Why Jumping Worms: Forests and Biodiversity
Forests are an amazing resource for humanity. Everyone, even in cities, depends on these valuable natural resources for their way of life.
Photo credit: Maryam Nouri-Aiin
Forests remove and store huge amounts of carbon from the air; they clean and protect our water supply; cool and purify our air; promote rainfall and protect waterways. They also supply billions in economic revenue, and offer food, fuel, shade, physical health benefits, and balm to the human spirit.
In North America, particularly in New England, the upper Midwest, and Canada, earthworms were eradicated during the last ice age. These forests then evolved with thick, organic soil layers made out of centuries worth of accumulated decayed leaf litter and wood. The top layer of that organic soil is called the O Horizon—it’s a soft, fluffy matter that sits right under the freshest leaf litter.
The O Horizon is the foundation of the forest system. This is where most of the soil nutrients are, where the native seeds germinate and root into, and where most of the soil biodiversity lives. The O Horizon is held tightly in place by roots and fungi, protecting the soils from erosion during rainstorms and soaking up water to keep roots and wildlife moist even during drought.
The organic horizon is the nutrient-rich layer of organic matter rich underneath the freshest leaf litter in a forest.
A healthy soil sample shows distinct layers of organic soil; jumping worm damaged soils loses these horizons, have less organic matter, and only a layer of castings at top.
Jumping worms preferentially consume the O Horizon and leaf litter and convert it into castings, creative negative ecological cascades that affect the entire forest:
Biodiversity collapses. Soil arthropods that feed on decaying leaves typically disappear, followed by their predators. The collapse in the smallest links in the food chain then affect larger wildlife who depend on them. Ground-nesting birds and small wildlife who depend on leaf litter and the understory lose their shelter and become vulnerable to nest predators.
Many native plants cannot root into the casting layer, or their seeds are lost from the seed bank, and small/young plants fail when their roots are exposed following the erosion of castings. These changes drastically impact forest regeneration: In a study of 47 sugar bushes in New England and New York, forests invaded by jumping worms had 0.5 maple seedlings per square meter, while uninvaded forests had 6 per square meter.
Mycorrhizal fungi networks, which form symbiotic relationships with plant roots to help plants obtain nutrients, are disrupted.
Mature trees are slower to change, but some hardwood species show signs of dieback and stress in jumping worm forests, and become more vulnerable to drought and other stressors.
In healthy forests, soil nutrients are broken down and made available in slow, evolutionary lockstep with native plant needs. Jumping worms release these nutrients too quickly and far in beyond what native plants can take up. These excess nutrients are then free to dissolve into rainwater and pollute local water bodies.
The castings themselves are light and loose, eroding easily in rainstorms, effectively removing mass and forest nutrients that were once bound into the healthy O Horizon. This type of erosion is 30 percent more extreme than in standard-till farm fields.
Without the O Horizon to act as a ‘mulch’ to the forest, opportunistic non-native invasive vegetation, which is often more resilient to jumping worm impacts, moves in.
These processes of erosion, biodiversity collapse, and plant failure permanently reduce soil fertility and ecosystem function, ensuring that the next generation of forest life is diminished.
We are using lab experiments, field studies, and collaborative science with our communities to find ways to stop the spread of jumping worms and promote healthy forests from the ground up.