A. van Laar

Interrelationships between Vegetation and Site Characteristics in the Gouna Forest

SUMMARY Sampling studies in the Gouna Forest indicated that the density of tree regeneration, density and height of onderbos—Trichocladus crinitus—and basal area/ha of different tree species groups are significantly different for different aspects. The height and density of onderbos, density of regeneration, basal area of tree species groups, density of individual tree species, density of ground flora species, slope, radiation index and canopy height are all interrelated. A table is presented giving the relative frequency, density and density per cent of different tree species.

The Effect of Initial Spacing on Some Growth Parameters of Eucalyptus grandis

ABSTRACT The relationship between the growth rate of Eucalyptus grandis and initial spacing was studied in a replicated spacing trial correlated Curve Trends (CCT) on the coastal plain of Zululand. The parameters of the Richard~ growth equation, applied to live basal area, were regressed on nominal stand density, An asymptotic regression was fitted to the observed mean diameters, the estimated parameters of which were subsequently regressed on Nnom An analysis of height growth revealed that mean height as well as top height are related to stems per hectare. Measurements of crown width and crown length served to evaluate the effect of stand density on crown parameters.

The Response of Pinus radiata to Initial Spacing

SYNOPSIS This paper deals with the statistical analysis of growth data, obtained from the C.C.T. spacing trial at Tokai in Pinus radiata. The Chapman-Richards growth model was used to fit equations with live basal area as predicted variable. The estimated parameters were subsequently regressed on nominal stems per hectare. A linear regression with log age as predictor variable was used to obtain estimates for mean diameter at different ages. The coefficients of this equation were also regressed on nominal stand stems per hectare. A regression equation with stems per hectare and mean height as independent variables was used to estimate top height, which was subsequently regressed on age. A regression analysis with nominal stems per hectare as independent and coefficients of the top height-age regression as dependent variables revealed a maximum top height in stands of medium stand density. The growth curves for u.b. volume were derived from the corresponding basal area growth curves. An analysis of the obs...

THE INFLUENCE OF ENVIRONMENTAL FACTORS ON THE RADIAL GROWTH OF PINUS RADIATA

SUMMARY 1. The daily growth of Pinus radiata in a 22-year-old stand at Jonkershoek between April 1964 and April 1965 was determined with 10 Fritts dendrographs. Multiple regression analyses were used to evaluate the influences of environmental factors. 2. The diurnal fluctuations of the stem diameter were highly significantly correlated to atmospheric water deficits. In addition to the difference between potential evapotranspiration and precipitation during the current 5-day period, diurnal fluctuations were also related to water deficit or surplus during previous 5-day periods. Diurnal fluctuations expressed satisfactorily the occurrence and magnitude of water stresses in the tree 3. Diurnal fluctuations on the south-eastern side of the trees were significantly greater than on the north-western side and reached a minimum near the base of the tree. 4. The apparent growth incorporates reversible changes and true growth. During the winter the apparent daily growth was directly and significantly related to p...

Equations for predicting the biomass of Acacia cyclops and Acacia saligna in the western and eastern Cape regions of South Africa: Part 2: stand-level models: scientific paper

Synopsis A forest inventory was carried out in coastal areas infested by the alien tree species Acacia cyclops and A. saligna on the West Coast, Agulhas and Eastern Cape Plains. Sample trees were felled to construct prediction equations, which were subsequently used to obtain regression estimates of wood mass for knee height diameter classes below 2.5 em, between 2.5 and 5.0 em and above 5.0 em respectively. Various regression models were tested. The single biomass component was regressed on log-transformed diameter, log-transformed commercial stem length and log-transformed biomass. The results were compared with a 10-parameter equation, which used the linear and quadratic term of diameter at knee height (DKH), and commercial stem length as well as four interaction variables as predictors. For practical reasons, it was recommended to use basal area and squared basal area as predictors and to ignore commercial stem length as independent variable. This produced a tariff-type estimator for biomass components. In addition, equations were developed to estimate leaf biomass from DKH and to evaluate the relationship between leafbiomass and wood biomass

Influence of tree parameters and stand density on diameter growth of Pinus radiata

SUMMARY This study deals with the growth distribution within the annual ring and with the influence of tree characteristics and stand density on diameter growth in two stands of P. radiata. An analysis of crown dimensions showed a curvilinear increase of crown length with DBH, a linear relationship between crown width and DBH and a slight decrease of the height above ground of the crown base with increasing DBH. The relative position of the point of the greatest crown width was not related to DBH. The South-Eastern winds, prevailing during summer, cause crown deformations. The smallest crown radius occurs on the South-Eastern and the largest radius on the North-Western side of the trees. Within the tree, diameter growth is directly related to crown radius, but for the same crown radius, the growth on the North-Western side of the stem exceeds that on the South-Eastern side. This might be explained in terms of a reduced photosynthetic output per unit leaf surface on the windward side or alternatively in te...

