Criteria for Evaluating Invasive Terrestrial Plants
The draft criteria developed by the steering committee are attached (Appendix 1). During the process of developing the criteria a number of different factors were discussed. The steering committee decided that prevention is the key when dealing with any type of invasive species, because once a species is established it is very difficult to control. They also noted the criteria needed to address potentially invasive plants not currently established in Maine. Furthermore, they agreed it was important to collect information from neighboring states and provinces, because Maine shares similar climate and growing conditions with Canada more often than states to the south.
There was a lot of discussion regarding hardiness zones and how plants would act in different parts of the state. For example, a plant might have invasive growth traits in York, but would be nonaggressive in Houlton. The steering committee discussed this issue and concluded it would be difficult to monitor, because of the difficulty of tracking a plant to its final location. Following the example above, a plant could be purchased in Houlton, but then be planted in York.
The topic of whether to include cultivars in the list of invasive plants was discussed at length. A cultivar is a cultivated variety of a plant and is basically a subgroup of a species. Cultivars are important in the horticulture trade because they provide new types of plants in the market place. These plants usually vary from the species in that they have a consistent and often unique trait such as flower color, leaf shape or growth habit. Many claim that some cultivars grow differently from the species and therefore should be considered separately from the species when evaluating invasiveness. The steering committee decided that cultivars would be included with a species until scientific evidence is provided to prove the cultivar grows differently than the species.
A list of definitions is included with the criteria to clarify the meaning of a number of terms. Not all quantifying terms were defined such as “numerous” and “high numbers”. This was to allow flexibility particularly if a species inhabited a specialized habitat. The steering committee acknowledged there would still be subjective interpretation using the criteria.
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