English ivy (introduced) with native Robin

English holly (introduced) with native Robin

Seed Rain n. 1. The deposition of seeds spread by bird, wind, humans, and animals, usually pertaining to non-native species degrading native habitat. 2. “Seed rain” describes the spread of vegetative or seed propagules crossing  public and private property boundaries.

Invasive Update: A 2014 study in St. Edwards State Park found that the number of English holly trees is doubling every six years, having "the potential to become a dominant species in both number of individuals and area covered within a few decades, transforming the region’s native forests on a large scale“ (Dr. David Stokes, UW Bothell). This projection of near-exponential growth of English holly is proving true in suburban forests but likely slowing in more shady regional forests. However, seed production does increase in sunnier clearcuts, therefore "feral holly poses a threat to timber and forestry production" and "can increase wildfire risks by acting as ladder fuels that carry a fire from ground level to the crown of trees."
More concerning, the quiet relentless spread of English ivy could eventually become entrenched "with complete domination of the forest understory degrading the forest overstory and (ultimately) no native wildlife" (King County Noxious Weeds). Without intervention, invasive monocultures will have devastating effects on our region's native flora and fauna, affecting pollinators, agriculture, timber, fishing,  and eco-tourism industries.

Birds moving introduced species by eating and then depositing in a nearby natural area

Wind spreading intoduced seed into a nearby natural area

Clematis vitalba: "Old man's beard," one of many aggressive introduced plants.