Biologists recognize plant communities
based on the observation that certain kinds of plants tend to
occur together in particular environments. Particular plants
grow in shady, moist spots, for example, while other kinds occur
in open, dry places. You won't find sagebrush growing in the
Olympic rain forest, nor will you see fir trees in the scrublands
of central Washington.
Plant communities differ in the kinds
of plants and the forms of plants that they include. For example,
a forest community typically has one or more kinds of trees (such
as pines and spruces), various smaller, woody shrubs, and many
even smaller herbaceous plants. In contrast, a grassland community
typically has one or more kind of grass and various other herbaceous
plants, but only a few shrubs and no trees.
The diversity of a plant community can
be affected by various factors. Climate (including rainfall,
temperatures, etc.), soil types, aspect (the direction a slope
faces), geography (location on the globe and altitude), topography,
and natural events such as regular flooding or fire can all influence
the diversity of plant communities. Abiotic factors such as mineral
content can strongly influence community diversity. For example,
serpentine soils, which are highly infertile because they are
low in available calcium, a required nutrient for plant growth,
are found in some locations in Washington. Few plants can grow
on serpentine soil, but those that can are often found only in
this specialized setting.
