Earthworm invaders alter northern forests

Earthworms are welcomed in gardens around the world; they aerate the soil and consume dead vegetation to form worm castings that enrich the soil and help plants grow. But it’s a different story in the forests of northern North America where a non-native species of earthworm from Europe, brought by early settlers, are creating conditions that decrease the diversity of native plants, according to a new study published September 3, 2016 in the journal Global Change Biology. The impact of non-native earthworms has been previously documented on a site-by-site basis. The study led by Dylan Craven of the German Centre for Integrative Biodiversity Research takes a broader view. He said, in a statement: The earthworm invasion has altered the biodiversity and possibly functioning of the forest ecosystems, because it affects the entire food web as well as water and nutrient cycles. How are earthworms affecting forest ecosystems that evolved without them? At the top soil layer, earthworms convert fallen leaves to humus. That’s a good thing if you’re growing a garden, but, in a natural forest, it causes a fast-tracking of the release of nutrients instead of allowing the leaf litter to break down more slowly, as it would without the earthworms. Also, as they burrow through the ground, earthworms disrupt the mutually beneficial symbiotic relationship between fungi and plants. Some deep-burrowing worm species change the pH of upper soil layers by mixing in alkaline soil from deeper in the ground. Burrows carved out by earthworms also speed up the drainage of rainwater, drying the soil faster...more