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- Volume 2005, Issue 205, 2005
Southern African Forestry Journal - Volume 2005, Issue 205, 2005
Volume 2005, Issue 205, 2005
Author Dennis OwenSource: Southern African Forestry Journal 2005 (2005)More Less
Extracted from text ... Southern African Forestry Journal - No. 205, November 2005 1 Editorial Comment New-look Southern African Forestry Journal - Progress We in forestry are living in challenging times and the pressures of day to day activities press heavily on the shoulders of our forestry practioners. It is these pressures that are one of the reasons that this edition does not have a Guest Editorial During the past few weeks I have seen several articles addressing the matter of pressures (Dyer, 2005 ; Manley, 2005 ; Southem, 2005). Quite correctly the authors address this subject with a positive approach and I quote ..
Post establishment survival of Pinus patula in Mpumalanga, one year after planting : scientific paperAuthor J.W. CrousSource: Southern African Forestry Journal 2005, pp 3 –11 (2005)More Less
Recent evidence indicated that the pathogen <I>Fusarium circinatum</I> might be contributing significantly to post-planting mortality. Consequently, sixteen experimental sample plots, widely distributed over many localities in Mpumalanga, were established over two growing seasons to quantify the extent of pest and pathogen related in-field mortality. Survival in all treatments was extremely low. There was large variation in response to treatments and survival in the different trials. A single application of fungicide at planting improved survival by 13% on average, while a single application of fungicide and insecticide at planting improved survival by 29% on average. Most of the mortality occurred between 30 and 140 days after planting. Visual inspection of the dead plants indicated that White grubs and <I>Hylastes angustatus</I> caused most of the insect-related mortality. Pathogen isolation from a sub-sample of dying plants indicated that 49% of dying plants were pathogen-free, while <I> F. circinatum</I> was the prevailing fungus, isolated from 42% of the dying plants. It is estimated (95% confidence level) that <I>F. circinatum</I> was responsible for an 18.5% to 31.5% decline in survival in the monitored compartments, planted between November 2002 and March 2004 in Mpumalanga.
Shoot morphology and site climate affect re-establishment success of Pinus patula in South Africa : scientific paperSource: Southern African Forestry Journal 2005, pp 13 –20 (2005)More Less
Operational experience has indicated that <I> Pinus patula</I> generally survives poorly on sub-optimal growing sites in South Africa, particularly when planted as cuttings. This observation will become increasingly important as softwood species of genetically selected stock are deployed as cuttings in preference to seedlings of lower genetic value. Methods to improve survival of this species are yet to be fully defined. Production of <I>P. patula</I> seedlings is currently based on broad prescriptions, which commonly include raising containerised stock for 5 to 7 months in the nursery and limiting planting to the early and late summer months. Little research has been conducted on determining optimal plant dimensions at planting or defining sites that are of high or low planting risk. This paper describes some effects of site climate and shoot morphology on post-planting survival and is the first to provide suggested guideline dimensions for <I>P. patula</I> cutting and seedling nursery stock raised in containers, 80 - 90 ml in volume. Further work is required to establish the validity of these dimensions.
An assessment of factors affecting early survival and growth of Pinus patula and Pinus elliottii in the summer rainfall region of southern Africa : scientific paperSource: Southern African Forestry Journal 2005, pp 21 –30 (2005)More Less
High initial mortality of pine seedlings planted in commercial timber plantations in the summer rainfall region of southern Africa has motivated research into possible causes. The objectives of this study were to assess whether survival and initial growth of <I>Pinus patula</I> and <I>Pinus elliottii</I> were related to site physiography, distribution of harvest residues and / or seedling size at planting. The study was carried out at three sites, situated in Mpumalanga, South Africa (1 trial), and Usutu, Swaziland (2 trials). Assessments of slope steepness, aspect, potential for water movement and harvest residue levels were made at three months after planting on 40-60 plots at each of the three trials. Survival, height and groundline diameter of the seedlings were also assessed at 1.5 months, 12 months, 18 months and 24 months after planting. Linear correlation, t-tests and analyses of variance were used to determine whether functional relationships existed between harvest residue levels, site physiography, seedling size, survival and growth. The outstanding results from this study were that neither site physiography nor harvest residues were found to be predictors of early survival, or growth, of <I>P. patula</I> and <I>P. elliottii</I>. The overall poor survival of <I>P. patula</I> in contrast to <I>P. elliottii</I>, despite similar exposure to stress inducing factors, highlighted the sensitivity of this species. One of the most interesting outcomes of this study was the indication of a positive relationship between initial seedling height and subsequent growth. While the results presented here cannot provide sound evidence for the strength of this relationship, the effect of seedling height (and more importantly size) at planting (and the causes there-of) and subsequent growth requires further investigation.
