Battling Invasive Species

By Jennifer Hunt (Content Writer), Jamie Lytton (District Manager), Bill Haslam (District Manager), and Brooke Durnin (Forester)

As many landowners already know, invasive species are a major threat to forest health and biodiversity. While invasives occur nationwide, the most problematic species and management techniques vary by region. Regardless of your geographical footprint, AFM foresters and land managers in the Northwest, Pacific Northwest, and Southeast are well-versed in invasive species prevention, early detection, appropriate treatment, and long-term monitoring. Let’s review each region’s differences and how AFM can help keep your forests healthy and thriving.

First, invasive species are non-native organisms that wreak havoc on forest ecosystems. This can take the form of insects, pathogens, and plants. Invasives are problematic for numerous reasons, as they compete with native vegetation, alter forest composition, affect wildlife biodiversity and habitat, increase management costs, interfere with natural regeneration, and potentially impact timber productivity on planted stands. Without the help of a trained forestry professional, certain management activities can lead to an increase in invasive species, including timber harvesting, road construction and management, storm damage, wildfire, development, or any other soil and vegetation disturbances. It’s important to know what potential invasive species may pop up as a result of these common forestry activities, so let’s jump into our first region of focus: the Northeast.

Northeast Invasive Species

While there are many invasive species that can potentially impact a forest or stand, the most common insect and worm threats are emerald ash borer, beech leaf disease, hemlock woolly adelgid, and invasive understory plant threats like Japanese knotweed, Asiatic bittersweet, glossy and common buckthorn, several species of bush honeysuckle, Japanese stiltgrass, and privet.

• Emerald Ash Borer: This insect is a threat to ash trees. They create D-shaped holes in trees as well as S-shaped galleries that are a result of larvae chewing. Woodpeckers can also leave a hint on trees. They love to snack on the larvae, which causes a “blonding” or light-colored flecking where birds chip away at the outer bark.
• Beech Leaf Disease: A newly discovered problem caused by a nematode (microscopic roundworm) that feeds on beech leaves after being stored in the buds over winter. It has spread throughout the region within the last 10 years. Long-term effects on American beech trees are not known, but infestations denude overstory and understory trees in a short period of time, causing significant damage to a stand and perhaps death to all the beech in the stand. Combined with beech bark disease, which trees have borne for a century, beech trees are likely at high risk of population decline.
• Hemlock Woolly Adelgid: The name is apt, as infested trees show white, fuzzy, cottony masses. Symptoms also include needle drop, a thinning canopy, and discolored foliage, specifically a grayish-green or yellow color.
• Japanese knotweed: The knotweed has been present in the northeast for decades and crowds out all other plants. It has large root masses that allow the plant to survive repeated chemical and mechanical removals. It spreads by its roots and by rooting stem sections that may float downstream or get carried by vehicles to new areas.
• Asiatic bittersweet: This vine has been popular as decorative wreaths for many years. Unfortunately, it spreads rapidly, crowding out native plants and climbing trees and breaking branches or stems.
• Glassy and Common Buckthorn: This plant looks similar to some cherries and other shrubs early in life, so they get missed easily with a casual glance. These shrubs can fully populate the understory of a forest in a decade, crowding out native plants and making tree regeneration difficult.
• Bush honeysuckles: In spring, before native trees leaf out, you can spot thick honeysuckle infestations by their thick, light green foliage. This early leaf-out helps them to outcompete native vegetation. If left untreated, honeysuckle can take over entire forest understories.
• Privet: Privets have often been planted in landscaping because they’re fast-growing and provide good privacy in hedgerows. They produce flowers and fruits that attract birds, further spreading their seeds. However, because they grow so easily and thrive in nearly any habitat, they leaf out early and shade out all of their competition, including native species.

The solution: In most cases, early detection and monitoring are key. This can require herbicidal and/or mechanical treatments. Some species are difficult to eradicate completely, so long-term monitoring may be necessary.

Pacific Northwest

There are a few culprits to watch out for in this region of the United States, namely Scotch broom and Himalayan blackberry.

• Scotch broom: This perennial shrub is identified by its dense shrubbery and yellow flowers. It has an affinity for recently logged and disturbed sites, and since it spreads so prolifically, it can overtake a site quickly, choking out native vegetation and interfering with forest regeneration. Scotch broom is estimated to cause multi-million-dollar losses to the Pacific Northwest timber industry annually.
• Himalayan blackberry: Considered the most invasive non-native species on the West Coast, Himalayan blackberry is a menace that inhibits wildlife mobility, displaces native plants, and causes significant economic impacts. It often outcompetes native plants in all areas that are essential to growth, including light, space, and nutrients like water and nitrogen.

The solution: After disturbances on a site, foresters and land managers must monitor for the emergence of these species, as they can be difficult to contain once they spread. To keep them at bay, land managers may consider a combination of mechanical treatments, prescribed burning (where appropriate), and herbicidal treatments.

Southeast

Lastly, there are several species worth highlighting in this region, including cogongrass, wisteria, Japanese Stiltgrass, and Chinese Privet. It’s common to see kudzu in this area, but the others are special concerns for plantations and stands managed for timber.

• Cogongrass: This is known as one of the most aggressive invasive species in the world thanks to its fast rhizomatous growth. Bright green leaves can grow several feet, and flowers are maroon before opening, then emerge as puffy and white. Its litter is extremely flammable, making it a considerable wildfire threat.
• Wisteria: Although the lilac-colored flowers are beautiful, non-native wisteria can have deadly effects on mature trees. This vine will grow on anything, shading and choking out native trees by growing high into the canopy.
• Japanese Stiltgrass: This grass has pale green lance-like leaves that form dense, tangled mats. It likes moist soils, shady wooded areas, forest edges, and lawns.
• Chinese Privet: Chinese Privet wins the award for one of the worst invasives in the South. It creates dense thickets that choke out native species.

The solution: Cogongrass often requires a combination of treatments to control its spread, and early identification is key. Cutting or mowing alone is not enough when these invasives can easily resprout or regenerate, so mechanical treatments should be accompanied by forestry herbicides. Seeds can spread through pine straw, so forests with pine straw operations should be carefully monitored by an AFM forester or land manager.

Prevention and early detection are generally less expensive and less disruptive than trying to fight against a well-established invasive species infestation. There is no one-size-fits-all solution to any of these species, as there are many variables that can impact how they should be treated. Things like forest type, terrain, accessibility, presence of native vegetation, size and density of the invasive species, environmental considerations, and client objectives all play a role in treatment and prevention plans. Even though land managers may achieve a level of success by visibly removing a particular species, it may not necessarily eliminate it altogether, reiterating the importance of long-term inspections and retreatment. Know which species are present in your area and engage with your AFM forester or land manager early to help prevent and control invasive species before they spread. Do not hesitate to contact AFM for professional guidance on how to keep your forests healthy and thriving.