Roadside Revegetation

PLANNING PHASE TWO: ASSESS SITE
Mitigating for Poor Rooting Depth
Increase Available Water-Holding Capacity
Improving the water-holding capacity of the existing soil will increase TAWHC. Mitigating
measures discussed in Section 5.3.1, Soil Texture, and Section 5.3.2, Rock Fragments, can be
used to increase soil moisture.
Tillage
If restrictive layers due to compaction are encountered, deep tillage should be considered.
Section 10.1.2, Tillage, provides guidelines for deep tillage.
Apply Topsoil
Increasing rooting depth and TAWHC can be accomplished by applying topsoil (see Section
10.1.4, Topsoil).
Planting Islands
Mitigating measures, such as applying topsoil, organic matter incorporation, deep tillage, and
other measures that increase water-holding capacity, can be focused in strategic locations,
such as planting islands. This will conserve materials and reduce costs (see Section 10.1.8,
Topographic Enhancements).
Blasting
Strategic blasting to shatter the parent material has been suggested as a possible means of
increasing rooting depth (Claassen 2006).
5.3.5 MYCORRHIZAL FUNGI
The discussion to this point has addressed the primary factors responsible for soil water storage
(soil texture, rock, and rooting depth) and ease of a plant through its roots to reach this water
(soil structure). In this section, the discussion turns to how plants increase the efficiency of
accessing water through mycorrhizae. While mycorrhizae provide many other benefits to the
site in addition to water enhancement, they are covered in depth in this section because of
the importance of water to establishing vegetation on highly disturbed sites in the western
United States.
Mycorrhiza is the unique symbiotic relationship between fungi (called mycorrhizal fungi) and
host plants. To the naked eye, many mycorrhizal fungi appear as a fine web or netting that
seems to connect the root system to the surrounding soil (Figure 5-19), and in essence, this is
exactly what is occurring. The extremely small hyphae of the mycorrhizal fungi are actually
taking on the form and function of an extended root. Because mycorrhizal hyphae are up to
five times smaller, they are able to access spaces in the soil not easily accessible by larger plant
roots. Mycorrhizal hyphae not only provide the plant with greater access to soil moisture and
nutrients, they also surround and protect roots from soil pathogens. In return, the host plant
supplies carbohydrates to keep the mycorrhizal fungi alive.
Mycorrhizae play a critical role in site restoration by building soil structure. Hyphae and water
stable organic “glues,” such glomalin, are excreted by the mycorrhizal fungi and bind soil
particles together into aggregates. These aggregates stabilize the soil, improving soil structure
(see Section 5.3.3, Soil Structure) important for good air exchange and water permeability. This
basic soil building process, or repair, facilitates the creation of nutrient reserves and nutrient
cycling essential for restoring ecosystems (Miller and Jastrow 1992). Mycorrhizal fungi can
also improve survival of tree and grass seedlings (Steinfeld and others 2003; Amaranthus and
Steinfeld 2005). A healthy population of mycorrhizal fungi has also been shown to increase plant
biomass and cover (Wilson and others 1991; Brejda and others 1993; Sobek and others 2000),
and increase the diversity of native species (Smith and others 1998; Charvat and others 2000).
Figure 5-19 | Mycorrhizal
fungi extend root systems
Mycorrhizal fungi can greatly increase
the surface area of the root system.
The ectomycorrhizal fungi attached
to the pine root system (A) comprise
most of the absorptive surface shown
in this photograph. The mycorrhizae
include brown branched structures
(B) and white hyphae or filaments (C).
(Photo courtesy of Mike Amaranthus,
Mycorrhizal Applications).
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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