Vegetation is a general term for the plant life of a region. It refers to the ground cover provided by plants, and is, by far, the most abundant biotic element of the biosphere. The term vegetation does not, by itself, imply anything regarding species composition, life forms, structure, spatial extent, "naturalness", or any other specific botanical or geographic characteristics. It is broader than the term flora which refers exclusively to species composition. Perhaps the closest synonym is plant community, but vegetation can, and often does, refer to a wider range of spatial scales. Primeval redwood forests, coastal mangrove stands, sphagnum bogs, desert soil crusts, roadside weed patches, wheat fields, cultivated gardens and lawns; all are encompassed by the term vegetation.
The word "natural" is widely used, broadly understood, and loosely defined. The term ?Natural vegetation? should be rather used to characterize those soils where vegetation grows without active and frequent intervention by people. Natural vegetation includes both native and introduced species.
Vegetation serves several critical functions in the biosphere, at all possible spatial scales. First, vegetation regulates the flow of numerous biogeochemical cycles, most critically those of water, carbon, and nitrogen; it is also of great importance in local and global energy balances. Such cycles are important not only for global patterns of vegetation but also for those of climate. Second, vegetation strongly affects soil characteristics, including soil volume, chemistry and texture, which feed back to affect various vegetational characteristics, including productivity and structure. Third, vegetation serves as wildlife habitat and the energy source for the vast array of animal species on the planet. Vegetation is also critically important to the world economy, particularly in the use of fossil fuels as an energy source, but also in the global production of food, wood, fuel and other materials. Perhaps most importantly, and often overlooked, global vegetation has been the primary source of oxygen in the atmosphere, enabling the aerobic metabolism systems to evolve and persist. Lastly, vegetation is psychologically important to humans, who evolved in direct contact with, and dependence on, vegetation, for food, sheleter, and medicines.
Much of the work on natural vegetation classification comes from European and North American ecologists, and they have fundamentally different approaches. In North America, vegetation types are based on a combination of the following criteria: climate pattern, plant habit, phenology and/or growth form, and dominant species. In the current US standard (adopted by the Federal Geographic Data Committee (FGDC), and originally developed by UNESCO and The Nature Conservancy), the classification is hierarchical and incorporates the non-floristic criteria into the upper (most general) five levels and limited floristic criteria only into the lower (most specific) two levels. In Europe, classification relies much more heavily, often entirely, on floristic (species) composition alone, without explicit reference to climate, phenology or growth forms. It often empahsizes indicator or diagnostic species which separate one type from another.
A primary characteristic of natural vegetation is its three-dimensional structure, sometimes referred to as its physiognomy, or architecture. Most people have an understanding of this idea through their familiarity with terms like "jungle", "woods", "prairie" or "meadow"; these terms conjure up a mental image of what such vegetation looks like. So, meadows are grassy and open, tropical rainforests are dense, tall, and dark, savannahs have trees dotting a grass-covered landscape, etc.
A landform comprises a geomorphological unit. Geography landforms are categorised by characteristics such as elevation, slope, orientation, stratification, rock exposure, and soil type. Landforms by name include berms, mounds, hills, cliffs, valleys, and so forth. Oceans and continents exemplify highest-order landforms. A number of factors, ranging from plate tectonics to erosion and deposition can generate and affect landforms. Biological factors can also influence landforms?see for example the role of plants in the development of dune systems and salt marshes, and the work of corals and algae in the formation of coral reefs. Many of the terms are not restricted to refer to features of the planet Earth, and can be used to describe surface features of other planets and similar objects in the Universe.