- Title
- The use of herbicides for the management of Eucalyptus coppice in South Africa
- Creator
- Roberts, Jonathan Cecil
- Subject
- Eucalyptus grandis -- South Africa Herbicides -- South Africa
- Date Issued
- 2017
- Date
- 2017
- Type
- Thesis
- Type
- Masters
- Type
- Degree
- Identifier
- http://hdl.handle.net/10948/20287
- Identifier
- vital:29205
- Description
- The effectiveness and relatively low cost of herbicides has led to the near exclusion of non-herbicide methods for controlling weeds in commercial forestry plantations. However, any herbicide used within the forestry context has the potential to be toxic and/or alter ecosystem dynamics. In response to increased public concern, perceptions of risk, and compliance associated with forest certification standards and criterion, there is an increased need to provide alternative methods that can reduce reliance on herbicides. Even though adequate research has been implemented regarding herbicide use, little research has examined the implications of herbicide use or non-use throughout the full rotation. Since herbicide use is integrated within the management of eucalypt regeneration, it is critical that a comprehensive understanding of herbicide use be obtained before informed management decisions can be made. Only once this has been obtained, can reduced and judicious recourse to herbicide use be considered, both within the requirements of certification criteria and of good management practice (economic and site sustainability). The main objective of this thesis was to increase the understanding of herbicide use, as well the cost involved within the context of eucalypt coppice regimes in South Africa. Three field trials (two rotation-end, and one short-term) were implemented to achieve this objective, with herbicide use aimed at either killing eucalypt stumps if replanting, or control of secondary coppice regrowth if coppicing. The first trial was situated in Mpumalanga and evaluated which method of control would be best suited to reducing cost (cost-effective) and reliance on herbicides for killing eucalypt stumps and control of resulting coppice regrowth. Selected cut-stump and basal-frill treatments were included with triclopyr (480 g L-1 a.i.) applied to the cambium of difficult-to-kill Eucalyptus macarthurii H. Deane & Maiden stumps that had previously been coppiced multiple times. The resulting coppice regrowth was either manually removed, or glyphosate (360 g L-1 a.i.) applied to foliage. These treatments were integrated with non-chemical control methods, where E. dunnii Maiden seedlings were planted either between each stump row or within the row, to determine whether such treatments could further reduce the level of coppicing through shading. At rotation end, the different treatments tested had no significant influence on any of the E. dunnii growth variates. As there were no significant differences, the treatment with the lowest overall cost and herbicide used would be preferred. The application of triclopyr to the cut-surface following felling was the most cost-effective treatment. The differences in cost obtained is directly related to required follow-up coppice regrowth control operations and quantity of total herbicide applied (both triclopyr and glyphosate). It was hoped that the non-chemical control method (planting position of seedlings) would reduce the level of coppicing, however, within this trial, this did not occur. The second trial was situated in Zululand on Eucalyptus grandis x E. urophylla coppice that investigated different methods to control secondary coppice regrowth through either manual removal with a bush-knife, or the application of glyphosate (360 g L-1 a.i.) to the foliage. A range of herbicide rates (0.6%, 1.2% and 1.8%) was applied to the foliage of the secondary coppice regrowth when it reached a predetermined mean height (0.5 m, 1.0 m and 1.5 m). The objective was to determine the optimum rate and timing of control and to avoid glyphosate from being over-applied when managing this regrowth. No significant differences were detected between the different treatments for any of the growth variates at rotation end. The use of glyphosate, irrespective of rate and/or timing of application (as assessed by secondary coppice regrowth height) proved to be more cost-effective compared to manual removal of secondary coppice regrowth. Treatment efficacy in terms of treating secondary coppice regrowth increased with an increase in the rate of glyphosate applied (0% < 0.6% < 1.2% < 1 .8%), especially when treated at either 1.0 or 1.5 m in height. Although the volume of the glyphosate used increased with increasing secondary coppice regrowth height (0.5 m < 1.0 m < 1.5 m) due to the larger foliar spraying area, there was little difference in total glyphosate used when comparing the same herbicide rate across the three different heights. The most cost-effective treatment was that where glyphosate was applied at 1.2% when the secondary coppice regrowth was 1-1.5 m. The third trial (also located in Zululand on Eucalyptus grandis x E. urophylla) was implemented to test the knowledge gained in trial two, thereby determinng coppice management regimes that would facilitate mechanised harvesting. In this trial, coppice shoots were reduced to one stem per stump in one thinning operation (coppice reduction heights of 3.5 m, 4.5 m and 6.5 m), with the impact of increased secondary coppice regrowth monitored together with the testing of different control methods. An additional control treatment was included (current best operating practice) with coppice shoots thinned to two stems per stump at shoot height of 3.5 m, and thereafter to original stocking at stem height of 6.5 m. Herbicide rate and timing of application was based on the results obtained in the second trial, with glyphosate applied at 1.2% when the secondary coppice regrowth reached a mean height of approximately 1 m. At the final measurement date, the diameter at breast height for all three coppice reduction height treatments (3.5 m, 4.5 m and 6.5 m) were significantly larger than the additional control treatment. This can be attributed to the allocation of resources to the remaining stem at an earlier age, resulting in a growth benefit. For stocking, the 6.5 m coppice reduction height was significantly higher compared to both the 3.5 m and 4.5 m coppice reduction treatments, while not significantly different from the additional control. In this trial, secondary coppice regrowth had no effect on tree growth. Due to the short duration of this trial, a longer trial period would be necessary to obtain a full understanding of the impacts of the various coppice reduction treatments, and the resulting secondary coppice regrowth influence on selected coppice growth if left untreated. As several previous studies have shown the importance of controlling secondary coppice regrowth, it is recommended not to view the results of this present trial in isolation. On the basis of the results of this research, it can be concluded that the control of coppice regrowth with herbicides is more effective than any of the manual removal treatments in terms of cost, with manual control requiring more follow-up control operations. Even though the manual removal of coppice regrowth had no influence on growth of the remaining stems or planted trees, the potential injury to labourers or growing stock is still of concern. Therefore, the use of herbicides for controlling coppice regrowth would be preferable. However, if reduced herbicide-use is a major criterion, then coppice regrowth can be controlled manually, although at a higher cost.
- Format
- xv, 77 leaves
- Format
- Publisher
- Nelson Mandela Metropolitan University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela Metropolitan University
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