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71.
Detailed studies have been undertaken to define pruning regimes for Eucalyptus nitens, but little is known of E. globulus responses to pruning although this is a more commonly planted species. This paper describes experiments that aimed to identify (a) levels of pruning that reduce E. globulus growth, (b) physiological processes contributing to those growth responses, (c) the incidence of decay and factors influencing decay incidence following pruning of E. globulus, and (d) comparative responses of E. nitens and E. globulus to live branch pruning. Results of a field experiment indicated that removal of between 30 and 50% of the crown length was appropriate for E. globulus plantations verging on canopy closure. The significant reduction in height growth associated with removal of 50 or 70% of crown length suggested pruning should remain below 50% of crown length if reduced stem growth of pruned trees was to be avoided. Stem volume was only significantly reduced over the period of the experiment by 70% pruning, but it was estimated that standing volume following removal of 50% of crown length would be reduced by 82 m3 ha−1 over a 20-year rotation if there were no other silvicultural interventions. The growth responses observed were probably related to large reductions in leaf area following 50 or 70% removal of crown length. Trees responded to pruning by changing patterns of biomass partitioning to favour stem growth at the expense of branch growth. A glasshouse study determined that light-saturated net CO2 uptake (Amax) increased following pruning. E. nitens seedlings had both a higher baseline Amax and higher Amax following pruning than did E. globulus, which could partially explain the greater effect of pruning on E. globulus growth than has been observed for E. nitens in other studies. This result, as well as apparently different patterns of foliage distribution through the crowns of E. globulus and E. nitens, suggested that models of pruning responses need to be parameterised for both species. In addition, a more conservative pruning regime may be appropriate for E. globulus than E. nitens. Pruning increased the frequency of branch traces with decay infection, and there was a trend towards increasing decay outbreaks with increasing pruning severity. Decay outbreaks were more likely to occur following pruning of high angle or larger diameter branches.  相似文献   
72.
Japanese oak and Japanese beech were sanded by hand with abrasive papers of varying grit number. Two three-dimensional parameters selected to characterize their surface roughness – one parameter for the distribution of roughness-profile peaks and the other for the relative area of the roughness-profile peaks above the threshold height – were compared against tactile roughness. The parameters were obtained from roughness profiles as determined by a robust Gaussian regression filter (RGRF) using seven cutoffs. The RGRF filtering process was adjusted specifically for the evaluation of wood surface roughness. Except for a cutoff wavelength of 0.25mm, the RGRF lent itself well to the determination of roughness profiles. No distortion of roughness profiles occurred around deep valleys, and there was a good correlation between the parameters and tactile roughness.Part of this study was presented at the 2002 Kansai Branch Office lecture meeting of the Japan Society for Precision Engineering, Kyotanabe, August 2002  相似文献   
73.
桉树立地生产力与养分生产力参数的确定   总被引:9,自引:0,他引:9  
桉树试验林样本分析结果表明,桉树树杆中氮,磷,钾养分浓度的倒数与养分吸收量早明显的负线性相关。基于这一相关性,对实测的数据作回归分析。估测的立地生产力极限和养分生产力参数值,以及相应的立地养分效应曲线具有较高的精确度。本文为研究林木生长和营养的动态函数关系提供了新的思路和方法。  相似文献   
74.
精密裁板锯试验模态分析   总被引:3,自引:0,他引:3  
以MJCll25型精密裁板锯为样机,对机床的动态特性进行了研究。在研究过程中,选取了与产品的表面精度有主要关系的固定工作台、双滚轮式移动工作台,并通过锤击法进行实验模态分析,得到了模态参数,从而评估了机床的动态特性.同时为该机床的动态优化设计提供了坚实的理论基础和可靠的数据,也为同类木工机床的动态特性研究提供了有效的途径。  相似文献   
75.
本文以高密度纤维板为原料,采用正交试验探究雕刻工艺对产品质量的影响,得到在该试验水平范围内最优雕刻工艺参数:主轴转速为24000 r·min-1,路径间距为0.20 mm,加工速度为6000 mm·min-1.为数控雕刻在高密度纤维板上应用提供了参考和技术支撑.  相似文献   
76.
