May 28, 2010
Once a population of invasive plants becomes established it can often take years of concentrated effort to control and eradicate even a small area. Individuals, natural resource managers, and scientists working on the problem of invasive plants all agree that prevention is the best approach.
Compared to the rest of the United States, Alaska is in the unique position of having a small invasive plant problem. This allows the state to focus more of its resources on prevention. It also allows Alaskans to learn from the wealth of research and practical experience developed from the decades of invasive plant control in the rest of the country. This knowledge could be used to develop effective strategies for the prevention of future invasions.
In 2004, the Forest Service's Alaska Region Forest Health Protection program partnered with the USDA Agricultural Research Service, to examine the ways invasive species have spread into Alaska. This research was recently published in the journal "Invasive Plant Science and Management."
ARS researchers Jeff Conn, Casie Stockdale, and Jenny Morgan determined that one potential pathway for the spread of invasive plants to Alaska could be seeds buried in the soil of container- grown ornamental plants. Ornamentals are typically grown in one location and then transported to other locations where they are planted as a part of gardens and lawns. Other kinds of seed may occur as contaminants in the ornamental stock container soil.
Dr. Conn decided to investigate just how many seeds from other plants hitchhiked along with the ornamentals that Alaskans commonly purchase at local greenhouses, nurseries and other retail outlets.
The researchers started by surveying retailers selling ornamentals in the Anchorage, Fairbanks, and Juneau areas. They recorded what kinds of ornamentals the retailers stocked, how many they sold each year, who their suppliers were and where the suppliers were located.
Using this information, they purchased plants from 25 different out-of-state suppliers and four Alaskan nurseries. They also visited nurseries and collected soil samples from the containers or root balls of large and expensive plants such as trees and shrubs. They transferred the soil from 26 different containers and from 29 suppliers into greenhouse flats, and carefully monitored what species grew from the soil.
To the surprise of Dr. Conn and his associates, 54 different species of plants emerged from the greenhouse flats. Of these different species, only three were native to Alaska, and the other 51 species were exotic weeds. Ten of these species are considered to be moderately to highly invasive to Alaska, and one (Canada thistle) is a prohibited species under Alaska law.
They found that the number of weeds varied depending on the type of ornamental; for example trees and shrubs with balled or burlapped roots had much higher number of weeds than herbs and vegetable starts. For plants with woody stems they found that the number of weeds was related to the vendor; some suppliers clearly used effective weed control practices, while others obviously did not.
What does this mean for invasive plant management in Alaska? It means that the shipment into Alaska of containerized woody ornamental plants from outside the state is a significant pathway for the introduction of invasive plant seeds.
With approximately 10,000 woody ornamentals being sold and planted in Alaska each year, most often in well-watered and fertilized yards and gardens, the potential for these species to become established is high. Alaskans should be aware of this risk.
Asking local greenhouses, nurseries, and other retail stores where they purchase ornamental plants if the soil is weed-free is a good start. Shoppers should bring weeds growing in containers to the attention of store managers. In addition, homeowners and landscapers can keep watch for exotic weeds that might emerge near transplanted ornamentals. It will be much easier to control any accidental imports if they are caught early.
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