Browsing Okavango Research Institute (ORI) by Title
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Chimbari, M.J.; Shiff, C.J. (Taylor & Francis, May 5, 2008)[more][less]
Abstract: Preliminary laboratory studies were conducted to determine the molluscicidal potency of Jatropha curcas, the physic nut. Biomphalaria glabrata and Bulinus globosus snails were exposed to varying concentrations of aqueous extracts of crushed J. curcas seeds from unripe, ripe and overripe fruits collected from two geographically different sites, (Bindura and Kariba, Zimbabwe). Snail mortalities were compared between different developmental stages of J. curcas and between seed collection areas, and LC50 and LC90 values for the different extracts tested were computed. Biomphalaria glabrata was most susceptible to unripe fruit seed extract (with LC50 values of 282 and 389 mg l-1 being recorded for Kariba-origin and Bindura-origin plants, respectively) and least susceptible to ripe fruit seed extracts (with LC50 values of 605 and 708 mg l-1 being recorded for Kariba-origin and Bindura-origin plants, respectively). Bulinus globosus was most susceptible to overripe fruit seed extract (Kariba-origin plants: LC50, 389 mg l-1) and least susceptible to unripe fruit seed extract (Kariba-origin plants: LC50, 687 mg l-1). The area from which fruits were collected did not influence the potency of J. curcas. The potency of J. curcas depends on both the developmental stage of the fruit and the species of the target snail. In view of its many other uses, besides as a molluscicide, we recommend further studies on J. curcas. URI: http://hdl.handle.net/10311/809 Files in this item: 1
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Lezine, A-M.; von Grafenstein, U.; Andersen, N.; Belmecheri, S.; Bordon, A.; Caron, B.; Cazet, J.-P.; Erlenkeuser, H.; Fouache, E.; Grenier, C.; Huntsman-Mapila, P.; Hureau-Mazaudier, D.; Manelli, D.; Mazaud, A.; Robert, C.; Sulpizio, R.; Tiercelin, J.-J.; Zanchetta, G.; Zeqollari, Z. (Elsevier, January 11, 2010)[more][less]
Abstract: Multi-proxy analyses on core JO2004-1 recovered from Lake Ohrid (40°55.000 N, 20°40.297E, 705 m a.s.l.) provide the first environmental and climate reconstruction in a mountainous area in Southern Europe over the last 140,000 years. The response of both lacustrine and terrestrial environments to climate change has been amplified by the peculiar geomorphological and hydrological setting, with a steep altitudinal gradient in the catchment and a karstic system feeding the lake. The karstic system was active during interglacials, leading to high carbonate production in the lake, and blocked during glacials as a result of extremely cold climate conditions with permafrost in the mountains. At the Riss–Eemian transition (Termination 2) the increase in lacustrine productivity predated forest expansion by about 10,000 years. In contrast, the Late Glacial–Holocene transition (Termination 1) was characterized by the dramatic impact of the Younger Dryas, which initially prevented interglacial carbonate production and delayed its maximum until the mid- Holocene. In contrast, forest expansion was progressive, starting as early as ca. 38,000 ago. The proximity of high mountains and the probable moderating lake effect on local climate conditions promoted forest expansion, and contributed to make the surroundings of Lake Ohrid favourable to forest refugia during the last glacial, usually steppic, period. Our study of sedimentology, mineralogy, geochemistry, magnetics, palynology and isotopes illustrates the non-linear response of terrestrial and lacustrine ecosystems to similar climate events, and demonstrates the potential of Lake Ohrid as an excellent paleoclimatic archive during the Quaternary. URI: http://hdl.handle.net/10311/607 Files in this item: 1
LakeOhrid.pdf (1.662Mb) -
Darkoh, M.; Mbaiwa, J. (Blackwell, http://www.wiley-blackwell.com, NaN, 2009)[more][less]
Abstract: This study assesses land-use conflicts in the Okavango wetland ecosystem. A survey of the livelihood activities of a sample of four villages has been carried out and a stakeholder approach used to identify and analyse the key actors involved in resource competition and conflicts in the area. Traditional and emerging stakeholders were identified and found to be in conflict not only with each other but within themselves. Institutional policies on land use in the area are not properly harmonized, and there has been a top-down approach to development planning and implementation of development programmes. As a result, land-use conflicts have escalated in the area. The Okavango Delta Management Plan adopted in 2007 should integrate and harmonize all the land-use policies, and land management in the area. URI: http://hdl.handle.net/10311/828 Files in this item: 1
