© 1999 Streamline Publications

As a conscientious landscape contractor, Sam completes the pre-planting leaf count.

Whether a construction project is under control of a government or private entity, it is subject to the oversight of an army of federal, state and local regulatory agencies. Most citizens appreciate the need for an Environmental Impact Report (EIR) before the bulldozers roll, but ecological concerns don’t end there. A major consideration driving many project engineering plans is revegetation and environmental mitigation. Before most highway projects can begin the site must be surveyed by a biologist who then makes recommendations to the project engineer and the landscape architect. This process is carried out years before earthmoving work begins and involves not only developing an inventory of existing native and non-native plants, but plans for replacement of the natives as well as removal of weeds and invasive species.

Repairing the Land

According to California Department of Transportation (Caltrans) Biological Resources Environmental Handbook (Volume 3), “California’s Native Plant Protection Act (NPPA) requires all State agencies to utilize their authority to carry out programs to conserve endangered and rare native plants. Provisions of NPPA prohibit the taking of listed plants from the wild [allowing] salvage [of] listed plant species that would otherwise be destroyed.”

Mitigation plans are developed when the construction site cannot be restored to the desired condition due to changes in the area involved—such as draining a wetland—or the physical impact of the project structures. Another site is then chosen as a trade-off to replace the disturbed area’s forage and nesting.

As with much in government, little is accomplished quickly or without controversy—particularly when there are environmental considerations. But there are a number of biological problems in the execution of these mandated and worthwhile goals.

Because of the emphasis on rare and endangered species conservation—non-native species are identified and destroyed. On its face, it would seem such a plan is what is really needed. There is a hitch though. In addition to reestablishment of native species, other plant-related site factors must be addressed—

• erosion control
• climate
• soil and rhizosphere

Pioneers

In the simplest expression of the problem, the pressure on native plants comes as a result of exotic species that possess a hearty, aggressive nature competing for dominance. Non-natives—the so-called exotics—are then often the best choice for pioneer crops on disturbed sites where only sterile subsoils remain. (Importing stored topsoils may create additional problems—see Nov/Dec ’97 LEAF-let, Erosion Control.) It is the aggressive nature of these exotics such as Barley, Annual Ryegrass and Rose Clover that best prepares the soil for introduction of the desired perennial native species. Without non-natives helping to “pave the way” the perennial natives have a poorer chance of establishing and thriving.

Cereal Barley and Annual Ryegrass will grow virtually anywhere—making climate much less a controlling factor—and will not reseed well, making these non-natives particularly suited for immediate erosion control and soil building.

The Confusing Nature of Nature

Typically, Caltrans and other government agencies’ specifications for revegetation are prescriptive rather than performance driven. Such an approach presumes that enough is known about a given patch of the environment to allow for a by-the-numbers revegetation plan. The fact is that the stunning complexity of nature and hidden symbiotic interactions of plants, animals, microbes, soil chemicals and other organisms challenges our best science. Neat quantification of planting requirements—while soothing to architects, engineers and project managers—fails as reestablishment of an ecosystem reveals itself to be as much art as science.

Science and Savvy

There is no question that science plays a preeminent role in plant biology, as is evidenced by frequent new discoveries about the rhizosphere and plants themselves. And that is the point. Nature does not respond in a linear manner and resists even the most sophisticated ecological prescriptions. Nevertheless, Caltrans revegetation plans address:

• Planting zones
• Desired percent composition for plant species
• Plant mixes/planting associations
• Planting spacing and density
• Seed mix and application rate

As years pass, plant biologists monitor these sites to understand how things have turned out then try to apply what they have learned to new projects. However, according to Caltrans, “Since monitoring funds are very limited, it is important that the monitoring activities are closely aligned with the original mitigation goals.” .

The prescription

Revegetation “goals” are developed by the landscape architect and project manager based on the biologist’s input but may be heavily affected by other considerations of cost and time and politics.

Nature’s labyrinthine system clearly shows that ecological reestablishment cannot be guaranteed through prescriptive specifications alone—that human intuition and experience also play a role.

Something to Consider

In the June ‘95 LEAF-let we reported that Caltrans made prescriptive specifications work through close monitoring and a “lessons-learned” approach. We suggested that other users of landscaping design and installation services should stick to performance— or outcome-based—specifications because few had the monitoring resources that were available in Caltrans. It appears that this is no longer true. We suspect that the “very limited” funds available for monitoring of highway landscaping reduces the scope of these later biological surveys.

This is particularly worrisome in the face of the increasing emphasis on revegetation using native species that may be slow to establish and to develop as a climax community. We believe that intelligent management of carefully chosen non-native pioneer species—which are already well established in California—will allow a more rapid achievement of a successional stand rich in desired native plants.

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