Landsat time series reveal forest loss and woody encroachment in the Ngorongoro Conservation Area, Tanzania

The Ngorongoro Conservation Area (NCA) of Tanzania, is globally significant for biodiversity conservation due to the presence of iconic fauna, and, since 1959 has been managed as a unique multiple land-use areas to mutually benefit wildlife and indigenous residents. Understating vegetation dynamics and ongoing land cover change processes in protected areas is important to protect biodiversity and ensure sustainable development. However, land cover changes in savannahs are especially difficult, as changes are often long-term and subtle. Here, we demonstrate a Landsat-based monitoring strategy incorporating (i) regression-based unmixing for the accurate mapping of the fraction of the different land cover types, and (ii) a combination of linear regression and the BFAST trend break analysis technique for mapping and quantifying land cover changes. Using Google Earth Pro and the EnMap-Box software, the fractional cover of the main land cover types of the NCA were accurately mapped for the first time, namely bareland, bushland, cropland, forest, grassland, montane heath, shrubland, water and woodland. Our results show that the main changes occurring in the NCA are the degradation of upland forests into bushland: we exemplify this with a case study in the Lerai Forest; and found declines in grassland and co-incident increases in shrubland in the Serengeti Plains, suggesting woody encroachment. These changes threaten the wellbeing of livestock, the livelihoods of resident pastoralists and of the wildlife dependent on these grazing areas. Some of the land cover changes may be occurring naturally and caused by herbivory, rainfall patterns and vegetation succession, but many are linked to human activity, specifically, management policies, tourism development and the increase in human population and livestock. Our study provides for the first time much needed and highly accurate information on long-term land cover changes in the NCA that can support the sustainable management and conservation of this unique UNESCO World Heritage Site.

Automated summary

The Ngorongoro Conservation Area in Tanzania is an important region for global biodiversity conservation, managed as a unique multiple land-use area since 1959 to benefit both wildlife and indigenous residents. This study demonstrates a Landsat-based monitoring strategy to accurately map the main land cover types in the area, revealing changes such as upland forests degrading into bushland and shifts in grassland to shrubland, indicating woody encroachment. These long-term land cover changes highlight the importance of sustainable management and conservation efforts in the Ngorongoro Conservation Area.