What is a mountain?

What is a 'mountain'? Why are mountains important for study, conservation and sustainable management?

Picture1Mountains are part of our global heritage

Around 22% of the earth’s land surface is covered by mountains which are complex and ever changing landscapes, inter-connected with the lowlands. Human development has been intricately linked to mountains, mountain passes, mountain citadels, summer grazing for livestock, impassable areas and sacred areas. Mountains not only provide sustenance and well-being to 915 million mountain people around the world, representing 13 % of global population, but indirectly benefit billions more living downstream. Threatened by global and climate change, mountain regions now face loss of rare and endangered species, modified water balances (including glacial melt), and changing land use, all of which can alter socio-economic conditions and the livelihoods of mountain and lowland people.

The increasing attention to the importance of mountains led the UN General Assembly to declare 2002 the UN International Year of Mountains and designate 11 December, from 2003 onwards, as ‘International Mountain Day’ (UN sustainable mountain development website, n.d.).

Mountains create novel life zones for biodiversity

Mountains have allowed for a massive proliferation of biological life at high altitudes and the extremely diverse topography of mountains has led to mountains hosting a larger proportion of the Earth's biodiversity than would be expected by area (Körner et al, 2011). Mountains are important refuges for species, given their inaccessibility and coverage of a wide spectrum of environmental conditions and are seen as key to biodiversity conservation in a changing world (Spehn et al, 2010), and many mountains are globally important for biodiversity reasons. Conditions on mountains can include tropical rain forests to permanent ice and snow, mountain climates from 12 m of annual rainfall to high-altitude deserts, and altitudes from sea level to almost 9 000 m in altitude.

Picture3Steep altitudinal changes mean that there is a compression of climatic zones over short distances and that other habitats which may stretch over thousands of kilometres in the lowlands may be located on a single mountain slope. This compression of life zones, each with its characteristic biological inventory, creates an assembly of contrasting biota on mountains. Mountain biodiversity also mirrors topographic and geological diversity. Exposure and inclination of slopes and relief has led to a multitude of microclimatic situations which, in combination with substrate types and associated water and nutrient regimes, has created a great variety of micro-habitats, each with characteristic organisms. Habitat isolation and fragmentation has also led to local or regional species diversification. In fact, mountains have been compared to 'archipelagos' surrounded by an 'ocean' of lowland life conditions which are often hostile for most mountain species.

Mountain climates are characterised by low night-time temperatures, even during the warmer months, and thus by relatively short seasons when minimum temperatures climb above freezing. In Europe, although daytime temperatures may rise significantly above freezing during the summer, they tend to be lower than those in the surrounding lowlands. Maximum temperatures are therefore relatively low, particularly at high latitudes. During the winter months, temperatures in most temperate mountain areas not only remain below freezing but are also lower than lowland temperatures at the same latitude (Mountain Areas, n.d.).

Mountains often offer migratory corridors for species, such as the east-west connection along the southern slopes of the Himalayas. Moderate disturbances such as landslides, avalanches, grazing by large herbivores and/or wildfires also tend to further increase habitat differentiation and species diversity (Spehn et al, 2010). Many mountains are becoming isloated from similar regions of biodiversity, meaning that the genetic diversity of their unique biodiversity can diminish over time, potentially leading to extinctions.

Mountains are important for people

Picture4As well as their biodiversity significance, mountains not only provide sustenance and well-being to 915 million mountain people around the world, representing 13 % of global population, but indirectly benefit billions more living downstream. Because of their remoteness, many of the world’s distinct human ethnic groups with their varied remnants of cultural traditions, environmental knowledge and habitat adaptations, have been able to maintain traditional lifestyles in mountainous areas and are all worthy in a rapidly changing world. Many of these human mountain populations are chronically poor and underdeveloped and frequently face political, social and economic marginalization and lack access to such basic services as health and education. Moreover, current global challenges such as climate change, economic developments and population growth exacerbate the hardships they face. Many mountain communities are also being impacted upon by lowland migrants who are seeking new lands for cultivation or settlement and the role of people in environmental change in mountains is now significant.

However, in socio-economic terms, the natural handicaps of mountain areas consist of two elements (Mountain Areas, n.d.):

• Altitude - winter temperatures decrease and temperature contrasts become
larger with increasing altitude and this limits the agricultural use of the land, makes road transport difficult during winter, increases heating costs, etc.

