Temperate forests represent one of the major biomes on Earth, covering 14% of Earth's terrestrial land surface. Along with boreal and subtropical/tropical wet and dry forests, temperate forests are one of the Earth's dominant forest types. In comparison to other types, temperate forests are intermediate in latitude, temperature, and precipitation.
The Earth has a wide range of forests, from wintry boreal forests to colorful temperate deciduous forests to humid temperate evergreen forests to diverse tropical forests and others. The Earth's forests encompass many tree growth forms, including needle-leaved evergreens such as pines (Pinus), and spruces (Picea), broad-leaved deciduous trees such as beeches (Fagus), and maples (Acer), and broad- leaved evergreens such as some species of oak (Quercus), and mahogany (Swietenia). These growth forms and the forests they characterize occur along gradients of environment, particularly climate. The major gradient in the Earth's forests is latitudinal, from high latitude boreal regions to equatorial tropical regions. This gradient better developed in the northern hemisphere which has larger land masses-encompasses changes in environment, composition, structure and diversity.
The latitudinal gradient includes increasing length of the growing season from the short growing season of the boreal region to the yearlong growing season of the wet tropics. This factor has dramatic effects on species composition, as boreal forests tend to be dominated by needle-leaved evergreen trees, while temperate deciduous forests are characterized by broad-leaved deciduous trees and temperate evergreen forests and tropical rainforests are dominated by broad-leaved evergreen trees, all adapted to the length of the growing season in their geographic region.
Temperate forests are found in the northern hemisphere. Temperate forests are found in eastern North America, most of Europe, eastern China, Korea and northern Japan. They are mostly made up of deciduous trees such as oak, hickory, maple and beech. Since they are home to a great variety of plant and animal species, they are very bio diverse. Therefore, protecting temperate forest means protecting biodiversity.
Temperate forests cover more than 20 million km² of the Earth's surface, including forest types such as boreal conifer forests, the mixed deciduous forests of the United States, Europe, western Asia, China and Japan, and the evergreen rain forests of Chile, New Zealand, and Tasmania. In the Northern Hemisphere, dominant tree genera are typically members of the oak family (Fagaceae) or conifers such as pines (Pinus) and spruces (Picea). Southern Hemisphere forests are often dominated by southern beeches (Nothofagus spp.), mixed with conifers such as members of the Araucariaceae and Podocarpaceae. While temperate forests tend to be lower in diversity of plant or animal species than tropical forests, the diversity of fungi, mosses, and lichens may often be very high, particularly in areas of high humidity. Those of the Southern Hemisphere are characterized by many species that have restricted distribution. Temperate forests can be structurally complex, with up to seven distinct canopy layers. The largest trees can reach over 50m in height with girths of 2m or more. Spatial variation in forest structure and composition is influenced by the pattern of natural and anthropogenic disturbance, such as wind or fire. When canopy trees die, the resulting gaps in the canopy are colonized by different elements of the forest flora. This process of "gap dynamics" is important in maintaining stand structure and diversity.
Deciduous trees lose their leaves each fall and grow a new set each spring. Most of the other plants and shrubs in the forest have a similar cycle of growth. They do all their growing in the spring, summer and fall and become inactive in the winter.
The temperate deciduous forests experience 4 seasons. Each season is about equal length. Temperate means moderate or not extreme. This refers to the moderate temperature range in these forests. The coldest temperature for these forests is usually 20 degrees below zero Fahrenheit. The hottest it gets is around 95 degrees Fahrenheit. Rain or snow falls evenly throughout the year. The temperate forests get between 30 to 60 inches of precipitation each year.
Climate is a fundamental factor in defining the temperate forest biome. Generally, a forest is considered temperate if it is located in a region with hot summers and cold winters. The annual range in temperature can be ±30°C, and the mean annual temperature is between 3 and 18°C, with mean midwinter temperature below 8°C and mean mid-summer temperature about 18°C.
In contrast to grasslands or desert ecosystems, temperate forests have a more complex structure composed of different layers of vegetation. Temperate forest layers typically include a layer of mosses and lichens on the forest floor (and often on tree trunks and limbs), herbaceous and shrub layers, a subcanopy of trees, and a taller dominant canopy tree layer. The complexity of the subcanopy and canopy layers can vary and often depend on the light requirements of the dominant tree species. Trees are the dominant life form of these ecosystems and can be either deciduous or evergreen.
Temperate forests undergo different stages in ecosystem succession, allowing for the coexistence of plant species with different life history strategies. These adaptations are often linked to specific growing conditions associated with different stages of forest growth. As a result, gradual transitions in plant community composition and forest structure change over time. A classic example of succession in northeastern temperate forests in North America is when pioneer tree/shrub species such as birch and poplar, which are fast growing and require high light availability, are often the first to establish following a disturbance. As trees grow and the canopy begins to close, conditions become more favorable for more long- lived, shade-tolerant species such as maple (Acer spp.), oak, beech, and hemlock. These later successional trees become dominant or co-dominant and eventually out-compete early successional species, reaching heights of 35-40 m. This process takes place over hundreds of years and can be reset at any time by a disturbance of natural or human origin. Indeed, within a relatively large and healthy naturally occurring forest area, all of these successional stages are present at once.
Temperate forests provide many services to people, including watershed protection and soil stabilization, and also account for more than half of the carbon stored in forest ecosystems. In many areas they provide significant recreational use. Natural temperate forests are important reservoirs of genetic material of timber trees of economic importance, such as oaks, beeches, pines, and eucalypts. However, more than 500 temperate tree species are now threatened with extinction, often as a result of overexploitation. Large areas of temperate forest have been cleared for agriculture. In Europe and parts of Asia, this process of deforestation has taken place over thousands of years, but continues to be a principal threat in many areas. Timber harvesting is also wide spread. As a result many temperate forests are highly fragmented and old growth forests are now very restricted in extent. Other main threats to temperate forests include invasive species, urban development, browsing by vertebrates, mining, acid rain, and air pollution.