Department of Botany
Permanent URI for this collection
Browse
Browsing Department of Botany by Author "Banyikwa, Feetham F."
Now showing 1 - 20 of 26
Results Per Page
Sort Options
Item Determinants of Woody Cover in African Savannas(2005) Sankaran, Mahesh; Hanan, Niall P.; Scholes, Robert J.; Ratnam, Jayashree; Augustine, David J.; Cade, Brian S.; Gignoux, Jacques; Higgins, Steven I.; Le Roux, Xavier; Ludwig, Fulco; Ardo, Jonas; Banyikwa, Feetham F.; Bronn, Andries; Bucini, Gabriela; Caylor, Kelly K.; Coughenour, Michael B.; Diouf, Alioune; Ekaya, Wellington; Feral, Christie J.; February, Edmund C.; Frost, Peter G. H.; Hiernaux, Pierre; Hrabar, Halszka; Metzger, Kristine L.; Prins, Herbert H. T.; Ringrose, Susan; Sea, William; Tews, Jörg; Worden, Jeff; Zambatis, NickSavannas are globally important ecosystems of great significance to human economies. In these biomes, which are characterized by the co-dominance of trees and grasses, woody cover is a chief determinant of ecosystem properties1, 2, 3. The availability of resources (water, nutrients) and disturbance regimes (fire, herbivory) are thought to be important in regulating woody cover1, 2, 4, 5, but perceptions differ on which of these are the primary drivers of savanna structure. Here we show, using data from 854 sites across Africa, that maximum woody cover in savannas receiving a mean annual precipitation (MAP) of less than ~650 mm is constrained by, and increases linearly with, MAP. These arid and semi-arid savannas may be considered ‘stable’ systems in which water constrains woody cover and permits grasses to coexist, while fire, herbivory and soil properties interact to reduce woody cover below the MAP-controlled upper bound. Above a MAP of ~650 mm, savannas are ‘unstable’ systems in which MAP is sufficient for woody canopy closure, and disturbances (fire, herbivory) are required for the coexistence of trees and grass. These results provide insights into the nature of African savannas and suggest that future changes in precipitation6 may considerably affect their distribution and dynamics.Item Developing the Environmental Long-Term Observatories Network of Southern Africa (ELTOSA)(2003) Henschel, Joh; Pauw, Johan; Banyikwa, Feetham F.; Brito, Rui; Chabwela, Harry; Palmer, Tony; Ringrose, Sue; Santos, Luisa; Sitoe, Almeida; van Jaarsveld, AlbertIn May 2001, we, scientists from six countries in southern Africa, formed the Environmental Long-Term Observatories Network of Southern Africa (ELTOSA). Further development was made at the ELTOSA conference on Inhaca Island, Mozambique, during July 2002. ELTOSA connects country Environmental Observatories Networks (EON), the African adaptation of LTER (long-term ecological research). The International Long-Term Ecological Research Network (ILTER) has accepted ELTOSA as a regional member, and currently three ELTOSA country members have individual ILTER membership (Namibia in 1999, Zambia in 2001, South Africa in 2002) and others are working towards membership. This position paper describes the development of a vision for EON in southern Africa. We outline the importance of developing EON and list the opportunities this offers for the natural and social sciences. Finally, we focus on some challenges that accompany the development of EON in the region, with suggestions on how to meet them.Item Developing the Environmental Long-Term Observatories Network of Southern Africa (ELTOSA)(2003-04) Henschela, Joh; Pauw, Johan; Banyikwa, Feetham F.; Brito, Rui; Chabwela, Harry; Palmer, Tony; Ringroseg, Sue; Santos, Luisa; Sitoed, Almeida; Jaarsveld, Albert V.Background In May 2001, we, scientists from six countries in southern Africa, formed the Environmental Long-Term Observatories Network of Southern Africa (ELTOSA). Further development was made at the ELTOSA conference on Inhaca Island, Mozambique, during July 2002. ELTOSA connects country Environmental Observatories Networks (EON), the African adaptation of LTER (long-term ecological research). The International Long-Term Ecological Research Network (ILTER) has accepted ELTOSA as a regional member, and currently three ELTOSA country members have individual ILTER membership (Namibia in 1999, Zambia in 2001, South Africa in 2002) and others are working towards membership. This position paper describes the development of a vision for EON in southern Africa. We outline the importance of developing EON and list the opportunities this offers for the natural and social sciences. Finally, we focus on some challenges that accompany the development of EON in the region, with suggestions on how to meet them.Item Ecosystem Catalysis: Soil Urease Activity and Grazing in the Serengeti Ecosystem(Wiley, 1997) McNaughton, S. J.; Zuniga, Gina; McNaughton, M. M.; Banyikwa, Feetham F.The activity of soil ureases was evaluated in the laboratory in soils from three locations in the Serengeti National Park, Tanzania, differing in the grazing intensities that the grasslands there support. Urease activity was assayed by the instantaneous release of NH4 as soon as soils drained to field capacity after application of an aqueous urea solution approximating N concentrations in ungulate urine. The appearance of NO3 and S04 in extracts was used as an index of biological activity and pH changes; neither responded to urea addition. Ammonium appearance in extracts of soils to which water but not urea was applied was