AskDefine | Define overstory

Extensive Definition

The canopy is one of the uppermost levels of a forest, below the emergent layer, formed by the tree crowns. Canopy trees refers to the trees in a forest which form the canopy. The uneven layers of the canopy is formed by both dominant and co-dominant trees. Emergents - of which there are typically one or two per hecatre - reach above the canopy.
The canopy of a rainforest is typically 10m thick, and intercepts around 95% of sunlight. With an abundance of water and a near ideal temperature, light and minerals are the two restricting factors on a tree's growth. Plants grow rapidly to reach the canopy, but have no need to grow any taller after reaching the light.
The canopy is home to a unique flora and fauna not found in other layers of a forest.
The term has also been adopted by the permaculture and forest gardening community, who use the distinction between canopy and secondary trees in their seven layer design system.
The canopy of an individual tree refers to the extent of the outer layer of a trees leaves. Shade trees normally have a dense canopy blocking out the light from lower growing plants. The Leaf Area Index can be used to measure the density of the canopy.
Canopy is also the name given to the upper layer of trees (mostly in tropical rainforests) which cover the forest's floor and protect it from strong winds and storms. Although the canopy protects the soil from winds and storms it also keeps sunlight from reaching it as well as a considerable amount of rain. As a consequence the rainforest floor has considerably less vegetation than the rest of the forest layers.
Trees in the canopy are able to photosynthesise very rapidly thanks to the large amount of light, so it supports the widest diversity of plant as well as animal life in most rainforests. Many rainforest animals have evolved to live solely in the canopy, and will never touch the ground.

See also

overstory in Danish: Krone (plantedel)
overstory in Spanish: Canopea (bosque)
overstory in French: Canopée
overstory in Japanese: 林冠
overstory in Portuguese: Dossel florestal
overstory in Finnish: Latvuskerros
overstory in Romanian: Foliaj
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