   Invasive Plant Species at Their Worst - February 28, 2001 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County I thought it would be a good idea to follow up last week's column on the invasive noxious weed sweet resinbush (Euryops subcarnosus) with a unique example of invasive plants gone awry. In researching this column, I traveled to a location where noxious weeds/invasive exotic plant species pose a serious threat to native vegetation and met with experts in the field of noxious weed management to learn more about the issue. So here I am in Kona, Hawaii attending the Society for Range Management Annual Meeting. This is true dedication. What can I say? I will do anything for my dedicated readers. As I traveled from the Kona Airport to my hotel, I noticed vaguely familiar grass but paid little attention to it as I was in awe of the arid, tropical landscape that covered the lava flow. In fact, several plants looked very familiar. Having never been here before, I just accepted it and went on enjoying the uniqueness of the landscape. On the beach and in the hotel gardens, I saw the coconut palms, ginger, ferns and other lush vegetation I associated with tropical islands. The next day, I attended an all-day session on invasive plant species. Then the light came on and I realized why the grass on the lava flow looked so familiar. It was fountain grass (Pennisetum setaceum), a common ornamental landscape grass. If we think invasive plants are an issue in Arizona (which they certainly are), take a few minutes to learn more about Hawaii's situation. The Hawaiian animals and plants began to evolve as much as 70 million years ago in nearly complete isolation; successful colonization through long-distance transport of species from elsewhere was infrequent. We now realize that islands are particularly vulnerable to exotic invasion because they experience long periods of evolution in isolation from outside forces faced routinely by plants and animals on continents (such as browsing and trampling by herbivorous mammals, predation by ants, virulent disease, and frequent and intense fires). Hawaii was particularly isolated, so these effects were amplified. The Hawaiian Islands were reached by Polynesians in about the fourth century A.D, probably from the Marquesas Islands. This was somewhat later than most other Polynesian islands. The human population reached 200,000 before contact with Europeans in 1778. Landscapes were modified through the use of shifting cultivation and fire and through the creation of sizeable wetlands for aquaculture. Polynesians introduced pigs, jungle fowl, dogs, Polynesian rats, and various stowaway geckos, skinks, and snails, as well as at least 32 plant species, including major food plants and species providing source materials for the manufacture of cloth, rope, and musical instruments. As trade increased and new transportation methods developed, the introductions of exotic species increased exponentially. Feral pigs still are a serious problem here. They root up the forest floor killing native plants and creating niches for exotic plants to become established. The landscape industry has also contributed to the problem. Foliage plants, fruits, flowers, etc. continue find Hawaii's climate very hospitable and newly introduced plant species continue to naturalize. The list of noxious weed species in Hawaii reads like the Sunset Western Garden Book: including Acacia, Lantana, Pyracantha, Schefflera, Wisteria, Buddleia, Eucalyptus, blackberry, and so on. The Hawaiian archipelago has more than 8,000 introduced plant species or cultivars: an average of 40 introductions per year over the past two centuries. 861 (11%) of these are now established and have reproducing populations. The issues are very complex and the stakes are high. For instance, fountain grass (and other introduced grasses) is well adapted to fire. When burned, it not only survives, it is invigorated. Natives are not adapted to fire. When a fire starts in a stand of fountain grass, it scorches the native plant killing it and giving the grass a competitive advantage. What is being done? The Hawaii Department of Agriculture, USDA, National Park Service and other land management agencies have joined forces with members of the private sector (tourism, development, landscapers, etc.) and formed Invasive Species Committees on each of the Hawaiian Islands. These groups meet regularly to plan, educate, and conduct restoration/control activities. Some examples of projects include fencing (to exclude pigs, sheep, and goats), herbicide treatments, and replanting. Inspections are also used to prevent new introductions. Hawaii's exotic species issues are worse by far than Arizona's. Seeing this gave me hope that we can make a difference through local efforts. Aloha. The University of Arizona Cooperative Extension has publications and information on noxious weeds and their control. If you have gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. The Yavapai County Cooperative Extension web site is http://ag.arizona.edu/yavapai/. |