Silviculture heading for structural heterogeneity creates many single trees standing at stand margins, inner edges or in remnant tree groups. As they played just a minor role in the age class forest, the growth behaviour of strongly released trees is rather unexplored. Here we show how retention cutting, presently spreading in the boreal of Québec province, affects stem and coarse root growth of remained single black spruce [Picea mariana (Mill.) Britton]. Increment cores from roots and stems of 125 trees show that retention cutting triggers coarse root growth of the remaining trees. Compared with reference trees retention trees accelerate root in relation to stem growth. Mean and variability of the root–stem allometry significantly rise after retention cutting. The found acceleration of root in relation to stem growth means mechanical stabilisation of the retention trees and corroborates the retention cutting method. Evaluation of silvicultural treatments can be incomplete and misleading as long as they are just based on aboveground reactions and neglect root growth.  相似文献   
77.
GPS手持机在森林资源连续清查中的应用探讨   总被引:1,自引:0,他引:1  
对手持式GPS接收机在森林资源连续清查中应用方法如:地理坐标参数的获取、计算和设置;在样地初设及复查时的应用作了论述,认为应用其可减少工作量,提高定位精度和复位率,有利于质量管理.  相似文献   
78.
野鸦椿主要经济性状遗传参数估算及优良家系选择   总被引:1,自引:0,他引:1  
野鸦椿(Euscaphis japonica)12个表型优良单株的半同胞子代测定结果表明:野鸦椿表型优良单株的半同胞子代家系间在单位面积果实产量、果穗长度、穗重、单穗果数等方面存在着显著或极显著差异;果穗长度、穗重、单穗果数、单位面积果实产量4个性状家系遗传力和单株遗传力都较高,性状间有明显的线性相关。通过方差分析、相关分析和聚类分析等方法,对各初选植株半同胞子代家系间的单位面积果实产量、果穗长度、穗重以及单穗果数分析比较,从初选的12个家系中进一步选择出经济性状表现优良的N1、N2、N5、N6、S1、S2、S3等7个优良家系。  相似文献   
79.
Although the effect of forest management on lichens in temperate forests has been widely examined, little is known about the influence of management-related factors on their biodiversity relative to factors that cannot be altered by management. Here we determined whether forest structure or climate determines lichen diversity in the Bavarian Forest National Park in southeastern Germany, taking spatial variables into account. We investigated 517 single tree stems along 4 transects in 113 pre-stratified plots (8 m in diameter) in this montane forest. We grouped environmental variables into three sets: climate (macroclimate, non-manageable), forest structure (manageable), and space. The explanatory powers of these sets of variables for lichen diversity were compared using variance partitioning for the lichen community, species density, and threatened species density. The relationships of single characteristics of forest structure with lichen species diversity were analyzed using generalized linear models (GLM). Lichen diversity was better explained by stand structures than by climate. Spatial effects influenced the number of species per plot. Among the structural features, the availability of dead wood and sycamore maple as well as forest continuity were most important for the enhancement of lichen diversity. Open canopy structures affected the total diversity positively. Although the availability of large trees was not an influential factor in the GLM at the plot level, high diversity levels were generally associated with large stem diameters at the level of single stems. We provide recommendations for sustainable forest-management practices that aim at specifically enhancing lichen diversity in temperate areas experiencing low levels of air pollution.  相似文献   
80.
根据史密斯桉(Eucalyptus smithii)苗期生长规律,设计不同容器类型试验,系统研究无底容器育苗对移植后90 d的苗木质量的影响(即幼苗从苗床移植到容器生长90 d后).结果表明:无底袋容器苗比有底容苗在苗高、根颈直径、叶片数、叶面积和植株总干重分别提高了13.0%,21.7%,28.1%,11.8%,16.6%.无底容器苗的地上干物质分配指数(86%)高于有底袋苗(84.5%).  相似文献   
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