http://hdl.handle.net/10628/208 2013-05-28T23:19:11Z http://hdl.handle.net/10628/255 Title: The potential impacts of wood harvesting of bush thickening species on biodiversity and ecological processes. Authors: Joubert, David F.; Zimmermann, Ibo Abstract: 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. Description: This paper was presented at the National Forestry Research Workshop held in Windhoek. 2002-01-01T00:00:00Z http://hdl.handle.net/10628/220 Title: The distribution and invasive potential of fountain grass pennisetum setaceum in Namibia. Authors: Joubert, David F.; Cunningham, Peter L. Abstract: 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. 2002-01-01T00:00:00Z http://hdl.handle.net/10628/212 Title: Mysterious circles in the Namib Desert. Authors: Jankowitz, W. J.; Van Rooyen, M. W.; Shaw, D.; Kaumba, J. S.; Van Rooyen, N. Abstract: There is currently still no scientifically sound explanation as to the origin of the so-called ''fairy circles'' in the Namib. An in situ experiment was conducted in the NamibRand nature Reserve to test hypothesis that the circles are the result of a semi-volatile gas that inhibits plant growth. Stipagrostis ciliata grass plants were planted in containers filled with soil from the circle or from outside the circle. Some containers were sealed at the bottom, to prevent any gases from entering from below, while others were left open. Containers were placed both inside the circle as well as outside the circle. The origin of the siol, i.e. whether it came from inside or outside the circle, did not affect the performance of the plants when they were growing in the same position and container type. All plants growing outside the circle, irrespective of the origin of the soil or the container type, performed better than those growing inside the circle. It is concluded that there is a factor inhibiting plant growth in the circle and that this factor could possibly be a semi-volatile gas, because growth was more negativelly affected in the open containers than in the sealed containers. 2008-01-01T00:00:00Z