The State of the Trees · Episode 12 of 13 · 23 min
The Underground: The Invasive Species Below the Forest
Some of the most destructive forest invasions happen entirely underground, in northern forests that spent more than 10,000 years with almost no earthworms. European nightcrawlers strip the duff layer northern hardwoods depend on, and Asian jumping worms, which breed without a mate and spread in mulch and bait, leave dry castings that won't hold water. Native wildflowers and ground-nesting birds fall, and disturbed soil opens the door to garlic mustard and buckthorn.
Who's who
- Charles Darwin+2 more episodesAuthor of the 1881 book praising earthworms as soil-builders
Where it happens
- Northern hardwood forests, North AmericaGlaciated region with no native earthworms for 10,000 years
- University of Wisconsin-Madison ArboretumJumping-worm population confirmed in 2013
Timeline
- c. 10,000 years agoRetreating ice sheet leaves northern forests worm-free
- 1600sEuropean earthworms arrive with colonists
- 1881Darwin publishes The Formation of Vegetable Mould
- 2013Jumping-worm population confirmed in Madison, Wisconsin
- 2019Global earthworm map published in Science
Still debated
Whether the dramatic garden-soil transformation by jumping worms adds up to stand-scale forest collapse is unsettled; the Wisconsin arboretum has reported limited effects so far in its forest plots.
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