Good Oak News

Sunday, October 21, 2012

Woodland Restoration By Seed

I recently had a potential client contact us asking about seeding into her woodland. The response I wrote her was pretty involved, so I thought it would be a good educational resource for others as well. Read on:

There are several factors to consider with seeding. If a woodland has a history of buckthorn infestation, it's important to know that buckthorn is allelopathic, meaning that it releases chemicals into the soil that inhibit the growth of other plants. Our understanding of how this works in buckthorn is in its infancy, but we do know that the chemicals affect some plants more than others and that it can take up to 4 years for these chemicals to break down or flush out of the soil after a dense infestation of buckthorn has been removed. It is possible that honeysuckle or other invasive plants are also allelopathic, but the research has not been done yet. Garlic mustard, for example, kills off beneficial soil fungus that form symbiotic relationships with many native plants. At the moment, we are recommending only planting live plants in dense buckthorn areas the first year after removal and waiting 2-4 years to do seeding.

Another factor to consider is sunlight availability. Seeds only do well when there is ample light. As we mention in our recent mailer, the woodlands in our area were originally more open than they are today with much more light to help these ground layer plants germinate, grow and prosper. Some woodland plants can be established by seed but many can only be established by live plants, including the most shade tolerant species. It is likely you may need to do additional tree thinning to open up the canopy enough for seedling plants (and young oaks!) to prosper. Trees we typically target right away are mulberry (also exotic) and boxelder. Other trees we selectively thin out to open the canopy include cherry, walnut, hackberry, ash, elm, basswood and maple.

This "Sugar Maple Deadzone" in a local woodland is much too dark to support productive ground-layer plants and will need to be thinned out before restoration can begin.

Otherwise, for more shaded areas you will have to stick to more shade tolerant, live plants. The more shade tolerant species tend to be difficult to establish by seed for various reasons due to difficulty in collecting, cleaning, storing and otherwise preparing the seeds (the more open woodland species are more often wind-born seeds which are easier to collect, process and store). These plants also tend to only bloom in the spring or not have showy flowers (such as ferns). A healthy woodland should have plants that are green and flowering year-round, so brush removal and tree thinning are an important first step, then a mix of planting and seeding are often necessary to reestablish the biological diversity of the habitat.

Lastly, seeds need good seed-to-soil contact and light to germinate. Most of our woodlands have a layer of leaf litter that prevents these two components from being found in the same place. Naturally regular, low-intensity ground fires would have removed this leaf litter letting the seeds meet the soil and the sun. So leaf-litter needs to be removed before seeding, usually we do this by a prescribed burn, in order to allow for germination.

The Vestal Grove in Somme Prairie Grove has been revegetated largely by seeding, with some remnant plants and some planting as well. Brush removal is the first step and prescribed fire is critical for maintenance. This is one of the best examples of a healthy woodland in the Midwest.

We have a custom seed mix we have developed with our seed supplier that includes many of the species on the below table, as well as some savanna species. This mix does pretty well in open woodlands, and can be planted in late fall or spring. But don't expect immediate results, these take a few years to get established. Also, there are many other species that should/could be seeded into a woodland that are not commercially available. A few that come to mind include white lettuce (a.k.a. lion's foot), yellow pimpernel, wild hyacinth, blue-eyed Mary, other woodland sunflowers, and a wide variety of sedges (Carex albursina, C. blanda, C. jamesii C. pensylvanica, C. radiata, C. rosea, and others depending on specific site conditions), but there are many others. These may need to be collected, with permission of the owner, from local sites.

Native Woodland/Savanna Plants available by seed in the Upper Midwest
Sci. Name Common Name
Agastache nepetoides Giant Yellow Hyssop
Agastache scrophulariaefolia Purple Hyssop
Allium cernuum Nodding Pink Onion
Anemone virginiana Tall Anemone
Aquilegia canadensis Wild Columbine
Aster drummondii Drummond's Aster
Aster lateriflorus Side-flowering aster
Aster sagittifolius Arrow-leaved Aster
Aster shortii Shorts Aster
Blephilia hirsuta Hairy Wood Mint
Bromus purgans
Carex springelii
Woodland Brome
Springell's sedge
Campanula americana Tall Bellflower
Dodecatheon meadia Shooting Star
Echinacea pallida Pale Purple Coneflower
Elymus histrix bottlebrush grass
Elymus villosus Silky Wild Rye
Elymus virginicus Virginia Wild Rye
Eupatorium purpureum Purple Joe Pye Weed
Eryngium yuccafolium rattlesnake master
Geranium maculatum Wild Geranium
Helianthus strumosus Woodland Sunflower
Monarda fistulosa Wild Bergamot
Penstemon digitalis Foxglove Beardtongue
Rudbeckia subtomentosa Sweet Black-eyed Susan
Rudbeckia triloba Brown-eyed Susan
Scrophularia lanceolata Early Figwort
Solidago caesia Blue-stemmed goldenrod
Solidago flexicaulis Zig-zag Goldenrod
Solidago ulmifolia Elm-Leaved Goldenrod
Tradescantia subaspera Zig-zag spiderwort
Tradescantia virginiana Virginia spiderwort
Veronicastrum virginicum Culver's Root
Zizia aurea Golden Alexander