Current issue: 51(2)
Under compilation: 51(3)
Genetically improved Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) are used extensively in operational Swedish forestry plantations to increase production. Depending on the genetic status of the plant material, the current estimated genetic gain in growth is in the range 10–20% for these species and this is expected to increase further in the near future. However, growth models derived solely from data relating to genetically improved material in Sweden are still lacking. In this study we investigated whether an individual tree growth model based on data from unimproved material could be used to predict the height increment in young trials of genetically improved Norway spruce and Scots pine. Data from 11 genetic experiments with large genetic variation, ranging from offspring of plus-trees selected in the late 1940s to highly improved clonal materials selected from well performing provenances were used. The data set included initial heights at the age of 7–15 years and 5-year increments for almost 2000 genetic entries and more than 20 000 trees. The evaluation indicated that the model based on unimproved trees predicted height development relatively well for genetically improved Norway spruce and there was no need to incorporate a genetic component. However, for Scots pine, the model needed to be modified. A genetic component was developed based on the genetic difference recorded within each trial, using mixed linear models and methods from quantitative genetics. By incorporating the genetic component, the prediction errors were significantly reduced for Scots pine. This study provides the first step to incorporate genetic gains into Swedish growth models and forest management planning systems.
Results on early survival, growth and shoot phenology of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) and poplar clones (P. trichocarpa Torr. & A. Gray, P. balsamifera L., P. maximowiczii A. Henry and their hybrids) in 13 Scandinavian field trials are presented. The trials were established on forest land (7 sites) or former agricultural land (6 sites) within the latitude range of 56° to 65° N and were assessed 3–4 years after establishment. The main aim was to evaluate phenotypic and genetic differences related to early survival, growth and phenology for hybrid aspen and poplar for different site types and latitudes. Growth and survival was generally higher for hybrid aspen than poplar at all sites. The poor performance of poplar compared to hybrid aspen is likely due to climatic maladaptation or high soil acidity. The early growth performance of the species need to be confirmed at a higher age. The genetic variation and genetic control for growth, phenology and survival was in general intermediate to large indicating good possibilities for effective clonal selection. The genetic site x site correlations (rGE) for growth were for hybrid aspen mostly strong, indicating a weak genotype by environment interaction, while rGE were inconsistent for poplars.The result suggests that southern Sweden can be treated as a single test and utilization zone and in northern Sweden the region along the coast may be another zone. It is too early to make any corresponding conclusions for poplar. In addition, the result backs up the current recommendations for utilization of selected hybrid aspen and poplar regeneration material in Sweden.
The literature on the most prominent forest damage related to even-aged and uneven-aged forest management regimes was reviewed. A questionnaire to expert researchers was conducted to estimate risks in even-aged and uneven-aged forest management chains in Finland. There are only a few empirical comparisons of damage risks in even- and uneven-aged stands in the literature. The results from the expert survey showed that the damage risks were higher in even-aged management in Norway spruce and Scots pine. However, the variation in the risks between individual chains and between individual causes was high. The highest risks in Scots pine were caused by moose (in even-aged chains) and harvesting damage (in uneven-aged chains). In Norway spruce, root rot caused the highest risks in both even-aged and uneven-aged chains. The higher risks in even-aged forestry are largely due to the many associated practices which favour various types of damage. However, there are some important exceptions: the damage risks may be higher in some uneven-aged stands, especially in Norway spruce stands infected with root rot where the utilization of undergrowth or natural regeneration can be risky. Moreover, the repeated thinnings in uneven-aged stands may lead to increased mechanical damage.
Accurate estimates of both above-ground biomass (AGB) and below-ground biomass (BGB) are essential for estimating carbon (C) balances at various geographical scales and formulating effective climate change mitigation programs. However, estimating BGB is challenging, particularly for forest ecosystems, so robust allometric equations are needed. To obtain such equations for savanna-woodlands of the West African north sudanian zone, we selected four common native woody species (Anogeissus leiocarpa (DC.) Guill. & Perr., Detarium microcarpum Guill. & Perr., Piliostigma thonningii (Schumach.) Milne-Redh. and Vitellaria paradoxa C.F. Gaertn.). At two sites in Burkina Faso, we determined the BGB of 30 trees of each of these species by excavation, and measured various above-ground dimensional variables. The root:shoot ratio varied widely among the species, from 0.1 to 3.4. Depending on the species, allometric equations based on stem basal area at 20 cm height, basal area at breast height and tree height explained 50–95% of the variation in BGB. The best generic equation we obtained, based on basal area at 20 cm, explained 60% of the variation in BGB across the species. Three previously published generic allometric equations underestimated BGB by 8 to 63%. The presented equations should significantly improve the accuracy of BGB estimates in savanna-woodlands and help avoid costly needs to excavate root systems.
Boom corridor thinning (BCT) has been proposed as a cost-effective technique for biomass thinning (BT) in young dense stands. The objective of this study was to determine how various BCT operations affect stand structure following biomass thinning and to compare the results with conventional selective thinning methods. Two series of field experiments were established; BCT 1-series: Three sites in south of Sweden (9 and 11 m in mean and dominating tree height) with five treatments, including a control, conventional selective thinning and three BCT treatments (1 m and 2 m wide corridors and selective BCT). The second BCT series: Three regions in Sweden (in the north, centre and in the south), with two stand sites in each region with different tree heights (4/9 m and 5/10 m in mean/dominating tree height). Treatments were control, pre-commercial thinning (PCT), conventional selective thinning and BCT (high and low thinning). Following the first biomass thinning, BCT regimes and selective thinning methods resulted in similar stand structures based on the number of possible future crop trees (>80 mm in diameter at breast height). However, BCT maintained a higher diversity of tree sizes as well as more stems per hectare, including deciduous species, than the selective thinning approaches. The stands after BCT should have more vertical complexity, especially when compared to pre-commercial thinning. The structural heterogeneity resulting from BCT may also increase stand biodiversity and ecosystem service values.