3.10 Inventorying of Site Resources

Most project sites contain resources that can be used to meet revegetation objectives. Identifying these potential resources early in the planning process is essential so that they are not inadvertently wasted. The more that local resources are used, the more cost-effective, efficient, and effective the revegetation efforts may be. Physical resources to inventory include topsoil, duff, litter, parent materials, woody materials, logs, plant materials (seeds, seedlings, and cuttings), large rocks, and water (seeps, springs, creeks). Intangibles should also be considered, such as community cooperation and the local knowledge base.

3.10.1 Topsoil

One of the most important site resources for revegetation is topsoil. If considered early in the planning process, topsoil can be salvaged and reapplied to disturbed sites after construction. This is one of the best ways of increasing productivity on a disturbed site.

Topsoil is inventoried early in the planning process to evaluate topsoil quality and quantity, costs, and the feasibility of removal and storage. Topsoil recovery is an expensive operation requiring knowledge of basic soil attributes. For this reason, it is a good idea to conduct a soil survey or assessment of those locations that will be disturbed. An example of soil and site information commonly collected for topsoil recovery is shown in Table 3-13. The road in this example is planned through undisturbed forested lands. Soils data is collected every 50 meters (at road stations) due to the high variability of the soils in this area. Where soils are very uniform, distances between plots can be increased. Soil texture, rock fragments, and depth of the topsoil are measured in the field. At selected intervals, or on different soil types, a sample is collected for lab analysis.

During topsoil survey, other site attributes that could affect the quality of topsoil should be noted, especially the locations of all noxious weeds. These weeds can be treated or removed prior to topsoil salvage or the weed-infested areas can be avoided to prevent the spread these weeds across the project area.

The outcome of the topsoil survey is a short report and map in the revegetation plan showing the areas and depth to salvage topsoil. The report should discuss the fertility of the topsoil, how it should be stored, and whether the duff and litter are removed and stored separately. Areas should also be identified where topsoil should not be collected, such as areas of noxious weeds or high rock. The volume of topsoil can be calculated based on soil depth and area of the road prism.

3.10.2 Duff and Litter

Duff and litter are the dead plant materials that have accumulated on the surface of the soil. The level of decomposition differentiates litter from duff. Litter is the layer of recently fallen, undecomposed leaves, needles, and branches; duff (which occurs immediately below the litter layer) is litter that is decomposed beyond recognition. The duff layer is a dark, light-weight organic layer. It is a large reserve of nutrients and carbon, and has a high water-hold capacity. Litter and duff layers protect the soil from erosion by absorbing the energy of rainfall impact and reducing overland flow. Combined, the litter and duff layers can be very thick, ranging from 1 to 4 inches depending on the productivity and climate of the site.

Litter layers typically have viable seeds originating from the overstory vegetation. Under the right conditions, these seeds will germinate. If collected, stored and reapplied correctly, this natural seed bank can be used as a seed source. Litter and duff layers can also contain mycorrhizal inoculum.

Litter and duff layers can be assessed concurrently with topsoil surveys by measuring their depths using a ruler. Refer to Section 5.2.3, see Litter and Duff, for a discussion of methods for collection and application.

3.10.3 Subsoil and Parent Material

Certain subsoils and parent materials can be salvaged during road construction and used to produce manufactured topsoil (Section 5.2.4, see Manufactured Topsoil). Textures low in rock content, including sandy loams, silt loams, loam, and sandy clay loams, are often good materials for manufactured soils. These are often found in areas where the parent materials are derived from alluvial or windblown deposits. They include river sands, pumice, volcanic sands, and loess.

3.10.4 Woody Material

Woody material consists of live and dead plant materials that are cleared in the early stages of road construction. This material includes tree boles, root wads, bark, and branches. During clearing and grubbing, these materials are often concentrated in piles and burned. All of these materials can be ground up as shredded wood and used as surface mulches (Figure 3-84) (Section 5.2.3, see Shredded Wood) or soil amendments (Section 5.2.5). Large wood can be used for biotechnical engineering structures, obstacles for erosion control, or placed upright or on the ground for pollinator habitat and site productivity. Substituting shredded wood derived from these materials for composts and soil amendments can lower overall project costs.

Suitable plant materials are often destroyed during road construction. These consist of seeds (Section 5.3.1), plants (Section 5.3.3), and cuttings (Section 5.3.2). If these materials are collected from the construction site prior to disturbance and stored correctly, they can be used, instead of propagated or purchased plant materials, to revegetate the project. Surveys of the project site prior to construction will indicate the location and abundance of appropriate plant materials.