Wednesday, 16 July 2014

Wednesday Science Limerick - Earthworms and Forests

In the States, on the old forest floor
There's a problem that we must deplore
For the earthworms at work
Bury all of the dirt
And the tree seeds won't grow any more.
It seems to be common knowledge to most of us, that earthworms are good for soils. When asked, most people express something along the lines that earthworms are good because they “mix and aerate soil” and “increase nutrients”. This concept likely comes from decades of research on the positive impacts of earthworm activity in gardens and farm fields where the soil can become compacted and less productive if it isn't broken up and organic material isn’t mixed in. But hardwood forests in the Great Lakes region developed for thousands of years since glacial retreat without any earthworms. The natural processes in these earthworm-free forests usually keep the soil loose and uncompacted. Hardwood trees produce tons of nutrient rich leaf litter each year. When leaf litter is produced faster than it decomposes, you can see the development of a thick forest floor, and beneath that forest floor a unique set of soil layers also develops…read more. As litter in the forest floor is decomposed by bacteria and fungi, nutrients are made available for understory plants and tree seedlings. The thick forest floor of earthworm-free hardwood forests turns out to be a central feature of these ecosystems since it is where most nutrient cycling occurs and where virtually all understory plants and tree seedling germinate and grow. When earthworms invade, the hardwood forest ecosystem begins to change rapidly as this forest floor is removed.

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