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51.
Trade-offs among wood production, wood quality and ecological characteristics in the management of harvested forest stands are explored through model simulation of various silvicultural regimes. Long-term production of merchantable wood, production of various types of high-quality wood, and the level of certain quantitative ecological indicators are projected for coniferous forests of Pacific Northwestern USA. The set of ecological indicators used is based on the species composition and physical structure of old, unlogged forest stands. Simulations are performed with an ecological model of forest stand dynamics that tracks the fate of live and dead trees. Short rotations (<50 years) produce the least amount of high-quality wood over the multi-century simulation period. They also fail to generate ecological attributes resembling those of old forest stands. Production of high-quality wood is moderate to high under all rotations of 80 years or more; however, most ecological indicators require longer rotations unless alternatives to clearcutting are applied. Alternatives examined include retention of 15% cover of live tree canopy at each harvest in combination with artificial thinning between harvests. Thinning from below can expedite the development of large live and dead trees, and canopy height diversity without greatly diminishing wood quantity or quality. Proportional thinning retains understory stems, thereby expediting the recruitment of shade-tolerant trees. A possible drawback to thinning, particularly proportional thinning, is the diminished production of clean-bole wood at rotations of 150 and 260 years. It is concluded that most wood quantity, wood quality and ecological objectives can be met with long rotations (ca. 260 years). Certain objectives can be met with shorter rotations (80–150 years) when treatments of thinning and canopy tree retention are applied. 相似文献
52.
Hypoglycemic effect of lupin seed γ-conglutin in experimental animals and healthy human subjects 总被引:2,自引:0,他引:2
Bertoglio JC Calvo MA Hancke JL Burgos RA Riva A Morazzoni P Ponzone C Magni C Duranti M 《Fitoterapia》2011,82(7):933-938
A lupin seed γ-conglutin-enriched preparation was tested in a glucose overload trial with both murine models and adult healthy volunteers. The results with rats showed a dose-dependent significant decrease of blood glucose concentration, which confirmed previous findings obtained with the purified protein. Moreover, three test-product doses equivalent to 630, 315, and 157.5 mg γ-conglutin, orally administered 30 min before the carbohydrate supply, showed a relevant hypoglycemic effect in human trials. Insulin concentrations were not significantly affected. The general hematic parameters did not change at all.This is the first report on the glucose-lowering effect of lupin γ-conglutin in human subjects. 相似文献
53.
Shuang-Huang-Lian (SHL), a traditional Chinese formula containing Lonicerae japonicae flos (LJF), Scutellariae radix (SR) and Forsythiae fructus (FF), is commonly used to treat acute upper respiratory tract infection, acute bronchitis and light pneumonia. Forsythoside A is one of the main active ingredients in Forsythiae fructus, a key herb in SHL. In the present study, effects of different compositions in SHL on the intestinal absorption of forsythoside A were investigated. The observations from in situ intestinal circulation model showed that A/%(h− 1) of forsythoside A in FF + LSF, FF + SR and SHL were all reduced greatly compared with that in FF. However, in pharmacokinetics study, Cmax and AUC0 → 1440 of forsythoside A all increased and T1/2 prolonged in SHL, FF + LJF and FF + SR compared with FF. The results indicated that the different compositions of SHL decreased absorption but increased bioavailability of forsythoside A, which may be related to its metabolism inhibited in intestine or liver. 相似文献
54.
55.
海南岛柚木的木材性质 总被引:1,自引:1,他引:1
11—13龄柚木20株,17—19龄7株,取自海南岛尖峰岭,用以研究木材比重及纤维长度的某些特性及测定标准物理力学性质。以胸高圆盘加权平均数为单元,比重0.466—0.588,平均0.516:纤维长度0.878—1.230mm,平均1.063mm。生长轮宽度与比重及纤维长度之间表现弱的负相关。第1轮和第9轮的材性存在显著的相关关系。材性在标地间的差异不显著,标地内株间的差异很显著。径向变异:髓心附近几轮的纤维长度和比重均增长很快,第8轮以后,前者增长缓慢,后者多起伏。轴向变异:1.心部系列(髓心向外6生长轮)第1轮纤维长度的轴向变异很小,其外几轮的纤维长度缓慢向上减轻或有起伏;基部各生长轮的比重很大,向上急剧减小至1.3m高度,此后各生长轮的变化不一致。2.边部系列(树皮向内6生长轮)纤维长度和比重均很快向上减小。讨论了影响纤维长度轴向变异的主要因素。提出标准物理力学性质的试验结果。 相似文献
56.
