| In
addition to the bank stabilization provided by good root systems,
both the amount and types of vegetation present in the riparian
area influence other functions of a riparian system. Riparian
vegetation protects the soil from erosion and compaction, traps
sediments and nutrients, and reduces water and soil temperature
and evaporation (Figure 2-19). |
Figure
2-19
The mix of trees, shrubs, and herbaceous plants along
this stream provides a great deal of diversity and contributes
to several riparian functions. |
|
Figure
2-20
Compare the capability of the riparian area in this
picture to slow floodwaters, trap sediments, and protect
the soil to that in figure 2-21, below. |
|
One
common way to estimate the amount of vegetation is by judging
"canopy cover." This is the percentage of a given
surface area which is shaded by vegetation when viewed from
directly above. Generally, the greater the percentage of canopy
cover, the better the protection provided (compare Figures
2-20 and 2-21). Assuming desirable species are present, the
greater the canopy cover, the higher the productivity of the
vegetation.
Not all
plant species are equally useful from a management perspective.
The presence of noxious weeds or other aggressive invader
species may be symptomatic of a riparian area with problems.
They reduce habitat diversity and quality as well as reducing
production of desirable species. Although undesirable species
such as dandelion, cheatgrass, Kentucky bluegrass, small clovers,
plantain, and pussy-toes are not considered as bad as noxious
weeds, their presence may indicate a trend away from the site's
potential. Often they indicate a high level of disturbance.
Moreover, they are usually low-producing species that provide
only limited soil- and bank-holding capability. |
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