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Darkoh, M.B.K.; Mbaiwa, J.E. (Wiley, NaN, 2009)[more][less]
Abstract: This study assesses land-use conflicts in the Okavango wetland ecosystem. A survey of the livelihood activities of a sample of four villages has been carried out and a stakeholder approach used to identify and analyse the key actors involved in resource competition and conflicts in the area. Traditional and emerging stakeholders were identified and found to be in conflict not only with each other but within themselves. Institutional policies on land use in the area are not properly harmonized, and there has been a top-down approach to development planning and implementation of development programmes. As a result, land-use conflicts have escalated in the area. The Okavango Delta Management Plan adopted in 2007 should integrate and harmonize all the land-use policies, and land management in the area. URI: http://hdl.handle.net/10311/730 Files in this item: 1
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Bond, J.M.; Veenedaal, E.M.; Hornby, D.D.; Gray, A.J. (Kluwer Academic Publishers, http://www.springerlink.com, November 28, 2002)[more][less]
Abstract: One of the major problems in determining the origin of invasive species is that often their arrival is unnoticed. Only when population levels increase is their presence noticed but by this time determining the point of arrival is confounded by the extensive spread of the species. Here we use molecular markers (ISSRs) to determine the origin of an invasive weed in the Kalahari region, a species for which several origins could be possible. We show that molecular markers can be useful tools in determining the origin of invasive species. URI: http://hdl.handle.net/10311/1025 Files in this item: 1
Bond_2002.pdf (2.049Mb) -
Meck, M.; Atlhopheng, J.; Masamba, W.; Ringrose, S.; Diskin, S. (Bentham Open, NaN, 2010)[more][less]
Abstract: This study set out to establish the major minerals at Dorowa and determine which of those are likely to host metals that may leach into surface and groundwater. This study comes after a preliminary assessment of the water quality in the Save River downstream of the Dorowa phosphate mine in Zimbabwe showed an increase in conductivity, iron content, manganese content, nitrates and hardness when compared to those taken before the mining area. X-Ray Diffractometry (XRD) was used to establish the major minerals at Dorowa whilst Inductively Coupled Plasma Mass Spectrometry (ICP- MS) was used to establish the chemistry of the rocks. The results from this study show that the major minerals in the rocks around Dorowa are feldspars, pyroxenes, apatite, magnetite and calcite. The metals hosted by the rocks include Ag, As, Be, Cd, Co, Cu, Pb, Hg, Ni, Sb, Se and Zn. The study concludes that the minerals likely to host metals are calcite and apatite. Metal hosting is higher in apatite minerals than in calcite. Metal hosting by the other minerals observed in the study area is low. URI: http://hdl.handle.net/10311/932 Files in this item: 1
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Moleele, N.M.; Ringrose, S.; Matheson, W.; Vanderpost, C. (ScienceDirect, www.sciencedirect.com, NaN, 2002)[more][less]
Abstract: the cattle-dominated grazing areas of Botswana. Bush encroachment species – for instance Acacia tortilis, A. erubescens, A. mellifera, Dichrostachys cinerea, Grewia flava, and Terminalia sericea –are increasing in cover and density around foci points (e.g. water points and kraals) at the expense of the grass cover. A number of factors have the effect of encouraging the germination and survival of bush encroachment species. The practice of cattle husbandry and continual shifting of foci points within grazing areas have resulted in the spread of the distribution of bush encroachment species across the country. This is evidenced by the potential extent of 37 000 km2 (6 4% of Botswana) of darkened and near infrared (NIR) reflective bush encroached areas in 1994. This paper suggests that specific management strategies should be adopted to help overcome the bush encroachment problem, which is causing a significant reduction in the extent of Botswana’s high quality rangeland. These strategies may vary from the enforced reduction of grazing intensity in areas identified as being heavily bush encroached to the selective management of opportunistic (communal) grazing in better quality predominantly grassland areas. Further work is however required to update this analysis and especially to consider trends since 1994–1995. While some work on the extent of woody cover and the further causes of bush encroachment is being undertaken under the SAFARI2000 project, more research is needed in specific areas to pinpoint causes and responses to the bush encroachment problem. URI: http://hdl.handle.net/10311/985 Files in this item: 1
