Ivy is an introduced ornamental that has escaped the garden and is taking over the parks. Birds love its fruit, which leads to a seed rain falling down on us all.
Ivy can grow in very low light conditions (someone told me 1% sunlight) so you can’t shade it out. It happily chugs along until it encounters an obstruction, and then grows up the obstruction. Ivy can create monocultures that provide little or no food and habitat only for rats.
When the ivy encounters a tree, it will climb eagerly toward the sunlight. Ivy doesn’t kill trees outright, but the massive roots can weigh down a tree. If the ivy reaches the crown of the tree, it gets enough sunlight to flower and fruit, providing food for birds and a vigorous seed source. The ivy will keep growing , reaching out its thickening stems further and further. Soon enough, the ivy acts as a massive sail on the tree, and pulls the tree over long before it would naturally die.
One of ivy’s great competitive features is that it can easily reroot — if ivy is pinned down by a fallen tree, everywhere the ivy touches the ground underneath the tree roots, forming a massive network. Ivy can form a thick carpet. Its shallow, easily broken roots easily resprout when it’s pulled.
Here is a picture from Green Seattle Partnership illustrating the problem:
Here is a chart showing what can happen if GSP and other organizations and volunteers weren’t working to remove ivy and other invasives:
Mirrored from Nature Intrudes. Please comment over there.