The encroachment of exotic herbaceous plants into the Olympic National Forest
Heckman, Charles W.
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A floral survey in the Olympic National Forest and its surroundings revealed that a considerable number of introduced ruderal plant species have made deep inroads into the stands of native flora. Some of them, which are mainly of European and Asian origin, have been planted deliberately to stabilize the soil along roadsides and after clear cutting and burning. However, they have already established reproductive communities that are capable of spreading rapidly without additional human help, as they have already done in almost all regions of the earth subject to a temperate climate. Plotting the data from the Geographical Information System, it was shown that 12% of an area totaling 388 km2, located mainly in the Olympic National Forest, was occupied totally or in large part by this mainly ruderal flora, which accounted for at least 50% and usually nearly 100% of all plants within the area on which they occurred. This represents a major qualitative and quantitative biogeographical alteration in the regional flora of a national forest generally considered to be only slightly affected by human activity