Temperate forests stack four living layers beneath canopies up to 61 metres tall
Walk into an oak or beech forest and you are passing through four storeys: a canopy that can tower 30 to 61 metres, a sub-canopy of waiting saplings, a shrub layer, and a ground layer that is usually the richest of all. Rainfall across this habitat ranges from about 300 millimetres to nearly 6,000.
The World Wide Fund for Nature groups temperate forests, mixed conifer forests and temperate rainforests into a single habitat type. It reaches its greatest richness and distinctiveness in central China and eastern North America. Other standout examples occur in the Himalayas, in Western and Central Europe, along the Black Sea's southern coast, in the Russian Far East, across Australasia and in the southwest of South America.
Structure is the key to these woods. Below the tall mature canopy trees, a shade-tolerant understory sits roughly 9 to 15 metres lower. Its top tier holds smaller adults, saplings and suppressed young trees biding their time until a gap opens overhead. Beneath that grow low woody shrubs, and at the bottom lies the herbaceous ground cover, which typically holds the greatest variety of species.
In the Northern Hemisphere, oaks, beeches, maples and birches dominate, and mixed forests add pines, firs and spruces to the canopy, sometimes as the main players. South of the equator the cast changes to endemic groups such as southern beech, Nothofagus, and Eucalyptus, with conifers from the Araucariaceae and Podocarpaceae growing among broadleaf trees rather than in separate stands.
These forests need distinct warm and cool seasons, with average annual temperatures of 3 to 23 °C, in humid continental, humid subtropical and oceanic climates. Annual rain usually exceeds 600 millimetres and often 1,500, but falls to around 300 in parts of the Middle East and climbs close to 6,000 in the mountains of New Zealand and the Azores. East Asia has a dry winter, while Mediterranean fringes dry out in summer. In places like Ussuriland and the American Upper Midwest the trees endure bitterly cold winters.
Source: Temperate broadleaf and mixed forests
