Equatorial rain forest
The equatorial rain forest is a broad-leaved evergreen formation found in the warm and moist areas of the tropics at low elevation. Overall,
moisture is the main factor influencing the distribution of equatorial rain forest, though other factors, such as soils, can be important locally.
Annual precipitation averages somewhere between 1,500 to 4,000 mm (380-1,010 in), and average temperatures are in the range 25-35˘XC (77-95˘XF). More
importantly, there is no pronounced dry season that results in severe moisture stress. Other than the upper canopy and emergents, there are
also two or more forest layers, or strata, made up mostly of seedlings, shrubs, and trees. Vines and epiphytes attached to the trees are often
abundant. As seen from the air the upper canopy is closed and little light reaches the forest floor.
Monsoon rain forest
Monsoon forests replace equatorial rain forest at the latter's climatic and latitudinal limits. Well-drained soils are characteristic of these is a
forests. There marked dry season when plant growth is limited by water stress. Most of these forests are found at elevations under 1,000 m (3,300 ft).
Generally they are shorter in stature than equatorial rain forest, many species become leafless during the dry season, and because more light
reaches the understorey they often have a dense and rich undergrowth. Lianas can be diverse and abundant. Due to seasonal drought, monsoon
forests are inflammable and when burned degrade into savannas or sparse woodlands. Monsoon forests are especially common in South-East Asia (for
example, India, Indochina, and Thailand) where annual rainfall is often less than 1,300 mm (330 in) and the dry season can last four or five
months. They are also extensive in Africa, but less so in South and Central America.
Sub-tropical rain forest
In eastern Australia, South-East Asia, and the east coast of South America evergreen rain forest extends into the subtropical regions. For example, there is
coastal rain forest south of Rio de Janeiro, a city which is almost on the Tropic of Capricorn. In general subtropical rain forests are
counterparts of their nearest main tropical forest, though they are usually less diverse and are shorter in stature the farther the distance
from the tropics. The subtropical rain forest on the east coast of Australia in Queensland is very similar to that of the Indo-Malayan
region, but gradually takes on other floral elements in New South Wales and Victoria.
Montane rain forest
As a tropical forested mountain is ascended, the species and structure of the vegetation begins to change, as also happens in temperate latitudes.
The latitudinal gradient of climate, including rainfall, temperature, wind, and moisture, is the most important factor affecting the vegetation,
although local geology also plays an important role. Mean temperature, for example, decreases about 0.4 to
0.7˘XC per 100 metres on tropical
mountains. Montane rain forest can be found between lowland rain forest, which reaches to about 1,000-1,500 m (3,300-4,950 ft), and at least
3,000 m (10,000 ft) in many cases where elevation permits. There is great variability in these upper limits, however, because of local
climates. In montane rain forests a purely tropical flora is left behind, and many of the species are derived from temperate plant groups.
The trees get smaller as higher zones are reached and diversity is reduced. Tree trunks become twisted and gnarled and overgrown with
mosses and liverworts which enjoy a mist or cloud-like environment around them. Ferns and bamboos can be common. Montane rain forests are
especially abundant in the Indo-Malayan and Austral-Asian area and along the eastern flanks of the Andes in South America. Sometimes these are called cloud-forests.
Mangrove
Tropical and subtropical coasts are often bordered by intertidal forest communities consisting of plants highly adapted to periodic inundation, boggy soils, and saline
conditions. These mangrove formations are not rain forests, but are mentioned here because they often fringe the latter at their coastal
limits. Plant diversity is low in mangroves compared to rain forests because of the stressful conditions presented by salt or brackish water,
and to some extent by tidal flooding. The greatest development of mangroves is found in brackish water areas. In the New World there are
fewer than ten mangrove species, but over 35 species in the Indo-Pacific region. Respiratory roots are common features of these plant
communities. The mangrove genera Avicennia (sometimes known as black mangrove) and Rhizophora (red mangrove) are widely spread in the tropics
and also extend beyond them. Forests that receive irregular rainfall (monsoons followed by a dry season) are moist deciduous forests. Trees in these forests may drop
their leaves in the dry season. Montane forests are found in mountainous areas and may contain plants
such as oaks, rhododendrons and pines, which are characteristic of temperate deciduous forests. At higher altitudes temperatures are
cooler. Even close to the equator, frost and snow can occur.
Lowland Forests
Lowland Forests are by far the most extensive, but since they are easily accessible, they have suffered the most damage and clearing. They are also
the most prolific of all the plant communities in the world. The canopy can reach more than 45 meters (150 feet) in height and consists of many
different tree species living close together. A few trees, known as emergent, break through the canopy, often attaining height
of 60 meters (200 feet) with straight, unbranched trunks up to 40-50 meters (130-165 feet) in height.
Mountain Rain Forests
Mountain Rain Forests are much smaller in stature, their growth restricted by a combination of low temperatures, unpredictable rainfall and the
lack of nutrients at higher altitudes. These stunted forests play a key role in protecting the environment. Without them, soil erosion in highlands
and flash floods in lowlands are the damaging consequences.
Flooded Rain Forests
It is found along the banks of rain forests rivers where large areas of lowland forest are inundated. Higher up the Amazon watershed where the
Amazon's tributaries flood for a short time after heavy rains, the flooded forest is called "várzea";
farther downstream, in the Amazonian lowlands, there is the swamp forest, or "igapó".
The largest temperate rainforests are found on the Pacific coast. They stretch from Oregon to Alaska for 1,200 miles. Smaller
temperate rainforests can be found on the southeast coast of Chile in South America. There are a few other coastal strips with temperate rainforests, to
include small areas in southern Australia and New Zealand, Norway, the United Kingdom and Japan. Today only about three percent of the temperate rainforest in the USA
remains, mostly inside the Olympic National Park in Washington State. More than a million acres of old-growth spruce and hemlock were on the Olympic Peninsula
prior to the arrival of homesteaders just over a century ago. Because of habitat destruction, many plants and animals have become "island dwellers"
inside the park now.
