Untersuchungen über die Holzeigenschaften von Douglasien aus linksrheinischen Anbaugebieten
The wood-properties of Douglas firs grown on various sites and under different growth conditions on the west-side of the Rhein in the districts Trier and Koblenz (mostly in the Eifel- and Hunsrück-hills) were investigated. Some of the test-trees were grown in pure stands, some in mixed stands between broadleaved species or spruces. Investigations comprehended year ring analysis, percentage of summerwood, thickness of branches, hardness, length of tracheids and wood density (based on volume when green and weight when ovendry). From several stems grown on a good site also the strength properties of wood were tested. For production of timber of high specific gravity and useful for deals and veneer an early limitation of diameter growth is desirable, however on better sites with abundant soil moisture supply is difficult to obtain. The best wood quality was found in densely stocked pure stands, while Douglas firs mixed in wide distance with broad-leaved species were rapidly grown, developed very big crowns with thick branches, conical trunks and broad annual rings. In the examined stands percentage of summer-wood was rather high. The average specific gravity value corresponded exactly with american second-growth stands of coast type. Test-trees from a fully stocked stand showed excellent stress properties, especially high values of bending strength, modulus of elasticity and shock resistance. The quality of the converted lumber cut from test-trees will be discussed in a following essay.
Impact of spacing and pruning on quantity, quality and economics of Douglas-fir sawn timber: scenario and sensitivity analysis
Controlling the long-term effect of management on the quantity and properties of individual boards is a fundamental challenge for silviculture. Within this basic study on Douglas-fir, we have investigated the sensitivity of the net present value (NPV) to three most common planting densities and a prominent pruning strategy. We therefore have applied an individual tree growth model, which represents intrinsic stem structure as a result of crown competition. The model extrapolated board strength development to the rotational age of 70 years, starting from real and comprehensive data recorded from experimental Douglas-fir plots at the age of 20 years. Total volume production increased from about 1600 m3 ha−1 for 1000 and 2000 trees ha−1 to 1800 m3 ha−1 for 4000 trees ha−1. The economic superiority of the lowest density stands increased considering the NPV at inflation-adjusted interest rates of 0%, 2% and 4%: Given an interest rate of 2% and no pruning, the NPV at 2000 was at about 50% of the one at 1000 trees ha−1. The NPV at 4000 trees ha−1 was even negative. Generally, artificial pruning was not effective. The revealed financial trade-off between growth and timber quality in young stands underlines the importance of silvicultural guidelines, which quantify the effect of management on yield per strength class and financial outcome.
Hydrostatische Verfahren zur Bestimmung der Rohdichte von Holzproben
ZusammenfassungDas hydrostatische Verfahren hat sich bei der Bestimmung der Rohdichte von Holzproben als sehr zuverlässig und genau erwiese. Es ist unabhängig von der Form, der Größe und der Oberflächenbeschaffenheit der Proben und mit verhältnismäßig einfachen Hilfsmitteln schnell durch-zuführen. Auf Grund dieser Eigenschaften ist es für eine kombinierte Gewichts- und Volumenbestimmung, insbesondere von kleinen Holzproben, vorzüglich geeignet. Zur Bestimmung der Raumdichte kann das Frischvolumen ohne weiteres durch Tauchung wassergesättigter Proben in Wasser ermittelt werden. Zur Bestimmung der Darrdichte müssen bei der Ermittlung des Darrvolumens Schritte untersnommen werden, die die Proben bei der Tauchung vor einer Gewichts- und Volumenzunahme durch Aufnahme von Tauchflüssigkeit schützen. Hier bestehen die folgenden Möglichkeiten: 1. Tauchung gestätrigter Proben in einer nicht quellend wirkenden Flüssigkeit. Als Tauchflüssigkeit werden dabei Petroleum oder Dekalin verwendet. 2. Tauchung der Proben in Wasser, nachdem sie mit einem wasserabweisenden Schutzüberzug versehen wurden. Als Schutzüberzug wurden bislang meist Öl oder Paraffin verwandt. Es wird ein Verfahren beschrieben, bei dem eine Schutzhülle aus Celloidin verwendet wurde. Es zeichnet sich durch geringen Aufwand und große Genauigkeit aus. Probemessungen an 60 Ahornholzproben von 0,2 bis 4,0 cm3 Größe ergaben nur geringfügige negative Abweichungen gegenüber den zum Vergleich stereometrisch ausgemessenen Volumina, die erfahrungsgemäß etwas zu hohe Werte ergeben.SummaryFor the determination of the density of wood samples, the hydrostatic method proved to be very reliable and precise. It is not dependent on shape, size, and surface condition of the specimens and can be carried through quickly with relatively simple means. Based on these characteristics, the method is excellently suited for the combined determination of weight and volume, particularly of small wood specimens. For the determination of density, the fresh volume can be found out by the immersion of water-saturated samples into water. For the determination of oven-dry density when sscertaining the oven-dry volume, steps have to be taken in order to protect the immersed samples against an increase in weight and volume by the absorption of the soaking-liquid. Here, the following possibilities exist: 1. Immersion of saturated samples in a liquid with a non-swelling effect. For this purpose, kerosene or decalin were used as soaking-liquid. 2. Immersion, of samples provided with a water-repellent protective coat in water. So far, oil or paraffin were used as protective coats. A method is described with which a protective coat of celloidin was employed. It is marked for its small consumption and great aceuracy. Test measurements on 60 maple specimens of 0,2 cm3…4,0 cm3 showed only insignificant negative deviations as against the volume stereometrically measured in comparison which, by experience, bring somewhat too high values.