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- Volume 2002, Issue 196, 2002
Southern African Forestry Journal - Volume 2002, Issue 196, 2002
Volume 2002, Issue 196, 2002
The impact of the addition of Eucalyptus grandis wood chips on nitrogen availability in plantation soils : scientific paperSource: Southern African Forestry Journal 2002, pp 9 –14 (2002)More Less
The impact of plantation residues, as a result of clearfelling, on nutrient availability in plantation systems, as well as the difficulties during subsequent planting and harvesting, should be considered in the development of plantation management strategies. The aim of this experiment was to determine if the addition of stump wood chips would result in the immobilisation of nitrogen. Soil from two plantations, one of the Kranskop soil form (0,57% nitrogen) and one of the Hutton soil form (0,23% nitrogen), were analysed in a laboratory experiment for changes in nitrogen availability. Soils were amended with wood chips and varying amounts of nitrogen fertilizer. Inorganic nitrogen was measured after 14,60 and 90 days of aerobic incubation. Net mineralisation rates, regardless of treatment or soil, ranged between -24,98 and +2,53 <SPAN lang=AF style="FONT-FAMILY: Symbol; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN style="mso-char-type: symbol; mso-symbol-font: Symbol">m</SPAN></SPAN>g nitrogen / g soil / day, over the 3-month incubation period. Immobilisation of nitrogen was found to occur in those treatments that received the highest nitrogen additions. Addition of wood chips on their own did not alter the nitrogen availability patterns. However, it was observed that wood chips, together with high levels of additional nitrogen, resulted in an extended period of release of nitrogen in these plantation soils.
Weed composition in relation to site in re-established pine compartments on the Mpumalanga Escarpment, South Africa : scientific paperSource: Southern African Forestry Journal 2002, pp 15 –20 (2002)More Less
A survey of weed species distribution patterns and abundance in clearfelled pine compartments in the Mpumalanga escarpment region was undertaken to determine the relationship between weed species and cover abundance in relation to environmental and compartmental factors. In total 359 transects were sampled each with 5 X 25 m<sup>2</sup> quadrats (1 795 square quadrats in total). <br><I>Phytolacca octandra</I> and <I>Solanum mauritianum</I> were found to be the most widespread species in the study area and dominated most transects. Less common were <I>Pteridium</I> spp., <I>Bidens pillosa, Oplismenis hirtillus</I> and <I>Senecio tamoides</I>, but these species had high cover abundance ratings where they did occur and therefore may be considered as having a high potential to compete with the tree crop for resources. <br>The most important factor affecting vegetation cover abundance and species composition was altitude. Other factors which were important in determining weed distribution patterns were the length of time since clearfelling, aspect, the proximity of the stand to indigenous woody vegetation in ravines, local moisture conditions as affected by slope shape and type and position in the landscape with respect to river valley systems. <br>Eight weed groups were identified in the survey area using discriminant function analysis to link environmental variables to weed communities. Each weed group is characterised by differences in cover abundance and relative proportions of different weed types. The weed groups and their association with environmental variables are used as a predictive tool for developing weed control strategies and control measures in forest operations.
The effect of bottom heat on rooting Pinus patula and Pinus elliotti x Pinus caribaea stem cuttings in South Africa : scientific paperAuthor R.G. MitchellSource: Southern African Forestry Journal 2002, pp 21 –26 (2002)More Less
Five trials, testing the effect of bottom heat on rooting, were set between January 1995 and December 1996 on <I>P. patula</I> and <I>P. elliottii x P. caribaea</I> cuttings as a method of improving root strike. In four out of five trials rooting percentages improved with the addition of bottom heat at optimal temperatures and in all trials, where root dry mass was assessed, bottom heat had a positive influence on root dry mass irrespective of season. The increase in root dry mass ranged between 97 % and 166 %. In one trial, where cuttings were set in the warmest months of the year, rooting remained unchanged. Rooting declined for those treatments where average media temperatures were raised to extreme levels (>300 <sup>o</sup>C). Optimum media temperatures, during the period of root initiation, were found to range between 250 <sup>o</sup>C and 280 <sup>o</sup>C. Rooting media temperature was also found to influence the amount of stem decay and basal callusing. Future research should concentrate on the relationship between moisture and heat requirements during rooting.
