Winter Identification of Deciduous Trees and Shrubs

In winter, trees and shrubs can be identified using twigs, bark, overwintering fruit and sometimes leaves. This post offers some tips and terms for winter ID. A printable version is available for free through the Downloads tab.  

Tip #1: If they're within reach, look at twigs. 

As in this photograph of Green Ash (Fraxinus pennsylvanica), look for the size, color, shape and texture of terminal, or end, buds and lateral, or side, buds (b). Lateral buds are attached at nodes (a) and are arranged in one of four patterns:

• Alternate: One bud per node   
• Opposite: Paired, or two buds per node
• Subopposite: Paired but not quite opposite
• Whorled: Three buds per node

Green Ash has opposite buds (d). 

The size and shape of leaf scars (c) can also help identify a species. These scars are left by petioles, or leaf stalks, when they fall from the tree. Green Ash typically has light, semicircular leaf scars.

    

Tip #2: Within leaf scars, look for vascular bundle scars.

These scars are made when strands of water- and food-conducting cells are severed in fall. Their size, number and arrangement are typical for a species. Some are easier to see with a magnifying lens. 

Above left: Green Ash bundle scars are small, brown dots arranged in a semicircle.

Center: The bundle scars of Red Elderberry (Sambucus racemosa) are raised, irregular shapes arranged at the points and along the sides of a triangular leaf scar. 

Right: The bundle scars of Northern Catalpa (Catalpa speciosa) are light brown dots arranged in an oval.

Tip #3: Look at bark. 

Bark color and texture are helpful clues but can change with age. Also look for lenticels, spots or irregular shapes on the bark of younger trees or shrubs. In the photographs of Green Ash below, lenticels are the white spots on the reddish-brown bark of the sapling shown on the left (arrows).

On the right is a mature Green Ash showing the typical honeycomb-like pattern of ridges and furrows of its bark.

Tip #4: Look for overwintering fruit.

Some species retain their fruits, or parts of them, well into winter. Also look under the shrub or tree for fruits that may be on the ground or on top of the snow.

Clockwise from top left: Red capsule walls of Winged Burning Bush, Euonymus alatus; samaras of Box Elder, Acer negundo; pods of Kentucky Coffee Tree, Gymnocladus dioicus, each 3 to 4 inches (7-10 cm) long; and the fruits of Amur Cork Tree, Phellodendron amurense. 

Tip #5: A few species hold on to their leaves.

Some trees are marcescent -- their leaves turn brown but aren't shed in fall. In this region, oaks (Quercus), Ironwood (Ostrya virginiana) and Blue Beech (Carpinus caroliniana) are among the few trees that are marcescent. 

Below is Ironwood, an understory tree that retains its leaves through winter. 

Tip #6: Remember MAD Cap Buck Horse.

Bud arrangement -- alternate, opposite, subopposite or whorled -- can quickly narrow choices for identification. One way to remember which species have an opposite arrangement is the mnemonic MAD Cap Buck Horse:

M            Maples (Acer)

A            Ash (Fraxinus)

D            Dogwoods (Cornus, except for alternate-leaved dogwood, C. alternifolia)

Cap        Plants that are or were in the family Caprifoliaceae, including honeysuckles (Lonicera), wolfberry or snowberry (Symphoricarpos), elderberry (Sambucus) and viburnums (Viburnum). 

Buck Horse    Ohio Buckeye (Aesculus glabra) and Horse Chestnut (Aesculus hippocastanum)

Although this mnemonic is helpful, it doesn't include all trees and shrubs with opposite buds. For example, Wahoo and Burning Bush, genus Euonymus, also have opposite buds. So does Bladdernut, Staphylea trifolia, an understory shrub.

Most remaining species have alternate buds. Common Buckthorn, Rhamnus cathartica, is unusual in having subopposite buds. Catalpa, another unusual species, has whorled buds. 

Tip #7: Look at the pith.

