My involvement with invasive species seems at times to be a single issue, negative presentation full of commands and limitations. The principle challenge of invasive species is the rampant attack and eventual competitive advantage of an invasive species which allows, eventually, in extreme cases, the creation of a “biodesert” or monoculture. The reduction of species diversity within natural areas becomes a beacon call to action. The endless calls to ban new plants and exotic species at times rise to tidal wave proportions, and yet, there always seems to be a missing positive or proactive side to the question at hand.
What is it that we are asking gardeners in our disturbed landscapes to do? Go native and forsake a millennium of gardening traditions? Replace exotics with natives within the landscape design paradigms on a one species substitution for another basis? If one of the premises underlying western gardening traditions is the taming of nature, and, if taming nature has come to mean, intentionally or unintentionally, the destruction of nature as we currently understand it, what purpose is served by item substitution working with the fundaments of traditional landscaping? From generations of gardeners and from agricultural; practices comes a desire for order and a sense pf the predictable. A meadow looks great from a distance, but close up, most of us do not have the familiarity with the vocabulary of life to deal with the apparent overwhelming diversity of species. In other words from a distance we reduce the complexities [Invasive complexities March 2007] to a more comprehensible whole, but close up we are at a loss to understand the syntax of the landscape in front of our noses.
As I have posted before, the issues surrounding and involving invasive species are a species of a wicked problem [Invasive Species; Wicked Inconvenience: part two Feb 2007], a problem whose complexity compels stakeholder to define the problem based on their particular end-goals or solutions, thereby creating a world of vibrantly differing definitions. A characteristic of a wicked problem is that there is usually one or more co-equal, and co-evolving wicked problems related to the primary problem. I have noted that global climate change fits the wicked problem definition quite nicely; however, I would submit that the definition of a sustainable (conservation) landscape would also rise to a wicked problem which is directly tied to invasive species.
I am beginning to suspect that the future of landscaping will be compelled to address the issue of biological species diversity loss. “Biodiversity losses are a clear signal that humanity’s life support systems are failing.” The quotes from Dr. Tallamy of the University of Delaware became epiphany-moments for me. “We need biodiversity because biodiversity runs the ecosystem on which we depend. The more diverse an ecosystem is, the more services (air, water, food, benign weather systems, carbon dioxide sequestration, garbage recycling etc.) it will provide for us. With ever growing human populations, we need more ecosystem services. But as we kill off our biodiversity, we are getting fewer and fewer services from our ecosystems. We are modifying nearly all of the earths land for our own purposes. Two million acres, an area the size of Yellowstone National Park, are lost to development each year.”
The landscape of the future needs to find a new philosophy which can seem at the present to be at odds with our thousand year tradition on at least one level. We must start to tear down the fences that delineate the garden from the outside and begin to see our personal spaces as part of a larger whole. Instead of asking what plant has not insect pest. We need to begin asking which species host the most insects, which in turn support our birds and other fauna. This is a difficult proposition. In our suburban landscapes we go to extremes to limit unpredictable biology and to present order. Sometimes we do this for personal health reasons, and sometimes for deeply imbedded fear. We strive to both keep ticks and snakes at a distance, preferably in a museum or other controlled environment.
The idea of going to a local garden center and asking which tree supplies the food requirements of the most caterpillars is, to say the least, not happening on any measurable scale. What is worse for those involved in invasive species issues in horticulture is that many of the plants that thrive well, and which are limited host companion plants for insect life in the ecosystems in which we live, tend to be the exotic invasives. A truly sustainable landscape would seem to be one that encourages biological diversity within the garden space and within the larger ecosystem. Designing such a garden such that the end user, close up, does not become disoriented and overwhelmed is a challenge.
I am not suggesting that the only consideration in the design and implementation of a sustainable landscape is biological diversity hosting and companion species planting, but I am thinking that this would be a major consideration. A sustainable landscape must be greater than the sum of its parts, and consideration must go to resources needed to execute the design and to maintain the plantings, as well as to public health and safety. Invasive plants, those that tend to limit biological diversity would be deselected under a sustainable decision matrix. The mandatory exclusion of all non natives is a differing debate, as there are some species whose exotic cousins are genetically so close as to host the same plethora of insect species: e. g. Salix.
I suspect, though, that research might possibly explain the apparent contradiction of exotics passing for native has fauna host species, when one turn to biota within the soil structure and the possible negative effects of exotics on soil life. However, since I am not proposing to base a landscape design entirely on its ability to serve as a nexus for biological diversity, but only to suggest that companion and host propensities be given a reasonably large measure of consideration when judging the design. The weighing of host plant tendencies should have a tendency to a native default, but would not exclude exotics from consideration, though many invasives might not be among the candidates because of their low host counts thereby tending to exclude them from the design.