Roadside Revegetation

PLANNING PHASE TWO: ASSESS SITE
Wind – How to Assess
Wind speed equipment is available but is most likely too costly for most designers. Site visits
during different times of the year can give some indication whether wind is a problem. Other
site characteristics, such as position on the slope (e.g., ridgelines are more prone than valley
floor), or proximity to forested environments – as forests often reduce wind speeds – can be
used to infer wind strengths and directions. In many environments, prevailing winds often come
from one, or sometimes two, directions. Existing vegetation can provide clues to prevailing
wind directions (e.g., trees bent away from the prevailing wind). Road construction itself may
change wind patterns (e.g., creating a wind tunnel by constructing a through cut or removing
a swath of existing vegetation). Some visual indicators of wind erosion are wind scour (see
Figure 5-40 in Section 5.6, Surface Stability), exposed roots, and areas of soil deposition.
County and state departments of transportation employees are often good resources for
local weather information.
Mitigating for High Wind
Road Design
Designing islands of undisturbed vegetation to help break up wind patterns can aid vegetation
establishment. The taller the plants left undisturbed, the greater the wind protection. Established
trees, particularly those with low-growing branches, provide the greatest protection from wind.
Wind Barriers
Obstacles that block wind at the soil surface can be effective for early seedling survival. These
obstacles can include trees and tall shrubs, filter fabric, stabilized logs, large rocks, berms, and
stumps. In using these structures, seedlings should be planted on the windward side.
Tree Shelters
Tree shelters completely surround seedlings and block them from the wind (see Section 10.4.4,
Tree Shelters). They are an effective means of reducing ET rates created by high winds during
early establishment. Once the vegetation has emerged from the top of the tube, however,
tree shelters no longer protect the emerging foliage from the wind.
Shade Cards
Shade cards are sometimes used to block wind, but they are less effective than the fully enclosed
tree shelter (see Section 10.4.3, Shade Cards). When used to block wind, shade cards must
be placed on the windward side of the seedling, which is not necessarily the same location
that cards would be placed if protection from sun is the objective. Often two shade cards are
placed around the seedling for added protection against the wind. Placement of the shade
cards at the height of the foliage affords greater protection to the seedling.
Appropriate Species Selection
The drying and damaging effects of wind are important considerations in appropriate species
selection. A simple assessment of soil type and rainfall may not account for the effects of
wind. Choosing hardier, wind-tolerant, and more drought-tolerant species may be necessary
to establish vegetation on windswept sites. Find reference sites in windy locations to indicate
which species are adapted to wind.
Leave Surface Roughened
A roughened soil surface can create a micro-basin or relief that protects young germinants
from the drying effects of wind during the establishment phase (see Section 10.1.2, Tillage).
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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