Mapping decadal land cover changes in the woodlands of north eastern Namibia using the Landsat satellite archive (1975-2014)

Woodland savannahs provide essential ecosystem functions and services to communities. On the African continent, they are widely utilized and converted to intensive land uses. This study investigates the land cover changes of 108,038 km**2 in NE Namibia using multi-temporal, multi-sensor Landsat imagery, at decadal intervals from 1975 to 2014, with a post-classification change detection method and supervised Regression Tree classifiers. We discuss likely impacts of land tenure and reforms over the past four decades on changes in land use and land cover. These changes included losses, gains and exchanges between predominant land cover classes. Exchanges comprised logical conversions between woodland and agricultural classes, implying woodland clearing for arable farming, cropland abandonment and vegetation succession. The most dominant change was a reduction in the area of the woodland class due to the expansion of the agricultural class, specifically, small-scale cereal and pastoral production. Woodland area decreased from 90% of the study area in 1975 to 83% in 2014, while cleared land increased from 9% to 14%. We found that the main land cover changes are conversion from woodland to agricultural and urban land uses, driven by urban expansion and woodland clearing for subsistence-based agriculture and pastoralism.

林地稀树草原（Woodland savannahs）为社区提供不可或缺的生态系统功能与服务。在非洲大陆，这类生态系统被广泛开发利用，并被转化为高强度土地利用类型。本研究采用多时间序列、多传感器的Landsat影像，以1975年至2014年的十年为时间间隔，结合分类后变化检测（post-classification change detection）方法与监督回归树分类器，对纳米比亚东北部108038平方千米区域的土地覆盖变化展开研究。本研究探讨了过去四十年来土地保有制度与相关改革，对研究区土地利用与土地覆盖变化的潜在影响。该区域的土地覆盖变化主要表现为优势土地覆盖类型间的面积缩减、扩张与类型转换：此类转换主要包括林地与农业用地间的合理转化，具体表现为为发展耕地农业而清理林地、耕地撂荒以及植被演替。最显著的变化为林地面积的缩减——农业用地面积持续扩张，尤其是小规模谷类种植与牧业生产的扩张，导致林地面积减少。1975年林地占研究区总面积的90%，至2014年这一比例降至83%；同期清理出的土地占比则从9%升至14%。研究结果表明，研究区主要的土地覆盖变化为林地向农业用地与城市用地的转化，其驱动因素包括城市扩张，以及为开展自给型农业与游牧业而清理林地。