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 m 3 ha −1 for 1000 and 2000 trees ha −1 to 1800 m 3  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.
SOME FACTORS AFFECTING WOOD DENSITY IN PINE STEMS
SUMMARY This paper was presented to the Fifth British Empire Forestry Conference in London, 1947, and is reprinted here with the kind permission of the Director of Forestry. Average data accumulated chiefly from dissection of from twenty to thirty stems from each of five different sites are used in an attempt to show that variations in wood density in pine stems, hitherto regarded as fortuitous, are actually systematic. Analysis of the data shows that whereas aggregate wood density, or the mean density across entire transverse sections, is in normal circumstances in direct correlation with rate of growth, that of wood formed many particular year is directly proportionate to a function of age. The influence on density of aspect, of edaphic factors, with special reference to moisture, and of seed selection, is also briefly discussed; and a method of research based on the density/age relationship for use in further attempts at isolation of environmental determinants, suggested.