Moleele_ et al_More_Woody_2002.pdf (3.119Mb) -
O'Halloran, L.; Shugart, H.; Wang, L.; Caylor, K.; Ringrose, S.; Kgope, B. (Elsevier, February 19, 2010)[more][less]
Abstract: The Kalahari Transect (KT) is an International Geosphere–Biosphere Programme mega-transect designed to examine hydrological and ecological patterns and processes throughout the savannas of southern Africa. The KT traverses a precipitation gradient ranging from w920 mm rain/year in the north to w260 mm rain/year in the south. Previous research shows a positive correlation between canopy cover and precipitation suggesting a water limitation on productivity. However, there has been minimal research on other possible sources of limitations, such as soil Nitrogen (N) and/or Phosphorus (P). We used a factorial in-situ experimental design to test for increased aboveground grass production (measured as peak season standing stock) under elevated soil P and Pþ N levels. Four sites along the KT precipitation gradient were used in this study: Mongu (Zambia), Pandamatenga (Botswana), Ghanzi (Botswana) and Tshane (Botswana). Soils at each site were amended with N and P fertilizers during the dry season. We extracted soil samples during the following growing season to analyze for plant available soil P. Vegetation samples were harvested from which we measured foliar P and aboveground grass biomass production. We saw differences in foliar P at the treatment and site level but not for the interaction between treatment and site. There were individual effects from site on biomass but not for any interactions with nutrient treatments. Despite higher levels of foliar P, we did not detect an increase in aboveground biomass. This may be explained by luxury uptake or allocation to below ground resources. URI: http://hdl.handle.net/10311/797 Files in this item: 1
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Magole, L.; Magole, L.I. (Elsevier, July 15, 2009)[more][less]
Abstract: The Okavango Delta is amongst the largest Ramsar sites (http://www.ramsar.org/sitelist.pdf) in the world and an important wetland for community livelihoods, conservation and tourism in Botswana. Over the years, the utilization of the delta has shifted from communal use to state control, with an increased use for conservation and tourism. This increased use for conservation and tourism has manifested in the physical expansion of the conservation area – Moremi Game Reserve and the formation of Wildlife Management Areas (WMAs) around the reserve, whose primary land use is wildlife utilization. The expansion of the conservation area has translated into several practical matters, including expansion of the area for non-hunting activities or photographic areas. The livelihoods of local communities of the Okavango delta who depended on fishing, hunter-gathering, livestock rearing, rain-fed agriculture and flood recession farming have been negatively affected by the expansion of conservation and tourism in the delta. The livelihoods alternatives in the form of Community Based Natural Resource Management (CBNRM) and tourism have not provided substitutes for the people as the communities are still reliant on the same old livelihood sources as in the past, albeit within smaller and restricted areas. This paper explores the ownership of the natural resources within the Okavango Delta. It asks and attempts to answer the following questions: Who owns and controls the use of the land? Who has access to other resources there in? Who makes the decisions on how the delta resources should be managed and used? Who benefits from the delta resources? We argue firstly that ownership of the delta as defined by legal parameters and demonstrated in natural resource management practice is vested on government. Secondly, government, after assuming ownership of the delta continues to sell its stake to the international community, at the expense of local ownership and access to resources. We conclude that in the process the ability of local communities to source a livelihood out of the delta as they previously used to, is compromised. This we argue works against the goal of sustainable development for improved livelihoods as proclaimed in government policy documents. URI: http://hdl.handle.net/10311/754 Files in this item: 1
The Okavango whose delta is it.pdf (853.1Kb) -
Magole, L.; Magole, L.I. (Elsevier www.elsevier.com/locate/pce, NaN, 2009)[more][less]
