3 days Ago By Justine Paradis, Outside/In
Every other Friday, the Outside/In team here at NHPR answers listener questions about the natural world. This week's question comes from Gio in Seattle, Washington. "I was wondering about all the leaves that fall to the ground that we rake and clear from our yard.
Does that disrupt the nutrient recycling that would normally occur if we just left the leaves there?" Producer Justine Paradis jumped in the leaf pile to see what she could find. Justine Paradis: There’s an official term for the layer of dead and decomposing leaves that wind up on lawns and forest floor: leaf litter. A term which might suggest that dead leaves are essentially trash, and they belong in the landfill.
But our listener is onto something. Asmeret Asefaw Berhe: Indeed..
. raking of the leaves ..
. disrupts the nutrient cycles and the ecosystems in a major way. Justine Paradis: This is Asmeret Asefaw Berhe, a biogeochemist at the University of California Merced.
As trees grow, they draw essential nutrients up from the soil and use them to build biomass like their leaves. Asmeret Asefaw Berhe: These are nutrients that they cannot complete their physiological cycles without things like nitrogen, phosphorus, potassium..
. Many of these essential nutrients ..
. plants can only get them from soil. Justine Paradis: When those leaves fall, the trees return their nutrients to the soil.
Insects and microbes digest and reintegrate them back into the dirt. And then the nutrients are available to be drawn back into the tree, and so on and so on. Because dead leaves are about half carbon – when they decompose, they become what we call “soil carbon.
” You can usually tell if dirt has a lot of soil carbon, just by looking at it. It’ll be dark and rich, because it’s really good at holding onto water and nutrients. Asmeret Asefaw Berhe: Soils that have a lot of carbon are like sponges.
They allow for more water to be held in soils. Justine Paradis: But when we rake and bag all our leaves, we’re depriving the soil of the return of those essential nutrients. In the US, the EPA estimates that 35 million tons of grass clippings and fallen leaves are removed annually.
Researchers have found that long-term litter removal in suburban yards reduced decomposition rates by 17%, and they held almost a quarter less soil carbon. Now, leaving all the leaves might not be feasible everywhere, like areas with high wildfire risk, and leaves left on top of grass don't always decompose quickly, so some folks recommend mulching leaf litter with a lawnmower. But it’s not all or nothing.
Maybe you can leave some leaves in a pile in one corner of the yard or put them in a compost pile and use them in your garden. You can also explore if your community offers state or municipal composting services, because with those programs, most likely..
. Asmeret Asefaw Berhe: ..
.It's going to be coming back into the soil somewhere..
. At least it's not just being left to decompose in a landfill, where it would only contribute to more greenhouse gas release..
. Soil stores close to about 3000 billion metric tons of carbon..
. more than the amount of carbon that's stored in all of the world's vegetation plus the atmosphere, combined and twice over. So.
.. any change can have a very important implication for.
.. the world's climate.
Justine Paradis: If you do leave the leaves in your yard, you’ll see benefits over the years. Like leaves create habitat for wildlife and insects. Including a crowd favorite: fireflies.
If you’d like to submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to [email protected] . You can also leave a message on our hotline, 1-844-GO-OTTER.
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