African Journals Online
Southern African Forestry Journal

Issue 198, July 2003
ABSTRACTS

Genotype by environment interaction for volume growth at 6 years of age in a series of five Pinus patula progeny trials in southern Africa: scientific paper

Kanzler, Arnulf; Hagedorn, Sieg F.; Hodge, Gary R.; Dvorak, William S.

Abstract: Genotype x environment interaction was investigated in a series of 5 Pinus patula progeny trials planted by the Institute for Commercial Forestry Research in southern Africa. The trials were established from Mpumalanga to the North-eastern Cape in a balanced 7x7 lattice design with 48 common treatments that comprised 45 unrelated, open-pollinated families and 3 genetic checks. The environments sampled represented a range of climatic and site quality gradients. All trees were assessed for height and diameter at 6 years of age. Survival was 87% and ranged from 83 to 92% across the 5 sites. Growth on the 5 sites varied from 0,034m³ to 0,065m³ / tree and single site heritability estimates ranged from 0,17 to 0,43. The interactions between site and treatment were highly significant. The overall GxE variance represented approximately 21% of the variance due to treatment. Estimated Type B genetic correlations averaged 0,76 for all pairs of sites with a range of 0,4 to 1,0 and were correlated with median rainfall during the spring period from September to November. The joint regression method was utilised to determine the stability of genotypes across sites. Some rank changes were detected across the 5 locations but these were limited to 15% of the families tested. Results indicate that GxE may be important for Pinus patula within southern Africa and that some form of regionalisation may be possible using some simple environmental variables such as rainfall.

Key words: Pinus patula, Genotype x environment interaction, Type B genetic correlations, Regression analysis, South Africa

The relationship between torsional rigidity and bending strength characteristics of SA pine: scientific paper

Burdzik, W.M.G.; Nkwera, P.D.

Abstract: The modulus of rigidity, G, and bending moment of elasticity, MOE, of SA pine are evaluated from a direct torsion test and bending tests. Specimens were subjected to a series of tests with the view to determining direct torsional rigidity, apparent bending modulus of elasticity and pure bending modulus of elasticity. Torsional rigidity and bending modulus of elasticity results from central point and third point loading are compared. Often timber is used as structural bending elements that are subjected to torsional and horizontal shear, the influence of which is in many cases neglected. The modulus of rigidity is especially important when calculating the lateral-torsional buckling resistance of bending members and when members are subjected to torsional loads. This study was based on a series of laboratory experiments on actual sized timber with the focus and emphasis on mechanical properties and statistical significance.

Key words: Modulus of rigidity, Torsion, Shear, Bending modulus of elasticity

Site and stand analysis for growth prediction of Eucalyptus grandis on the Zululand coastal plain: scientific paper

Du Plessis, M.; Zwolinski, J.

Abstract: The integration of site information with that of tree growth is of special importance in Zululand, where sustainable supply of timber is essential for local processing and export commitments. Site prediction growth models need to be based on easily attainable input variables that are suitable for operational implementation by planners and for deployment of advanced silvicultural technology. Recently concluded growth studies based on permanent sampling plots established across Eucalyptus grandis plantations yielded useful information for revising the current knowledge on site-growth relationships in the region. The Chapman-Richards model was used to define the height growth curves over a range of sites. Standspecific site indices were calculated for trees of five years of age and regressed against a range of site variables. The multiple regression analysis showed that a large portion of the variation (r²=0, 63) in the site index could be explained by topsoil organic carbon and clay content in the subsoil. The soil data in the routine survey format and modelled climatic data in a grid pattern did not contribute significantly to the models. It is clear that the variables capturing the nutrient status of the soil and the soil's ability to store and make water available to the trees are the most important ones on the Zululand coastal plain when site prediction growth modelling is performed. Future research on site productivity modelling should include site variables specifically designed for that purpose and should further be enhanced with studies including their influence on wood quality.