• Topography - rough terrain constrains regional accessibility, makes
communication and other infrastructure investments more expensive, and makes
modern agricultural or industrial production more difficult.

In terms of benefits, mountains form the ‘water towers’ of the world and because of their altitude or location intercept rainclouds to create precipitation, providing freshwater to at least half of the world’s people. However, mountains are also high-risk environments - avalanches, landslides, volcanic eruptions, earthquakes and glacial lake outburst floods threaten life in mountain regions and surrounding areas. Despite their importance, mountains have been ignored as a site for sustainable human development until very recently. To achieve sustainable mountain development, the United Nations notes that it is essential that all concerned stakeholders are involved and that awareness is raised about mountain ecosystems, their fragility and prevalent problems, and about ways of addressing them. The sustainable development and protection of mountain regions and the improvement of local livelihoods should be at the core of mountain legislation. Such legislation needs to address the protection of ethnic minorities and the cultural heritage of mountain people, and to recognize community-based property rights. Many mountain ranges are transboundary, so sustainable mountain development requires international cooperation (UN Website, n.d.).

So, what is a mountain?

Picture6Mountains are often seen as high, cold, inaccessible places and attempts to define mountains using universally applicable rules go back to 19th century Europe. The beginning of an exact and legally binding delineation of mountain areas occurred in the second half of the 20th century, starting with France in 1961, Italy in 1971 and Switzerland in 1974 and several criteria such as elevation (altitude above sea level), volume, relief and steepness were employed, but were often inconsistent at a global scale (Pantic, 2015). In a basic one-factor definition, it is altitude (metres above sea level) that defines mountains, although this is complicated by the fact that many mountains do not appear very high (200 masl in the UK) compared to the European Alps which may be up to 3500 masl.

Körner et al (2011: p74) state that

"mountains cannot be defined by elevation alone, simply because there are elevated plateaus such as the North-American short-grass Prairies at around 2000 m elevation or the vast plateaus in central Asia, while steep coastal ranges may exemplify 'real' mountains near sea level. Similarly, mountains cannot be defined by climate, given that any cold category would include Arctic and Antarctic lowland and tropical mountains range from equatorial rain forests to arctic life conditions near their summits. The only common feature of mountains is their steepness (slope angle to the horizontal) which causes the forces of gravity to shape them and create habitat types and disturbances typical of mountains and which make exposure a driving factor of life."

The UNEP-WCMC 2000 global delineation is based on altitude and slope, but does not include areas with marked topography at altitudes below 300 m. However, in several parts of Europe, including the Iberian Peninsula, the British Isles, Greece, and Fennoscandia, there are mountains along the coasts, extending down to sea level. A European delineation should therefore be based on a combination of altitude and topography (Mountain Areas, n.d.). Also, the Mountain Areas report (Mountain Areas, n.d.) states that is essential that the mountain area was approximated to municipal boundaries. First, an assessment was made of the proportion of each municipality falling into the mountain delineation, derived from the analysis based on the above-mentioned criteria. To be considered as mountainous, a municipality had to have at least 50% of its area within the area delimited as mountain. A further analysis was made of the relative proportions of ‘mountain’ land within non-mountainous municipalities and ‘non-mountain’ land falling within the boundaries of mountainous municipalities.

Körner et al (2011) explains that, for example, the Mountain Biodiversity Portal (MBP) (MBP, n.d.) has adopted 'ruggedness' as a simple and pragmatic proxy for steepness to uniformly define mountains across the globe. Ruggedness is defined as the maximal elevation difference among neighbouring grid points. Calculations are based on the digital elevation model (DEM) used by WorldClim. Elevation of every cell in a 3000 grid is compared with elevation of its eight neighbouring cells. If the difference between the lowest and highest of these nine 3000 grid cells exceeds 200 m, the central cell is assigned as 'rugged' i.e. belonging to mountain terrain, as a matter of convention (Körner et al., 2011). Effective mountain delineation across all aspects now requires consideration of not just elevation, but also steepness of slope and terrain roughness.

