共查询到20条相似文献，搜索用时 93 毫秒
1.
Die bisher erarbeiteten Ergebnisse lassen sich wie folgt zusammenfassen:
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Bei der Fichte korrelieren Jahrringbreite und Holzdichte und damit die wesentlichen Festigkeitseigenschaften, wie Biegefestigkeit,
Biege-E-Modul, Druckfestigkeit.
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Die Holzdichte als wesentliche Eigenschaft steht in enger Beziehung zum Sp?tholzanteil.
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Die Astst?rke korreliert direkt mit der Wachstumsgeschwindigkeit, d. h. ebenfalls mit der Jahrringbreite.
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Astst?rkensumme und Jahrringbreite zusammen erkl?ren einen gro?en Teil der technischen Holzeigenschaften.
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Durch Wert?stung kann ein Teil der negativen Wirkungen des schnellen Wachstums auf die Festigkeitseigenschaften ausgeglichen
werden.
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Dies bedeutet allerdings nicht, da? die Holzdichte als wesentliches Merkmal an Bedeutung verliert.
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Eine weitgehend zu erwartende Reihung ist also aus holztechnologischer Sicht eindeutig festzustellen:
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— engringig und wertge?stet auf dem 1. Platz, verspricht also h?chsten Holzwert,
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— engringig, nicht wertge?stetes Holz steht an 2. Stelle,
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— weitringig, wertge?stet im Mittelfeld, nur knapp nach Position 2
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— weitringiges, nicht wertge?stetes Holz verliert, mit Abstand an letzter Stelle stehend.
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Results achieved till now may be summarized as follows:
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With spruce, annual ring width is correlated with wood density, and thus with the essential strength properties such as bending
strength, bending-E-module, and tensile strength.
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Wood density as an essential property is closely related to the share of late wood.
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There is a direct correlation between knot size and growth rate, i. e. also annual ring width.
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The sum of knot diameters and annual ring width together explain a large part of the technical wood properties.
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High pruning may compensate for some of the negative effects of rapid growth on strength properties.
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This, however, does not imply that wood density is becoming less important as an essential property.
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From the wood-technological viewpoint, a largely to be expected ranking can be clearly established:
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— narrow growth rings and high-pruned stands in first place, thus promising the highest timber value,
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— narrow growth rings but not pruned comes second,
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— wide growth rings and high-pruned ranks about in the middle, only slightly behind position 2,
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— wood showing wide growth rings and not being from pruned trees falls way behind.
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相似文献
2.
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• Effects of thinning on epicormics have rarely been demonstrated especially due to inaccurate surveying methods. 相似文献
3.
Der Wald ist für den Naturschutz
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— aus grunds?tzlichen Erw?gungen,
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— wegen seines hohen Wertes als Lebensraum für Pflanzen und Tiere,
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— im Hinblick auf seinen gro?en Fl?chenanteil, auch in seiner Form als Wirtschaftswald von besonderer Bedeutung.
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Die naturschutzfachlichen Anforderungen an eine naturvertr?gliche Waldbewirtschaftung lassen sich insbesondere mit Hilfe des
Arten- und Biotopschutzprogramms und anderer konzeptioneller Arbeiten immer besser formulieren; es bedarf aber noch weiterer
Grundlagenerhebungen, insbesondere einer ?kologischen Werterfassung im Wald. 相似文献
4.
利用SPAD-502型叶绿素计测定了不同氮水平下高山杜鹃不同生长时期、不同叶位的SPAD 值,分析SPAD值与叶绿素含量和叶片总氮含量的关系。结果表明,不同生长期第1轮和第2轮叶片的SPAD值与叶绿素含量均呈显著线性正相关,其中新梢生长期第1轮叶片的SPAD值与叶绿素含量的相关性最强,而叶绿素各参数中对SPAD值影响最大的是叶绿素b的含量。在不同氮水平下, SPAD值及相对叶色差与单位干重的总氮含量具有显著线性正相关关系, SPAD值的变化能够反映60％的单位干重叶氮含量的变化。因此,可以利用SPAD-502型叶绿素计对高山杜鹃进行快速、无损的氮素营养诊断。 相似文献
5.
