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Title: Characterizing pathways of invasive plant spread to Alaska: I. propagules from container-grown ornamentals

Author
item Conn, Jeffery
item STOCKDALE, CASIE - SELF EMPLOYED
item MORGAN, JENNIFER - UNIV OF ST LOUIS

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2008
Publication Date: 10/20/2008
Citation: Conn, J.S., Stockdale, C., Morgan, J. 2008. Characterizing pathways of invasive plant spread to Alaska: I. propagules from container-grown ornamentals. Journal of Invasive Plant Science and Management. 1:331-336.

Interpretive Summary: Invasive plants are brought to Alaska by numerous routes or pathways. Characterization of invasion pathways can aid in the design of effective strategies for prevention of invasive plant infestations by targeting the largest pathways first. As first in a series of studies characterizing pathways of invasive plant movement into Alaska, this research reports on the pathway resulting from importation of soil with container-grown ornamentals containing weed seed. Soil from container-grown ornamentals was obtained from vendors and was incubated in the greenhouse. Emerging seedlings were identified and counted. Fifty four plant species were identified growing in containers or germinating from the soil, and included Canada thistle, a prohibited weed in Alaska and nine other species listed as invasive in Alaska. The number of species and estimated seedbank were very low for soil from vegetables/herbs and herbaceous bedding plants (< 2 seedlings/L soil) but was greater for soil from containers containing woody plants, and especially balled and burlapped ornamentals (20 seedlings/L soil). We found that potting soil held very few weed seeds while mineral soil contained an average of 20 seeds/L of soil. Suppliers of ornamentals and vendors also influenced the size of the container seedbank suggesting that weed management practiced during production and at the point of sale can greatly influence seedbanks of ornamental containers. This pathway for alien plant introduction could be reduced through consistent use of sterilized soil and good weed management. The pathway could be eliminated by prohibiting importation of soil to Alaska. Ornamentals could be shipped bare root and planted into Alaska soil after arrival.

Technical Abstract: To determine the size and nature of container-grown plant soil as a pathway for introduction of exotic plant species to Alaska, soil from ornamentals was obtained from vendors and was incubated in the greenhouse. Fifty four plant species were identified growing in containers or germinating from the soil, and included Canada thistle, a prohibited weed in Alaska and nine other species listed as invasive in Alaska. The number of species and estimated seedbank were very low for soil from vegetables/herbs and herbaceous bedding plants (< 2 seedlings/L soil) but was greater for soil from containers containing woody plants, and especially balled and burlapped ornamentals (20 seedlings/L soil). Type of soil used in the containers was strongly related to container alien plant seedbank size. Potting soil contained 1.2 germinating seed/L, native soil 5.5 seed/L, and mineral soil 18.7 seed/L. Suppliers of ornamentals and vendors also influenced the size of the container seedbank suggesting that weed management practiced during production and at the point of sale can greatly influence seedbanks of ornamental containers. This pathway for alien plant introduction could be reduced through consistent use of sterilized soil and good weed management. The pathway could be eliminated by prohibiting importation of soil to Alaska. Ornamentals could be shipped bare root and planted into Alaska soil after arrival.