Native Vs. Nonnative

Underpinning the stability and the services provided are processes such as primary production, soil development and maintenance, nutrient cycles, pollination, predation, and competition.

These processes are the work of myriad organisms that reside within an ecosystem, whose residence can be described in terms of their composition, distribution, and structure.

Thus, the health or stability of an ecosystem and the services it provides are dependent on the composition, distribution, and structure of the ecosystem.

Generally, healthy ecosystems can be described by five primary characteristics:

  • Diversity
  • Productivity
  • Stinginess
  • Dynamics
  • Stability.

Diversity describes all of the species of an ecosystem, including flora, vertebrates, invertebrates, and microorganisms (which are often overlooked) as well as the genetic variability of these organisms, and the variation of community composition over the landscape.

Productivity describes the primary production and net-gross photosynthesis of an ecosystem, as well as the fecundity and mortality of other organisms within the community.

That, in turn, is closely related to soil development and water and nutrient retention, or stinginess.

Dynamics refers to the continual adjustment in populations of species, fluxes in nutrient intake and release, and seasonal changes within a community’s structure as conditions change throughout the year and from year to year.

Stability describes an ecosystem’s ability to adapt to or overcome perturbation with minimal change in other fundamental characteristics. These are the primary modeling criteria for ecosystem restoration or for the design of a sustainable and functional urban landscape.

A focus on these characteristics as design modeling criteria shifts the debate about nonnative species and novel ecosystems from abstract to pragmatic principles. Aesthetics and concerns over human perception, often cited as justification for the need of nonnative species, are completely compatible with characteristics of healthy ecosystems.

These ecosystems are able to adjust to a wide range of environmental perturbations, from pests and disease to variations in climate.

Natural ecosystems are comprised of a diverse suite of species adapted to the local environment that collectively contributes to resiliency. Resiliency is the result of the linkages and redundant functions of component species and their interactions, such as competition, predation, disease, parasitism, and herbivory.

It follows that healthy natural ecosystems, called “reference areas,” are ideal models. The challenge is finding healthy ecosystems in a comparable habitat.

Reference area ecosystems adapt to the local environmental conditions. They are comprised of native species and communities that have adapted for thousands of years in glaciated regions, and longer elsewhere.

Questions about how many generations are required for nonnative species to be sufficiently integrated into natural ecosystems suggest a misunderstanding about the length of time required for delicate balances to develop, and ignore the implied conclusion that these species should integrate with a native system.

This is not to conclude, however, that nonnative species cannot fill niches in a native ecosystem and begin the development of a novel ecosystem. It does suggest, however, that nonnative species will likely alter the ecosystem processes, even if the change is subtle, thereby leading to a different ecosystem.

Impact On Stability And Ecosystem Processes

The horticultural to agricultural continuum is the frontier of nonnative and invasive species because of repeated introduction of species and reduction or elimination of natural ecosystems, thereby providing ample opportunity for the establishment of nonnative species.

Many nonnative species are well adapted to human disturbances and become invasive where environmental resistance to their population expansion is compromised by human development.

Environmental resistance is the sum of adaptations by native species to stressors, such as disease, parasites, predators or herbivores, and competitive relationships with other species.

Ecological stability is achieved when reproduction and environmental resistance are in balance. Interestingly, introduced species often remain quiescent for years, and then populations begin spreading rapidly.

Reasons are unclear. However, in the case of some species, invasion was no doubt exacerbated by massive planting or introduction efforts of humans.

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