Abstract: The Okavango Delta is amongst the largest Ramsar sites (http://www.ramsar.org/sitelist.pdf) in the world and an important wetland for community livelihoods, conservation and tourism in Botswana. Over the years, the utilization of the delta has shifted from communal use to state control, with an increased use for conservation and tourism. This increased use for conservation and tourism has manifested in the physical expansion of the conservation area – Moremi Game Reserve and the formation of Wildlife Management Areas (WMAs) around the reserve, whose primary land use is wildlife utilization. The expansion of the conservation area has translated into several practical matters, including expansion of the area for non-hunting activities or photographic areas. The livelihoods of local communities of the Okavango delta who depended on fishing, hunter-gathering, livestock rearing, rain-fed agriculture and flood recession farming have been negatively affected by the expansion of conservation and tourism in the delta. The livelihoods alternatives in the form of Community Based Natural Resource Management (CBNRM) and tourism have not provided substitutes for the people as the communities are still reliant on the same old livelihood sources as in the past, albeit within smaller and restricted areas. This paper explores the ownership of the natural resources within the Okavango Delta. It asks and attempts to answer the following questions: Who owns and controls the use of the land? Who has access to other resources there in? Who makes the decisions on how the delta resources should be managed and used? Who benefits from the delta resources? We argue firstly that ownership of the delta as defined by legal parameters and demonstrated in natural resource management practice is vested on government. Secondly, government, after assuming ownership of the delta continues to sell its stake to the international community, at the expense of local ownership and access to resources. We conclude that in the process the ability of local communities to source a livelihood out of the delta as they previously used to, is compromised. This we argue works against the goal of sustainable development for improved livelihoods as proclaimed in government policy documents. URI: http://hdl.handle.net/10311/746 Files in this item: 1
Magole_L_PCOE_2009.pdf (1.650Mb) -
Kgathi, D.L.; Kniveton, D.; Ringrose, S.; Turton, A.R.; Vanderpost, C.; Lundqvist, J.; Seely, M. (Elsevier; www.elsevier.com/locate/jhydrol, NaN, 2006)[more][less]
Abstract: The Okavango basin comprises the Cuito and Cubango active catchment areas in Angola, in addition to the Kavango's Okavango non-active catchment in northern Namibia and Botswana. The Okavango River water and its ecosystem resources are critically important sources of livelihoods for people in the basin. Pressures from livelihoods and development are already impacting on the environment. These pressures may increase in the future due to the rapid increase in population, the peace process and associated resettlement activities in Angola, and major development initiatives in Botswana and Namibia. For instance, possible future increase in water abstraction from the Okavango River may affect the long-term environmental sustainability of the Okavango Delta by minimizing channel shifting and thereby reducing spatial biodiversity. The paper argues that while conservation of the natural environment is critical, the pressing development needs must be recognized. The reduction of poverty within the basin should be addressed in order to alleviate adverse effects on the environment. The paper recommends that the development of sustainable tourism and community-based natural resource management initiatives may be appropriate strategies for reaching the Millennium Development Goals of poverty alleviation and achievement of environmental sustainability in the Okavango Basin. These initiatives have a comparative advantage in this area as demonstrated by the performance of the existing projects. URI: http://hdl.handle.net/10311/154 Files in this item: 2
kgathi_j_hydrology_2006.pdf (6.004Mb)license.txt (1.998Kb) -
Ringrose, S.; Kampunzu, A.B.; Vink, B.W.; Matheson, W.; Downey, W.S. (John Wiley & Sons, Ltd. http://www3.interscience.wiley.com/journal/117935722/grouphome/home.html, NaN, 2002)[more][less]
