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Functions
& Conditions -
Evaluating the Biological Features
Presence
of trees and shrubs
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Figure
2-22
This reach is in transition toward a better functioning
condition as the result of a grazing management change.
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Not all riparian
areas should have trees and/or shrubs, but for those areas that
have them or could have them, they can perform important riparian
functions. The root systems of woody plants are excellent bank stabilizers,
while their spreading canopies offer protection to soil, water,
livestock, and wildlife. A healthy woody plant community offers
a variety of food and cover needs for birds and mammals while providing
forage and protection for livestock when necessary.
Determining
if a stream reach could have woody species is sometimes difficult.
As a rule of thumb, if there are trees or shrubs present, the reach
can probably support a woody community. The presence of woody plants
along similar reaches of the stream or along similar streams in
the area may indicate the potential for woody species.
The sites shown
in Figures 2-22 and 2-23 are on the same reach less than two miles
apart. Until recently, the pasture in Figure 2-22 was grazed season
long, while that in Figure 2-23 has been grazed for short periods
several times during the growing season for many years. After the
photo was taken, a change in management on the first pasture resulted
in a reduction in bare ground and the obvious presence of four different
willow species along the river. A change in the amount of water
in the system or time of flow may influence the continued presence
of woody plants.
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Figure
2-23
This reach of the same stream as the previous picture
has been grazed annually for more than 20 years and
retains healthy woody as well as herbaceous communities.
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One possible
exception to determining appropriate presence of woody plants is
cottonwoods. These species rarely reproduce at the same location
because their seeds require bare mineral soil which is usually not
co-located with mature trees. In most instances, future generations
of cottonwoods should be sought downstream or upstream rather than
under an existing stand.
When we look
for woody species in a riparian area, we need to consider not just
whether they are present but also how likely it is they will continue
to be there. Thus, we are really looking at three things: (1) the
presence of woody species and some idea of whether the reach could
have trees or shrubs; (2) the age classes present; and (3) how heavily
they are being impacted, regardless of what animals are doing the
impacting.
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