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Bush cover and range condition assessments in relation to landscape and grazing in southern Ethiopia 总被引：6，自引：0，他引：6
Progressive growth of bush cover in dry savannahs is responsible for declines in range conditions. In southern Ethiopia, the Booran pastoralists assisted our understanding of spatial patterns of bush cover and range conditions in 54 landscape patch types grouped into six landscape units within an area of 30000 km2. The size of landscape patches sampled was 625 m2. We assessed the relationships between bush cover, grass cover and bare soil and grazing pressure and soil erosion and changes in range condition. Externally, political conflicts and internally, break down of land use, and official bans on the use of fire promoted bush cover and the decline in range conditions. Bush cover was negatively correlated with grass cover, and positively correlated with bare soil. Grass cover was negatively correlated with bare soil and grazing pressure in most landscape patch types. Grazing pressure was not significantly correlated with bush cover or bare soil, while soil erosion was directly related to bare soil. Soil erosion was absent in 64% of the landscape patch types, and seemingly not a threat to the rangelands. The relationship between bush cover, grass cover, bare soil and soil erosion is complex and related to climate, landscape geology, and patterns of land use. Main threats to range conditions are bush climax, loss of grass cover and unpalatable forbs. Currently, >70% of the landscape patch types are in poor to fair range conditions. Decline in range conditions, unless reversed, will jeopardise the pastoral production system in southern Ethiopia. 相似文献
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This study reconstructed 21 years of household cattle population data in key resource (tula wells) and non-key resource (pond-water) rangelands in southern Ethiopia, as well as 15 years of government cattle breed conservation ranch data, to analyze the relationship between long-term rainfall and cattle population dynamics. For the key-and-non-key resource rangelands, we assessed the reproductive life of cows and the number of calves. For both the communal and ranch systems, we analyzed impacts of multiple droughts on calving rates and herd die-offs. Relationships between pre-drought and post-drought cattle populations were used to evaluate evidence of density-dependence. Breeding females in the key resource tula well rangelands had a longer reproductive life than in the pond-water rangelands, and they produced more calves per reproductive life. Average calving rates were 55% for the communal and 52% for the ranch. Greater reductions in calving rates during droughts implied reduced herd growth potential. Breeding females and immature animals were influenced to a much greater degree by inter-annual rainfall variability than were mature males. The data showed a downward spiral for the total cattle holdings over a 21-year period, with a decline of 54%. The evidence of density-dependence was relatively important at the local land use level as compared with the regional level. Cattle population below carrying capacity under ranch management did not reduce herd die-offs, suggesting that rainfall variability, not density, had greater influence on cattle population dynamics. Long-term trends of cattle populations in the communal and ranch systems synchronized with mean deviations of rainfall. Our results indicate that rainfall variability under the different management systems strongly influenced the dynamics of cattle population, calving rates and mortality. The claim that ranching could be a superior model for range management in Borana over the communal system was not confirmed. The decline in cattle population in southern Ethiopia indicates a need for improved drought management policy. The evidence that droughts were more harmful to breeding females and immature animals than to mature males suggested that drought management needs to focus on herd recruitment potential. For the herders in southern Ethiopia, drought management involved herd mobility and accumulation of herds during periods of favourable rainfall. In the future, the importance of government ranch could be in breed conservation for the maintenance of the Borana cattle breed through distribution of bulls during the drought recovery phase. 相似文献
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We examine how the system of grazing management of cattle in savanna rangelands affects the herd response to drought. We have used long-term time series data to evaluate the effects of management on drought-induced cattle mortality using traditional livestock management practices. There was no control of stocking densities, as compared to a government ranch where stocking densities would be adjusted in accordance with available pasture. We tested the responses under two scenarios. Scenario 1: Response of cattle herds to inter-annual rainfall variability (IRV) under a regulated grazing management system; this provides more reliable predictions of cattle population and performance in terms of herd mortality and calving rates than does the communal land use system. Scenario 2: Regardless of the management system, similar trends in cattle populations will be observed in response to IRV. The results of the study showed that fluctuations in cattle numbers, herd mortality and calving rates were highly correlated with IRV, with stronger linear impacts in accordance with scenario 2. In both management systems, cattle herd sizes and calving rates declined during periods of drought, followed by slow recovery. Cattle populations in Borana rangelands in southern Ethiopia did not recover for a period of two decades. We conclude that a management system based on control of stocking densities did not improve herd survival, as compared with traditional drought management strategies. This contradicts common expectations. Increased drought frequencies aggravated cattle mortality and lowered calving rates. The implication of the findings is that regardless of adjusted stocking density, livestock populations in the arid savanna ecosystems of southern Ethiopia remain at risk from climate change. 相似文献
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