Abstract: Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an 'upper surface (1095 m) containing abundant sil-calcrete, an intermediate surface (1085 m) in which sil-calcrete underlies nodular calcrete and lower (1075 m) surface in which sil-calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing Si02 content (and increasing CaC03 content) with depth from the highest to the lowest surface levels. The calcretes and sil-calcretes represent modifications of pre-existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++ -rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying-induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid-Pleistocene age for sil-calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late st~ge dissolution of CaC03 from pre-existing surface calcretes or sil-calcretes led to the formation of pedogenic case-hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. URI: http://hdl.handle.net/10311/310 Files in this item: 1
Ringrose_ESPL_2002.pdf (3.095Mb) -
Vanderpost, C. (Population Environment; Springer Netherlands; http://www.springerlink.com/content/0t141ml76q32717m/, January NaN, 2006)[more][less]
Abstract: Intensification of human sprawl in buffer zones of globally important African wilderness areas is of worldwide concern. The paper identifies two major conflicting (yet potentially reconcilable) pathways of rural sprawl in African wilderness buffer regions, described as the subsistence pathway and the wildlife-tourism pathway. Containment of rural sprawl near important ecological reserves requires addressing both pathways and their underlying conflicts. Reconciliation of subsistence sprawl with wildlife-conservation based tourism may occur through adequate compensation for community subsistence resource losses by the creation of sufficient alternatives to local communities that may reduce the need to rely on subsistence resources. URI: http://hdl.handle.net/10311/59 Files in this item: 2
cvanderpostpathwaysprefinalversion.pdf (725.4Kb)license.txt (1.998Kb) -
Meck, M.L.; Atlhopheng, J.; Masamba, W.R.L.; Ringrose, S. (Elsevier. http://www.elsevier.com, August 20, 2010)[more][less]
Abstract: The study set out to determine the weathering and dissolution of metal hosting minerals at Dorowa for purposes of deducing pollution potential to the nearby Save River. Phosphate rock is mined at Dorowa for the production of phosphate fertilizer. The major minerals found in the ring complex are feldspars, pyroxenes, apatite, magnetite and calcite. Chemical analysis established that the rocks are associated with metals that include copper, lead, zinc, cobalt, nickel, tin and cadmium. Among the many minerals present apatite and calcite host metals more than the other minerals due to their crystal structure. This study investigated the weathering and dissolution of these two minerals. Both apatite and calcite dissolve in natural environmental conditions prevalent at Dorowa. From the analysis the study concludes that the potential availability of metals trapped in the calcite and apatite structures is high. The understanding of weathering and dissolution of metal hosting minerals is important in predicting quality of water around the study area, because most villagers use the Save River as their primary drinking water source. URI: http://hdl.handle.net/10311/833 Files in this item: 1
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VanderPost, C.; Ringrose, S.; Seely, M. (Botswana Society, NaN, 2005)[more][less]
Abstract: Image processing in the upper Okavango catchment resulted in ten generalised classes which may be used as base line data for monitoring future overall land-use/cover change assessments over the entire upper catchment. Specific work was undertaken using single images for more detailed land-use/cover mapping in a 10 km buffer along all tributaries of the upper Okavango in Angola and Namibia. In terms of the under-developed Angolan upper catchment there is relatively little land clearing at present, and impacts on water use and quality are expected to be minimal in the near future. This is a consequence of 20 years of civil war, while the return of refugees is being inhibited by the prevalence of land-mines. Much more extensive development is taking place in Namibia along the southern bank of the Kavango river. This area is likely to become more intensively used as Namibia attempts to develop greater food security. Further work is required to monitor the impacts from Namibian agricultural expansion. These are likely to be pervasive in terms of the ecology of both the Mahango Game Reserve in Namibia and the Okavango Delta in Botswana. URI: http://hdl.handle.net/10311/936 Files in this item: 1
VanderPost 2005 Prelim.pdf (2.370Mb) -
Dallas, H.F.; Mosepele, B. (African Journal of Aquatic Science http://www.nisc.co.za/journals?id=2, NaN, 2006)[more][less]
