Nature Conservation

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http://196.216.167.205/handle/10628/943

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Browsing Nature Conservation by Author "Joubert, David F."

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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.