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Item Potential distribution of major plant units under climate change scenarios along an aridity gradient in Namibia(Vegetation Classification and Survey, 2024-06-13) Leena Naftal; Vera De Cauwer; Ben J. StrohbachObjectives: Climate change is expected to have major impacts on plant species distribution worldwide. These changes can affect plant species in three ways: the timing of seasonal activities (phenology), physiology and distribution. This study aims to predict the effect of shifting climatic conditions on the major vegetation units along an aridity gradient through Namibia. Study area: Namibia’s vegetation is characterised by open woodland in the northeast to low open shrubland in the southern part of the country. These differences are a result of increasing aridity from north to south with a rainfall gradient from 100 mm to 600 mm. Namibia is projected to have an increase in annual mean temperature of 2°C by the end of the 21st century. Methods: A vegetation classification was done for 1,986 relevés using cluster analysis, a Multi-Response Permutation Procedure and indicator species analysis. The current distribution of the vegetation classes was modelled with Random Forest. Future projections for the most important climate variables were used to model the potential distribution of the vegetation units in 2080. This modelling approach used two scenarios of Representative Concentration Pathways (4.5 and 8.5) from two Global Climate Models – the IPSL–CM5A–LR and HAdGEM2–ES. Results: The predicted distribution shows a high expansion potential of Eragrostis rigidior-Peltophorum africanum mesic thornbush savannas, Combretum africanum-Terminalia sericea broad-leafed savannas and Senegalia mellifera-Dichrostachys cinerea degraded thornbush savannas towards the south under both scenarios. Conclusions: The model indicated the ability to classify and predict vegetation units to future climatic conditions. Half of the vegetation units are expected to undergo significant contraction. Overall, RCP8.5 conditions favour the proliferation of certain vegetation types, particularly Combretum collinum-Terminalia sericea broad-leafed savannas and Senegalia mellifera-Dichrostachys cinerea degraded thornbush savannas, potentially displacing other vegetation types. Taxonomic reference: Klaassen and Kwembeya (2013) for vascular plants, except Kyalangalilwa et al. (2013) for the genera Senegalia and Vachellia s.l. (Fabaceae). Abbreviations: CDM = Community Distribution Model; CMIP5 = Coupled Model Inter-comparison Project Phase 5; EVI = Enhanced Vegetation Index; GCM = General Circulation Model; IV = Indicator Value; ISA = Indicator Species Analysis; MAP = mean annual precipitation; MAT = mean annual temperature; MRPP = Multi-Response Permutation Procedure; NMS = Non-Metric Multidimensional Scaling; RF = Random Forest; RCPs = Representative Concentration Pathways; SDM = species distribution model.Item A first syntaxonomic description of the vegetation of the Karstveld in Namibia.(Vegetation Classification and Survey/Pensoft Publishers, 2023-10-24) Strohbach, Ben J.; Strohbach, Marianne M.Aims: The Karstveld in Namibia has been recognized as an area of high plant diversity. However, this area is also recog nised as a hotspot of various forms of degradation including bush encroachment. Minimal baseline data on the compo sition and diversity of vegetation in this area is available, therefore this paper is a first attempt to rectify this data defi ciency. Study area: The Karstveld in Namibia is formed around the Otavi Mountain Range in northern Central Namibia, consisting of strongly karstified carbonate bedrock, rising up to 2000 m a.s.l. The Karstveld includes the Ovambo Basin plains with shallow calcrete soils north of the range, up to the Omuramba Ovambo. Because of orographic effects, the area receives some of the highest rainfall in Namibia, with up to 600 mm per year. Methods: A set of 889 relevés with 868 species was selected from the GVID ID AF-NA-001 database. A partial data set, using trees, shrubs, dwarf shrubs and grasses only, was used for the classification with modified TWINSPAN. The initial result yielded four main groups, according to which the data was split and further classified. Several vegetation types observed during field surveys were not reflected in the classification results; these were refined using Cocktail with known characteristic species. Results: The four main units represented wetlands and grasslands with six associations, a Thornbush savanna – Karstveld tran sition zone with four associations, Kalahari vegetation with four associations and the Karstveld proper with eight asso ciations. The latter are grouped together as the Terminalietea prunioides, with two orders and three alliances recognised under them. We describe 16 associations according to the ICPN. Conclusions: Although the associations presented in this paper are clearly defined, there exists a high degree of diversity within these. The Karstveld is also extraordinary species rich within the context of the arid to semi-arid Namibian environment. Taxonomic reference: Klaassen and Kwembeya (2013) for vascular plants, with the exception of the genus Acacia s.l. (Fabaceae), for which Kyalangalilwa et al. (2013) was followed. Abbreviations: ga = annual grass; gp = perennial grass; GPS = Global Positioning System, referring to a hand-held ground receiver; hl = herb layer, containing all hemicryptophytes, therophytes and geophytes, but excluding grasses (Poaceae); ICPN = International Code of Phytosociological Nomenclature (Theurillat et al. 2021); MAP = mean annual precipitation; NMS = nonmetric multidimensional scaling (Kruskal 1964); RDL = Red Data List (IUCN Species Survival Commission 2001); s1 = tall shrubs, i.e. multi-stemmed phanerophytes between 1 and 5 m; s2 = short shrubs, i.e. cha maephytes or ‘dwarf shrubs’ below 1 m; SOTER = Global and National Soils and Terrain Digital Database (FAO 1993); t1 = tall trees, > 10 m; t2 = short trees, between 5 and 10 m; t3 = low trees, i.e. single-stemmed phanerophytes between 2 and 5 m; TWINSPAN = Two Way Indicator Species Analysis (Roleček et al. 2009); WGS84 = World Geodetic System, 1984 ensembleItem 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.Item The SASSCAL/MAWF Weather Stations Network in Namibia: Overview of equipment and data transfer.(2014) Strohbach, Ben J.Through the BIOTA project (2000 - 2009) 21 high end weather stations meeting WMO standards have been bought for deployment in Namibia. Some of these stations are replacing older equipment at the BIOTA observatories (Jürgens et al., 2010), while some are / will be placed in new strategic localities. These 21 stations update their readings hourly on the web via the cell network or satellite communication. The Ministry of Agriculture, Water and Forestry (MAWF) supported this project with 17 Automatic Weather Stations (AWS) on their research stations. In addition, 14 other weather stations of different technical standard are currently operated by private individuals and primarily tourism lodge operators across the country. Data from these stations is displayed on the web under the Namibia Weather Network. The Namibia Meteorological Service runs a number of automatic and manual weather stations. The World Meteorological Organizations lists 127 rainfall stations for Namibia.Item 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, IboStudies 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.Item 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.Item Mysterious circles in the Namib Desert.(Elsevier, 2008) Jankowitz, W. J.; Van Rooyen, M. W.; Shaw, D.; Kaumba, J. S.; Van Rooyen, N.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.