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.
Nadelbiomasse, Zuwachs und Zuwachsverteilung von Pinus radiata in Südafrika unter dem Einfluß von Durchforstung und Astung
Die vorliegende Untersuchung soll einen Beitrag zur quantitativen Erfassung der Zuwachsreaktion auf Umwelt und Waldbehandlung an Hand fortentwickelter Arbeitsverfahren der Waldwachstumskunde liefern. Untersuchungsziel im engeren Sinne war eine Erfassung und statistische Prüfung der Wirkung von Durchforstung und Astung auf den Zuwachs von P. radiata-Versuchsflächen in Südafrika sowie eine Schätzung des Einflusses des Zeitfaktors auf diese Abhängigkeitsbeziehung. Die erzielten Arbeitsergebnisse bieten der neuzeitlichen Waldbautechnik erweiterte und verbesserte Grundlagen für die Beurteilung forstlicher Produktionsmöglichkeiten. Weiter wurde versucht, die Wachstumsvorgänge innerhalb des Baumkörpers und deren Beziehungen zur Blattbiomasse sowie die Korrelation zwischen Baumkrone und Zuwachs, die Wechselbeziehungen zwischen den Bäumen innerhalb von Biogruppen und die Abhängigkeit des Zuwachses von meteorologischen Faktoren zu erforschen und darzustellen. Die Untersuchungen wurden in einem integrierten Forschungsprojekt, gestützt auf biometrisch begründete Versuche und Auswertungsmethoden, durchgeführt. In 1963, a thinning-pruning experiment was established in a 10-year old P. radiata stand in the South-Western Cape Province of South Africa. Tables 1 and 3 give the basal area- and volume increment for the nine combinations of stand density and severity of pruning, which were tested in the experiment. The experiment also revealed a depressing effect of pruning on height growth. Stem analysis indicated that pruning induces a more cylindical stem form. This effect, however, is most pronounced during the first year after pruning. A thinning experiment, which was established in 1964 in a 10-year old stand on the slopes of Table Mountain, showed a curvilinear response for the period 1964–1971 (Eq. 7 and 8). The needle-biomass of 76 sample trees, which were felled in the plots of the thinning-pruning experiment, was estimated by sampling. Table 6 gives the relationship between tree needle weight and volume growth. The needle weight distribution within the live crown was related to basal area growth at four positions within the crown. It indicated a productivity gradient of the needles which could not be explained merely from a vertical gradient in photosynthetic efficiency. The conclusion is, that the growth distribution within the stem is necessarily controlled by internal factors, in addition to needle weight distribution patterns. An experiment, to study short-term responses to pruning, showed that daily fluctuations of the stem diameter were reduced from the first day, daily growth from the fifth day after pruning. Studies of the relationship between climate and ring width showed that September rainfall is negatively, March rainfall positively correlated with ring width. The daily growth of nine trees was recorded with dendographs and subsequently related to environmental factors (Eq. 26 and 27).
Experience of using rating scales for the assessment of vocational trainees in general practice.
For two years trainers in the northern half of the south western region have been asked to assess their trainees with a condensed version of the new Manchester rating scales for vocational training in general practice and to send copies to the regional adviser. The condensed version retains the 23 scales but does not include the subscales. Trainers' workshops and comments from individuals suggested that no radical improvements to the scales were required and that they were an adequate statement of what was required from trainees. The response rate of 89% for returning at least one assessment and 38% for returning all three suggested that use of this condensed version would be more feasible than using the full version of the scales. Analysis of 86 first assessments and 48 sets of three assessments showed a range of variation both in trainee ratings and use of individual scales that was consistent with expectations. A lack of significant rank correlations between the scales indicated that each of the scales measured a different characteristic of behaviour. We suggest that the most useful way to achieve systematic assessment of vocational trainees is by the use of the 23 main rating scales, with regional variations where appropriate.