Ecological degradation in cities: impact of urban agriculture In Harare, Zimbabwe

A journal article on the impact on the environment of urban agriculture in Zimbabwe.The effect of the increasingly widespread practice of urban agriculture in the City of Harare on the natural biodiversity was investigated. Vegetation surveys noting species presence-absence and abundance were undertaken in seven field areas, identifying the components of the natural vegetation of both the clay soil-type areas developed on basic rock, and the sandy soil-type areas developed on granite, that typify the city. Change brought about by the increasingly widespread practice of urban agriculture was determined, and knock-on effects for other aspects of the city's ecology were investigated. Most open space areas in Harare are vlei land. Detrended Correspondence Analysis (DCA) illustrated significant differences in the species composition of uncultivated vlei areas with distance from the vlei channel, reflecting change in the water-logging conditions of the soil. A higher diversity of faunal species, and larger species count, prior to cultivation was also noted. The effects of cultivation on the vegetation were a change in species composition (with the natural vegetation being replaced by mainly alien arable weeds), the loss of the spatial diversity in species presence and dominance, a significantly reduced ground cover, and a loss of habitat diversity. The implications of these changes for the amenity value of the city environment is discussed. The need for a more sensitive management of open-land areas within Harare, while the possibility of their conservation as areas of viable natural ecological diversity is still available, is highlighted

Short-Term Influence of Fire on Herbaceous Composition, Diversity and Grass Biomass Production in Semi-Arid Savanna Woodland in Windhoek, Namibia

Abstract A co mparative study on short term in fluence of fire on herbaceous composition and grass biomass production was conducted in a semi-arid savanna woodland in Windhoek, to assess differences in herbaceous composition and grass biomass production after a late dry season fire. The study revealed that herbaceous composition and grass cover differ significantly between the burned and unburned areas. Grass cover differed significantly (p< 0.001) between the burned and unburned areas. Fire removes aging grass materials, growth inhib itors and moribund hence, enhancing the vitality grasses. There were no significant differences in species richness (t = -1.402, p > 0.05), species diversity (t = -1.391, df = 28, p > 0.05), grass biomass production (t = 1.724, p > 0.05) and forb densities (t = 0.361, p > 0.05) between the burned and unburned areas..The study findings suggested that short term fire does have a significant impact on grass cover and herbaceous dominance and insignificant impact on grass biomass production, forb densities, species richness and diversity in short term, but fire impact on these plant attributes also depend on the intensity of fire and time frame

The charcoal trap: Miombo forests and the energy needs of people

<p>Abstract</p> <p>Background</p> <p>This study evaluates the carbon dioxide and other greenhouse gas fluxes to the atmosphere resulting from charcoal production in Zambia. It combines new biomass and flux data from a study, that was conducted in a <it>miombo </it>woodland within the Kataba Forest Reserve in the Western Province of Zambia, with data from other studies.</p> <p>Results</p> <p>The measurements at Kataba compared protected area (3 plots) with a highly disturbed plot outside the forest reserve and showed considerably reduced biomass after logging for charcoal production. The average aboveground biomass content of the reserve (Plots 2-4) was around 150 t ha^-1, while the disturbed plot only contained 24 t ha^-1. Soil carbon was not reduced significantly in the disturbed plot. Two years of eddy covariance measurements resulted in net ecosystem exchange values of -17 ± 31 g C m^-2y^-1, in the first and 90 ± 16 g C m^-2in the second year. Thus, on the basis of these two years of measurement, there is no evidence that the <it>miombo </it>woodland at Kataba represents a present-day carbon sink. At the country level, it is likely that deforestation for charcoal production currently leads to a per capita emission rate of 2 - 3 t CO₂y^-1. This is due to poor forest regeneration, although the resilience of <it>miombo </it>woodlands is high. Better post-harvest management could change this situation.</p> <p>Conclusions</p> <p>We argue that protection of <it>miombo </it>woodlands has to account for the energy demands of the population. The production at national scale that we estimated converts into 10,000 - 15,000 GWh y^-1of energy in the charcoal. The term "Charcoal Trap" we introduce, describes the fact that this energy supply has to be substituted when woodlands are protected. One possible solution, a shift in energy supply from charcoal to electricity, would reduce the pressure of forests but requires high investments into grid and power generation. Since Zambia currently cannot generate this money by itself, the country will remain locked in the charcoal trap such as many other of its African neighbours. The question arises whether and how money and technology transfer to increase regenerative electrical power generation should become part of a post-Kyoto process. Furthermore, better inventory data are urgently required to improve knowledge about the current state of the woodland usage and recovery. Net greenhouse gas emissions could be reduced substantially by improving the post-harvest management, charcoal production technology and/or providing alternative energy supply.</p