The pith is the center of a branchlet or twig. The appearance of the pith -- hollow or solid, color, texture -- can help confirm the identity of a tree or shrub. For example, honeysuckle shrubs (Lonicera, left photo below) have hollow piths, and Red Elderberry (Sambucus racemosa, right photo below) has a soft, yellow pith.

Tip #8: Try these guides.

The LEAF Program from UW-Stevens Point is a K-12 forestry education initiative that offers many online resources. Under Curriculum & Resources, choose LEAF Tree Identification Tools. The LEAF Winter Tree ID Key is available there as a downloadable PDF.

Pocket Reference for Winter Tree Identification. Champaign County Forest Preserves, Mahomet, IL.

Fruit and Twig Key to Trees and Shrubs, by William M. Harlow, PhD. Reprint edition, 1959. Dover Publications, Inc., New York. ISBN 0-486-20511-8. 

Progress in Buckthorn Management

Seedlings of Common Buckthorn rise from the seedbank after an area is cleared of larger plants. Suppressing reinvasion
is a major challenge of Buckthorn management. 

Researchers at the University of Minnesota rank Buckthorn high on their list of problem invaders. They’ve been studying Common Buckthorn, Rhamnus cathartica, and Glossy Buckthorn, Frangula alnus, for years, and last summer they shared some of their findings.

Their white paper, Managing Invasive Buckthorn, focuses on two areas of research: goat browsing to manage Buckthorn growth and native plant cover to suppress reinvasion. Here are highlights from their work.

Goat Browsing Has Potential – and Pitfalls

On steep hillsides or other inaccessible places, goats are an alternative for removing buckthorn. Their browsing and trampling can reduce Buckhorn abundance and open the canopy, allowing more light to reach other plants.

Goats are most effective on small Buckthorn within the animals’ reach. To limit damage to other plants, fall is the best time to release the animals, but that’s also when they’re most at risk of acquiring meningeal worms. These brain parasites can infest snails and slugs that the goats also consume while browsing. Co-grazing ducks and geese with goats can lessen the risk, as waterfowl can eat infested snails and reduce their numbers but not get sick.  

Goats don’t eat just Buckthorn; they’ll eat other plants, too, including desirable ones. Some plants may rebound the following year, but they’ll be competing with Buckthorn that also resurges under the newly opened canopy. As explained in the next section, that’s why establishing cover is important after Buckthorn is removed, whether by goats or other means. A good way to suppress Buckthorn’s return, the researchers found, is to increase competition.

Part of this Buckthorn thicket was cleared with a forestry mower. Just a few 

years later, it has regrown to become as dense as the unmowed portion.

Native Cover Suppresses Reinvasion and Rebuilds Communities

Buckthorn management doesn’t end when the plants are cleared from an area. Reinvasion and a return to dominance are common, because Buckthorn can regrow from the seed bank or from cut stumps that weren’t treated with herbicide.

Fortunately, the researchers discovered a way to suppress reinvasion. They experimented with dense plantings or seedings of trees, shrubs, grasses and forbs and found that if light availability under plant cover drops below 3-4%, Buckthorn regrowth is limited. In closed forests with less light, planted trees and shrubs worked best to establish that cover. In more open areas, such as oak woods, both planted stock and seeded grasses and wildflowers were effective. The scientists are now experimenting with less dense planting and seeding.

Even after plant cover is introduced, it is important to monitor a site for germinating or sprouting Buckthorn.  As the native planting matures and casts more shade, removing Buckthorn should become easier as fewer plants survive. It’s a years-long effort, but with the right combination of techniques, Buckthorn should recede as the native plant community returns.

More Resources

For help identifying Buckthorn in winter, see this updated post from January 2021 or download this free, two-page guide. Additional Buckthorn information is available from the Minnesota Department of Natural Resources and the Minnesota Department of Agriculture.

Reference

Bernhardt, C., et al. 2022. Managing Invasive Buckthorn. University of Minnesota College of Food, Agricultural and Natural Resource Sciences and the Minnesota Invasive Terrestrial Plants and Pests Center.  CFANS-Buckthorn-White-Paper-June-2022.pdf (umn.edu)