Key words: Eucalyptus grandis, Site quality prediction model, Site index, Organic carbon content, Clay content

Reverting urban exotic pine forests to Macchia and indigenous forest vegetation, using cable-yarders on the slopes of Table Mountain, South Africa: management paper

Ackerman, Pierre; Talbot, Bruce

Abstract: This paper discusses some of the issues faced during the initial phases of a 12-year long project, which will ultimately result in the transformation of 53 ha of urban pine forests to a more diverse natural vegetation cover. Public sentiment, harvesting procedures and future management practices are addressed. The forests are currently managed for recreation and are a heavily utilised public amenity. Efforts have been made at every opportunity, to minimise disturbances to the recreational and biological capacity of the forest area. Public participation was encouraged at all stages, from a local to a national level. Harvesting operations were planned to make the transition from high open pine forest to mixed scrub Macchia and moist indigenous high forest as gradual, though complete, as possible within the given time frame. An aerial cable extraction system with a fixed skyline was applied in extracting the timber to minimise site impacts. Successful marketing of the timber together with the application of industrial harvesting technology meant that the project could be self-financing, which was an important prerequisite. Both public and vegetational response has been encouraging, and the inevitable, unforeseen problems and compromises, that have had to be met since project inception have been dealt with in an open and constructive participatory forum.

Key words: Strip-cutting, Cable yarding, Participatory planning, Shelterwood, Urban forests

Socio-economic impact of ox skidding project to the surrounding villages of Mount Meru forest plantations, Northern Tanzania: management paper

Abeli, W.S.; Maximillian, J.R.; Kweka, A.E.; Shemwetta, D.T.K.

Abstract: The ox skidding project was initiated with the objective of using oxen for transporting logs from the stump sites to the landings. It was supposed to be a participatory research project aimed at integrating scientific knowledge with practical skills and resource base of the local farmers. Specifically the main objective of the project was to encourage local farmers (villagers) to use their animals to skid logs in the surrounding forest plantations in order to improve their incomes and create employment opportunities to the surrounding communities especially the youth. A socio-economic survey was carried out after 6 years to assess the impact of the project to the ox owners who have been participating in the project, the ox handlers, the surrounding villages and the forest plantations. Data was collected through administering semistructured questionnaires to ox owners, village leaders, ox handlers and the management of the forest plantations. Results indicate that the ox skidding project has been a reliable and valuable source of income besides offering employment to young people with only limited education. The project has improved the household income, life style and standard of living of some farmers and above all, changed the local peoples' attitudes towards the importance of the surrounding forest resources. Most of the local people feel that they are now part of the surrounding forests as they participate to some extent in the management and protection of these forest resources. The project has in addition created awareness among the community that oxen can also be used in forest operations besides undertaking agricultural activities. The project found that given the operating conditions of the skidding tractors in this area, ox skidding was more reliable and more cost effective than the tractor skidding system. Through this project, it has been possible to improve the working relationships between the surrounding villages and forest plantations management. The project has also led to some of the surrounding villages establishing village environmental committees, which work very closely with forest plantation management. The sustainability of the ox skidding system introduced in this area is likely to continue since farmers surrounding these plantations keep cattle and there are not many alternative job opportunities for the young people.

Key words: Ox skidding logging system, Ox handlers, Ox owners, Environmentally sound harvesting system, Tractor skidding system

The wood quality of the South African timber resource for high-value solid wood products and its role in sustainable forestry: review paper

Malan, F.S.

Abstract: Maximising volume growth and yield per unit area is generally recognised as an important objective towards maintaining or enhancing forest productivity. However, the forest industry's future success will also be judged on how well it understands the qualities of the timber supply, how successful it is with the implementation of appropriate wood quality improvement strategies and how willing it is to introduce new species and hybrids which are unique and different from the other commercial species grown locally. It will also depend on how well the wood product processing industry can relate knowledge of the market for manufactured wood products to resource characteristics. These are important elements of sustainable wood production, required to optimise conversion efficiency and effective utilisation into products which meet international standards with regards to predictability and performance characteristics. These should be seen as major challenges, considering the continuous changes in the qualities of the timber supply combined with the rapidly increasing demands for wood products in terms of quality and diversity. This paper discusses the existing resource characteristics, qualities that still need to be improved and the importance of having a proper understanding of the characteristics of the raw material supply for solid wood products and their impact on end-product quality and value.