A new approach to modelling streamflow reductions resulting from commercial afforestation in South Africa : scientific paperSource: Southern African Forestry Journal 2002, pp 27 –36 (2002)More Less
The Department of Water Affairs and Forestry has, for some time, needed a comprehensive tool to incorporate the impacts of commercial afforestation on water resources into water use authorisation and allocation processes. Simulation modelling on a national scale, using the <i>ACRU</i> model, was identified as one possible solution. However, in order to establish confidence in the national simulation results, it was necessary to first verify model output against reliable observed data from process studies and long-term catchment afforestation experiments. In the verification phase, long term reductions in streamflow resulting from afforestation were satisfactorily simulated for five research catchments. Some problems were experienced with catchments in the Western Cape, with verifications on shorter duration experiments and the simulation of specific evaporative processes. Modelling of low flows was less successful than for total flows. In the second phase (the generation of the national database), simulations were first performed for the dominant Acocks (1988) veld type (i.e. 0% afforestation) within 843 Quaternary Catchments exhibiting afforestation potential (to determine baseline streamflow), followed by simulations of streamflow after 100% afforestation with eucalyptus, pine and wattle respectively. The difference between the unafforested and afforested simulations equated to streamflow reduction caused by afforestation. <br>This culminated in the generation of maps and tables expressing reductions in streamflow per Quaternary Catchment, which represents a working solution for immediate application but may be improved upon with further work.
Stand stability in pines : an important silvicultural criterion for the evaluation of thinnings and the development of thinning regimes : management paperSource: Southern African Forestry Journal 2002, pp 37 –40 (2002)More Less
This article deals with the role played by the stability factor (SF) in the evaluation of thinnings in fastgrowing, even-aged pine stands. It also illustrates how the stability factor is influenced by thinnings and site over time. The SF is expressed as the ratio between breast height diameter in centimeters and tree height in meters. The minimum cut-off values used by SAFCOL are 0,85 for P. radiata and 1,15 for the other major commercial pines. Most of the data was collected in the late 70's and was lost during the many changes in the Department of Forestry and SAFCOL. <I>(See Editorial Comment on page 40)</I>
A framework for analyzing workforce dynamics in forest harvesting in South Africa : management paperSource: Southern African Forestry Journal 2002, pp 41 –48 (2002)More Less
People are the industry's most valuable asset. However, due to its dynamic nature, labour cannot be owned but only rented. A framework for measuring, monitoring and managing labour dynamics is used and tested in forest harvesting operations in South Africa and the results presented. Overall, the workforce in forest harvesting is unstable : the median labour turnover (monthly basis) and absenteeism (daily basis) are 4 % and 6 %, respectively. Of further concern are : high instability in some individual contractor businesses (employees were much more stable with private grower companies than presently with contractors) ; and contractors not measuring and monitoring labour turnover. Labour turnover rates depend primarily on the conditions of employment offered by the contractor. The framework and results presented in this article are prerequisites for sustainable development. Efforts should be made to put appropriate short, medium and long term measures in place to reduce labour turnover and absenteeism, and to manage it.
