martes, 27 de abril de 2010

Darwin's Earthworms

Who knew that earthworms are an invasive species in the Northeast? Darwin sure didn't. He did, however, find out that earthworms bring benefits to their native environments through soil turning, enhanced decomposition, and nutrient-rich castings. His experiment involved placing coal in the feild behind his home in London and watching it become covered in soil by earthworms over the course of two or three decades. This is according to a recent article in the Bennington Banner that describess how the earthworms Darwin came to appreciate are now affecting the Northeastern United States. Earthworms disappeared from the region during the last ice age and have slowly been migrating back, at a rate of five yards per year, or about a total of 28 miles in 12,000 years. They have been helped along in this migration by hapless fisherman. Other earthworm species have also been introduced by European colonizers. Since then, they have been churning up the soil and hurting native species, such as the red-backed salamaders. Their offspring need a thick duff layer and a good number of ground insects, both of which diminish with increased numbers of earthworms. The uninvited earthworms also help non-ntive plant species invade the area through their introduction of nutrients to the soil. Darwin was right in thinking that earthworms play a beneficial role in habitats, not just the role of a pest. He did, however, miss the invasive potential of these tiny earthmovers.


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