长白落叶松人工林树冠形状的模拟 总被引:17,自引:3,他引:17
以长白山地区 2 6a生长白落叶松人工林为研究对象 ,采用枝解析的方法 ,测定了 2 5株林木 (直径 10 5~2 4 9cm)的树冠变量 ,并建立了预测树冠外侧形状的冠形模型。基于枝条着枝深度 (DINC)和林木变量所建立的树冠形状模型包括 :基径、枝长、着枝角度和弦长等预估模型。对于大小相同树木的主要枝条来讲 ,这些树冠变量是随着DINC的增加而增大 ;而林木的胸径 (DBH)和树高 (HT)变量很好地反映了不同大小树木的冠形变化。冠形预测模型预测效果良好 ,充分体现了树冠结构的变化趋势 :树冠形状在树冠的中上部呈抛物线体 ,而在树冠的下部则为近圆柱体。文中所建模型 ,可以合理地描述长白落叶松人工林的树冠形状及其变化规律。 相似文献
57.
The effect of tool angles on the shapes of chips generated by parallel-to-grain and end-grain milling was explored for China
fir and maple under fixed spindle and feed speeds and cutting depth. The milling path was up-milling by straight router-bits
with a diameter of 12 mm. The chip shapes could be distinguished as five types: spiral, splinter, flow, thin, and granules
or powder. The flow and thin chips were generated most often (on a weight percentage basis) for all tool angles investigated
for parallel-to-grain and end-grain milling of China fir and maple. More granule chips were produced with parallel-to-grain
milling than with end-grain milling for both woods. The measured chip thickness (t′) was thicker than the calculated thickness (t
max). Thicker and longer maple chips were produced by end-grain milling than by parallel-to-grain milling. The tool geometries
of 40°/15° (sharpness of the angle–rake angle), 50°/15°, and 60°/15° for China fir and 40°/25°, 50°/5°, and 60°/5° for maple
produced relatively more flow chips with parallel-to-grain milling. Furthermore, the tool geometries of 40°/5°, 50°/15° and
60°/25° produced more flow chips (weight percentage) by end-grain milling of China fir and maple.
Received: May 23, 2001 / Accepted: June 28, 2002
Acknowledgment This study was supported by a grant from the National Council of Science, Taiwan (NSC89-2313-B-415-011). 相似文献
58.
A study was conducted in northwest Florida, USA, to investigate root development and morphology of cotton (Gossypium hirsutum L.) under pecan (Carya illinoensis K. Koch) trees in an alleycropping experiment. Root:shoot ratio, root biomass, total root length and root length density
were examined under three treatments: (1) barrier (separating belowground interspecific competition by trenching to a depth
of 120 cm and installing polyethylene barrier), (2) non-barrier (root systems were free to interact), and (3) monoculture
of cotton (without above and belowground interspecific competition with trees). Results indicated that plants in the barrier
and non-barrier treatments had lower root:shoot ratios compared to the monoculture treatment. Belowground competition for
resources between pecan and cotton in the non-barrier treatment resulted in 25 and 33% reduction of total root length (359 cm)
when compared to that of the barrier (477 cm) and monoculture (539 cm) treatments, respectively. The non-barrier plants also
exhibited the lowest root length density. Specific root length was highest for the monoculture (179 cm g−1) and lowest for the non-barrier treatment (146 cm g−1) with the barrier treatment being intermediate (165 cm g−1). Interspecific competition with pecan significantly altered root development and morphology of cotton plants. Research in
agroforestry should take into account the developmental differences in root systems of the associated crop species so that
better models incorporating nutrient and water uptake can be developed. 相似文献
59.
森林采运系统中原条流最优控制的研究 总被引:2,自引:0,他引:2
运用系统分析理论,揭示了森林采运系统中原条流具有时空性、连续性、服务性、可控性和经济性的特征。以与原条流量有关的生产和贮存费之和最小,组织原条运输和贮木场作业均衡生产为目标,运用现代控制理论建立了原条流宏观和微观控制的数学模型。通过实例证明了“两段式运材工艺”比“冬贮夏运(流)工艺”,具有显著的经济效益。 相似文献
60.