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Watching autumn leaves fall
by -- September 14th, 2015

There is little waste in a natural ecosystem. When essential plant nutrients such as nitrogen are taken up by plants, they are returned to the soil when the plants die and decompose. What is eaten by animals is later excreted or otherwise returned to the soil when they die. We call the internal cycling of nutrients in a forest, its biogeochemical cycle. In modern urban developments, the cycle is broken.

Yard wastes, including grass clippings and fallen leaves, are now largely removed in plastic bags or sucked up in giant vacuum cleaners from roadside piles. Water that once percolated through the soil carrying nutrients to plant roots is encouraged to run to the nearest drainage way and river. Meanwhile, we find that we must fertilize our lawns and gardens because of nitrogen deficiencies.

For neighborhoods in the City of Boston, Professors Pam Templer and Lucy Hutyra and their students at Boston University found that the removal of yard waste removed about 1/3 of the nitrogen needed by urban trees. Retention of yard waste could potentially reduce the demand for fertilizer in Boston suburbs by one-half. Overall, the City of Boston collected 8000 tons of yard waste, carrying 64 tons of nitrogen offsite.

Being autumn, neighborhoods across the eastern and Midwestern states are soon to roar with the sound of leaf-blowers, as residents try to clear their yards of fallen leaves. I have a different suggestion: keep the fallen leaves in your yard. My suggestions for leaf-raking closely follow my suggestions for reduced lawn mowing in my post here of 29 June 2015.

Fallen leaves can be raked under shrubbery to provide a layer of mulch. Rotary mowers can grind fallen leaves, returning their nutrients to nourish your lawn in spring.   We need to think of leaves as a resource and not a waste product. Municipalities could save considerably by not providing transport of leaves in plastic bags to the local landfill. Already, some municipalities collect leaves for compost, rather than burial, but think of the energy and tax dollars that could be saved by not picking up yard waste at all.

I have lived in suburban neighborhoods for more than 30 years and never sent a bag of fallen leaves out of my yard. Try it, and your Saturday afternoon will be more peaceful as nature quietly completes her cycle.

 

References

Templer, P.H., J.W. Toll, L.R. Hutyra, and S. Raciti. 2015. Nitrogen and carbon exported from urban areas through removal and export of litterfall. Environmental Pollution 197: 256-261.

1 Comment

  1. Michael Tennesen
    Sep 14, 2015

    “We need to think of leaves as a resource and not a waste product.”
    Another gem!

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