What comes to mind when picturing a mountain landscape? Beautiful scenery of towering peaks and rolling valleys? Howling winds, icy slopes, and jagged rock formations? Thriving life, including thousands of different plants and animals? In fact, the surprisingly rich biodiversity of mountain habitats has important implications for the health of these ecosystems and humans across the globe.
Mountains harbor over 85% of Earth’s amphibian, bird, and mammal species despite occupying only 25% of the world’s land area. This high biodiversity deviates from documented patterns of species richness, which predict biodiversity to be highest at the equator and decrease with greater distance from the tropics and higher altitudes. This mysterious phenomenon is called Humboldt’s enigma, named after Alexander von Humboldt — a 19th-century German naturalist considered the “father of ecology” who extensively studied mountain vegetation patterns.
Researchers have developed several hypotheses to explain Humboldt’s enigma. Variations in topography and climate may be key drivers behind the numerous species in mountain regions. Rock formations create varying temperature, water, soil, and light conditions along mountain slopes, resulting in a concentrated collection of unique microclimates. These diverse habitats support a wide assortment of species, and their patchiness further encourages the development of distinct species. Meanwhile, lowlands have more consistent topographies and stable climate conditions, resulting in less habitat diversity per unit area and fewer chances for speciation.
“Mountains harbor over 85% of Earth’s amphibian, bird, and mammal species despite occupying only 25% of the world’s land area.”
Mountain landscapes also challenge populations to develop unique adaptations specialized to environmental extremes such as low pressure and low oxygen at higher altitudes. Therefore, mountains host high numbers of endemic species — those found in one specific geographic range and nowhere else.
However, numerous threats imperil mountain ecosystems’ biodiversity by disrupting the conditions responsible for Humboldt’s enigma, with climate change being the greatest risk. Rising temperatures result in retreating glaciers, melting snowpack, and thawing permafrost. These changes reduce the habitat complexity of mountain landscapes by altering microclimates. Habitat loss is a particularly imminent danger to endemic species adapted to these unique habitats. While some species may move to a higher elevation, others face extinction as their suitable habitat disappears.
Additional pressures from human activities exacerbate mountain ecological degradation, including pollution, non–native invasive species, land–use change, and resource overexploitation. Collectively, these impacts endanger mountain biodiversity by damaging habitats and ecosystem processes.
These threats also harm human health due to the strong connection between mountain ecosystems and human well-being. The existence and underlying mechanisms of Humboldt’s enigma translate to direct benefits for people. Mountain biodiversity provides essential food, timber, and medicinal resources. The variable topography of these regions regulates climate and air quality, reduces the risk of natural disasters, and mitigates extreme weather events. Melting snow and ice from mountain summits also supply water for 22% of the world’s population. Consequently, the impacts of climate change and other stressors on mountain landscapes jeopardize these essential ecological functions that support billions of people.
Addressing these pressing risks requires collaboration across multiple scales, with local communities playing a key role in protecting mountain ecosystems. Community–based management plans that promote sustainable agriculture, forest restoration, and water resource conservation benefit mountain biodiversity, mitigate climate change, and empower local people. Engaging Indigenous groups is a critical aspect of community conservation. Upholding Indigenous land rights enables their continued stewardship of biodiversity, and incorporating their traditional ecological knowledge enhances sustainable land management plans. Integrating these local efforts into larger regional, national, and international actions provides additional resources for monitoring and facilitates coordinated protection of mountain landscapes.
The well–being of thousands of species and billions of people around the world depends on conserving mountain ecosystems. Humboldt’s enigma highlights the complex relationship between physical landscape characteristics, climate, biodiversity, and human well–being. Yet, the progressing consequences of climate change threaten these connections. Ensuring the resiliency of these diverse mountain ecosystems requires a collective effort that empowers local communities as sustainable land stewards, protecting both mountain biodiversity and human health.