Print PageSince Ilex aquifolium’s introduction into Oregon in 1874, this plant has readily adapted to the Pacific Northwest’s mild climate and dispersed far from its initial point of establishment. Although this plant is an agricultural commodity, Ilex aquifolium’s presence in city, state, and national forests and parks is troublesome as the plant is observed to out-compete native vegetation. Removal of Ilex aquifoliumfrom parks and forests is undertaken by local governments and non-profit organizations and involves a steep cost of labor and time.
My research question is whether stand attributes, such as basal area and trees per acre, or stand stage, are correlated to presence of Ilex aquifolium. If so, future germination sites could be predicted and monitored to prevent the plant’s establishment.
A survey is being conducted in Grays Harbor County, Washington State on 344 acres of private forestland containing stands in various development stages and overstory species composition. An important feature of the site is the planting of the first mother Ilex aquifolium is known, and its dispersal can be observed over a twenty-year period. To determine if control or Ilex plots have statistically significant difference in stand attributes, 336 1/20 acre plots are being placed across the research area.
Results/Conclusions
Ilex aquifolium is an understory species in its native European deciduous forests of beech, alder, and oak. Preliminary results of 66 plots across five stages suggest that this plant favors those same closed-canopy conditions in the Pacific Northwest’s conifer forests. An Analysis of Deviation shows basal area per acre, volume per acre, and stand stage are significant stand attributes relating to presence of Ilex aquifolium within a forest - basal area per acre P <0.074, volume per acre (P < 0.042), and stand stage (P < 0.069). When basal area and average tree size are combined into relative density, this measurement proves the most significant – (P < 0.017). Graphing the data shows Ilex aquifolium is present on plots where these stand attributes are higher than compared to the control plots. Closed-canopy conditions are likely also linked to seedling survival as Ilex aquifolium seedlings are vulnerable to direct sunlight. Unexpectedly, the course woody debris with a dbh of .5 – 1.9 proved significant (P<0.034), with more of this material present on Ilex aquifolium plots than control plots. This variable is worth exploring further to determine how it is relates to presence of Ilex aquifolium.
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