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College Park Wild : Leave the leaves

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Posted on: November 10, 2022

By Rick Borchelt

It was the height of midsummer, and my spearmint was in bloom. The flowers are favorites of many pollinators — small bees, tiny wasps, a host of moths in the twilight and evening. But its special visitor for me is red-banded hairstreak, a modest looking butterfly the size and color of a nickel when viewed from above, but branded with brilliant red-flamed insignias on its underwings. 

Later the same week, a shimmering pale moth as large as my hand with streamers as long as its body settled, quivering under the outdoor floodlight it had been circling for 10 minutes or so.  A luna moth with silvery green wings, a fair imitation of the color of a summer moon.  

And during our first cool snap this fall, I was sitting at the table on the patio when I heard a loud rustling in the hostas and ferns, followed by the sharp squeak and squeal that usually means some lawn creature has met its end. And surely enough, a large white-footed mouse is struggling for its life among the foliage, hopelessly it seems. Astonishingly, its attacker is only a third its size and could have been a smaller mouse, save for a mouth full of razor-sharp teeth and pointed snout — a mole in miniature. The mouse stills, and I get a better look at the predator as it sets to work quickly devouring its meal. It’s a shrew, a northern short-tailed shrew by the looks of it.

Northern short-tailed shrews are found throughout Maryland and are surprisingly common but secretive. They spend most of their time patrolling leaf litter and grass for prey.
Courtesy of Gilles Gonthier (photo is under Creative Commons license)

As different as these three visitors to my yard may have been, they have something very special in common: None of them would be here if I had raked my leaves and had them hauled off last fall.  

“Leave the leaves” has become a common refrain among those of us who welcome wildlife back into our yards and our lives. And it’s one of the easiest ways to increase biodiversity in your urban or suburban yard. 

The value of leaves on trees in the summer is well known: They convert sunlight into food for the tree, with the byproduct of oxygen for us. They shelter bird nests and fledglings. They pull up moisture from the fastness of the earth and transpire it into the air around them, cooling the hot days with evaporation. 

And then, of course, we love their bright fall colors. But for most people, the utility of leaves is over when they brown and crisp and blanket the ground. The obvious course is usually to rake them to the curb and let the city pick them up — and then maybe pay for the privilege of having them returned to you as compost in the spring.

But fallen leaves are as important to the environment as living ones are. They are rich in nutrients and trace minerals they pulled up from the ground, along with water, while they were still alive. The soft layer they create under trees is a haven for overwintering insects — from queen bumblebees to fireflies to luna moths, snug in their cocoons. As these leaves decay, they provide food for soil microorganisms, fungi and invertebrates. They keep the soil moist when winter winds dry the earth, and they keep the soil an even temperature for the bulbs and roots and seeds below the soil’s surface. Lawns and gardens exposed to the elements without a quilt of fallen leaves dehydrate quickly and are slow to moisten again, even in spring rains. Exposed soils alternately freeze and thaw, a cycle that ruptures the roots and corms of so many flowers we love to see in the spring. And every time you send your leaves away, you export a summer’s worth of hard labor by the trees as they pump nutrients back into the ecosystem — every leaf pile you lose is as valuable as that canister of fertilizer pellets you buy at the big-box store in the spring.  

The large and spectacular luna moth needs leaf litter under trees so its caterpillars can snuggle their cocoons into the leaves over winter.
Courtesy of Wikimedia (photo is under Creative Commons license)

There are so many reasons to leave the leaves, from the purely practical to the aesthetic — the sizzle of sleet on dead leaves, the snow that sticks and accumulates on leaf litter long before it bedizens the sidewalks and streets, the swirling eddy when the winds of fall blow.  

You’ll get red-banded hairstreaks, too — it’s the only butterfly in our area whose caterpillars feed on dead and decaying leaves. You could have luna moths, who bundle themselves up in dead leaves for their cocoon instead of the large, brown silk bags other silk moths leave exposed on branches. And you’ll get shrews patrolling your yard for worms, grubs, spiders — and even mice. 

So this fall, let’s #leavetheleaves. Your yard — and its wildlife — will thank you.



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