Unique and Valuable Ecosystems

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Unique and Valuable Ecosystems	Food For Thought
Impacts of Climate Change	Literature Cited
Why are Cloud Forests so Vulnerable?	Biology 217 Homepage

Distribution Covering a total area of less than 400,000 square kilometers, tropical cloud forestscompose just 2.5% of the world’s tropical rainforests (Bubb et al., 2004).A typical altitude for an inland mountain cloud forest might fall between 2000 and 3500 m, while isolated mountains and those closer to the coast may occur at lower elevations (Foster, 2001). Tropical cloud forests have been observed at 736 sites in 59 countries (10). Most of these locations are in Asia (~ 60%), Latin America (~ 25%), and Africa (~15%) (2). Figure 1:Relative land areas of cloud forest versus other tropical mountain forest for Asia, Africa, and the Americas ( Bubb et al., 2004)	Composition Moving along an increasing elevational gradient on a tropical mountain, trees decrease in height and leaves become thicker, smaller, and harder (21). If the mountain is consistently immersed in cloud cover, the effects on vegetation are magnified, resulting in dwarfed or elfin trees, bearing leaves similar to xeromorphic desert species (7). Rooted in cold, acidic, nutrient-poor soils, trees grow in width by only about a millimeter each year (19). Trees from the Weinmanna family and tree ferns from the Cyatheacae family are common representatives in these systems around the world (7). Perhaps the most defining characteristic of the cloud forest is the abundance of epiphytes, which thrive here at incredible densities. Up to a quarter of all cloud forest species are classified as epiphytes (7). The combination of steady cloud cover and a canopy packed with arboreal flora creates a damp, dark understory that houses a unique array of flora and fauna. Elevational distributions of forest types on a tropical mountain (Foster 2001)

Distribution

Covering a total area of less than 400,000 square kilometers, tropical cloud forestscompose just 2.5% of the world’s tropical rainforests (Bubb et al., 2004).A typical altitude for an inland mountain cloud forest might fall between 2000 and 3500 m, while isolated mountains and those closer to the coast may occur at lower elevations (Foster, 2001). Tropical cloud forests have been observed at 736 sites in 59 countries (10). Most of these locations are in Asia (~ 60%), Latin America (~ 25%), and Africa (~15%) (2).

Figure 1:Relative land areas of cloud forest versus other tropical mountain forest for Asia, Africa, and the Americas ( Bubb et al., 2004)

Composition

Moving along an increasing elevational gradient on a tropical mountain, trees decrease in height and leaves become thicker, smaller, and harder (21). If the mountain is consistently immersed in cloud cover, the effects on vegetation are magnified, resulting in dwarfed or elfin trees, bearing leaves similar to xeromorphic desert species (7). Rooted in cold, acidic, nutrient-poor soils, trees grow in width by only about a millimeter each year (19). Trees from the Weinmanna family and tree ferns from the Cyatheacae family are common representatives in these systems around the world (7). Perhaps the most defining characteristic of the cloud forest is the abundance of epiphytes, which thrive here at incredible densities. Up to a quarter of all cloud forest species are classified as epiphytes (7). The combination of steady cloud cover and a canopy packed with arboreal flora creates a damp, dark understory that houses a unique array of flora and fauna.

Elevational distributions of forest types on a tropical mountain (Foster 2001)

Bioiversity and Endemism

The isolation and unique vegetative structure of tropical cloud forests encourage high levels of speciation and endemism. The ranges of many of these species are incredibly limited, some even endemic to particular mountain peaks (2). The Centinella ridge in Ecuador, for example, houses 90 species that are endemic to a 20 km region of forest (9). On a global scale, nearly 10% of all range-restricted birds are either confined to or found primarily in cloud forests (2). Of the 327 threatened bird species of the Americas, 38 are cloud forest species (2). Peru, in particular, relies on cloud forests to sustain many of its rare species. Nearly 30% of its endemic mammals, anurans, and birds are found primarily in cloud forest ecosystems (14).

Water Supply

In addition to housing an array of threatened and endemic species, tropical cloud forests also provide an important year-round source of water for millions of people. Frequent cloud contact provides vegetation with an additional source of water than precipitation. Through a process referred to as horizontal precipitation or “cloud stripping”, plants capture water from clouds via direct contact or enhanced condensation (18). This additional water becomes particularly important during the dry season, when a greater portion of a forest’s moisture may come from horizontal, rather than vertical, precipitation (18). Stream flows from cloud forests are greater and more dependable than other sources during the dry season, and therefore become key water providers for regional inhabitants. Tegucigalpa, Honduras, home to 850,000 people, receives more than 40% of its water supply from the cloud forests of La Tigra National Park (2).