Homewood K, Lambin E F, Coast E, Kariuki A, Kikula I, Kivelia J, Said M, Serneels S, Thompson M
Anthropology Department, University College, Gower Street, London WC1E 6BT, United Kingdom.
Proc Natl Acad Sci U S A. 2001 Oct 23;98(22):12544-9. doi: 10.1073/pnas.221053998.
Declines in habitat and wildlife in semiarid African savannas are widely reported and commonly attributed to agropastoral population growth, livestock impacts, and subsistence cultivation. However, extreme annual and shorter-term variability of rainfall, primary production, vegetation, and populations of grazers make directional trends and causal chains hard to establish in these ecosystems. Here two decades of changes in land cover and wildebeest in the Serengeti-Mara region of East Africa are analyzed in terms of potential drivers (rainfall, human and livestock population growth, socio-economic trends, land tenure, agricultural policies, and markets). The natural experiment research design controls for confounding variables, and our conceptual model and statistical approach integrate natural and social sciences data. The Kenyan part of the ecosystem shows rapid land-cover change and drastic decline for a wide range of wildlife species, but these changes are absent on the Tanzanian side. Temporal climate trends, human population density and growth rates, uptake of small-holder agriculture, and livestock population trends do not differ between the Kenyan and Tanzanian parts of the ecosystem and cannot account for observed changes. Differences in private versus state/communal land tenure, agricultural policy, and market conditions suggest, and spatial correlations confirm, that the major changes in land cover and dominant grazer species numbers are driven primarily by private landowners responding to market opportunities for mechanized agriculture, less by agropastoral population growth, cattle numbers, or small-holder land use.
半干旱非洲稀树草原栖息地和野生动物数量下降的情况被广泛报道，通常归因于农牧人口增长、牲畜影响和自给农业。然而，降雨、初级生产、植被和食草动物种群的年度极端变化以及短期变化，使得在这些生态系统中很难确定方向性趋势和因果链。本文根据潜在驱动因素（降雨、人类和牲畜种群增长、社会经济趋势、土地保有制、农业政策和市场），分析了东非塞伦盖蒂-马拉地区二十年的土地覆盖变化和角马数量变化。自然实验研究设计控制了混杂变量，我们的概念模型和统计方法整合了自然科学和社会科学数据。该生态系统肯尼亚部分出现了快速的土地覆盖变化，多种野生动物物种数量急剧下降，但在坦桑尼亚一侧却没有这些变化。生态系统肯尼亚部分和坦桑尼亚部分的时间气候趋势、人口密度和增长率、小农农业的发展以及牲畜种群趋势并无差异，无法解释观察到的变化。私有土地与国有/公共土地保有制、农业政策和市场条件的差异表明，且空间相关性证实，土地覆盖和主要食草动物物种数量的主要变化主要是由私有土地所有者对机械化农业市场机会的反应驱动的，而非农牧人口增长、牛的数量或小农土地利用。
