Restoring Woodland Understory
When most people imagine a forest, they usually picture a thick collection of trees. In Iowa that might be a mix of oaks, shagbark hickories, and walnuts casting their shadows down onto the forest floor. The trees, while certainly magnificent, have far less going on up top as they do down at their roots. These often-overlooked layers of shrubs, wildflowers, seedlings, mosses, and decaying logs knit the forest together, and is called the understory.
If you’re restoring or aiming to improve woodland areas in Iowa, paying attention to the understory is just as important as protecting the big trees. In fact, a rich and diverse understory is one of the best indicators of a thriving woodland. Much of Iowa’s understories are riddled with honeysuckle, buckthorn, knotweed, and multiflora rose. But what happens after those get cleared out?
Photo by Carl Wycoff
What is the Understory?
The woodland understory is everything growing below the canopy. For Iowa, this might looks like:
Shrubs prickly ash, coralberry, or elderberry
Herbaceous plants spring ephemerals, ferns (cinnamon fern is endangered), sedges, virginia bluebells
Tree seedlings and saplings
Mosses, lichens, and fungi much of the fungi in a forest is going to be within the soil itself
Coarse woody debris fallen branches, and decaying logs
Leaf litter and organic matter
Snails, Amphibians, Reptiles, Squirrels, and other Mammals
Some things to be thinking about in a woodland project of any kind is boosting biodiversity and fueling soil regeneration. Many people hear diversity and they think: I’ll just plant more types of trees. We want diversity on every level of the forest!
Diversity in the Soil?
When I analyze soil samples of a woodland area, I want to see lower bacterial levels compared to fungal levels. A grassy prairie— think high bacteria! But woodland forests rely on lots of fungi in the soil. When I sample areas of highly degraded woodland areas, perhaps near a recently constructed neighborhood, these soils are often very low in fungi. This mycorrhizal fungi enhances the tree’s ability to access nutrients and water, as well as buffering against disease in ways currently being studied.
When restoring, we want to feed that fungi (allow the forest to have a variety of organic matter, fallen logs, leaf litter, etc) to support the amazing things it does for the soil biology and tree health. Considering herbicide use, as well, can be an essential factor with restoring woodland areas. Some of the herbicides commonly used against woodland invasive weeds (like Triclopyr) can stay in the soil for an extended period of time, modifying the soil biology in ways we don’t fully understand yet. There have been some studies that show Triclopyr inhibits mycorrizal fungi, which is the fungi trees need in the soil around them.
To learn more on soil biology and trees, read The Hidden Life of Trees by Peter Wohlleben or Entangled Life by Merlin Sheldrake
Coralberry plant, offering great food in winter for songbirds and deer.
Why the Understory Matters
1. Buffer for Wildlife
Much of Iowa’s wildlife has had to adjust profoundly to agriculture. Woodland areas provide habitat for larger animals like deer to take shelter and bed down. The woodland ecosystem of Iowa, while certainly very degraded, remains an important wildlife buffer. Many developers have difficulty completely removing a woodland area, so they build around it. These areas, even if they are small, can provide essential cover, food, and nesting sites for a wide variety of animals:
Songbirds like thrushes, warblers, and towhees forage and nest in dense shrubs.
Small mammals like chipmunks, rabbits, and voles use ground-level cover like shrubs or woody debris to hide from predators.
Pollinators, frogs, salamanders, and invertebrates depend on a rich, moist ground layer and seasonal bloom cycles.
Woodland snails are nutrient cyclers, helping decompose organic matter and are also a food source for many larger animals.
A woodland with no understory is like a neighborhood with no homes—there’s nowhere for wildlife to live. When wildlife have nowhere to live, they end up displaced.
2. Future Forests
Young trees often struggle to grow in woodlands overrun by the invasive plants I mentioned earlier, or they end up choked out due to dense shade. A healthy understory provides the right mix of light, soil, and moisture conditions for oak, hickory, and other native species to regenerate.
Squirrels and birds distribute seeds into the understory—but it’s the quality of that area that determines if seedlings survive. If they are doing this in an area with dense honeysuckle, their hard work is not going to produce many native and thriving trees.
