Hundreds of more precise definitions of forest are used throughout the world.

incorporating factors such as tree density, height, land use, legal standing and ecological function. 

According to the widely used Food and Agriculture Organization’s researches, forests covered 4 billion hectares (9.9×109 acres) (15 million square miles) or approximately 30% of the Earth’s land area in 2006.

Forests are the dominant terrestrial ecosystem of whole Earth. 

Forest’s account for 75% of the gross primary production of the Earth’s biosphere, and contain 80% of the Earth’s plant biomass.

Net primary production is estimated at 21.9 gigatonnes carbon per year for tropical forests, 8.1 for temperate forests and 2.6 for boreal forests.


There can be more than 800 definitions of forest which is used around the world. 

A Forest is usually defined by the presence of trees, under many definitions an area completely lacking trees may still be considered a forest.

There are three broad categories of forest definitions in use.

  • Administrative 
  • Land use
  • Land cover


Administrative definitions are based primarily upon the legal designations of land.

It’s commonly bear little relationship to the vegetation growing on the land.

Land use

It’s based upon the primary purpose that the land serves.

For example, a forest may be defined as any land that is used primarily for production of timber.

Under this definition, cleared roads or infrastructure within an area used for forestry.

Land cover

This can be define forests based upon the type and density of vegetation growing on the land.

Under this definitions, an area of land can only be known as forest if it is growing trees.

There is considerable variation on where the cutoff points are between a forest, woodland, and savanna.

Under some definitions, forests require very high levels of tree canopy cover, from 60% to 100%.

Other definitions consider savannas to be a type of forest, and include all areas with tree canopies over 10%.


The word forest derives from the Old French forest (also forès), denoting “forest, vast expanse covered by trees”.

forest was first introduced into English as the word denoting wild land set aside for hunting without the necessity in definition of having trees on the land. 

Possibly a borrowing, probably via Frankish or Old High German, of the Medieval Latin foresta, denoting “open wood”, Carolingian scribes first used foresta in the Capitularies of Charlemagne specifically to denote the royal hunting grounds of the King.


The First known forests on Earth arose in the Late Devonian (approximately 380 million years ago), with the evolution of Archaeopteris. Archaeopteris was a plant that was both tree-like and fern-like, growing to 10 metres (33 ft) in height. 

Archaeopteris quickly spread throughout the world, from the equator to subpolar latitudes. 

Archaeopteris formed the first forest by being the first known species to cast shade due to its fronds and forming soil from its roots. 

Archaeopteris was deciduous, dropping its fronds onto the forest floor. The shade, soil, and forest duff from the dropped fronds created the first forest. 


Forests account for 75% of the gross primary productivity of the Earth’s biosphere, and contain 80% of the Earth’s plant biomass. 

Forest ecosystems can be found in all regions capable of sustaining tree growth, at altitudes up to the tree line, except where natural fire frequency or other disturbance is too high, or where the environment has been altered by human activity.


A forest consists of many components that can be broadly divided into two categories that are biotic (living) and abiotic (non-living) components.

The biotic parts include trees, shrubs, vines, grasses and other herbaceous (non-woody) plants, mosses, algae, fungi, insects, mammals, birds, reptiles, amphibians, and microorganisms living on the plants and animals and in the soil.

The abiotic feature of a forest ecosystem may not be obvious, Tangible abiotic factors include soil, minerals, rocks and water.


we can say that a forest is made up of many layers. The main layers of all forest types are the forest floor, the understory and the canopy.

The emergent layer exists in tropical rainforests.

Each layer has a different set of plants and animals depending upon the availability of sunlight, moisture and food.

  • Forest floor contains decomposing leaves, animal droppings, and dead trees. Decay on the forest floor forms new soil and provides nutrients to the plants. The forest floor supports ferns, grasses, mushroom and tree seedlings.
  • Understory is made up of bushes, shrubs, and young trees that are adapted to living in the shades of the canopy.
  • Canopy is formed by the mass of intertwined branches, twigs and leaves of the mature trees. The crowns of the dominant trees receive most of the sunlight. by this part of the trees maximum food is produced. The canopy forms a shady, protective “umbrella” over the rest of the forest.
  • Emergent layer exists in the tropical rain forest and is composed of a few scattered trees that tower over the canopy.


Forests can be classified in different ways and to different degrees of specificity.

One such way is in terms of the biome in which they exist, combined with leaf longevity of the dominant species (whether they are evergreen or deciduous).

Another distinction is whether the forests are composed predominantly of broadleaf trees, coniferous (needle-leaved) trees, or mixed.

  • Boreal forests occupy the subarctic zone and generally evergreen and coniferous.
  • Temperate zones support both broadleaf deciduous forests (e.g., temperate deciduous forest) and evergreen coniferous forests (e.g., temperate coniferous forests and temperate rainforests). Warm temperate zones support broadleaf evergreen forests, including laurel forests.
  • Tropical and subtropical forests include tropical and subtropical moist forests, tropical and subtropical dry forests, and tropical and subtropical coniferous forests.
  • Physiognomy classifies forests based on their overall physical structure or developmental stage (e.g. old growth vs. second growth).
  • Forests can also be classified more specifically based on the climate and the dominant tree species present, resulting in numerous different forest types (e.g., Ponderosa pine/Douglas-fir forest).


According to some researches the number of Trees in the world, in 2015 estimate, is 3 trillion, of which 1.4 trillion are in the tropics or sub-tropics, 0.6 trillion in the temperate zones, and 0.7 trillion in the coniferous boreal forests.

The estimate is about eight times higher than previous estimates, and is based on tree densities measured on over 400,000 plots.

It remains subject to a wide margin of error, not least because the samples are mainly from Europe and North America.

Forests can also be classified according to the amount of human alteration. 

Old-growth forest contains mainly natural patterns of biodiversity in established seral patterns, and they contain mainly species native to the region and habitat.

Different global forest classification systems have been proposed.

UNEP-WCMC’s forest category classification system is a simplification of other more complex systems

E.g. UNESCO’s forest and woodland ‘subformations’.

we’ll discuss more about forest in our next post

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