Also, since life in mountains is not driven by elevation per se, but by the climatic conditions associated with elevation, thermal belts of life offer a simple, temperature-only driven zonation of mountains, for example, tree lines. For a global comparison of mountain biota it is essential that the latitudinal change in life conditions with elevation is accounted for. Hence, elevational belts are converted into climatic belts for the MBP model. The MBP model subdivides mountains vertically into seven thermal life zones (thermal belts) defined by temperature only and, thus, accounting for the latitudinal change in elevation of thermally similar areas. In the MBP model, all belts refer to the best defined biome boundary in mountains, the high elevation climatic treeline, separating the treeless alpine and the potentially forested montane belts. From there, one can go up (alpine and nival belts) or down (montane and lower) based on temperature criteria. The Mountain Biodiversity Portal also adopts the position of the potential, climatic high elevation treeline as the main reference line for life zones in mountains. The snow line is another key elevational marker in the model for European or northern hemisphere mountains (Körner et al (2011).

(Photo: Tree line, USA. Photo credit http://jordanmayor.com/montane-elevational-gradient-ecology-)

Delineating the mountain

Picture7For conservation and other management initiatives, it is important to be able to determine which part of the landscape is considered ‘mountain’ and which is not. Using elevation and steepness is often not enough to reflect landscape complexity. There are now various modern rule based methods for landform classification which provide a straightforward solution to situations where mountain extent is poorly resolved.

It would seem straightforward to identify a mountain, particularly based on altitude, however Platts et al. (2011) shows that problems arise in trying to determine the transition to lowlands and making sense of the climatic and biodiversity gradient that exists from coastal regions to high-altitude regions. Landform, geology, climate, vegetation and evolutionary history, as well as cultural and political considerations, are all important in delineating a mountain and its lowlands. In practice no single solution is optimal for all applications in all regions (Platts et al., 2011). Freely available digital elevation data, for example that from UNEP WCMC (2000) on mapping mountain forests, together with improvements in desktop mapping software, have brought advances in the development of a systematic process by which to define and study mountains. Practitioners can now experiment with different rule-based ways of bounding their region of interest for study purposes, and thereby using quantitative rule-based delineation tools, increasing the prominence of such regions and their specific management challenges on the political stage (Platts et al., 2011). Various maps of the Eastern Arc Mountains, Tanzania, from Platts et al., (2011) are shown below. Interestingly, the delineation approach of Platts et al. (2011) includes buffer zones of various distances (10 km, 10-20 km and 20-30 km away from the actual mountain delineation). Buffer zones are very important in understanding where human pressures must be moderated if the mountain system is to be protected from degradation.

There are globally defined elevational classes which need to be treated sensibly depending on the mountains being studied, for example, where mountains occur along a coastline or are associated with a high altitude inland plateau. Vegetation classes are also used in delineation of mountains, for instance, SPOT multi-spectral satellite images as well as local ground truthing can be used to identify areas that may belong to montane categories despite lower elevations. Other decisions that need to be taken in a mountain delineation programme is whether to include or exclude ‘hills’. This can be done based on vegetation affinities and is largely a decision that depends on the particular mountain system being studied.

It is also a challenge to delineate biodiversity in mountains. The University of York’s Eastern Arc Mountains (EAM) research programme is dealing with this challenge. Since the 1980s, the EAM have been recognised as biologically distinct from surrounding Afromontane habitats. Exceptional concentrations of rare species are explained by long-term consistency of rain-bearing winds from the Indian Ocean, in combination with long-term isolation of the mountains; the substrate is Precambrian crystalline basement rock, uplifted from the African plateau during the Miocene c. 30 MY ago. While a qualitative definition has been widely applied (sensu Lovett 1990), precise spatial limits for the area of endemism have been lacking. Thus, fundamental biogeographical questions such as “what is the area of the EAM?” and “how many (endemic) species occur there?” have been troublesome to address with consistency.

Downscaled projections for climate change in African mountains.

Through the CORDEX initiative of the World Climate Research Project (WCRP), outputs from regional climate models (RCMs) have become available for Africa. Global Climate Models (GCM) can provide us with projections of how the climate of the earth may change in the future. A Global Climate Model (GCM) can provide reliable prediction information at a large scale (around 1000 by 1000km) and covering what could be a vastly varied landscape with many different features (mountains, cities, rivers, forests) with greatly varying potential for floods, droughts or other extreme events. Something that relates to the actual landscape is needed to provide projections for local adaptation planning. Regional Climate Models (RCM) and Empirical Statistical Downscaling (ESD), applied over a limited area and driven by GCMs, can provide information on much smaller scales supporting more detailed impact and adaptation assessment and planning, which is vital in many vulnerable regions of the world. Nested within GCMs, regional models simulate climate at finer spatial and temporal resolutions, yet at ~50 km, they also remain too coarse-grained for many applications in ecology (WRCM, 2016). In the paper of Platts et al. (2015), a range of observational baselines to empirically downscale RCM outputs to resolutions amenable to ecological applications at local scales (up to 1 km). Results for the middle and late 21st century are available online https://webfiles.york.ac.uk/KITE/AfriClim/

Also check out https://www.york.ac.uk/environment/research/kite/resources/

See also Platts PJ, Omeny PA and Marchant R (2015). AFRICLIM: high-resolution climate projections for ecological applications in Africa. African Journal of Ecology. pp. 103-108. ISSN 0141-6707.