Key words: Wood quality, Solid wood products, Forest productivity, Tree breeding, Silviculture, Modelling

Effect of planting depth on growth of open-rooted Pinus elliottii and Pinus taeda seedlings in the United States: review paper

VanderSchaaf, Curtis L.; South, David B.

Abstract: Three studies in the Coastal Plain of Georgia were remeasured 7 or 8 years after planting to determine the effects of planting depth on field performance of open-rooted seedlings [root-collar diameter (RCD) ≥ 5 mm]. Average planting depth (i.e. shoot height before planting minus shoot height above ground after planting) for machine planted P. elliottii was 14 cm while hand-planted P. taeda seedlings averaged 9-11 cm deep. P. taeda showed no adverse effects on growth when planting seedlings up to 15 cm deep. Data for machine planted P. elliottii indicated that seedlings were planted 9 mm deeper on double-beds than on single-beds. Small-diameter pine seedlings (< 5 mm RCD) were not planted as deeply as seedlings with large diameters (RCD > 5 mm). For P. elliottii planted on double-beds, seedlings planted more than 15 cm deep had slightly smaller diameters at breast height than seedlings planted 10 cm deep. Although most tree planting guides recommend planting seedlings 7, 5 cm deep or less, many company plantations have been established by planting at greater depths.

Key words: Pinus elliottii, Pinus taeda, Survival, Seedling quality, Planting quality, Reforestation

The economic value of Acacia karroo in small-scale farming systems and game farming in northern KwaZulu-Natal, South Africa: research note

Mkhabela, T.S.

Abstract: The purpose of the investigation was to examine current knowledge, by local people, of the agroforestry roles and the economic importance that the Acacia karroo tree plays in the farming systems of small-scale farmers and game farming in the Dundee district in the KwaZulu-Natal Province. Interviews were conducted in 111 selected households and game farms using a rapid appraisal approach. Results showed that the entire sample population was aware of the beneficial roles played by Acacia karroo in the agro-ecosystem and had a least one tree in their homestead, field and / or grazing land. The roles identified by the respondents were: providing shelter to people and animals (98%), fodder for game and livestock (96%), fuel (93%), indicator of "sweet veld" good soils and good grazing (87%), controlling soil erosion (71%), indicator of water in arid areas (37%), maintaining soil fertility and productivity (36%), dependence of certain butterfly larvae species and birds that feed on these larva (8%) and the use of wood ash to ameliorate soil acidity (4%). Despite the benefits of A. karroo on farms and nature reserves being well appreciated, the deliberate utilisation of this tree for agroforestry purposes is minimal. Due to the prevailing soil acidity problems and extensive land degradation, it is suggested that the tree has potential in agroforestry to change and improve the sustainability and profitability of both agriculture and ecotourism through game farming in the area. It is also acknowledged that for any land use to expand in a sustainable manner, appropriate research and development is imperative. Some suggestions are made on future research.

Key words: Acacia karroo, Economic, Small-scale farming systems, Game farming, Sustainability

Ploidy determination of black wattle (Acacia mearnsii) using stomatal chloroplast counts: research note

Beck, Sascha L.; Fossey, Annabel; Mathura, Sadhna

Abstract: The arrangements of chloroplasts and numbers within the stoma were examined as a rapid indirect technique for the identification of ploidy level in black wattle (Acacia mearnsii de Wild). Chloroplast counts were made from stomatal guard cells from leaves of known diploid (2n=2x=26) and tetraploid (2n=4x=52) plants grown under nursery conditions. Three-month-old plant material was used and five plants were chosen at random across six lines (3 diploids, 3 tetraploids). For diploids the mean number of chloroplasts per stoma was 9, 89 ± 0, 170 and 22, 75 ± 0, 170 for tetraploids. Chloroplasts in diploid guard cells were polarized into the corners, while evenly distributed in the tetraploids. These differences noted between the ploidy levels were significant (P<0, 01). The analysis of stomatal chloroplast number and arrangement have proven to be an accurate indirect technique to distinguish between diploid and tetraploid black wattle.

Key words: Black wattle, Chloroplasts, Ploidy, Stoma