Browsing by Author "Goldsmith, Angel Aphelele"
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- ItemThe combined effect of slash burning and repeated disc harrowing on changes in fuel loading, soil properties, root growth and stand productivity of eucalypts in Mpumalanga : South Africa(Stellenbosch : Stellenbosch University, 2019-12) Goldsmith, Angel Aphelele; Du Toit, Ben; Stellenbosch University. Faculty of AgriSciences. Dept of Forest and Wood Science.ENGLISH ABSTRACT: In many South African plantation forestry regions, repeated disc harrowing (after clear felling and during stand development) among other objectives is used as a fuel load reduction measure to minimise wildfire damage. This study reports the effects of this treatment on fuel loading, soil properties and stand growth. The implementation of repeated disc harrowing throughout the rotation of Eucalyptus grandis x nitens stands significantly reduced fuel loading of the most active (i.e. the finer) fuel classes. In a fence line study of adjacent experimental plots, repeated disking (BD) was contrasted with non-disking (B0) treatments. Repeated disc harrowing reduced the average oven dried fuel loading of the 1 hour fuel class by 29.0 t ha-1 and that of the 10 hour fuels by 4.3 t ha-1 when compared to the non-disked treatments. Repeated disc harrowing significantly altered the forest floor structure. The non-disking treatment consisted of the litter (L), fermented (F), and humus (H) strata on top of the mineral soil (MS) layer. Following numerous harrowing application in the BD treatment, the forest floor structure was reduced to only a sparse L layer directly on top of the MS layer. This indicated a considerable change in fuel loading and forest floor structure as a result of disc harrowing. Repeated disc harrowing significantly increased topsoil exchangeable cation quantities, S-value, and reduced bulk density. Topsoil exchangeable K, Ca, Mg, Na, and S-valueincreased by 0.04, 0.34, 0.12, 0.01 and 0.51 cmolc kg-1 respectively following repeated disking. The topsoil pHKCl, extractable P, total N and C were not significantly different among the two treatments. The above and below ground tree growth variables examined in this fence line study indicated no significant differences following repeated disc harrowing treatment. The BD treatment exhibited similar stand density of 1168 stems ha-1 over 1141 stems ha-1 for B0 treatment. Likewise, stand productivity was similar among treatments, with basal area, volume, and plant biomass in the B0 treatment being 24.6 m2 ha-1, 212.5 m3 ha-1and 134.4 t ha-1 versus 23.5 m2 ha-1, 202.6 m3 ha-1 and 127.5 t ha-1 for the BD treatment. Using a profile wall root study method, B0 treatment was observed to have a non-significantly higher root count of 30% on the top 10 cm soil depth when contrasted to BD treatment, which was 22% (percentage of the total root count on a 1 x 1 m vertical profile wall). All the differences observed on the tree growth and stand productivity parameters among the two treatments were not significant at (p<0.05). The negligible growth reduction in repeatedly disked treatment is surpassed by the significant fuel load reduction and reduced wildfire risk.