Jacobs Ladder, a common native
3. Erosion Control/Soil Health
Herbaceous plants and mosses form a living blanket that protects the soil from erosion, especially during heavy rains. Their roots stabilize the ground, while leaf litter and organic debris add nutrients back to the soil. Fungi and invertebrates break down dead material, building a healthy, living soil layer.
In degraded woodlands, this layer is often missing—but with the right management, it can recover surprisingly quickly.
Ecosystem Threats to Keep In Mind
Over the years, many factors have chipped away at Iowa’s woodland understories:
Invasive species like bush honeysuckle, garlic mustard, and multiflora rose quickly dominate the shrub and ground layers.
Fire suppression has allowed aggressive species to take over, reducing biodiversity.
Compacted soils can prevent native plants from germinating.
Diseases (tree) can alter the entire woodland quickly, especially when there is a fast rate of spread
If you walk into a woodland and all you see are big trees, bare ground, and nothing but a few small violets, it’s a sign that the ecosystem is out of balance.
Milkwort, a beautiful native pink flower. Photo by Joshua Mayer
How to Restore the Understory
Bringing back the understory takes time and intention. Here are some of the approaches I take when looking at restoring an understory, in no particular order.
Invasive species removal (mechanical, chemical, or seasonal)
Taking active steps towards clearing the woodland
Plant and monitor as you go, introducing native competition in areas you have cleared, in hopes what you plant grows and beats out whatever seeds are remaining of the invasive species.
Selective thinning to open the canopy and allow light to reach the ground
This is for more advanced, older woodlands
Thinning ideally would only be of non-native trees
Prescribed burning, when appropriate, to reset the system and stimulate native growth
This is NOT always appropriate, especially for those that have woodland area as apart of their home property
Consider time of year to minimize effect on nesting wildlife or young wildlife. Consider what type of diversity you have, and if burning is a viable option. For example, not all trees & mosses can survive fire.
Woodland areas do not need to be burned frequently
Native planting—especially spring ephemerals, sedges, and shrubs that are adapted to local conditions
More and more nurseries are opening state-wide that sell woodland plants
One rule of thumb I use is if I plant one shrub, I make sure to also plant two woodland flowering plants, and three sedges
There are a lot of native sedges, some of which can be very hardy and great growers
Soil restoration, including reducing compaction and reintroducing organic matter
Keep some fallen logs down for wildlife cover, or if you have the time, you can cut them into 4-foot chunks and stack them for an even better cover option
Monitoring deer pressure
Don’t be afraid to use a wire mesh wrapped around tree stakes to protect new trees in areas with lots of deer pressure
If your woodland area is also near a stream, consider beaver pressure as well. Same as above, fencing off young trees to give them a good start.
Be mindful of what was there before you
Despite invasive weeds, the ecosystem might not have been perfect, but perhaps it was still functioning. It is important to never plan a woodland restoration so rigidly that you can’t adjust as you discover a beautiful stand of moss, the perfect rabbit structure, a thick chanterelle patch, or a fox nest.
My motto is: leave what is working for last, reassess as you go. Is there an area with NO understory whatsoever? Focus there for your plantings, rather than pulling up an area that already has some functioning diversity and habitat. Focusing on problem areas first will allow you embrace the dynamic ecosystem. Things never fully go as planned.
Gems of the Woodlands of Iowa
Spring ephemerals like bloodroot, wild ginger, Dutchman’s breeches
Sedges and woodland grasses like Carex blanda or bottlebrush grass
Ferns like lady fern and Christmas fern, or the endangered Cinnamon fern
Shrubs like coralberry are amazing food for wildlife
Mosses and fungi, especially near logs and moist slopes
The return of these species signals a woodland that’s moving in the right direction.
Wild ginger; photo by Ron Frazier
Cinnamon fern
Conclusion
The woodland understory is more than just filler between homes in a neighborhood. Without it, we lose biodiversity, soil health, and the next generation of trees. But when we restore it, we create thriving woodlands that support wildlife, protect water, and build resilience for decades to come.
So the next time you walk through a forest, don’t just look up—look down, and around. That quiet patch of green might just be the most important part of the whole system. You might just see something you haven’t seen before.
