Patterns and Geographical Mechanism of Altitudinal Belts in Tropical African Mountains

Altitudinal belts exhibit substantial variation across the world's mountains in number, typology, combination patterns, and vertical range. However, the conditions under which specific belts occur and the climatic factors influencing their vertical range remain poorly understood. Therefore, this study focuses on tropical African mountains, which are characterized by massive volcanic cones, rich biodiversity, and complete altitudinal belt structure, as a representative region. We compiled 23 spectra of altitudinal belts from published literature for 10 representative tropical African mountains. Integrating climatic data of WorldClim V2.0 and topographic data from SRTM 90 m DEM, we investigated the vertical ranges and combination structures of altitudinal belts, and analyzed their relevant driving climatic factors using stepwise regression. The results show that: (1) Tropical African mountains usually have five to eight altitudinal belts which constitute a complete altitudinal belt spectrum from tropical vegetation to nival zones. (2) The upper montane regions are typically characterized by the development of bamboo forest, cloud forest, and ericaceous forest belts, but with different patterns of single belt, dual belts and triple belts. (3) Climate-altitudinal belt regression models could well explain the vertical range of the highest forest belts (ericaceous forest) and low forest belt (monsoon rainforest) (R ² = 0.72-0.75), and could moderately explain the vertical range of mountain forest belt, bamboo forest belt and cloud forest belt (R ² = 0.31-0.44). (4) The normal establishment of a specific altitudinal belt primarily depends on annual hydrothermal conditions or on a compensatory interplay between temperature and precipitation under suboptimal conditions, while the vertical range of any altitudinal belt is closely associated with the intra-annual or seasonal variations of hydrothermal conditions. This study further highlights the complexity and diversity of tropical African mountains, providing a more solid scientific foundation for altitudinal belt theory development.