low and identical; appearance in extracts where urea had been added was high and differed between sites, increasing with the level of grazer activity at a site. The data document ecologically meaningful levels of soil urease in Serengeti soils and a positive associa- tion of those levels with grazing intensity.Item Ecosystem Catalysis: Soil Urease Activity and Grazing in the Serengeti Ecosystem(1997) McNaughton, S. J.; Zuniga, Gina; McNaughton, M. M.; Banyikwa, Feetham F.The activity of soil ureases was evaluated in the laboratory in soils from three locations in the Serengeti National Park, Tanzania, differing in the grazing intensities that the grasslands there support. Urease activity was assayed by the instantaneous release of NH4 as soon as soils drained to field capacity after application of an aqueous urea solution approximating N concentrations in ungulate urine. The appearance of NO3 and SO4 in extracts was used as an index of biological activity and pH changes; neither responded to urea addition. Ammonium appearance in extracts of soils to which water but not urea was applied was low and identical; appearance in extracts where urea had been added was high and differed between sites, increasing with the level of grazer activity at a site. The data document ecologically meaningful levels of soil urease in Serengeti soils and a positive association of those levels with grazing intensity.Item Endangered Mangrove Ecosystems. The Case of the Kunduchi and Mbweni Mangrove Forests(1986) Banyikwa, Feetham F.; Semesi, A. K.Item Fuzzy Set Ordination and Classification of Serengeti Short Grasslands, Tanzania(Wiley, 1990) Banyikwa, Feetham F.; Feoli, Enrico; Zuccarello, VincenzoSpecies abundance data from 32 representative stands are used to evaluate the vegetation in the heavily grazed Serengeti short grasslands. The abundant species are: Kyllinga nervosa, Sporobolus ioclados, S. kentrophyllus and Eustachys paspaloides, all occurring in elevated areas, and Hypoestes forskalei, which is found in the drainage areas. Numerical classification and fuzzy set ordination revealed four main grassland communities associated with a topographic gradient. The communities are considered distinct since their niches, as computed in the community and environmental fuzzy system space are not overlapping. Leaching, erosion and animal disturbance effects correlated with the topographic gradient are found to determine species composition and overall community structure in the grasslands.Item The Geographical Distribution of Mangrove Forests along the East African Coast.(UNESCO, 1986) Banyikwa, Feetham F.Item Growth Analysis of Groundnuts (Arachis Hypogea) In Competition with Ageratum Conyzoides.(1985) Banyikwa, Feetham F.; Rulangaranga, Z. K.Item The Growth Response of Two East African Perennial Grasses to Defoliation, Nitrogen Fertilizer and Competition(1988) Banyikwa, Feetham F.Two East African perennial grasses, Digitaria macroblephara (Hack) Stapf. and Sporobolus ioclados (Trin.) Nees, were grown in pure and mixed culture in a factorial treatment design of defoliation, nitrogen fertilizer and plant density for a period of 90 d. With regard to controls, defoliation reduced total yield of both species per plant by 81%; higher density decreased total yield per plant by 56%; and intraspecific competition decreased total yield per plant 24% more than interspecific competition. High nitrogen promoted total yield per plant by 168%. Total yield per plant of D. macroblephara was 3.2 times greater than that of S. ioclados. With defoliation, density dependent competition decreased total yield per plant by 42% while, without defoliation, density dependent competition decreased total yield per plant by 601%. With defoliation, high nitrogen increased yield per plant by 9% while without defoliation high nitrogen increased yield per plant by 315%. The results suggest that the magnitude of the negative aspects of density dependent competition may be lessened by defoliation and growing plants in mixed culture. It is concluded that in grazing ecosystems it may be advantageous to grow plants in mixed culture since the negative effects of interspecific competition are less than those arising from intraspecific competition.Item The Growth Response of Two East African Perennial Grasses to Defoliation, Nitrogen Fertilizer and Competition(Wiley, 1988) Banyikwa, Feetham F.Two East African perennial grasses, Digitaria macroblephara (Hack) Stapf. and Sporobolus ioclados (Trin.) Nees, were grown in pure and mixed culture in a factorial treatment design of defoliation, nitrogen fertilizer and plant density for a period of 90 d. With regard to controls, defoliation reduced total yield of both species per plant by 81%; higher density decreased total yield per plant by 56%; and intraspecific compe- tition decreased total yield per plant 24% more than interspecific competition. High nitrogen promoted total yield per plant by 168%. Total yield per plant of D. macro- blephara was 3.2 times greater than that of S. ioclados. With defoliation, density dependent competition decreased total yield per plant by 42% while, without defolia- tion, density dependent competition decreased total yield per plant by 601%. With defoliation, high nitrogen increased yield per plant by 9% while without defoliation high nitrogen increased yield per plant by 315%. The results suggest that the magni- tude of the negative aspects of density dependent competition may be lessened by defoliation and growing plants in mixed culture. It is concluded that in grazing ecosystems it may be advantageous to grow plants in mixed culture since the negative effects of interspecific competition are less than those arising from intraspecific competition.Item Loss of Ascorbic Acid Due to Wilting in Some Green Leafy Vegetables(1983) Seeramulu, N.; Banyikwa, Feetham F.; Srivastava, V.Item Optimal Weeding Period for Groundnuts (Arachis Hypogea L.)