Gardeners love them! And why shouldn’t they? After all, these wrigglers make their lives easier by making their soil more fertile and enabling plants to grow faster. Also knows as the ‘Ecosystem engineers’, earthworms have been relentlessly ploughing the soil, eating and decomposing the soil minerals and organic matter. This, in turn, helps air and water to reach roots and seeds of the plants which affect their growth and health. Farmers love them as an increase in earthworm density can influence soil structure and chemical process in a positive way; it is estimated that it can boost crop yield by 25 per cent. While this fact may paint them as heroes in one part of the world, but in the northern part of North America, the advent of non-native earthworms have triggered a stress response in the scientific community. With climate change raising the global average temperature, many animals and plants have been shifting toward the poles in search of suitable living conditions. As the temperature warms in boreal forests, the number of earthworms has grown dramatically which does not augur well for these forests. Now, these worms threaten the entire landscape of boreal forests ecosystem.
The invasive earthworms which today crawl the surface of boreal forests are not native to North America. It is estimated that they were wiped out some 10,000 years ago during the ice age. The worm-less environment in the boreal region was conducive to the survival and growth of what today comprises tall and thick trees of boreal forests. Without earthworms, the rotting leaves and fallen woods make a thick layer above the mineral soil which protects seeds from the freezing temperature, herbivores and help them to grow. This thick layer also reduces competition from smaller and sun-loving plants. However, the last centuries have seen earthworms arriving these forests in numbers. Native to southern Europe, these invasive earthworms were introduced to North American soil, in the temperate regions, by European settlers — mostly as a fishing bait — in the 1800s.
This invasive species of the earthworm, Dendrobaena octaedra, in the boreal forests of North America devours the leaf litters and stays in the upper layer of soil. This has been exposing the younger seedlings to freezing temperature and other herbivores and leading them to die. Further, the nutrients freed up from the decomposition of litters now reach deeper in the soil, making them inaccessible to the roots of younger plants. The invasion of earthworms in boreal forests is bad news for climate activists too. As their numbers grow, more carbon is now getting released into the atmosphere as a result of breakdown and decomposition of leaves and organic matter from thick layer, which earlier remained intact in the biomass without earthworms.
Scientists worry that in the next 50 years, these earthworms — along with rising temperature due to climate change — can lead to a massive die-off and the tall and thick boreal trees would be replaced by small shrubs and grasses, thus transforming the entire boreal forest ecosystem. Unfortunately, scientists have not been successful in eradicating these earthworms from boreal forests and the only way to prevent their proliferation is by putting an end to their movement due to human activities.