Montane Shrub

Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial factor in shaping plant community, biodiversity, metabolic processes and ecosystem dynamics for montane ecosystems. Dense montane forests are common at moderate elevations, due to moderate temperatures and high rainfall. At higher elevations, the climate is harsher, with lower temperatures and higher winds, preventing the growth of trees and causing the plant community to transition to montane grasslands, shrublands or alpine tundra. Due to the unique climate conditions of montane ecosystems, they contain increased numbers of endemic species. Montane ecosystems also exhibit variation in ecosystem services, which include carbon storage and water supply.

Life zones

As elevation increases, the climate becomes cooler, due to a decrease in atmospheric pressure and the adiabatic cooling of airmasses. The change in climate by moving up 100 meters on a mountain is roughly equivalent to moving 80 kilometers (45 miles or 0.75° of latitude) towards the nearest pole. The characteristic flora and fauna in the mountains tend to strongly depend on elevation, because of the change in climate. This dependency causes life zones to form: bands of similar ecosystems at similar altitude.

One of the typical life zones on mountains is the montane forest: at moderate elevations, the rainfall and temperate climate encourages dense forests to grow. Holdridge defines the climate of montane forest as having a biotemperature of between , where biotemperature is the mean temperature considering temperatures below to be . Above the elevation of the montane forest, the trees thin out in the subalpine zone, become twisted krummholz, and eventually fail to grow. Therefore, montane forests often contain trees with twisted trunks. This phenomenon is observed due to the increase in the wind strength with the elevation. The elevation where trees fail to grow is called the tree line. The biotemperature of the subalpine zone is between .

Above the tree line the ecosystem is called the alpine zone or alpine tundra, dominated by grasses and low-growing shrubs. The biotemperature of the alpine zone is between . Many different plant species live in the alpine environment, including perennial grasses, sedges, forbs, cushion plants, mosses, and lichen groups a set of related ecoregions into the "montane grassland and shrubland" biome. A region in the Hengduan Mountains adjoining Asia's Tibetan Plateau have been identified as the world's oldest continuous alpine ecosystem with a community of 3000 plant species, some of them continuously co-existing for 30 million years.

Climates with biotemperatures below tend to consist purely of rock and ice.

Montane forests

Montane forests occur between the submontane zone and the subalpine zone. The elevation at which one habitat changes to another varies across the globe, particularly by latitude. The upper limit of montane forests, the tree line, is often marked by a change to hardier species that occur in less dense stands. For example, in the Sierra Nevada of California, the montane forest has dense stands of lodgepole pine and red fir, while the Sierra Nevada subalpine zone contains sparse stands of whitebark pine.

The lower bound of the montane zone may be a "lower timberline" that separates the montane forest from drier steppe or desert region.

Montane forests differ from lowland forests in the same area. The climate of montane forests is colder than lowland climate at the same latitude, so the montane forests often have species typical of higher-latitude lowland forests. Humans can disturb montane forests through forestry and agriculture. On isolated mountains, montane forests surrounded by treeless dry regions are typical " sky island" ecosystems.

Temperate climate

Montane forests in temperate climate are typically one of temperate coniferous forest or temperate broadleaf and mixed forest, forest types that are well known from Europe and northeastern North America. The trees are, however, often not identical to those found further north: geology and climate causes different related species to occur in montane forests.

Montane forests outside Europe tend to be more species-rich, because the major mountain chains of Europe are oriented east–west.

Montane forests in temperate climate occur in Europe (the Alps, Carpathians, Caucasus and more), in North America (Cascade Range, Klamath-Siskiyou, Appalachians and more), south-western South America, New Zealand and the Himalayas.

Climate change is predicted to affect temperate montane forests. For example, in the Pacific Northwest of North America, climate change may cause "potential reduced snowpack, higher levels of evapotranspiration, increased summer drought" which will negatively affect montane wetlands.

Mediterranean climate

Montane forests in Mediterranean climate are warm and dry except in winter, when they are relatively wet and mild. Montane forests located in Mediterranean climates exhibit towering trees alongside high biomass. These forests are typically mixed conifer and broadleaf forests, with only a few conifer species. Pine and juniper are typical trees found in Mediterranean montane forests. The broadleaf trees show more variety and are often evergreen, e.g. evergreen oak.

This type of forest is found in the Mediterranean Basin, North Africa, Mexico and the southwestern US, Iran, Pakistan and Afghanistan.

Subtropical and tropical climate

In the tropics, montane forests can consist of broadleaf forest in addition to coniferous forest. One example of a tropical montane forest is a cloud forest, which gains its moisture from clouds and fog. Cloud forests often exhibit an abundance of mosses covering the ground and vegetation, in which case they are also referred to as mossy forests. Mossy forests usually develop on the saddles of mountains, where moisture introduced by settling clouds is more effectively retained. Depending on latitude, the lower limit of montane rainforests on large mountains is generally between while the upper limit is usually from .

Tropical montane forests might exhibit high sensitivity to climate change. Climate change may cause variation in temperature, precipitation and humidity, which will cause stress on tropical montane forests. The predicted upcoming impacts of climate change might significantly affect biodiversity loss and might result in change of species range and community dynamics. Global climate models predict reduced cloudiness in the future. Reduction in cloudiness may already be affecting the Monteverde cloud forest in Costa Rica.

Subalpine zone

The subalpine zone is the biotic zone immediately below the tree line around the world. In tropical regions of Southeast Asia the tree line may be above , whereas in Scotland it may be as low as . Species that occur in this zone depend on the location of the zone on the Earth, for example, Pinus mugo (scrub mountain pine) in Europe, snow gum in Australia, or subalpine larch, mountain hemlock and subalpine fir in western North America.

Trees in the subalpine zone often become krummholz, that is, crooked wood, stunted and twisted in form. At tree line, tree seedlings may germinate on the lee side of rocks and grow only as high as the rock provides wind protection. Further growth is more horizontal than vertical, and additional rooting may occur where branches contact the soil. Snow cover may protect krummholz trees during the winter, but branches higher than wind-shelters or snow cover are usually destroyed. Well-established krummholz trees may be several hundred to a thousand years old.

Meadows may be found in the subalpine zone. Tuolumne Meadows in the Sierra Nevada of California, is an example of a subalpine meadow.

Example subalpine zones around the world include the French Prealps in Europe, the Sierra Nevada and Rocky Mountain subalpine zones in North America, and subalpine forests in the eastern Himalaya, Western Himalayan subalpine conifer forests, western Himalaya, and Hengduan mountains of Asia.

Alpine grasslands and tundra

Alpine grasslands and tundra lie above the tree line, in a world of intense radiation, wind, cold, snow, and ice. As a consequence, alpine vegetation is close to the ground and consists mainly of perennial grasses, sedges, and forbs. Annual plants are rare in this ecosystem and usually are only a few inches tall, with weak root systems. Other common plant life-forms include prostrate shrubs; tussock-forming graminoids; and cryptogams, such as bryophytes and lichens