Roadside Revegetation

PLANNING PHASE TWO: ASSESS SITE
seedlings so that the stem and lower portion of the seedlings are shaded from the afternoon
sun (Helgerson and others 1992).
Obstacles
Large obstacles that cast significant amounts of shade on young seedlings will create a more
favorable environment for seedling establishment and increase seedling survival (Minore 1971).
These include stabilized logs, large rocks, berms, and stumps. Seedlings should be planted on
the north and east side of these features to be shaded from the afternoon sun.
Mulch
On south exposures, the use of mulches as a moisture barrier should be considered for seedlings,
seeds, and cuttings (see Section 10.1.3, Mulches). Avoid placing mulch in direct contact with
the stem of the seedling.
Species Mix
The composition of species will probably be different for north and south aspects. Species
adapted to hotter and drier environments are used for revegetating south exposures; those
adapted to cool, moist environments are used on north aspects. Elevation can offset the effects
of aspect. For example, species that grow on low elevation, north aspects often occur several
thousand feet higher on south aspects because of the difference in temperatures. Reference
site vegetation surveys will guide in the selection of appropriate species for each exposure.
Plant Material Rates
South aspects often require a higher density of seedlings, cuttings, and seeds than north
aspects to offset the expected higher mortality rates. Adjusting for increased mortality rates
is made when calculating plant materials rate for seeds (see Section 10.3.1, Seedling), cuttings
(see Section 10.2.2.5, Determine Survival Potential), and plants (see Section 10.2.6, Nursery
Plant Production).
Planting and Sowing Windows
Take advantage of warmer spring and fall soil temperatures on the south exposures by sowing
and planting earlier on these sites (see Chapter 6).
5.4.3 COMPETING VEGETATION
Controlling competing vegetation around planted seedlings, whether native or non-native,
reduces the rate at which water is withdrawn from the root zone and increases the potential for
survival and growth. The rate at which water is depleted is a function of the type and amount
of competing species. Grass species, for example, have a very fibrous root system in the upper
soil horizon that allows them to withdraw moisture very quickly and efficiently during dry
weather. Unless grasses are controlled, especially in the western United States, it is very difficult
to achieve good survival or growth of planted seedlings in areas with high densities of grass.
Perennial forbs are generally less competitive than grasses because their root systems are
deeper and less concentrated in the surface where the seedlings are withdrawing moisture.
Revegetating with a seed mix is also affected by the type and quantity of competing vegetation.
Those species that germinate earlier than the seeded species in the spring or fall will deplete
soil moisture before the seeded species can establish. Cheatgrass is an example of an annual
species that establishes quickly when soil temperatures are cool during early spring, depleting
the surface soil moisture just as perennial species are beginning to germinate. How to assess
and mitigate for competing vegetation is discussed in detail in Section 5.8, Weeds.
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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