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 14 / 23 approximately 18% in 1976, compared to 6% in 2002 and only 1% in 2022. This decline may be due to rapid economic development at an even higher rate than population growth increasing per capita demand for resources, e.g., via higher availability of machinery or pesticides, with this increasing land use intensity and reducing natural areas. Fig 3 gives an impression of the extent to which the vegetation at the southern foot of Kilimanjaro has been reshaped by humans. For the entire Kilimanjaro region, including the five study districts and the Pare Mountains, Gross Domestic Product (GDP) grew about 5.7 times from 1980 to 2020 [49]. During this time, GDP per capita in Tanzania increased approxi- mately 1.8 times [55], indicating that economic growth was much more rapid in Kilimanjaro. In our study area, reflected through construction activities as indicators of economic growth, Fig 4 shows an annual growth rate of built-up areas at 5.9% between 1976 and 2022, and 6.1% from 2002 to 2022, surpassing population growth. This aligns with global satellite-derived built-up area statistics named GHS-BUILT-S from the Global Human Settlement Layer (GHSL) project (see Supplementary Information S1 Text; Table 5). Trends post-2000 indicate significant expansion of built-up areas com- pared to the 1975–2000 period. This is also in line with trends on a continental level: Africa’s urban areas will more than double until 2025. The growth

in urban area expansion is projected to outpace urban population growth, at 3.2% compared to 2.3% per year. The total urban footprint is projected to increase from 175 000 square kilometres to 450 000 square kilometres between 2020 and 2050 with an increasing number of urban agglomerations from 9,000 to over 11,000 [56]. The trend of house building activities and the development of new town centers between 1990 and 2016, particularly in the lowlands of Hai and Siha districts on the southwestern side of Kilimanjaro, is illustrated in Fig 8. This aligns with GHS- BUILT-S (Table 5). The role of KINAPA as a barrier against encroachment by settlements is notable in Fig 8, highlighting the importance of governance through governmental protection of nature that delivers ecosystem services to Tanzania’s people. Demographic and socio-economic factors have driven many land-use changes at Kilimanjaro. By 2000, a corridor of submontane forest that once connected Kilimanjaro and Mt. Meru had been largely replaced by human settlements and agriculture (Fig 5B). This forest corridor was crucial for the dispersal of forest animals [21], but Kilimanjaro is now increas- ingly isolated, impacting biodiversity and endemism. On a positive note, the growth of Chagga homegardens – a sustainable land-use practice supporting various natural species [31,53,57] – has helped mitigate biodiversity loss, especially as these gardens have expanded at the expense of agricultural fields (Fig 5C). From 1976 to 2022, the area of homegardens more than doubled to 849 km2.

Climate change was not an important driver of the observed biodiversity trends A reanalysis of meteorological data for East Africa shows an approximate surface temperature increase of 0.95 K over the past 60 years (specifically between 2.5° to 5.0° South and 37.5° to 40.0° East). Additionally, the RCP6.0 scenario projects a further increase of 3 K by 2100 [58]. However, such modeled climate data for tropical mountains is sometimes very unre- liable [35]. Beside increasing trends of temperature no consistently significant rainfall trends over the period 1973–2014 Table 5. Built-up surface (km2) from GHS-BUILT-S. District 1975 2000 2020 1975 → 2000 2000 → 2020 Siha 3.34 4.97 10.70 + 49% + 115% Hai 7.82 12.08 20.85 + 54% + 73% Moshi Rural 23.26 32.02 42.93 + 38% + 34% Rombo 19.79 21.85 25.03 + 10% + 15% Moshi Municipal 6.32 9.82 11.04 + 55% + 12% https://doi.org/10.1371/journal.pone.0334184.t005