(1988) Rulangaranga, Z. K.; Banyikwa, Feetham F.Item The Physical and Chemical Characteristics of a Phycocolloid from the Red Alga Sarcodia Montagneana j. Agardh of Tanzania(1987) Semesi, A. K.; Banyikwa, Feetham F.A phycocolloid from Sarcodia montagneana has been evaluated by chemical and physical analyses. The study has revealed that the phycocolloid has a yield of 39.6 per cent (percentage dry weight of alga), an IR spectrum similar to that reported for .lambda.-type carrageenan, an SO4-2 content of 22.5 per cent, a 3, 6-anhydrogalactose content of 5.1 per cent, a galactose content of 51.5 per cent (percentage dry weight of phycocolloid) and a negative optical rotation. The polysaccharide does not form a gel and cannot be modified by alkaline borohydride. It may be used in the food industry as an emulsifying agent.Item Plant Communities and Herbivory(1995) McNaughton, S. J.; Banyikwa, Feetham F.Item Promotion of the Cycling of Diet-Enhancing Nutrients by African Grazers(1997) McNaughton, S. J.; Banyikwa, Feetham F.; McNaughton, M. M.Experiments in Serengeti National Park, Tanzania, provide direct evidence that large, free-ranging mammalian grazers accelerate nutrient cycling in a natural ecosystem in a way that enhances their own carrying capacity. Both nitrogen and sodium were at considerably higher plant-available levels in soils of highly grazed sites than in soils of nearby areas where animal density is sparse. Fencing that uncoupled grazers and soils indicated that the animals promote nitrogen availability on soils of inherently similar fertility and select sites of higher sodium availability as well as enhancing that availability.Item Promotion of the Cycling of Diet-Enhancing Nutrients by African Grazers(1997) McNaughton, S. J.; Banyikwa, Feetham F.; McNaughton, M. M.Experiments in Serengeti National Park, Tanzania, provide direct evidence that large, free-ranging mammalian grazers accelerate nutrient cycling in a natural ecosystem in a way that enhances their own carrying capacity. Both nitrogen and sodium were at considerably higher plant-available levels in soils of highly grazed sites than in soils of nearby areas where animal density is sparse. Fencing that uncoupled grazers and soils indicated that the animals promote nitrogen availability on soils of inherently similar fertility and select sites of higher sodium availability as well as enhancing that availability.Item A Quantitative Study of the Ecology of the Serengeti Short Grasslands(1976) Banyikwa, Feetham F.Item Root Biomass and Productivity in a Grazing Ecosystem: The Serengeti(1998-03) McNaughton, S. J.; Banyikwa, Feetham F.; McNaughton, M. M.Does grazing by large wild mammals, an intense form of aboveground herbivory, influence belowground productivity? The vast majority of literature data concentrate on short-term pot studies and indicate that clipping consistently retards root growth. Field studies are few and contradictory, but tend to indicate that grazing has little effect on grassland belowground production. We sampled root-soil cores at 0–10 and 10–20 cm increments, at 11 locations across the Serengeti ecosystem, on 10 dates over an annual cycle, sampling monthly during the rainy and early dry seasons and every 2 mo during peak dry season. Fenced and unfenced plots were replicated (n = 2 or 3) at each location. Live roots, identified visually by brightness and texture, were sorted, washed, dried, and weighed. In addition, profiles were sampled at 10-cm increments to 50 cm in fenced and unfenced plots in short, mid-height, and tall grasslands, representing a gradient of grazing, during the month of peak root biomass. Exclosures erected 22–25 yr previously were similarly sampled in short and tall grasslands to a 30-cm depth. Root biomass reached a pronounced minimum in mid-wet season (February) and a decided maximum at the beginning of the dry season (June). Net productivity, based on maximum–minimum biomass, ranged from 100 to 600 g·m−2·yr−1 to a 20-cm depth, with minima ranging from 40 to 150 g/m2 and maxima from 230 to 700 g/m2, according to location. There was no evidence that grazing reduced root productivity over the annual cycle. Vertical biomass profiles at peak standing crop were similar for short, mid-height, and tall grasslands, with root biomass dropping sharply with depth, except for short grasslands on soils that, atypically, lack a hardpan. In those grasslands, shallow root biomass was lower than in other grasslands, but biomass at depth was distinctly greater. For long-term protected grasslands, root biomasses at peak were identical in short grasslands, whether fenced or unfenced, but fenced tall grasslands had a lower root biomass than grazed plots. We conclude that intense herbivory does not inhibit root biomass or belowground productivity of Serengeti grasslands over either the short or the long term.