Summergreen deciduous forest, sometimes called temperate deciduous forest, is familiar to inhabitants of eastern North America and Western Europe as a native forest type. It is dominated by tall, broadleaf trees, which provide a continuous and dense canopy in summer but shed their leaves completely in the winter. Lower layers of small trees and shrubs are weakly developed. In spring a luxuriant low layer of herbs quickly develops, but this is greatly reduced after the trees have reached full foliage and shaded the ground.
Summergreen deciduous forest is almost entirely limited to the middle-latitude landmasses of the northern Hemisphere. Common trees of the deciduous forests of eastern North America, southeastern Europe, and eastern Asia (all in the humid-continental climate) are oak, beech (Fagus), brich (Betula), hickory (Carya), walnut (Juglans), maple (Acer), basswood (Tilia), elm, ash, tulip tree, sweet chestnut (Castanea), and hornbeam (Carpinus). In western and central Europe, under a marine west coast climate dominant trees are mostly oak and ash, with beech (Fagus syluatica) in cooler and moister areas.
In poorly drained habitats, the deciduous forest consists of such trees as alder, willow, ash, and elm, and many hygrophytic shrubs. Where the deciduous forests have been cleared in lumbering pines readily develop as second-growth vegetation.
The summergreen deciduous forest represents a response to a continental climatic regime, which at the same time receives adequate precipitation in all months. There is a strong annual temperature cycle with a cold winter season and a warm summer. Precipitation is markedly greater in the summer months (especially so in eastern Asia) and this increases at the time of year when evapotranspiration is great and the moisture demands are high. Only a small water deficit is incurred in the summer, while a large surplus normally develops in spring. In eastern Asia the winter is exceptionally dry, but this factor is compensated for by cold.
The pedogenic process associated with summer green deciduous forest is that of podzolization, but moderate by the warm wet summers. As a ~result, the soils are characteristically of the gray-brown forest groups. Towards lower latitudes the tendency to laterization becomes stronger and red-yellow podzolic soils are encountered; toward the continental interiors the tendency to calcification sets in and the deciduous forest extends into regions of darker soils of the grasslands (prairie and chernozem soils). In the sumnmergreen deciduous forests a thick layer of fallen leaves covers the ground and there is abundant humus in the soil.
Because the regions of summergreen deciduous forest have for centuries been the areas of dense populations, few remnants of a primeval forest have survived. Instead, most existing forests are modified by practices of tree fanning. Large areas are completely and permanently removed from forest growth by farming urban development, and roadways.
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