Although the word forest is commonly used, there is no universally recognised precise definition, with more than 800 definitions of forest used around the world.Although a forest is usually defined by the presence of trees, under many definitions an area completely lacking trees may still be considered a forest if it grew trees in the past, will grow trees in the future, or was legally designated as a forest regardless of vegetation type.
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[17] without the necessity in definition of having trees on the land.
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.