Strategic Water Resource Areas

As we know, mountains are important sources of freshwater for the adjacent lowlands. In view of increasingly scarce freshwater resources, this contribution should be clarified. This indicates that there are various ways of clarifying mountains and mountain assets, for example, investigating and quantifying mountains as water towers or catchments. In the report on Strategic Water Towers in South Africa, the World Wide fund for Nature (WWF) used an algorithm was used to identify certain mountain areas in South Africa as Strategic Water Resource Areas. Once these areas have been identified, the message is that specific measures must be used to management them for long term sustainability. This assessment needs to be performed for other mountains in African countries. These efforts to quantify and evaluate mountain catchments relates to the work of Viviroli et al (2012, 2003) where strategic water towers (mountains) around the world were evaluated for their importance. The Drakensberg Escarpment in South Africa was one of the global areas identified. It is important to be able to quantify the value of mountains as catchments so that both changes can be monitored and investment can be made in protecting the catchments as they are seen as having ‘strategic’ value.


Körner C., Paulsen J. and Spehn E.M (2011). A definition of mountains and their bioclimatic belts for global comparisons of biodiversity data. Alpine Botany (2011) 121:73–78.

MBP (n.d.). Mountain Biodiversity Portal (MBP). http://gmba.unibas.ch/portal/portal.htm

Mountain Areas (n.d.). Mountain Areas in Europe. Final Report. http://ec.europa.eu/regional_policy/sources/docgener/studies/pdf/montagne/mount4.pdf

Pantic M. (2015). Delineation of mountains and mountain areas in Europe – a planning approach. J. Geogr. Inst. Cvijic. 65(1) (43–58). DOI: 10.2298/IJGI1501043P

Platts P.J., Burgess N.D., Gereau R.E., Lovett J.C., Marshall A.R., McClean C.J., Pellikka P.K.E., Swetnam R.D. and Marchant R. (2011). Delimiting tropical mountain ecoregions for conservation. Environmental Conservation 38 (3): 312–324 Foundation for Environmental Conservation 2011

Platts P.J., Omeny P.A. and Marchant R. (2015) AFRICLIM: high-resolution climate projections for ecological applications in Africa. African Journal of Ecology. 53: 103 - 108

Spehn E.M., Rudmann-Maurer K., Körner C. and Maselli D., (eds.) (2010). Mountain Biodiversity and Global Change. GMBA-DIVERSITAS, Basel.

UNEP WCMC (2000). In 2000, UNEP-WCMC (in collaboration with the Environmental Change Institute and supported by the Swiss Agency for Development and Co-operation) made a first attempt to map the mountain forests of the world. http://www.unep-wcmc.org/resources-and-data/mountains-and-forests-in-mountains

Viviroli, D., Weingartner, R. and Messerli, B. 2003. Assessing the hydrological significance of the world’s mountains. Mountain Research and Development 23: 32-40.

Viviroli D, Messerli B, Schädler B and Weingartner R (2012). Water Towers in a Changing World. In: Kohler T. and Maselli D. (eds) 2012. Mountains and Climate Change - From Understanding to Action. Published by Geographica Bernensia with the support of the Swiss Agency for Development and Cooperation (SDC), and an international team of contributors. Bern.

WWF Report (2013). Defining South Africa’s water source areas. WWF-World Wide Fund For Nature (Formerly World Wildlife Fund), Cape Town, South Africa.

WCRP (2016) CORDEX website and Regional Downscaling. World Climate Research project (WCRP).

Photo credits

Alpine mountains http://www.worldwildlife.org/habitats/mountains

Tree line: http://jordanmayor.com/montane-elevational-gradient-ecology-

Other photographs: SJ Taylor, Clarens/Ficksburg area of the Maloti Drakensberg, South Africa. April 2016.

Page updated on 13 July 2016.