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In the United States, the EPA and the United States Geological Survey (USGS) are the principal federal agencies working with the CEC to define and map ecoregions. Ecoregions may be identified by similarities in geology, physiography, vegetation, climate, soils, land use, wildlife distributions, and hydrology.
These maps show a scale, or index of greenness, based on several factors: the number and type of plants, leafiness, and plant health. Where foliage is dense and plants are growing quickly, the index is high, represented in dark green. Regions with sparse vegetation and a low vegetation index are shown in tan.
Regions in which permafrost has thawed and trees have fallen take centuries to recover. Canadian and Russian governments enacted a Protection Belt, which covers 21.1 million ha, and initiatives like the Far East Association for the use of non-timber forest products, give economic significance to the forests while avoiding logging.
A tropical moist broadleaf forest in Central America, for example, may be similar to one in New Guinea in its vegetation type and structure, climate, soils, etc., but these forests are inhabited by animals, fungi, micro-organisms and plants with very different evolutionary histories.
The taiga experiences relatively low precipitation throughout the year (generally 200–750 mm (7.9–29.5 in) annually, 1,000 mm (39 in) in some areas), primarily as rain during the summer months, but also as snow or fog. Snow may remain on the ground for as long as nine months in the northernmost extensions of the taiga biome.
The terrain of the Southeastern Plains is dissected, rolling to smooth plains.The Cretaceous sands, silts, and clays of this region contrast geologically with the older metamorphic and igneous rocks of the Piedmont ecoregion, and with the Paleozoic limestone, chert, and shale of the Interior Low Plateaus ecoregion.
Treeless alpine (low-alpine): Characterized by a closed carpet of vegetation that includes alpine meadows, shrubs and sporadic dwarfed trees. Because of the complete cover of vegetation, frost has less of an effect on this region, but due to the consistent freezing temperatures tree growth is severely limited.
The adversity of soil and climatic conditions proves to low production levels, as well as little biomass accumulation due to slow rates of nutrient release in cold and wet soils, specifically as a result of limited nitrogen and phosphorus (Nadelhoffer et al. 1996) Additionally, there are low temperatures and strong winds in the tundra causing most vegetation to be dominated by woody plants ...