Deforestation since independence: a quantitative assessment of four decades of land-cover change in Malawi

Land cover has changed rapidly across the tropics over the past century; however, detailed historical information describing the extent and possible drivers of such change is widely lacking. Here, we constructed a history of land-cover change at the district level in Malawi over a 37-year period from 1972 to 2009, the immediate post-colonial phase. Overall, there was a loss of 12 760 km2 (36%) of original forested area but also 11 161 km2 of new forest establishment, resulting in a relatively modest overall net loss of 1 599 km2 (5%). We correlated changes in deforestation and forest establishment with changes in socio-economic variables derived from spatially explicit data from the same time period. Deforestation was positively correlated with (in order of influence) changes in male school attendance, sex ratio, population density, hospital bed numbers, protected areas and dependency rate, but negatively correlated with changes in cattle density; forest establishment broadly showed the inverse relationships with the same variables. Although direct drivers of deforestation are well known for Malawi and much of Africa, the significance of socio-economic variables within this study can help to understand the underlying social pressures behind such drivers. In particular, development, population pressure and demographic factors are important predictors of deforestation rate within our study area.

过去一个世纪以来，全球热带地区的土地覆被变化迅猛，但目前仍普遍缺乏能够系统阐明此类变化的规模与潜在驱动因素的详实历史资料。本研究构建了1972年至2009年（即马拉维后殖民初期阶段）37年间马拉维区级尺度的土地覆被变化历史序列。整体而言，研究区内原生林地共减少12760平方千米，占初始林地总面积的36%；同时新增林地面积11161平方千米，最终仅实现1599平方千米（占初始林地5%）的小幅净损失。本研究将森林砍伐与新增造林的变化幅度，与同期空间显式（spatially explicit）数据衍生出的社会经济变量变化进行了关联分析。结果显示，森林砍伐与以下社会经济变量的变化呈正相关（按影响程度降序排列）：男性入学率、性别比、人口密度、医院床位数、保护区数量以及抚养比，但与牲畜密度的变化呈负相关；而森林新增则与上述所有变量大致呈相反的相关关系。尽管马拉维乃至非洲大部分地区的森林砍伐直接驱动因子已较为明确，但本研究中社会经济变量的显著相关性，有助于进一步解析此类驱动因子背后潜藏的社会压力。其中，发展水平、人口压力与人口统计因素是本研究区域内森林砍伐速率的重要预测因子。