One of the hot subjects in horticulture these days is the issue of the invasiveness of introduced plants. Since they did not evolve here, they lack natural enemies, and whereas most are harmless, some have engulfed vast areas of wilderness, national forests, range and farm lands. This has led some people to campaign for “natives only” and others to attack the introduction of new plants as an ecological nightmare. In response to these attacks some in the plant industry have dismissed these fears as invalid over-reactions. As Colorado gardeners, most of us can be both excited by new plant introductions that are well-adapted to Colorado conditions, and feel very protective of our natural ecosystem and our native plants. In a series of articles, we hope to uncover some truths regarding these issues and to educate ourselves about how to work with this situation in a constructive manner.
One thing that seems obvious is that there are some truly noxious weeds that need to be controlled. In order to learn to identify these, I will profile a few noxious weeds in every issue. Currently 100 million acres of land are infested with noxious or invasive plants and these are spreading at the alarming rate of 3 million acres a year, which is an area twice the size of the state of Delaware. I asked Charles Henry, director of Colorado Weed Management Association why noxious weeds have only recently become an important issue. He explained that a number of factors have started adding up in the last 5 to 7 years. One factor is the critical biomass that has been achieved by certain weed species. Whereas they may have been in America for a hundred years, they now are producing enough seed or have domination by roots/rhizomes that they have taken over certain areas. For another thing, he said, people tend to not pay attention to a problem until it begins to impact them economically, and the costs to farmers and ranchers for controlling these weeds is skyrocketing. Another factor is that with the geometric increase in human population, earth disturbance and spread of seed and plants has increased dramatically. And also, he explained, there is now more value placed on biodiversity, on native plants and on trying to save endangered species. These factors are coupled with a growing body of data evidence which prove the harmful effects of these noxious weeds on native populations of plants and wildlife.
In response to this evidence, the Colorado Noxious Weed Act was passed in 1996. It states “The general assembly hereby finds and declares that the noxious weeds designated by rule are a present threat to the economic and environmental value of the lands of the state of Colorado and declare it to be a matter of statewide importance that the governing bodies of counties and municipalities include plans to manage such weeds as part of their duties pursuant to this article.” More recently a list of noxious weeds has been identified and effective July 1, 2000 thirteen species of ornamental plants have been classified as noxious weeds and are no longer allowed to be sold in the state of Colorado.
So what can we do to keep the noxious weed problem from getting worse? Let’s start by getting to know the Ten Worst Weeds and the 13 Invasive Ornamentals. And we’ll see how plant explorer Dan Hinkley is responding to this problem; we’ll look at a model for testing invasiveness, and we’ll ask questions of our excellent local horticulturists and native plant enthusiasts.
In February of this year, Colorado State Weed Coordinator Eric Lane met with Barbara Baldwin the president of the Denver Garden Club and Rob Proctor, current director of horticulture at the Denver Botanic Garden. They discussed the issue of plant introductions and potential invasiveness and, although we have not been able to confirm this report, it is possible that the DBG may organize and host a conference on this subject, possibly in 2001.