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What Lives in the Leaves

ConservationIssue 3NatureNature Issue 3

I have many memories of growing up in Burlington in autumn. My family had five individual trees in a twenty meter radius from our house and each fall I can remember spending hour’s carefully raking leaves into neat and orderly piles only to instantly demolish our efforts. We would run, jump, and thrash through the leaves–toss them high in the air and shove bunches down each other’s jackets. I remember all the joy and I also remember the abrupt end to our fun. About a week after the leaves fell, the leaves would become slimy and smelly.  For me, the moment I spotted a slug or beetle, I was done with the leaves for the season.  We would bag them up, stick them on the curb, and not think of leaves for another year. What I didn’t realize then was that there were more species in the leaves besides beetles.

There is an entire ecosystem, alive and flourishing, beneath the thin detritus layer of fallen leaf litter. Fallen leaves provide a complex and diversified biotic community, which support countless microorganisms and invertebrates. These ambiguous creatures account for more than 95% of all animals on Earth and play a lead role in ecological recycling. Collectively known as detritivores, they are the insects, fungi and microbial bacteria that feed on dead and decomposing material.  They work to restore organic and inorganic matter back into the food web.  This hidden ecosystem not only nurtures life, but it also contributes to essential biogeochemical cycles of which all living Earth relies.  They are also responsible for aspects of the carbon, nitrogen and phosphorus cycles by re-releasing these elements back into the atmosphere.

Without detritivores we would live in a world overwhelmed by mass amounts of dead plant and animal material and, in their absence, we would find the landscape devoid of all life as we know it. That being said, detritivores can have a negative impact on the global climate by adding to the amount of carbon dioxide (C02) in the atmosphere. This is because dead leaves contain abundant carbon that is returned to the soil and atmosphere through the breakdown by the detritivores. The resulting phenomenon is referred to as the greenhouse effect, a process by which radiation from Earth’s atmosphere warms the surface to above average temperatures.  Human contributions to greenhouse gas emissions are largely to blame but any source, natural or man-made, are a threat to ecosystems, biodiversity and people.

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In addition to supporting the small but mighty detritivores, leaf litter communities provide food and shelter for many birds, mammals, reptiles and amphibians.  Much foraging happens at the ground level fueled by fruits, nuts and seeds produced from nearby vegetation.  Among the insects, squirrels, snakes and thrushes, salamanders are particularly characteristic of forest floors. In Ontario there are eleven species that can be found living among detritus and foraging under leaf cover.  As a group, they prefer cool moist habitats thus burrow in mineral soil or hide under rotting woody debris, rocks or throughout moss.  They are among some of the most cryptic animals this community sustains, yet they are also the most prolific. By weight salamanders have been found to be twice as abundant as birds and equally abundant as mammals living in the same forest system. This suggests that salamanders are significant regulators of climate change due to their reduction of beetles, earthworms and ants. That is, they help to keep the amount of carbon released into the atmosphere down by feeding on the detritivores responsible.

In short, a fallen leaf may not be alive so-to-speak, but it will continue to contribute to the productivity of living things and play an important role in the biogeochemical cycles and climate change. Although the leaves in our yard may not be nurturing the same communities as a forest, they still play an important role in sustaining life on a smaller scale and should not be considered waste.  Leaves left on the lawn may result in brown spots and even kill the grass growing beneath it but shredded leaves mixed with manure will make for a healthy addition to the compost or garden come spring.  Many municipalities have organic collection programs that help to divert materials from landfills however it is still estimated that up to 13% of solid waste is made up of leaves.

Leaves still signify the seasons end, the closure of a productive summer and, now too, the continuation of natural processes. Although I still cringe at the thought of a slimy leaf on my skin, I now see the beauty in leaves, no matter what stage of their life cycle.

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Last modified: September 5, 2017

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