter class 40–50mm, and for silver birch sprouts (2.3±0.2), for the 30–39mm stumps. The diameter at breast height, height and weight of individual sprouts 9 years after cutting were significantly different between downy and silver birches and the diameter classes. The mean downy birch sprout weight (1.00±0.01kgd.w.stump−1) varied between diameter classes and the heaviest sprout weight (1.18±0.02kgd.w.stump−1) was produced by 30–39mm stumps. The heaviest silver birch sprout, 1.94±0.04kgd.w., was also produced by 40–50mm stumps. The mean weight was 1.55±0.05kgd.w. The sprout biomass per living stump was significantly different between the species and the diameter classes. The mean sprout biomass per downy birch stump was 1.76±0.15kg and for silver birch sprouts 2.19±0.22kg. Equations for estimating the aboveground biomass (stem+branches) from diameter at breast height were developed for downy and silver birch sprouts. [Copyright &y& Elsevier]

Mixed stands are the most frequent type of stand in Nordic countries. A mixture of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) is the most common stand type in the region. But for most foresters and persons familiar with forestry, a mixed stand implies a conifer species and at least one broad-leaved species.Management and silviculture of mixed stands of conifers and broad-leaves has increased rapidly during the last 15 years. Efficient management of mixed stands increases profits for the owner as well as wood quality in the stand.Practical examples of how to manage mixed stands of birch (Betula pendula Roth and Betula pubescens Ehrh.) and Norway spruce are now available. In Finland, Norway and Sweden this is a common alternative to management of pure stands of conifers. In Norway, as well as mixed stands of birch and spruce, there are examples of mixed stands of European aspen (Populus tremula L.) and Norway spruce.Existing yield information for mixed stands is based on studies of stands which were managed improperly prior to the start of the study. The yield for birch at 35 years of age was 100 m3 ha−1. The growth of Norway spruce was reduced by 10% compared with spruce growing in pure spruce stands. In a mixed stand of European aspen and Norway spruce growing on farm land, the 36-year-old aspen overstory produced 480 m3 ha−1. The spruce understory had a reduced yield compared with pure spruce stands.Depending on the biofuel price and the market for utilisation of biofuel the forest owner might use the broad-leaves as biofuel. Some studies indicate that the harvested biomass yield of birch in a mixed stand of birch and spruce could be 48 t d.w. ha−1. [Copyright &y& Elsevier]

Growth data were collected from 38 stands of European aspen (Populus tremula L.) growing on forest land in Sweden. The stands ranged in latitude from 56 to 65°N. The mean age of European aspen was 46 years (range 26–91), the mean stand density 1246 stems ha−1 (range 245–3866), and the mean diameter at breast height (over bark) 20 cm (range 11–36 cm).Soil types in the aspen stands were divided into five groups: sandy–silty till (14 stands), light clay till (6), fine sand (5), light clay (4) and sandy till (3). Soil types represented by only one or two stands were not included in the analysis. No statistically significant differences in site index were found between the five soil-type groups in aspen stands.The mean total standing dry weight above stump level (≈200 mm) for aspens was 148 tonnes ha−1 with a range of 28–501 tonnes ha−1. In addition to estimating conventional dry weights of trees and tree components, specific leaf area, total surface area and LAI, among other measures, were estimated.A practical implication for management of aspen stands for biofuel production is to cut the aspen after 10–20 year-rotation. Otherwise the stand could be thinned for pulpwood and timber production and the removal is used for biofuel. [Copyright &y& Elsevier]