Evidence that the Human Pathogenic Fungus Cryptococcus neoformans var. grubii May Have Evolved in Africa

Most of the species of fungi that cause disease in mammals, including Cryptococcus neoformans var. grubii (serotype A), are exogenous and non-contagious. Cryptococcus neoformans var. grubii is associated worldwide with avian and arboreal habitats. This airborne, opportunistic pathogen is profoundly neurotropic and the leading cause of fungal meningitis. Patients with HIV/AIDS have been ravaged by cryptococcosis – an estimated one million new cases occur each year, and mortality approaches 50%. Using phylogenetic and population genetic analyses, we present evidence that C. neoformans var. grubii may have evolved from a diverse population in southern Africa. Our ecological studies support the hypothesis that a few of these strains acquired a new environmental reservoir, the excreta of feral pigeons (Columba livia), and were globally dispersed by the migration of birds and humans. This investigation also discovered a novel arboreal reservoir for highly diverse strains of C. neoformans var. grubii that are restricted to southern Africa, the mopane tree (Colophospermum mopane). This finding may have significant public health implications because these primal strains have optimal potential for evolution and because mopane trees contribute to the local economy as a source of timber, folkloric remedies and the edible mopane worm

Ecological Thresholds in the Savanna Landscape: Developing a Protocol for Monitoring the Change in Composition and Utilisation of Large Trees

BACKGROUND: Acquiring greater understanding of the factors causing changes in vegetation structure -- particularly with the potential to cause regime shifts -- is important in adaptively managed conservation areas. Large trees (> or =5 m in height) play an important ecosystem function, and are associated with a stable ecological state in the African savanna. There is concern that large tree densities are declining in a number of protected areas, including the Kruger National Park, South Africa. In this paper the results of a field study designed to monitor change in a savanna system are presented and discussed. METHODOLOGY/PRINCIPAL FINDINGS: Developing the first phase of a monitoring protocol to measure the change in tree species composition, density and size distribution, whilst also identifying factors driving change. A central issue is the discrete spatial distribution of large trees in the landscape, making point sampling approaches relatively ineffective. Accordingly, fourteen 10 m wide transects were aligned perpendicular to large rivers (3.0-6.6 km in length) and eight transects were located at fixed-point photographic locations (1.0-1.6 km in length). Using accumulation curves, we established that the majority of tree species were sampled within 3 km. Furthermore, the key ecological drivers (e.g. fire, herbivory, drought and disease) which influence large tree use and impact were also recorded within 3 km. CONCLUSIONS/SIGNIFICANCE: The technique presented provides an effective method for monitoring changes in large tree abundance, size distribution and use by the main ecological drivers across the savanna landscape. However, the monitoring of rare tree species would require individual marking approaches due to their low densities and specific habitat requirements. Repeat sampling intervals would vary depending on the factor of concern and proposed management mitigation. Once a monitoring protocol has been identified and evaluated, the next stage is to integrate that protocol into a decision-making system, which highlights potential leading indicators of change. Frequent monitoring would be required to establish the rate and direction of change. This approach may be useful in generating monitoring protocols for other dynamic systems

A floristic classification of the vegetation of a forest-savanna boundary in southeastern Zimbabwe

The vegetation of Chirinda Forest boundary was classified into eight types using Two-way Indicator Species Analysis (TWINSPAN) and Detrended Correspondence Analysis (DCA). The moist forest comprises three types:  Strychnos mellodora-Chrysophyllum gonmgosanum Forest on deep dolerite soils; Chrysophyllum gorungosanum-Myrianthus holstii Forest on shallow dolerite soils; and  Teclea iiobilis-Ehretia cymosa Forest on drier, but deep dolerite soils. The non-forest vegetation comprises five types: Themeda triandra Grassland on shallow dolerite soils; Psidium guajava Bushland on sandstone; Bridelia micrantha-Harungana madagascariensis Mixed Woodland not restricted to any one particular soil type; Acacia karroo- Heteropyxis dehniae Woodland on shallow soils derived from sandstone but sometimes on dolerite; and  Julbemardia globiflora-Brachystegia spiciformis (Miombo) Woodland on sandstone

