Native Vs. Nonnative

Such is the case of kudzu (Pueraria lobata), which was planted across the southern United States. Other examples include hemp (Cannabis sativa), parsnips (Pastinaca sativa), Queen Anne’s lace (Daucus carota), Dame’s rocket (Hesperis matronalis), European buckthorn (Rhamnus catharicus and R. frangula), Tartarian honeysuckle (Lonicera tartarica), multiflora rose (Rosa multiflora), and hundreds more, including plants and animals, and probably microorganisms.

Not all species contribute equally to diversity or ecosystem processes. Indeed, invasive species ultimately result in loss of overall diversity, but not always loss of stability.

Usually, the loss of diversity leads to loss of ecological functions that further impoverish the ecosystem. It is because of nonnative species that natural areas often require active management. A remarkably widespread belief that natural ecosystems will take care of themselves is no longer valid.

Ecosystem restoration design begins by addressing the underlying physical, chemical, and hydrological changes associated with deterioration. Restoration usually involves directly or indirectly mitigating the stressors, then controlling invasive species and reintroducing native species that have been lost or diminished within the community structure.

With restoration, the aim is not necessarily to duplicate past conditions, although by using reference area ecosystems, we gain insight into a community’s composition, structure, and diversity that existed prior to human disturbance.

Instead, the goal is ecological stability and restoration of lost functions or services. As we begin to understand novel ecosystems better, we may gain insight into which nonnative species are invasive, and which are compatible.

Some nonnative species may contribute to desired ecosystem processes, especially if they are better suited to stressors that cannot be corrected.

Where nonnative plants are given the opportunity to grow, prosper, and spread, they may have both positive and negative effects on other species, as well as on ecosystem processes.

Thus, it is necessary to consider each species and each situation independently. Kudzu, for example, is effective in preventing erosion, intercepting precipitation, and providing screening against noise. It is a legume with nitrogen-fixing capability, produces beautiful, fragrant flowers that can attract some native pollinators, and is edible.

However, kudzu is aggressively invasive and leads to a dramatic reduction of all other plants.

Nonnative species especially may be useful where no native species are adapted to the highly altered conditions, but it should be a matter of ethics that new species are screened for invasive potential before being used.

Summary

Designing with nature requires knowledge that increases with experience, often more quickly than one might expect.

When designers and ecologists collaborate, the durability of design is improved, and the experiences of users are enhanced, while the designs of novel ecosystems in isolation have fallen short.

Focusing on establishing appropriate ecosystem community characteristics—diversity, productivity, stinginess, dynamics, and stability—in order to maximize beneficial ecosystem services invariably leads to a native-plant dominated palette.

The debate over native versus nonnative species is largely moot when the models of appropriate ecosystem services are derived from reference ecosystems. Within the ecosystem-characteristics framework proposed above, locally adapted native species provide comparable or often superior performance than nonnative counterparts in a novel ecosystem, usually at lower cost.

Native species are less risky. This applies in both large and small areas. In urban lands and pocket parks, native species not only provide the cultural landscape desired but also support rare pollinator insects, a range of beneficial soil organisms, and even birds or larger organisms not common in the urban fabric.

If these are not reasons enough, now more than ever the marketplace encourages the use of native plants and discourages the use of nonnative species.

The indirect cost of invasive species, estimated at hundreds of billions of dollars annually, can no longer be ignored.

The framework proposed above is a refinement of McHarg’s charge; it does not alter his premise but provides greater detail for landscape architects and planners when designing and managing ecosystems.

For the land designer and the land steward, this refinement opens even more common ground to explore with practicing and experienced restoration ecologists.

Steven I. Apfelbaum is a Senior Ecologist certified with the Ecological Society of America, and Chairman of Applied Ecological Services, which works worldwide on the design and construction of urban landscapes and ecological restoration projects.

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