Yield potential of selected Eucalyptus genetic stock on the sandy soils of the South African Cape West Coast

Synopsis Land available for afforestation in the Western Cape Region has largely been subordinate to agriculture. Eucalypt species have never been tested intensively along the West Coast. Climatic matching suggests planting of species from West Australia as native habitat introductions, or from seed sources in the Mediterranean region where eucalypt species have been tried successfully, such as Morocco and Israel. Promising growth of eucalypt hybrids on marginal sites in the summer rainfall areas of South Africa prompted the inclusion oflocal as well as some hybrid seedlots obtained from Morocco. The terrain of the trial site is an almost flat old dune area (slopes < 3%)with a westerly aspect and 7 km from the sea. The mean annual rainfall is about 400 mm, with most rain falling during winter. The other months are usuallywindy and dry, and the summermonths are hot (maximum tern perature > 35°C). The sandy soils have a coarse texture within the normal rooting depth. During winter water tables were observed on all soils within 2-3 m from the soil surface. The trial was planted during the winter of 1991. It consisted often local hybrid families of different species involving Eucalyptus grandis, 14 E. camaldulensis seedlots from Australia, Morocco and Israel, 7 hybrid lots from Morocco, 4 E. grandis ex Morocco and 11 other species including E. gomphocephala and E. cladocalyx. The results indicate the potential for correct species/provenance selection. Potential yields of 8 to 10 m3/annum/ha are predicted on the assumption that goodgenetic stock and correct silvicultural procedures are used. Most notable was the expected performance of the well known West Australian species (E. gomphocephala, E. cladocalyx). The group of 14 E. camaldulensis seedlots can be regarded as representing a series of provenances from Australia, except for three from Israel and one from Morocco. As expected, the different provenances survived well but performed variably, generally ranking in the bottom 50 %. However, two seedlots - the provenance from Lake Albacutya and the seedlot from Morocco - are worth noting as they actually ranked among the top ten for index score. Generally, the provenances from Queensland (e.g. Petford) and New South Wales that normally do well in summer rainfall regions did not do well. As the relevant parent species originate in summer rainfall regions, the phenomenal growth rate of many of the hybrid families came as a surprise in this trial. The yield of the best E. grandis x E. camaldulensis (GXC) family would have been equivalent to that of E. gomphocephala if the survival was equally good. The E. grandis x E. tereticornis (GXT)family did survive and performed equally well. The second best GXCfamily would have yielded even better than the GXT if it had a better survival. The GXC and GXT families were all within the top 50 % ofthe trial.

Sampling For Above-Ground Biomass ForPinus radiataIn The Bosboukloof Catchment At Jonkershoek

SYNOPSIS A sampling trial for the estimation of the above biomass was undertaken in the Bosboukloof catchment at Jonkershoek State Forest. Eighty-five trees were felled, after which the oven-dry weight of stem-wood, bark, branches and foliage was estimated by subsampling. The weight of stemwood and bark of each sample tree was obtained from a subsample within each tree, that of branchwood and foliage by the application of regression analysis to combined subsamples of branches.

A biomass study in Pinus radiata D. Don

Abstract This paper deals with a preliminary study of the aboveground biomass of Pinus radiata in the Jonkershoek State Forest. A sample of 25 twenty-nine year old trees was selected from comp. 35A. The oven-dry stem mass was estimated by subsampling each stem and regressing the estimated oven-dry mass on DBH (r = 0,9767). Similarly, a sample of branches, representing the range of branch diameters, was drawn, their oven-dry mass was determined and subsequently regressed on branch diameter (r = 0,9751). Branch mass per tree was estimated by sampling the distribution of branch diameters for each tree separately. A reliable estimate of crown mass (r = 0,8385) and total aerial mass (r = 0,9776) from DBH is also made. Total estimated above-ground biomass for the stand amounted to 184860 kg ha-1 , of which 89 per cent was stem wood and the remainder crown.

The growth of unthinned Pinus patula in relation to spacing

Abstract The present article deals with the influence of planting espacement on the rate of growth of Pinus patula in the spacing trial Mac-Mac in the eastern Transvaal. The Richards growth equation was applied to express basal area- and volume production as a function of age. The estimates of the parameters of the equation were regressed on stand density, the objective being to produce two sets ofgrouitti curves, for live basal area and live volume respectively. In order to study the effect of spacing on stem form and branch characteristics by means of destructive sampling, 400 sample trees were felled. The stem form factor was determined for each tree separately, branch diameter, branch length and branch volume were measured in a subsample of branches of the first order. The statistical analysis discloses that initial spacing influences stem form and branch volume per tree significantly, but total branch volume per hectare was not related to initial density.