Biome: Midlatitude Deciduous Forest

Structure and Composition

Extending throughout the Eastern United States, much of Europe, parts of Eastern Asia, Southern [Page 224]South America, Eastern Australia, and New Zealand, the deciduous midlatitude biome is characterized by broad-leaf trees that undergo a dormant season due to low temperatures. North American, European, and Asian deciduous midlatitude forests are similar in structure and composition, although diversity in European deciduous forests is much lower compared with its American counterpart. The difference in diversity is mainly due to the position of mountain ranges in Europe and North America and glacial advances on both continents. Mountain ranges run north to south in North America and east to west in Europe. Mile-high glaciers advanced south during the last glacial maximum, displacing the deciduous tree species in North America and Europe. Trees were able to migrate south in North America but the deciduous tree species in Europe encountered a barrier. Many deciduous species went extinct in Europe, resulting in lower diversity.

Considering the forest composition, the genera of deciduous trees in the different forests of North America, Europe, and Asia are, in general, the same with some combination of maple (Acer spp.), chestnut (Castanea spp.), beech (Fagus spp.), ash (Fraxinus spp.), oak (Quercus spp.), basswood (Tilia spp.), and elm (Ulmus spp.), among others present in different forests. Some evergreen trees, such as pine (Pinus spp.) and hemlock (Tsuga spp.), and evergreen shrubs, such as holly (Ilex spp.), are also present in the deciduous midlatitude forest.

In addition to the similarity in the forest composition, the structure in deciduous midlatitude forests of North America, Europe, and Asia is also similar. In general, four layers exist in these forests. Mature canopy trees (20 to 30 m [meters] tall) dominate the overstory. Subcanopy trees are not as tall as mature canopy trees but still receive direct sunlight at the top of the tree's canopy. Subcanopy trees usually fill a gap produced by a dead canopy tree and will eventually grow to become part of the mature canopy trees. Understory trees only receive minimal sunlight through the canopy and consist mainly of shade-tolerant saplings. Finally, the ground layer consists of tree seedlings and shrubs, ferns, and herbs.

Several animals are associated with the eastern deciduous forest in North America, among them mammals such as the white-tailed deer (Odocoileus virginianus), gray squirrel (Sciurus carolinensis), American beaver (Castor canadensis), and black bear (Ursus americanus). Birds in this biome include owls, crows (Corvus spp.), hawks, pigeons, and jays among many others. A once very common bird in North America, which became extinct in the late 1800s and early 1900s, is the passenger pigeon (Ectopistes migratorius), and before its extinction, it took days for a flock to pass by. Billions of passenger pigeons existed when European settlers came to North America. However, due to overexploitation by hunting and loss of habitat, their numbers declined. Because the passenger pigeon is a social creature that requires large flocks to live, it did not survive. Today, the most prominent animal in the eastern deciduous forest in North America is probably the white-tailed deer. Brought to very low numbers in the early 1900s due to hunting pressures and habitat destruction, the population rebounded to pre-European levels, exceeding those numbers by several million today.

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