Vorläufige Ergebnisse eines Pappel-Durchforstungs-Versuches in Südafrika
The present article deals with the response ofP. deltoides to thinning. In 1965 an experiment was laid out in an 8-year old poplar plantation, site class, 0.5 in the mist belt of Natal. The S% defined as the ratio mean distance between the trees mean height of the stand = 100 was used to express stand density and to characterize the degree of thinning. Three thinning degrees, designated as A, B and C, with an S% of 24,31 and 36 respectively, were tested in a completely randomized design wth four replications. The plot areas were 0.144 hectare and each plot was surrounded by a 5.4 m. wide buffer zone. In 1965, immediately after the thinning of the plots, the mean basal areas per hectare of the A, B and C plots were: A: 23.0 m2(= 100) B: 15.5 m2(= 66) C: 11.3 (= 49) The relationship between basal area at the beginning of the growing season and the basal area increment during the first growing season was expressed by the equation: basal area increment (m2/hect./annum) = -10.417+21.9258 (log basal area) - 8.3256 (log basal area)2 the multiple correlation coefficient being equal to 0.860. During the second growing season there was a weakly significant negative correlation between basal area and basal area increment. During the third year stand density and growth were not related. An analysis of the relationship between periodic current volume growth during the 3-year growth period and the mean stand density during this period, the latter defined as the average of the stand densities at the beginning and end of the period, revealed that basal area is more suitable to express stand density than S%. In the regression analysis, the residual variation with S% as explanatory variable was 8.3% of the total variation, as against 2.0% with mean basal area as explanatory variable. There was a linear relationship between basal area and periodic current volume increment. For a mean basal area during the growth period of 28.0 m2 per hectare, the annual volume increment was 49 m3, for a basal area of 14 m2, it was 35.5% below this maximum. During the third growing season the A-plots reached the “natural stocking density”, defined as the maximum basal area which the stand can carry on a certain site and at a given age. In the financial calculations, the indicating per cent was defined as: $$w = 100 \cdot \left[ {\sqrt[n]{{\frac{{2(A_{x + n} - A_x ) - n(O \cdot op)V}}{{Hk_x + Hk_{x + n} + 2B}} + 1 - 1}}} \right]$$ where: Ax, Ax+n = net-value of the stand at x, x+n years n = length of period in years V = capitalized annual general cost Hkx, Hkx+n = cost value of stand at x, x+n years B = market value of land p = rate of interest. The indicating per cent as calculated for each of the 12 plots and the following equation fitted: Ind.% = -2.25 + 1.967 (mean basal area) - 0.04498 (mean basal area)2 The optimum basal area therefore was 22 m2 per hectare, i.e. 71-73% of the natural stocking density.
Über Brauchbarkeit des Verfahrens von HART-BECKING zum Festlegen der Durchforstungsstärke
Auf der Arbeitstagung der „Sektion Ertragskunde“ im Mai 1959 wurde u. a. über die Methodki künftiger Durchforstungsversuche beraten und in diesem Zusammenhange auch das Verfahren vonHart-Becking als mögliches Verfahren zum Kennzeichnen der Durchforstungsstärke in zwei Referaten behandelt. Da ein allgemeines Interesse für diese Fragestellung vermutet wird, soll das Referat des Verfassers nachstehend veröffentlicht werden.
Measurement and Demonstration of Thermal Expansion Coefficient
There are many classroom demonstrations, such as the ball-and-ring experiment, for showing the existence of thermal expansion of solids. The coefficient of linear expansion α (= increase in length divided by the original length times the change in temperature) may be measured in high school laboratories using a number of methods.1–4 In this paper we describe an especially simple experiment for determining α for a metal rod. It is based on the well-known optical lever method and is suitable for either a laboratory experiment or a classroom exercise.