الغابات الجبلية
.jpg?sfvrsn=9cfccb17_0 "©Jan Mosimann/Flickr")
Basic knowledge
What are mountain forests?
Mountain forests can be defined as forests on land with an elevation of 2 500 m above sea level or higher, irrespective of slope, or on land with an elevation of 300–2 500 m and a slope with sharp changes in elevation within a short distance.
Mountain forests cover about 900 million hectares of the world’s land surface, constituting 20 percent of the world’s forest cover. They are hotspots of biodiversity and provide important environmental services far beyond the mountains themselves. Mountain forests exist on every continent (except Antarctica) and in every climatic zone. Mountain forests cover large proportions of (for example) the Alps, Pyrenees and Balkan and Carpathian mountain ranges in Europe, the Appalachian and Rocky mountain ranges in North America, the Australian Alps, the Guiana Highlands in South America, the mountains in Central Africa, and the Andes Mountain Range in South and Central America.
Why do they need particular attention?
Mountain forests are fragile ecosystems because of their steep slopes and often-extreme climates and weather events. Mountain forest management should aim to prevent forest overuse and degradation because this can lead to environmental problems such as soil erosion, landslides, rockfalls, increased water runoff or reduced water storage, the drying of springs and the loss of biodiversity, and it can have severe impacts on livelihoods and even cause human deaths. Special planning and adequate measures to secure the productive, protective, social and cultural functions of mountain forests may be required.
الوحدات ذات الصلة
- Collaborative conflict management
- Forest management planning
- Forest tenure
- Management of non-wood forest products
- Protected areas
تساهم الغابات الجبلية في تحقيق أهداف التنمية المستدامة:
Key aspects for mountain foresters: planning and monitoring
Land-use planning needs to take into account the higher risk environment presented by mountains. Mountain forest zoning should identify areas that are especially important for certain forest functions, such as protection from hazards, nature conservation, water management, forest pastures and wood production. The purpose, type and impact of any intervention in mountain forests require careful consideration. Factors that need to be taken into account include terrain, site and environmental parameters (e.g. temperature range, precipitation, steepness, soil condition, watercourses, and exposure to the sun); accessibility; silviculture (e.g. tree species composition, increment and regeneration requirements); and biodiversity (e.g. endangered species). Forests should be monitored for the early detection of change.
Particular consideration should be given to:
- forests that protect assets from natural hazards;
- forest harvesting and regeneration in mountains; and
- mountain forests and adaptation to climate change.
In more depth
The natural environment of mountain forests
Site conditions in mountain forests can vary significantly over short distances – for example, one mountain slope might be dry and hot but, within 100 m or so, another might be cold and wet. Understanding the natural environment of mountain forests helps in making good management decisions. Mountain forests are characterized by altitudinal gradients: from the foot of a mountain to its peak, temperature decreases, precipitation – in form of rainfall, fog and snow – increases, soils become shallower and solar radiation becomes more intense. Precipitation increases with altitude because humid air arriving at the foot of a mountain condenses as it is forced to rise. In addition, evaporation also decreases with growing altitude, thus precipitation falling as snow is stored and becomes available when needed. Infrastructure, such as forest roads, should be designed to cope with high water runoff (i.e. effective drainage systems are required).
Forest soils develop more slowly on mountains than elsewhere because of the cooler climate (and therefore low vegetation growth rates) and continuous erosion. The large-scale clearfelling of mountain forests should be avoided: it can lead to high rates of erosion in extreme rainfall events and the widespread loss of seedlings in regeneration because large open areas are more prone to desiccation. Altitude and aspect are key determinants of species and stand structure composition in mountain forests, as well as of tree growth and form.
Forest growth is usually slower in mountains than in
lowlands because of the harsher climatic conditions, shorter growing
seasons and shallower soils. Species composition and growth differ
between slopes exposed to the sun (favoured by species that can tolerate
drier soils and higher solar radiation) and those oriented away from
the sun (where soil moisture is higher but exposure to sunlight is
lower). Mountain foresters need to consider such growth differences and
species mixtures in their silvicultural planning. The altitude of the
climatic tree line – beyond which trees do not grow in significant
numbers – varies widely, depending on latitude and climate, for example
from 700 m or below in the far north to above 4 500 m in parts of the
subtropical Andes. Ecosystems at the climatic tree line may have no
special economic value but can play important environmental roles, for
example as habitat for endemic species and by contributing to water
supply; they may need special management and protection measures.