Abstract: The spatial distribution of aquatic macroinvertebrates in the Okavango River Delta, Botswana, was investigated during the low-water period in February 2003. This complements an earlier study undertaken during high-water in June 2000. Seventy-five samples were taken in a range of aquatic habitats at 29 georeference points in four focal areas: Upper Panhandle (UPH), Lower Panhandle and Guma Lagoon (LPH), Moremi Game Reserve/Xakanaka (MGR), and Chief’s Island (CI). Over 180 morphospecies (approximately 63 families) were recorded during the survey. Multivariate analyses of macroinvertebrate assemblages indicated that assemblages in each of the four focal areas were at least 54% similar at morphospecies level, and 71% similar at family level, although some taxa were more or less common in different areas. Differences in macroinvertebrate assemblages were observed amongst different habitat types, with differences most pronounced between the deltaic habitats and isolated seasonally-flooded pools and temporary rain-filled pools in MGR and CI. The highest number of taxa was recorded in the MGR (125), followed by the UPH (96), CI (93) and the LPH (89) areas. The most families were recorded in the Hemiptera (11), followed by Mollusca (10), Diptera (nine), Coleoptera (nine), Crustacea (six), Ephemeroptera (six) and Odonata (four). Three families of Hirudinea and Trichoptera, and one family of Lepidoptera, were also recorded. Hydracarina were common but not identified beyond order, while Oligochaeta were less frequently recorded. With respect to the different aquatic habitats sampled, the highest number of taxa was recorded in marginal vegetation in the channels and lagoons, although inundated floodplains, floating vegetation and marginal vegetation in backwaters also supported many taxa. The fewest taxa were recorded in sediment. This survey, whilst representing a ‘snapshot’ of the system under low-water conditions, highlights the importance of maintaining a mosaic of aquatic habitats in the Delta. Further studies would enhance our knowledge of the aquatic macroinvertebrate biodiversity of the Okavango Delta, thereby contributing to its conservation. URI: http://hdl.handle.net/10311/869 Files in this item: 1
Dallas_AJAS_2007.pdf (1.160Mb) -
Mosepele, K.; Mosepele, B.; Williams, L. (Botswana Society, NaN, 2005)[more][less]
Abstract: This study investigates the feeding ecology of Schilbe intermedius across its entire life history. Data were collected using experimental fishing nets in two habitats in a seasonal floodplain. The results showed that S. intermedius has an ontogenetic shift in feeding behaviour where the young fish are primarily generalist predators, feeding on aquatic invertebrates while the older fish are more specialised predators feeding primarily on fish. This study showed that there is a higher potential for intra-specific competition among the older fish than in the younger size classes. However, it was recognized that this study is a snap-shot of the feeding ecology of S. intermedius and that a longer time series study is needed to study its feeding ecology. URI: http://hdl.handle.net/10311/940 Files in this item: 1
Mosepele 2005 Prelim.pdf (1.295Mb) -
Mbaiwa, J.E. (John Wiley and Sons, http://www.wiley.com, NaN, 2004)[more][less]
Abstract: This paper uses the concept of sustainable rural livelihoods and income diversification to assess the role that basket making as a cultural tourism activity can play in improving rural livelihoods in the Okavango Delta, Botswana. Using both primary and secondary data sources, this paper points out that shocks and natural causes such as drought, disease and changing flood levels in the Okavango River, particularly the drying of the Thaoge (one of the distributaries of the Okavango), have contributed to a decline in livestock and crop yields and increased poverty levels in the region. Therefore, alternative livelihood options that can diversify rural incomes from agricultural production need to be identified. This paper argues that basket making has the potential to diversify rural incomes and improve livelihoods in the Okavango. Baskets are a cultural tourism product that can raise income earning and employment opportunities for rural residents in the Okavango. For this to be successful, basket making will need to be developed as part of cultural tourism. A sustainable cultural tourism sector where baskets are key products requires the sustainable use of natural resources used for basket making. These resources are at present overharvested and are threatened with depletion. There is also a need to promote the empowerment of basket weavers particularly in entrepreneurship and managerial skills in the tourism business, attract young and educated people and promote the preservation of traditional basket making skills, which are important in the development of cultural tourism. URI: http://hdl.handle.net/10311/935 Files in this item: 1
