Vegetation

Vegetation refers to assemblages of plant species and the ground cover they provide.It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader than the term flora which refers to species composition. Perhaps the closest synonym is plant community, but vegetation can, and often does, refer to a wider range of spatial scales than that term does, including scales as large as the global. 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.

Vegetation type refers to vegetation in an assemblage where there is a characteristic dominant species or species, or a common aspect of the assemblage, such as an elevation range or environmental commonality.

Contents

1 Classification

• 2 Dynamics
  • 2.1 Temporal dynamics
  • 2.2 Spatial dynamics
  • 3 References and further reading
  • 4 External links
    • 5.1 Classification
    • 5.2 Mapping-related
    • 5.3 Climate diagrams
      

      Tundra   Taiga   Temperate broadleaf and mixed forest   Temperate steppe   Subtropical moist forest

      Mediterranean   Monsoon forest   Desert   Xeric shrubland   Dry steppe   Semi-desert

      Grass savanna   Tree savanna   Tropical and subtropical dry forest   Tropical rainforest   Alpine tundra   Montane forest

      Much of the work on 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 theFederal 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 often relies much more heavily, sometimes entirely, on floristic (species) composition alone, without explicit reference to climate, phenoloogy or growth forms. It often emphasizes indicator or diagnostic species which may distinguish one classification from another.
      

      Dynamics

      Like all the biological systems, plant communities are temporally and spatially dynamic; they change at all possible scales. Dynamism in vegetation is defined primarily as changes in species composition and/or vegetation structure.

      Temporal dynamics

      Temporally, a large number of processes or events can cause change, but for sake of simplicity they can be categorized roughly as either abrupt or gradual. Abrupt changes are generally referred to as disturbances; these include things likewildfires, high winds, landslides, floods, avalanches and the like. Their causes are usually external (exogenous) to the community—they are natural processes occurring (mostly) independently of the natural processes of the community (such as germination, growth, death, etc.). Such events can change vegetation structure and composition very quickly and for long time periods, and they can do so over large areas. Very few ecosystems are without some type of disturbance as a regular and recurring part of the long term system dynamic. Fire and wind disturbances are particularly common throughout many vegetation types worldwide. Fire is particularly potent because of its ability to destroy not only living plants, but also the seeds, spores, and living meristems representing the potential next generation, and because of fire's impact on fauna populations, soil characteristics and other ecosystem elements and processes (for further discussion of this topic see fire ecology).

      Spatial dynamics

      As a general rule, the larger an area under consideration, the more likely the vegetation will be heterogeneous across it. Two main factors are at work. First, the temporal dynamics of disturbance and succession are increasingly unlikely to be insynchrony across any area as the size of that area increases. That is, different areas will be at different developmental stages due to different local histories, particularly their times since last major disturbance. This fact interacts with inherent environmental variability (e.g. in soils, climate, topography, etc.), which is also a function of area. Environmental variability constrains the suite of species that can occupy a given area, and the two factors together interact to create a mosaic of vegetation conditions across the landscape. Only in agricultural or horticultural systems does vegetation ever approach perfect uniformity. In natural systems, there is always heterogeneity, although its scale and intensity will vary widely. A naturalgrassland may be homogeneous when compared to the same area of partially burned forest.