Vegetation represents the cleaning health of plant life and the amount of ground soil
provided by plants and animals . Vegetation has no particular taxa, life forms, structure,
spatial extend, or any other specific botanical or good characteristics. It is broader than
flora which refer 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 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.
Classification
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, and originally developed
by UNESCO and The Nature Conservancy), the classification is hierarchical and incorporates
the non-floristic criteria into the upper five levels and limited floristic criteria
only into the lower two levels. In Europe, classification often relies much more heavily,
sometimes entirely, on floristic 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. In the FGDC standard, the hierarchy levels,
from most general to most specific, are: system, class, subclass, group, formation, alliance,
and association. The lowest level, or association, is thus the most precisely defined, and incorporates
the names of the dominant one to three species of a type. An example of a vegetation type
defined at the level of class might be "Forest, canopy cover > 60%"; at the level of a formation
as "Winter-rain, broad-leaved, evergreen, sclerophyllous, closed-canopy forest"; at
the level of alliance as "Arbutus menziesii forest"; and at the level of association as
"Arbutus menziesii-Lithocarpus densiflora forest", referring to Pacific madrone-tanoak
forests which occur in California and Oregon, USA. In practice, the levels of the alliance
and/or association are the most often used, particularly in vegetation mapping, just as
the Latin binomial is most often used in discussing particular species in axonomy and in general
communication. Victoria in Australia classifies its vegetation
by Ecological Vegetation Class. 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 like wildfires, high winds, landslides,
floods, avalanches and the like. Their causes are usually external to the community—they
are natural processes occurring independently of the natural processes of the community.
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. Temporal change at a slower pace is ubiquitous;
it comprises the field of ecological succession. Succession is the relatively gradual change
in structure and taxonomic composition that arises as the vegetation itself modifies various
environmental variables over time, including light, water and nutrient levels. These modifications
change the suite of species most adapted to grow, survive and reproduce in an area, causing
floristic changes. These floristic changes contribute to structural changes that are
inherent in plant growth even in the absence of species changes, causing slow and broadly
predictable changes in the vegetation. Succession can be interrupted at any time by disturbance,
setting the system either back to a previous state, or off on another trajectory altogether.
Because of this, successional processes may or may not lead to some static, final state.
Moreover, accurately predicting the characteristics of such a state, even if it does arise, is
not always possible. In short, vegetative communities are subject to many variables
that together set limits on the predictability of future conditions.
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 in synchrony 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, 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 natural grassland may be homogeneous when compared to the same area
of partially burned forest, but highly diverse and heterogeneous when compared to the wheat
field next to it. See also
Biocoenosis Biome
British National Vegetation Classification Ecological succession
Ecoregion Ecosystem
Tropical vegetation Vegetation and slope stability
References and further reading Archibold, O. W. Ecology of World Vegetation.
New York: Springer Publishing, 1994. Barbour, M. G. and W. D. Billings. North American
Terrestrial Vegetation. Cambridge: Cambridge University Press, 1999.
Barbour, M.G, J.H. Burk, and W.D. Pitts. "Terrestrial Plant Ecology". Menlo Park: Benjamin Cummings,
1987. Breckle, S-W. Walter's Vegetation of the Earth.
New York: Springer Publishing, 2002. Burrows, C. J. Processes of Vegetation Change.
Oxford: Routledge Press, 1990. Feldmeyer-Christie, E., N. E. Zimmerman, and
S. Ghosh. Modern Approaches In Vegetation Monitoring. Budapest: Akademiai Kiado, 2005.
Gleason, H.A. 1926. The individualistic concept of the plant association. Bulletin of the
Torrey Botanical Club, 53:1-20. Grime, J.P. 1987. Plant
strategies and vegetation processes. Wiley Interscience, New York NY.
Kabat, P., et al.. Vegetation, Water, Humans and the Climate: A New Perspective on an Interactive
System. Heidelberg: Springer-Verlag 2004. Macarthur, R.H. and E.O. Wilson. The theory
of Island Biogeography. Princeton: Princeton University Press. 1967
Mueller-Dombois, D., and H. Ellenberg. Aims and Methods of Vegetation Ecology. The Blackburn
Press, 2003. Van Der Maarel, E. Vegetation Ecology. Oxford:
Blackwell Publishers, 2004. Vankat, J. L. The Natural Vegetation of North
America. Krieger Publishing Co., 1992. External links
Classification Terrestrial Vegetation of the United States
Volume I – The National Vegetation Classification System: Development, Status, and Applications
Federal Geographic Data Committee Vegetation Subcommittee
Vegetation Classification Standard [FGDC-STD-005, June 1997]
Classifying Vegetation Condition: Vegetation Assets States and Transitions
Mapping-related Interactive world vegetation map by Howstuffworks
USGS - NPS Vegetation Mapping Program Checklist of Online Vegetation and Plant Distribution
Maps VEGETATION image processing and archiving
centre at VITO Spot-VEGETATION programme web page
Climate diagrams Climate Diagrams Explained
ClimateDiagrams.com Provides climate diagrams for more than 3000 weather stations and for
different climate periods from all over the world. Users can also create their own diagrams
with their own data. WBCS Worldwide Climate Diagrams
References