Browsing by Author "Maubane, Johannes Tshepo"

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    Effects of burning of slash piles of Acacia spp. and Eucalyptus camaldulensis biomass on soil physicochemical properties within Western Cape riparian and terrestrial areas
    (Stellenbosch : Stellenbosch University, 2016-12) Maubane, Johannes Tshepo; Jacobs, Shayne Martin; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Removal of woody invasive alien plants from riparian and terrestrial fynbos ecosystems usually leads to the accumulation of large volumes of plant biomass. The three study species, Acacia mearnsii, Acacia saligna and Eucalyptus camaldulensis are well known for their ability to considerably increase above-ground biomass production. While some biomass may be removed for use as timber, or chipped for export, in cases where there is no alternative use for this biomass, or where site accessibility is an issue, burning of biomass in the form of piles or rows is practiced as a way of destroying biomass in situ. However, this approach has been reported to produce high temperatures, which may lead to altered soil properties and destroyed soil stored seed banks. Burn scars may develop on soil surfaces that were exposed to the burning of slash piles, which may remain unvegetated for extended periods of time. As a consequence, restoration may be patchy, uneven or delayed in post-clearing landscapes. The aim of this study was to evaluate the seasonal and spatial effects of burning of slash piles of Acacia spp. and Eucalyptus spp. biomass on soil physicochemical properties. Four riparian study areas (Hermon and Robertson, both dominated by Eucalyptus camaldulensis prior to clearing, and Wit River and Rawsonville, Acacia mearnsii dominated) and one terrestrial study area (Blaauwberg; Acacia saligna) were selected within the fynbos biome. Burning was conducted in spring 2014 (Hermon and Blaauwberg) and winter 2015 for all other study areas. Acacia mearnsii and A. saligna piles had a volume of between 21.01 and 88.17m3 and E. camaldulensis stacks had a volume of between 93.93 and 116.68 m3. Soil samples were collected from the topsoil layer, 0-10 cm depth, prior to burning, post-fire and three subsequently seasons, from within the burn scars (in the centre, an intermediate position, i.e. between the edge and centre, and the edge), from the soil matrix (about 2 m from the edge), from a recovering reference site and from an invaded reference site. The collected samples were subjected to laboratory analyses for pH, electrical conductivity (EC), total carbon (C) and nitrogen (N), available N, available phosphorus (P), exchangeable cations and hydrophobicity. At all study areas, soil pH (water), EC, available P and exchangeable cations increased significantly immediately after burning and had returned to pre-fire levels within one year of sampling, with the exception of soil pH, which persisted longer. This was with the exception of the Wit River riparian study area, where soil pH increased significantly and had returned to pre-fire within 3-4 months of sampling and soil EC was not affected at all. Total C and N responded differently across study areas, where it remained unchanged at Hermon and decreased significantly at Rawsonville. Available N was not initially affected by fire at any of the study areas, but later showed higher levels within fire scars in Acacia invaded areas. No such difference emerged within fire scars of Eucalyptus camaldulensis invaded areas, suggesting that nitrogen may be more readily available in fire scars of riparian Acacia invaded areas. Hydrophobicity increased only at Rawsonville (Acacia mearnsii) as a result of fire and was not affected by fire in other areas. At the terrestrial site, soil pH, EC and available P increased significantly, but returned to pre-fire levels after a few seasons, with the exception of pH, which remained significantly higher. The results from this study indicate that certain parameters such as soil pH, EC, available P and cations generally increase immediately after fire. In addition, the response of other properties including total C and N, available N and hydrophobicity may be governed by the characteristics of the ecosystem, soil type, burn fuel and seasonal variations. The implications of the study are that using fire as a tool for biomass management in post clearing landscapes may introduce unwanted soil physicochemical alterations, which may impact recovery, especially of native species.