Leave the Leaves for Understory Habitats

Red, orange, yellow, gold, brown – every autumn, the canopies of the Northeast transform into a picturesque glory of color. Once they fall though, our opinions of these very same leaves may quickly change. Are they yard waste, an annoying nuisance to be cleaned up or something quite different and much more important? 

Leaves are actually critically important to the health of your yard. The simplest thing you can do to help support sustainable natural ecosystems in your area is to leave the fallen leaves on the ground during autumn.

Mature deciduous trees are often hosts to hundreds of different species of butterflies, moths, birds and mammals whose lifecycles are deeply intertwined with those of the tree. So, when the leaves turn their shades and fall to the ground along with the tree’s seeds and nuts, it is an expected change that coincides with many of these creatures’ overwintering routines. 

Leaves are full of nutrients, so when they fall and then decompose, they act like a natural fertilizer, releasing into the soil the necessary vitamins and minerals that nearby plants need to thrive, including the tree itself. But these leaves also act as a shelter, a home to overwintering pollinators. Many bees, butterflies and moths enter either dormancy or a pupae phase that requires the covering of fallen leaves for protection from predators, wind, cold temperatures and snow. Otherwise, they may perish. 

“This goes along with general biodiversity and ecology principles. It basically follows how a forest would operate typically,” says Curator of Entomology Jon Gelhaus, who is also a professor in Drexel’s Biodiversity, Earth and Environmental Sciences department. “Leaving fall leaves in place in the garden provides decomposition to form humus, which increases the organic content of the soil and provides nutrients to plants. But it also provides homes and food for soil invertebrates, which serve as food for other animals like vertebrates, such as snakes, lizards, salamanders, birds and small mammals.”  

Without these leaves, the soil becomes degraded, and pollinators are exposed to the elements reducing their survival rates drastically. Come next spring, many spectacular and critically important plants will have to grow in poor soil and are left without their necessary winged visitors — which can again reduce crop and seed production.

Subsequentially, with lower populations of insects, many animal species are then left without their needed sources of bug food to live healthily and reproduce. In short, the falling leaves belong to a cycle, and removing them can deeply impact everything else.  

“No one rakes the forest,” says Diane Ehrich, owner of Collins Nursery, a retail nursery outside Philadelphia that grew and sold only native plants. “The forest is a layered plant community of canopy trees (like oaks), smaller understory trees (like redbuds), shrubs (like spicebush) and herbaceous plants. And all these plants are growing out of the leaf litter. Fallen branches decompose. Dead plant material is left to decay.  All these processes sustain insects and birds in a dynamic ecosystem. The idea of ecological horticulture is to take cues from nature and natural processes.” 

So how do we mimic the powerful process of natural land in our own gardens and yards to not only promote the health of local plants, pollinators, animals and soil that exist there, but also create something we find aesthetically pleasing? For one, simply moving the fallen leaves from your yard into your garden beds or under the trees is an easy solution.  

“I do rake my leaves on my lawn areas and then run it through the reverse of my leaf blower (leaf vacuum) which chops them up a bit so they stay in place over the fall, winter and spring. But then I put it over my garden as a blanket to protect plants and their roots during the winter,” Gelhaus offers.  

Another method is to create an understory bed of various native plants ranging in size and height around any large tree or shrub in the yard that will just naturally collect these fallen leaves. Understory plants — both herbaceous (non-woody annuals and perennials) and woody shrubs and young trees — provide additional structural complexity to the ecosystem. These understories also provide diversity of plants which then increases the diversity of native animals, as well as homes such as nests for birds.  

Planting native understories, sometimes called soft landings, is like creating a little forest that models the ecological, sustainable system found there.  

“So the idea of soft landings, coined by Heather Holm, is to recreate these processes in our own yards so that we sustain the insects and birds that need this habitat to survive,” explains Ehrich. “Planting native plants is one part. Leaving the leaves is another part. I think another aspect is embracing a different aesthetic for our gardens, one that encourages nature and natural processes.” 

In theory, if we can slowly transform parts of our yards from flat grass lawns to soft landing understories that collect fallen leaves for us, we can easily promote sustainable growth and biodiversity while also having a pleasing garden — year-round. It’s a win-win solution. 

“Without this understory, we lose ground nesting forest birds, lose spring ephemeral wildflowers and the bees and other insects that depend on them,” Gelhaus says. “So structural complexity, variety of plants, reduction of non-natives, leaving the leaves — all this just increases overall diversity and health.” 

Written by Brigette Brown, Editor