COMPARISON OF DIURNAL AND SEASONAL PATTERNS OF FEEDING BEHAVIOUR OF COWS AND CALVES AT NEUDAMM FARM IN NAMIBIA

This paper aims to compare the seasonal and diurnal feeding behaviour of cows and calves at Neudamm Farm in central Namibia. Seasonal bite rates of cows, diurnal bites of cows and calves, and diet composition and preference were assessed and compared. Ten cows and ten calves were followed and observed from a distance, in the morning and in the afternoon. The observations were done on the same cows during the wet and dry seasons while calves were only observed during the wet season. The number of bites taken by each animal within a continuous period of 5 minutes was recorded. Herbaceous plant inventory was done in the foraging area using a step-point method. Each herbaceous plant intercepted was assessed for evidence of grazing and its life form was recorded. Bite rates were compared between morning and afternoon, and between seasons using a two-sample t-test. Preference for life forms and species were tested using a Chi-Square test. The morning bite rate of 38 bites/minute of cows during the wet season was significantly higher than that of the morning dry season of 34.9 bites/minute. This is attributed to the high abundance of nutritious forage resources during the wet season when animals did not have to do much searching compared to the dry season. Afternoon bite rates of cows did not significantly differ between seasons. Morning bite rates were significantly lower in the mornings than in the afternoons in winter. This was because cold morning temperatures slowed down animal feeding rates but increased with the progression of the day. Bite rates of calves did not significantly differ between morning and afternoon during the wet season because they were still learning to forage while being dependent on the mothers for milk. Cattle preferred Schmidtia pappophoroides, Eragrostis trichophora, Heteropogon contortus and Eragrostis nindensis due to their palatability and high grazing value. Nidorella resedifolia, despite being very abundant, was avoided because it contains a toxic alkaloid

COMPARISON OF DIURNAL AND SEASONAL PATTERNS OF FEEDING BEHAVIOUR OF COWS AND CALVES AT NEUDAMM FARM IN NAMIBIA

This paper aims to compare the seasonal and diurnal feeding behaviour of cows and calves at Neudamm Farm in central Namibia. Seasonal bite rates of cows, diurnal bites of cows and calves, and diet composition and preference were assessed and compared. Ten cows and ten calves were followed and observed from a distance, in the morning and in the afternoon. The observations were done on the same cows during the wet and dry seasons while calves were only observed during the wet season. The number of bites taken by each animal within a continuous period of 5 minutes was recorded. Herbaceous plant inventory was done in the foraging area using a step-point method. Each herbaceous plant intercepted was assessed for evidence of grazing and its life form was recorded. Bite rates were compared between morning and afternoon, and between seasons using a two-sample t-test. Preference for life forms and species were tested using a Chi-Square test. The morning bite rate of 38 bites/minute of cows during the wet season was significantly higher than that of the morning dry season of 34.9 bites/minute. This is attributed to the high abundance of nutritious forage resources during the wet season when animals did not have to do much searching compared to the dry season. Afternoon bite rates of cows did not significantly differ between seasons. Morning bite rates were significantly lower in the mornings than in the afternoons in winter. This was because cold morning temperatures slowed down animal feeding rates but increased with the progression of the day. Bite rates of calves did not significantly differ between morning and afternoon during the wet season because they were still learning to forage while being dependent on the mothers for milk. Cattle preferred Schmidtia pappophoroides, Eragrostis trichophora, Heteropogon contortus and Eragrostis nindensis due to their palatability and high grazing value. Nidorella resedifolia, despite being very abundant, was avoided because it contains a toxic alkaloid

Vegetation-environment relationships in a catchment containing a dambo in central Zimbabwe

Seasonally saturated wetlands, known as dambos. are a common landscape element throughout much of southern  Africa. The diversity of species composition within catchments containing dambos is widely attributed to hydrological conditions, but plant-water relationships are poorly established. In this paper a detailed classification and a vegetation map are presented for a small catchment in central Zimbabwe containing a dambo. Canonical Correspondence Analysis has been applied to explore the link between vegetation composition and environmental variables. This confirms that water is a key influence in species distribution and small-scale patterning of vegetation within the catchment