The effect of planting density on the wood quality of South African-grown Eucalyptus grandis : scientific paperAuthor F.S. MalanSource: Southern African Forestry Journal 2005, pp 31 –37 (2005)More Less
This paper presents the results of a wood property and sawn board quality study performed on disc samples and sawlogs taken from a 23-year-old <I>Eucalyptus grandis</I> Nelder 1a spacing trial at J.D.M. Keet plantation near Tzaneen. Ten trees from each of four markedly different planting densities were chosen to provide contrasting material to study the effects of growth rate on the quality of the wood produced. Spacing treatment diameter means ranged from 18.9 to 57.9 cm. <BR>An inverse relationship was found between planting density and wood density. Typical pith-to-bark density profiles for trees at this age occurred in the trees with rapid growth, i.e. steep gradients from the pith towards the bark during the early stages of growth, followed by a gradual transition into more constant mature wood density values. Trees of which the growth had been curbed by higher planting densities, on the other hand, showed little sign of levelling off. As a result, the faster growing trees contained significantly larger proportions of relatively homogeneous wood compared to the slower grown trees, giving them an obvious quality advantage over slower grown trees. Accelerated growth thus seems to yield trees that can be utilized more effectively and converted into products with more reliable performance characteristics. <BR>Fast growth seemed to promote interlocking grain, but the correlation with interlocking grain severity was too poor to be of any practical significance. Mean splitting showed a downward trend with decreasing planting density, but statistically the differences were non-significant. A statistically significant correlation was found between the amount of splitting in logs and the proportional length of sawn boards affected by splits immediately after wet-mill processing. At the end of the sawmilling process, however, such correlation did not exist any longer, suggesting that the boards responded differently to drying stresses and impacts during handling and transport with regard to further splitting. No significant effect of planting density on sawn volume losses due to splitting or collapse could be detected.
Author Maria J. DiamantopoulouSource: Southern African Forestry Journal 2005, pp 39 –44 (2005)More Less
The financial exploitation of forests constitutes an important part of human activity. This effort is being made in order to conserve the sustainable exploitation while avoiding the degradation of the environment. One of the most important operations in forest mensuration is the estimation of the volume of sample trees. Such estimation may be used in order to conduct a large stand inventory, construct volume tables, develop tree competition and growth models, predict tree mortality from diameter growth, and implement a number of other activities. Efficiency, the trade-off between cost and precision, is of paramount importance in the estimation of volume. <BR>The aim of this paper is to examine the applicability of Artificial Neural Network models (ANNs), in the prediction of fir trees stem over bark diameters at 5.3, 9.3, 13.3, 17.3, 21.3, 25.3, 29.3 and 33.3 meters above ground. The values of these diameters are necessary for an efficient estimation of a single tree volume using the well-known Smalian's sectional method. The system proposed in this paper can be applied in forest inventory making an accurate estimate of the volume of a sample tree based on only two diameter measurements (stump diameter, <I>d</I><SUB>0.3</SUB> and diameter at breast height, <I>d</I><SUB>1.3</SUB>) and an estimate of the total tree height <I>(h)</I>. Training of the ANNs was achieved through the cascade correlation algorithm, which is a feed-forward and supervised algorithm. Kalman's learning rule was used to modify the artificial neural networks weights. These networks are designed by putting weights between neurons, through the use of the hyperbolic-tangent function of training. The estimation system proposed is capable of replacing many standard forestry mensuration procedures due to its efficiency and accuracy. The neural network models were found to be appropriate and accurate for the prediction of all diameters.