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991.
992.
《Scandinavian Journal of Forest Research》2012,27(1-4):364-369
In single‐tree selection, trees removed by harvest or lost through mortality are replaced by ingrowth from the seedling/sapling bank. Because the level of ingrowth is governed not only by the recruitment rate of new seedlings, but also by mortality and growth rates within the seedling/sapling stratum, knowledge of how these processes are related to the tree stratum is important for successful application of single‐tree selection. Therefore, Norway spruce (Picea abies (L.) Karst.) regeneration (0.1 m ≤ height ≤ 2.0 m) was measured on seventy 100 m2 circular subplots at each of two sites in central and northern Sweden. Both sites had previously been selectively logged, but the time elapsed since the last harvest was at least 30 yrs. Basal area of trees of at least 2 m height within three different radii from the subplot centres was measured. Measurements on regeneration included height and leader length. Influence of local stand basal area on density and growth of regeneration was analysed by ordinary least‐squares linear regression for each of four height intervals. Regeneration was significantly aggregated at both sites, but number of Norway spruce seedlings and saplings per circular subplot was not correlated to local stand basal area. Out of 36 regressions, only eight showed a significantly (p < 0.05) negative correlation between seedling and sapling height growth and local stand basal area. In five of these cases, removal of one point (subplot) made p > 0.05. The results suggest that density and growth of Norway spruce regeneration in selectively logged uneven‐aged Norway spruce stands is affected more by ground conditions than by local stand basal area. 相似文献
993.
994.
实践过程中针对养殖方法、产卵期、孵化期、变态期以及黑龙江林蛙日活动规律进行了对比分析。结论,在每年4月28日至5月12日期间出现产卵高峰;在5~7℃、10~12℃、14~15℃池水温度范围有较高孵化率;采用混合饲料喂养的蝌蚪变态率均在68%以上;黑龙江林蛙每天9~11时和15~17时活动频繁,是最佳喂食时间;冬季经过越冬池越冬后,选择春眠后放养的技术思路,来提高幼蛙成活率,起到冬眠后的缓冲作用。在放养场内散养期间,人工控制饵料投放量,促使黑龙江林蛙主动捕食场内野生昆虫,激发林蛙适应生态环境的潜在习性。 相似文献
995.
《Scandinavian Journal of Forest Research》2012,27(3):241-249
The Brinell hardness and equilibrium moisture content (EMC) were measured from thinning-aged silver birch wood. Wood material both from the trees harvested in the first commercial thinning and from trees remaining on site after the thinning was included. The average Brinell hardness was 19.40 MPa. It correlated significantly with the basic density of wood. With respect to the distance from the pith, the Brinell hardness of air-dried wood was higher than that of artificially dried wood. The average EMC of the conditioned (20°C, 65% relative humidity) wood was 12.0%. The EMC of the wood also varied, with the EMC being higher for air-dried wood than for kiln-dried wood. EMC was the highest at a distance of 30–40 mm from the pith, decreasing towards both pith and log surface. Seasonal variation in both the Brinell hardness and the EMC of the wood was found. It was presumed to be a consequence of season-dependent physiological changes in trees. 相似文献
996.
《Scandinavian Journal of Forest Research》2012,27(1):14-29
Genetic parameters were estimated for wood and growth traits in two 19-yr-old clonal trials and a 40-yr-old full-sib progeny trial of Norway spruce [Picea abies (L.) Karst.]. In the clonal trials high (>0.4) broad-sense heritabilities were found for wood density traits, lignin content, number of internal cracks, growth traits, spiral grain and number of resin canals. Moderate (0.2–0.4) heritabilities were found for tracheid lumen diameter and cell wall thickness, microfibril angle and tracheid length, while low heritabilities (<0.2) were found for pulp yield, fibre strength, wood stiffness and wood colour. Lignin content and pulp yield showed low genetic variation, whereas the genotypic coefficient of variation for most other traits ranged between 5 and 15%. Most traits showed low levels of genotype by environment interaction. Among the wood properties, latewood proportion, earlywood density and ring density showed significant, adverse correlations with volume in both clonal trials. 相似文献
997.
《Scandinavian Journal of Forest Research》2012,27(6):534-538
Abstract The recent finding of a new way to assemble two pieces of wood by mechanically induced wood welding opens a new and challenging perspective for producing more environmentally friendly wooden products, i.e. without glue. This process, recently applied to solid wood, needs to be better understood to investigate the dependence of the variability of wood properties on the welding parameters. The two applications presented are the linear vibration welding and direct rotational friction welding. In each case different wood species were tested. In the most favourable cases the wood joints yielded structural grade strength. The resulting bond densification was analysed by the mean of wood density maps for oak, beech, spruce and pine. If this technique proves successful, it could change significantly the future of the furniture industry. The objectives of this article are to present the main results obtained so far and to suggest different research areas needed to improve this new way of jointing solid wood. 相似文献
998.
《Scandinavian Journal of Forest Research》2012,27(4):347-357
Abstract The study focused on constructing models for the establishment and seedling height development of naturally regenerated seedling stands in the natural regeneration of Scots pine by the seed-tree method in Lapland, northern Finland. Modelling was used to describe the dynamics of the regeneration process and to analyse the principal ecological factors and management activities influencing regeneration success. Models for the density of seedling stands were developed with the generalized linear mixed model method. The most significant variables affecting seedling establishment were elevation, time since the establishment cutting, the interaction of forest site type and site preparation, and stoniness. The results indicated that the average stocking level tends to remain unsatisfactory on moist, fertile site types without site preparation. Seedling height development was modelled as a function of age using the linear mixed model. Age explained 97% of the variance of seedling height. Other independent variables in the model were effective temperature sum, site preparation and the presence or absence of seed trees. 相似文献
999.
《Scandinavian Journal of Forest Research》2012,27(3):214-226
Abstract The quantitative effect of pine-dominated edge stands in southern Finland on the density and growth of pine saplings was addressed in the study. The cumulative effect of a mature edge stand on the development of a pine sapling stand with variable cutblock sizes was also estimated. The data were acquired from 10 study sites with a Scots pine sapling stand with a current dominant height of 1–6 m and an adjoining middle-aged to mature edge stand dominated by Scots pine. Tree level models were constructed to describe and simulate the structure and development of the sapling stands. The results indicated that dividing an average regeneration area (2 ha) into smaller cutblock units (1.0–0.5 ha) appreciably increased the edge stand effect. Total stand volume growth was 6% lower on 1 ha cutblocks, and 31% lower on 0.5 ha blocks, than on 2 ha blocks. 相似文献
1000.