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 13 / 23 (0.9%) between 1976 and 2022. In 1976, approximately 30% of the population resided in the lowlands, a proportion that increased to about 50% by 2022. In the causal chain of factors affecting biodiversity, demography acts as an indirect driver via the direct drivers [7], at Kilimanjaro by controlling land use change as direct driver. In other regions of Tanzania, it was also the population growth that led to the expansion of cultivated land [54]. The observed growing population density results in the overall reduction of natural habitats since 1911 (Fig 4), with increasing annual reduction rates from 1.0%, 1.9% and 2.4% between 1911 and 1976, 2002 and 2022. This can be shown in more detail for the period 1976–2022 at ward level (Fig 7). In addition to the clear correlation between increasing population density and decreasing natural vegetation, Fig 7 shows that not only the mean share of natural vegetation was higher in 1976 than in 2002 and 2022, as also seen in Fig 4, but also, that at a given population density, e.g., of 1000 people/km2, the natural vegetation share was Fig 7. Changing share of natural habitats over time in correlation to population density per km2 at ward level on Kilimanjaro. Blue symbols 1976, red symbols 2002, green symbols 2022 with logarithmic regressions. Pearson’s correlation coefficient r 1976: −0.594, p < 0.001; 2002: −0.475, p < 0.001; 2022: −0.407, p < 0.001. https://doi.org/10.1371/journal.pone.0334184.g007

Fig 6. Changes of land cover/land use (LULC) on Kilimanjaro between 1976 and 2022. (A) Extent of LULC classes in 1976, 2002 and 2022. (B) Net and gross changes of LULC between 1976 and 2022. Anthropogenic LULC types increased on expense of natural vegetation. (C) Sankey diagram, illustrating relative LULC change flows between 1976 (left), 2002 (middle) and 2022 (right). https://doi.org/10.1371/journal.pone.0334184.g006 Table 4. Changes in species numbers 1976-2022 (mean at ward level). 1976 2002 2022 Pearson’s r All plants 704 640 636 −0.892 ns Natural plants 340 250 184 −0.996* Savanna plants 162 132 101 −1.000** Neophytes 90 105 120 1.000** Pearson correlation with population density: ** p < 0.01, * p < 0.05, ns: non significant. https://doi.org/10.1371/journal.pone.0334184.t004