Guidelines for the design and management of artificial raptor perches and nest-tree stands on forestry estates in South Africa : management paperSource: Southern African Forestry Journal 2002, pp 49 –54 (2002)More Less
The aim of this paper is to provide timber growers with silvicultural guidelines for the establishment of raptor perches and nest stands on forestry estates. Rodents do extensive damage to young saplings and as an ecologically friendly alternative to rodenticides, we provide guidelines on perch height and densities that can be implemented to facilitate rodent-eating, perch-hunting raptors. For example, if eight, 2-m high, even spaced poles are erected per hectare, the raptors will be able to hunt the entire area. The aim of creating nest stands on forestry estates is to establish 3-6 small (625 m<sup>2</sup>) designated areas where raptors can breed separately from commercial forestry activities. Guidelines for small, tree-nesting raptors include dense stands (1000 trees / ha) to hide nests from predators, whereas stands for intermediate size raptors must be thinned to 163 trees / ha to allow an increase in trunk diameter that, in turn, allows the trees to support bigger nests. Cultivating large trees for large raptors is problematic as these birds require trees with open branch structures and easy access, features not associated with single-stem, commercial trees. If timber growers adhere to the above recommendations they will be able to combine wildlife and timber management objectives on forestry estates.
Management options for Australian Blackwood (Acacia melanoxylon) in Southern Cape Forests, South Africa : management paperAuthor A.H.W. SeydackSource: Southern African Forestry Journal 2002, pp 55 –66 (2002)More Less
Australian Blackwood (<I>Acacia melanoxylon</I>) was actively introduced into the indigenous forests of the southern Cape until about 1930. On the perception that this exotic species constituted a threat to the indigenous forest, a policy of eradication was followed. This perception that Blackwood is capable of progressively replacing the native biota was questioned periodically. Recent investigations support the contention that the species is subject to constraints to its effective self-replacement within the indigenous forests. In the context of a policy re-evaluation, it is recommended that in the medium-term and until monitoring has provided clarity on outstanding issues, the control programme be restricted to areas where exotics are inherently unacceptable, as is the case for nature reserves. Two harvesting options for the remaining old-growth Blackwood timber in the forest are presented. According to the short-term depletion harvesting option, <I>ca</I> 2000 m<sup>3</sup> of timber can be harvested annually until the year 2003. The medium-term optimisation option makes provision for annual harvest of 1500 m<sup>3</sup> until 2010. Particularly in the case of the second option care must be taken to harvest the more senile trees early in the sequence if an acceptable degree of mortality pre-emption is to be achieved.
Knowledge on Sclerocarya birrea subsp. caffra with emphasis on its importance as a non-timber forest product in South and southern Africa : a summary : part 2 : commercial use, tenure and policy, domestication, intellectual property rights and benefit-sharing : review paperSource: Southern African Forestry Journal 2002, pp 67 –78 (2002)More Less
<I>Sclerocarya birrea</I> (marula) forms an integral part of the diet, tradition and culture of rural communities in southern Africa and also is central to various commercial initiatives. This second part of a review on the species provides an overview of current commercial activities, the policy framework within which commercialisation occurs, and future prospects with regard to domestication. Much work has been conducted over the years on the properties of <I>S. birrea</I> fruit, juice, nuts and oil. Despite this research there has been little commercialisation. Two main commercial enterprises trade marula products in South Africa : one, a large corporation, and the other, a rural development project. In Namibia, marula commercialisation is undertaken through a collaborative project between primary producers, a cooperative, contract processors and a local NGO. Commercialisation is influenced by a wide set of customary and government laws which regulate marula use in southern Africa, comprising different tenure systems, access rights, and levels of protection. Strong customary rules can be linked to the long history of marula use in the region, with clear evidence of early domestication and the selection of desirable traits by local people. Such knowledge has been applied in the development of marula domestication strategies, both by private plant breeders in Israel and southern Africa, and by the International Centre for Research in Agroforestry (ICRAF), which works with small-scale farmers to develop agroforestry options. A number of issues are raised by the domestication of marula which relate to intellectual property and benefitsharing. They include the compensation of small-scale farmers and original holders of local knowledge for the commercial use of such knowledge ; the impact of Plant Breeder's Rights on communities using marula; and the possibility of domestication shifting benefits from poorer groups of farmers to richer ones. Current and future commercialisation strategies clearly need to take these factors into account, and to balance associated costs and benefits.