Gain and loss: Human and environmental wellbeing – drivers of Kilimanjaro’s decreasing biodiversity

PLOS One | https://doi.org/10.1371/journal.pone.0334184 October 29, 2025 2 / 23 on the biodiversity of ecological systems and the benefits they provide to humans (known as nature’s contribution to people, NCP, formerly “ecosystem services”) [4–6], making anthropogenic impacts on nature a growing concern [7,8]. While climate change has attracted much attention as one of the drivers of biodiversity loss [8–10], it is not the only one [11–13], necessitating further examination of which drivers have the greatest effects on biodiversity [14]. Additionally, research has mainly focused on impacts rather than the drivers of global environmental change [15,16]. Kilimanjaro, the world’s highest free-standing mountain, features diverse ecosys- tems, high species diversity, and distinct land use systems [17]. The NCP provided by this tropical volcano includes climate and water regulation, food and timber provision and the spillover of crop pollination services into adjacent agro-ecosystems [18,19]. Due to increasing human pressures, Kilimanjaro’s ecosystems face severe threats [20,21], classifying it as a biodiversity hotspot [22]. It exhibits typical aspects of envi- ronmental change in tropical Africa while combining various features and challenges on one mountain, making it an excellent model for the investigation of the relationship between nature and humans. The objective of this study is to investigate how the main direct and indirect anthropogenic factors (with the exception of pollution, for which no data are available)

affect biodiversity at Kilimanjaro and to assess the role of conservation in relation to biodiversity. The focus is on floristic and vegetation diversity, as vegetation is closely related to the diversity of other taxa and plays a fundamental role in ecosystem func- tioning and thus NCP. Our biodiversity assessment is restricted to richness of plant species (overall species numbers and numbers of indicator species). First, we investigate the spatial and temporal relationship between population growth and economic development (as indirect drivers) and land use (as a direct driver) by relating changes in population density and economic development to changes in land use and vegetation cover. For this, we use historical German maps and census data from the beginning of the 20th century to get an overview of the most important changes between 1911 and 1976. A more detailed insight into the sit- uation since then is provided by the availability of satellite imagery. We focus on the inhabited areas of Kilimanjaro below the national park where no people live. Further- more, we convert these changes in land cover into changes in biodiversity by using the number of species of different plant groups as an indicator. To do this, we use a large dataset of 1600 vegetation plots with almost 3000 plant species that have been established throughout the mountain range since 1996. With this approach we want to answer the following questions: (i) Which of the anthropogenic factors addressed have the greatest impact on

biodiversity and how have the impacts of these anthropogenic factors changed in recent decades? (ii) How does climate change affect biodiversity? (iii) How is biodiversity changing? (iv) Can nature conservation mitigate the negative effects? Tanzania. 1978. Population and Housing Census 2002. Bureau of Statistics. Available: https://catalog.ihsn.org/catalog/2876/get-mi- crodata, National Bureau of Statistics Tanzania. 1988. Population Census. Analytical report. Bureau of Statistics, Planning Commission, President’s Office, Dar es Salaam, Tanzania. Available: https://microdata.nbs.go.tz/index. php/catalog/23/get-microdata National Bureau of Statistics Tanzania. 2003. Population and Housing Census 2002. National Bureau of Statistics, Planning Commission, President’s Office, Dar es Salaam, Tanzania. Available: https://microdata.nbs.go.tz/index.php/cat- alog/24/get-microdata National Bureau of Statistics Tanzania. 2013. 2012 Population and Housing Census. National Bureau of Statistics, Ministry of Finance, Dar es Salaam and Office of Chief Government Statistician, President’s Office, Finance, Economy and Development Planning, Zanzibar. Available: https://microdata. nbs.go.tz/index.php/catalog/44/get-microdata National Bureau of Statistics and President’s Office. 2022 The 2022 Population and Housing Census: Initial Results. – Ministry of Finance and Planning, Office of the Chief Government Statistician, Zanzibar. Dodoma, Tanzania. Available: https://microdata.nbs.go.tz/index.php/ catalog/45/get-microdata. Funding: German Research Foundation (DFG),

(HE 2719/14-1), Dr. Andreas Hemp. Competing interests: The authors have declared that no competing interests exist.