Inset 3-6 | Case Study—Defining limiting factors and selecting mitigating measures

Site Inventory—During the planning stage of a revegetation project in central Oregon, the soils assessment (Section 3.6.2) highlighted several limiting factors that would negatively affect plant growth.

Limiting Factors—From the list of limiting factors outlined in Figure 3-11, factors affecting plant growth at this site were narrowed down to low precipitation, low water storage, high water loss, and low nutrients.

Mitigating Measures—For each of these factors, a list of possible mitigating measures (described for each limiting factor in Section 3.8) was developed.

Site Resources—A review of the site resources was made at this point to determine if there were any resources on the site that could be used in developing mitigating measures (Section 3.10). It was found that there were several areas where weed-free, high quality topsoil could be salvaged and reapplied. In addition, the project would produce a large amount of slash from cleared shrubs and trees that could be processed into shredded wood and used as a mulch. Other resources available were a local municipal waste treatment plant had Class A biosolids available for application in lieu of bringing in fertilizer, loam borrow from a source of pumice deposit, and an excavator that would be available for subsoiling.

Maintenance—The potential effects of these treatments on long-term maintenance was then considered (Section 3.11). It was determined that deep tillage was not compatible with safety in Zones 1 and 2 but would be done in Zone 3, otherwise there were no foreseen maintenance problems.

Treatment Selection—It was decided to salvage topsoil; however, the amount of topsoil would not cover all the project needs. It was determined that a manufactured topsoil would be created by using shredded wood processed the slash from road right-of-way clearing, loam borrow from excavated pumice, and biosolids from the local municipal waste treatment plant. To increase infiltration and rooting depth, it was decided that once the topsoil and manufactured topsoil was applied that it would be subsoiled only in subsoil Zone 3 but not in Zones 1 and 2. At planting, lupine would be included in the seed mix for additional nitrogen and inoculum would be applied to the seed mix. Because there would be additional shredded wood, it would be blown over the seed as a mulch.