Roadside Revegetation

PLANNING PHASE TWO: ASSESS SITE
5.4.4 SOIL COVER
The thickness and composition of material that covers the soil surface influence many important
soil properties covered in this manual, such as infiltration rates, interception losses, soil
temperatures, surface erosion, runoff, and soil moisture loss. The following discussion focuses
on soil cover as it affects soil moisture loss through evaporation.
Under undisturbed conditions, soil cover is predominantly composed of duff, litter, and stems
that block the escape of soil moisture through evaporation (Figure 5-25). Mulches are also
unfavorable seedbeds for weed seeds because duff and litter dry out quickly. Disturbed soils,
on the other hand, are mostly composed of bare soil. Evaporation from the surface of bare soil
can be high, extending to at least 6 inches below the soil surface, affecting seed germination
and seedling establishment rates. Until roots of planted or seeded seedlings have extended
farther into the soil profile, surface drying will negatively affect seedling establishment,
especially on sites where water input and storage are already limiting.
Air
Rainfall
Evaporation
Soil Cover – How to Assess
Soil cover can be measured on undisturbed and disturbed reference sites or post-construction
sites through the ground cover monitoring procedures outlined in Section 12.2, Soil Cover
Procedure. In this procedure, the percentage of area in litter, duff, rock, vegetation, and bare
soil is recorded and periodic measurements of litter and duff thickness are made.
Mitigating for Low Soil Cover
Mulches for Seedlings and Cuttings
Mulches create a more favorable environment for establishing seedlings and cuttings not only
by reducing surface evaporation, but also by decreasing the amount of competing vegetation.
There are two types of mulches for seedlings and cuttings – organic aggregate and sheet
mulches. The organic aggregates are thickly applied ground wood or bark, while the sheet
mulches are made from non-permeable or slightly permeable plastic, newspaper, or geotextile.
Both types are placed around the base of the seedling and cover at least a radius of 1.5 feet
from the base of the seedling (see Section 10.1.3, Mulches, for how to install).
Mulches for Sown Seeds
Selecting and applying mulches over sown seeds differ from those selected for planted
seedlings and cuttings. Mulch application for seedlings and cuttings is typically too thick for
seeds to germinate and grow through. An ideal seedbed mulch is one that is applied at the
highest rates without affecting seedling emergence. Long-fibered mulches, such as straw,
hay, shredded wood, or wood strands, create the greatest loft or thickness. At the optimum
thickness, these mulches allow some light to penetrate and space for seedlings to emerge.
Short-fibered mulches, such as wood fiber and paper found in hydromulch products, are
more compact and create less loft. While these products reduce erosion rates, they are not
necessarily good as seed covers (see 10.3.2 Hydroseeding).
Figure 5-25 | Effective mulch cover
An effective mulch for seed cover is one
that is stable and allows good airflow
and rainfall entry, while reducing evaporation
from the soil surface.
5.5 NUTRIENT CYCLING
Nutrient cycling is the process by which sites store and release essential nutrients for plant
survival and growth. There are 13 elements, or mineral nutrients, and each fills a specific role or
function in plant development and each possesses individual characteristics of movement and
storage in the soil. This manual will not attempt to explain the role and function of each mineral
nutrient (there are many good textbooks on this subject). It will instead focus on how nutrients
cycle through vegetation and soils; how they are captured, stored, and released; and what site
components are essential to support these processes. In contrast to an agricultural system of
managing optimum growth in crops through fertilization, the goal in wildlands revegetation
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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