Mbaiwa 2004 Int Journ Tourism.pdf (3.700Mb) -
Tesfaye, G.; Teketay, D.; Fetene, M.; Beck, E. (Elsevier, www.elsevier.com, NaN, 2010)[more][less]
Abstract: Regeneration of seven indigenous tree species having significant ecological and economic importance was investigated in the Munessa-Shashemene dry Afromontane forest (MSF), southern Ethiopia. Densities and distributions of seedlings, saplings and trees were assessed along gradients of altitude, light and disturbance using quadrat sizes of 10×5 m (for seedlings) and 20×20 m (saplings and trees) following line transects. The number of individuals, frequency and height of the study species were recorded in the quadrats at every 100 m drop in altitude. Seedling densities varied markedly among the species and altitudes. Mean densities (number of individuals ha−1) of seedlings ranged from zero (Polyscias fulva) to 5334 (Prunus africana), and from three (Polyscias fulva) to 102 (Podocarpus falcatus) for trees and saplings. Canonical Correspondence Analysis revealed that seedlings of Celtis africana and Croton macrostachyus were highly favored by disturbance and, hence, were concentrated in canopy gaps within the forest. Based on their population structures, the study species could be categorized into three groups: (1) Species that showed the highest proportion of individuals in the lowest height class and with a gradual decrease towards the upper height classes, which suggests good regeneration; Podocarpus falcatus, C. africana, C. macrostachys and P. africana belonged to this group. (2) Species that showed higher proportions of individuals in the lowest height class and with missing individuals in the subsequent middle height classes, indicative of hampered regeneration; Syzygium guineense and Pouteria adolfi-friederici belonged to this group. (3) Species with no individuals in the lowest and middle height classes but represented by individuals in upper height classes; P. fulva belonged to this group. The species categorized in the last two groups exhibited hampered regeneration, and P. fulva is in the verge of local extermination. High seedling densities (e.g. C. africana and P. africana) and/or adaptive defense mechanisms to herbivory (e.g. P. falcatus and C. macrostachyus) were common attributes of species, which exhibited good regeneration. Regeneration problems were largely attributed to human disturbance, lack of suitable habitat for seed germination or problems associated to seed set (seed predation or abortion). Our study indicated that P. fulva, P. adolfi-friederici and S. guineense require the highest immediate attention for conservation in the MSF. URI: http://hdl.handle.net/10311/827 Files in this item: 1
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Caylor, K.K.; Dowty, P.R.; Shugart, H.H.; Ringrose, S. (November 23, 2011)[more][less]
Abstract: The observed variability in vegetation structure within landscapes was used as the basis for model estimates of the range of annual productivity of landscape patches at four sites along a moisture gradient in southern Africa ranging from 879 to 365 mm mean annual rainfall. Principal components of patch-scale variability in leaf area, woody biomass and vertical leaf profiles were derived from intensive characterization of the small-scale spatial structure of woody vegetation at each site. For each site, the mean and extremes of the principal component distribution parameterized an ecophysiology model of vegetation productivity. Vegetation was most heterogeneous at intermediate locations along the rainfall gradient. Variability in vegetation structure led to a range of annual productivity within one site (600 mm) that accounted for 68% of the total range in mean productivity across all sites. Patch-scale estimates of tree productivity were found to be primarily correlated to annual rainfall (r2=0.66, P=0.001) and not woody leaf area (r2=0.01, P=0.75), while grass productivity was found to be related to values of woody leaf area (r2=0.77, P<0.001) and not annual rainfall (r2=0.11, P=0.29). This result indicates that life-form interactions have a significant role in controlling vegetation productivity across the rainfall gradient. The findings of this study emphasize the importance of considering heterogeneity rather than mean structure when modeling productivity, particularly when considering dynamic vegetation structure, where differences between landscape patches may not be well represented in the mean structure. URI: http://hdl.handle.net/10311/933 Files in this item: 1
Caylor Ringrose 2004.pdf (1.770Mb)