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• Mixed forests feature competitive interactions of the contributing species which influence their response to environmental
change. 相似文献
6.
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• Fine root responses to potential climate change are relatively unknown in spite of their central role in ecosystem functioning. 相似文献
7.
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• Carbon isotope composition (δ13C) is a complex trait involved in acclimation, adaptive processes and related to water use efficiency (WUE) and/or productivity. 相似文献
8.
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• Canarian Juniper woodlands, now very scarce, are rich in endemic and endangered plants. However, many aspects of juniper
regeneration are almost unknown. 相似文献
9.
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• Previous studies on competitive interactions among silver birch, Scots pine, and Siberian larch have not addressed the direct
importance of the species identity of nearby competitors. 相似文献
10.
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• To withstand and to recover from severe summer drought is crucial for trees, as dry periods are predicted to occur more
frequently over the coming decades. 相似文献
11.
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• We present the results of a two-year (2007–2008) greenhouse study investigating the effect of water availability and nitrogen
fertilization on the growth, biomass partitioning, and foliar nutrient content of Abies fraseri (Pursh) Poir. 相似文献
12.
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• The effect of water stress on host selection and performance during the shoot feeding phase, by the Mediterranean pine shoot
beetle Tomicus destruens, was studied. 相似文献
13.
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• We combined stem volume increment analysis with dendroecological tools to address two unresolved issues concerning oak dieback
in Mediterranean areas: early detection of changes in stand growth, and identification of mechanisms for observed growth declines. 相似文献
14.
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• Paternity was established in a field trial of Abies nordmanniana with open-pollinated (OP) offspring from a clonal seed orchard (CSO) comprising 23 clones. 相似文献
15.
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• Multivariate statistical analysis was used to define different developmental stages for stone pine (Pinus pinea L.) considering tree size and cone production, without site-specific information. 相似文献
16.
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• Tree mortality is an important process in forest ecosystem dynamics and is one of the least understood phenomena, because
of the complex interactions between different environmental stresses, minimal understanding of whole-plant mortality processes,
and a chronic shortage of data. 相似文献
17.
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• Radiata pine (Pinus radiata D. Don) is the main exotic plantation tree species grown in New Zealand for wood production and as such represents a significant
component of the terrestrial carbon cycle. 相似文献
18.
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• The managed area of the North-American boreal forest has been studied extensively. However, because of their inaccessibility,
the growth and dynamics of trees at higher latitudes remain unknown, so precluding the possibility of quantifying their productive
and economic potential and, if any, their exploitation. 相似文献
19.
? The potential of a chlorophyll meter (CCM-200, Opti-Sciences, Tyngsboro, MA, USA) for the estimation of total leaf chlorophyll contents was evaluated in leaves of different developmental stages for Quercus pyrenaica Willd., Q. faginea Lam., Q. suber L. and Q. ilex L. subsp. ballota (Desf.) Samp. ? For all species and leaf stages, a strong non-linear relationship (P < 0.0001) was found between the chlorophyll content index (CCI) and leaf chlorophyll content per unit area. In all species, the slope of the CCI-chlorophyll content relationship varied during leaf development, suggesting that caution should be exercised when using the CCM-200, since the interpretation of CCI readings should be limited to samples of similar leaf age. Also, the data indicate that the models should also be speciesspecific, owing to differences in the intercept and/or slope of the equations. ? The addition of fresh LMA as a complementary parameter improved the accuracy of chlorophyll estimation in non-species-specific equations to a considerable extent when leaf samples of similar development were considered. ? After due consideration, it may be concluded that the CCM-200 chlorophyll meter is a reliable method for acquiring an estimation of chlorophyll contents in Mediterranean Quercus species, with potential use as an effective tool in forest management. 相似文献
20.
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• This study investigated the short-term changes in neutral genetic variation that would occur if a mature, second-growth,
black walnut (Juglans nigra L.) stand was harvested following either a diameter-limited or value-limited cutting regime. 相似文献
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