Browsing by Author "Joubert, David F."

Now showing 1 - 6 of 6
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    Case study of adaptive rangeland management by an innovative Kalahari farmer.
    (2008) Zimmermann, Ibo; Joubert, David F.; Smit, G.N.
    Scientists can learn a great deal from innovative farmers who apply adaptive management principles based on experience gained over decades. This paper records 31 observations that a farmer, Jan Labuschagne, made on his farm to the south of Gobabis. The observations relate to aspects such as animal behaviour and performance, animal trampling, and applications of grazing and fire. They are tabulated together with their possible explanations and their management applications. The conceptual model the farmer has built to aid his understanding and decision making is also shown as a diagram and explained. Of critical importance is the strategic timing of management interventions on different parts of the farm in relation to rainfall events, texture and organic content of the soil and maturity of the vegetation. Data are presented to support some of the observations
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    A crude quantification of wood that is and can be harvested from bush thickening species in Namibia.
    (Namibia, Ministry of Environment and Tourism, 2002) Zimmermann, Ibo; Joubert, David F.
    The increasing rate at which thickening bushes are being harvested in Namibia requires better information on the availability and sustainability of the resource, in order to improve management. Two sources of data from the literature were combined to give a rough approximation of the standing biomass of wood of appropriate size for charcoal production, in each of nine bush-thickened zones. The overall estimate came to roughly 135 million tons of dry wood in about 260 000 square kilometres of Namibia, or an average of just over 5 t/ha. The legal commercial harvest for the 1999/2000 financial year came to the equivalent of just under 0.2 million tons of dry wood. Interviews with ten charcoal producers, and field data gathered at one site, suggest that harvesting could take place at intervals of roughly 20 years, provided that harvesting is selective and leaves sufficient bushes of different size classes for regeneration. However, it is likely that subsequent harvests would be lower and more difficult to obtain. Previously chopped bushes could then only be re-harvested on every third or fourth cycle, preferably after being pruned to maintain a more appropriate growth form, which is easier to harvest and more conducive to grass growth.
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    The distribution and invasive potential of fountain grass pennisetum setaceum in Namibia.
    (Dinteria, 2002) Joubert, David F.; Cunningham, Peter L.
    Pennisetum sataceum is an exotic alien grass species from North Africa which invasive potential in Namibia. The distribution and invasive potential of this species was investigated. The current distribution of this species was compared with the reported distribution in the mid 1980s. It has increased its range in Namibia dramatically since then and is now found in a number of locations throughout Namibia, albeit mostly on road verges and other distributed areas predominantly in the Highland Savanna and Mountain Savanna biomes. It's popularity as an ornamental grass, particularly amongst farmers, is responsible for it's introduction and spread. Observations on a dense stand of P. setaceum west of Windhoek indicate this species preference for road verges and schist cuttings in association with relatively mesophytic grasses such as heteropogon contortus, Cenchrus ciliaris and panicum maximum. Its ability to form a major component of the vegetation of each of these habitats suggests that it has a broader tolerance range than the associate indigenous grasses. A range of control measures is suggested to prevent the species spreading further whilst it is still feasible.
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    The effects of 'pebble mulch' on acacia mellifera seedling responses to rain.
    (Namibian Scientific Society., 2009) Joubert, David F.
    "Pebble mulch" (a layer of quartz and schist pebbles that often forms an almost 100% cover on the slopes of the Highland Savannah in Namibia) influences the dynamics of this vegetation type. A controlled experiment to determine the effects of "pebble mulch" on seed germination and early seedling establishment of Acacia mellifera (ubsp. detinens) was conducted. A. mellifera forms dense thickets in the area. Seeds were germinated under four treatments: A: planted below soil (2 seed widths depth) without pebble cover; B: planted below soil (2 seed widths depth) with pebble cover; C: plated on top of soil underneath a 100% pebble cover; and D: planted on top of a 100% pebble cover. Emergence/germination in all cases was high (overall 82% s.d. 17.5%). Soil moisture was significantly higher in all "pebble mulch" treatments (B, C and D). Although initial establishment was poor in Treatment D (33%), survival thereafter of seedlings whose radicals reached the soil was very high (97%). Seedling survival and vigour were significantly higher in all "pebble-mulch" treatments. The implications of these results for bush encroachment on Highland Savannah rangelands are discussed.
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    The potential impacts of wood harvesting of bush thickening species on biodiversity and ecological processes.
    (Namibia, Ministry of Environment and Tourism, 2002) Joubert, David F.; Zimmermann, Ibo
    Studies of the effects of bush clearing have mostly focussed on economic issues such as production. In this paper, biodiversity and ecological effects of bush clearing were investigated, largely through a literature survey. Vertebrate and plant taxa were focussed upon. Two future scenarios were discussed. The first scenario was that future wood harvesting would follow Forestry Stewardship Council Principles and Forestry Guidelines. The second scenario was that demand exceeded supply and that sound sustainable principles would be abandoned in certain areas, in order to chase demand. In the first scenario, biodiversity would be improved, as would ecological processes. In the second scenario, arboreal species, including cavity users, and species requiring microhabitats and shelter would be badly affected, with local extinctions of these species likely. Management recommendations are provided. Biodiversity research should be viewed as a priority, in order to better understand the effects of different wood harvesting management strategies.
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    A problem tree to diagnose problem bush.
    (2008) Zimmermann, Ibo; Joubert, David F.; Smit, G.N.
    The term “problem tree” refers to a conceptual model used as a diagnostic tool to analyse a sequence of events that leads to a problem (such as bush encroachment in rangelands). A problem tree is useful because the consequences of different interventions can be visualised and understood more easily in diagrammatic form, thereby guiding management decisions regarding the problem. A problem tree was constructed to show multiple causes of bush encroachment. It was generalised by considering many possible causes, and not only those applying to particular areas of encroachment or specific species of bush. If the problem tree is to be useful in decision-making, one needs to determine which of the multiple pathways are of greater significance in any particular situation. Management decisions are bound to be more effective in the long run if they address causes higher up in the tree and closer to the root causes, than the proximate causes or symptoms at the bottom of the tree.