Introduction to Girdling & Frilling of Woody Invasive Species
Girdling or frilling of woody invasive plants involves removing a strip of bark around the entire circumference of the plant’s trunk or stems. It is only practicable on relatively large single-stemmed plants. Girdling alone is often ineffective for long-term control of woody invasive species due to their ability to regrow from the root system. However, girdling and frilling may be combined with herbicide treatment for greater effectiveness (see girdle treatment/stem injection method).
How it works
Girdling or frilling a woody plant, sometimes also called ring-barking, involves removing the protective outer bark and the vascular tissue directly under the outer bark in a ring around the entire trunk. Girdling disrupts the ability of a woody plant to move water and sugars between the roots and the shoots/stems, and eventually kills the plant above the girdle, though regrowth may occur below the girdle. Healthy, mature trees can take several years to die if girdled (Kilroy and Windell 1999).
Methodology in Detail
To girdle a stem, a bladed tool is used to make a cut all the way around the circumference of the stem or trunk. The cut should be deep enough to completely penetrate the outer and inner bark (cambium). A second cut is made 3-4” above and parallel to the first, again all the way around the trunk. A bladed tool is effective at cutting or prying the inner and outer bark away between the two parallel cuts (Kilroy and Windell 1999).
A frill is a specific type of girdle made to small and thin-barked trees where the girdle is made with downward cuts with a machete or hatchet, and the bark is left attached at the bottom of the cuts creating a frilled appearance (Stelzer 2006).
Girdling is most effective and easiest to perform in the spring or early summer when root resources are lowest and when the cambium is active and moist (Kilroy and Windell 1999).
It may be possible to kill mature individuals of certain large tree species by girdling if they are not able to produce new growth below the girdle fast enough to feed large root systems. Large tree species that are not known for vigorous root sprouting such as Norway maple, Amur cork tree, Siberian elm, and white mulberry are the best candidates for girdling.
Certain species sprout from the entire root system in response to stem damage. Girdling may increase the density of the infestation of these species and is not recommended. Species known for aggressive root sprouting in response to stem damage include black locust, white poplar, tree-of-heaven, Russian olive and Asian bittersweet. However, recent research indicates that regrowth of black locust following girdling is less severe than regrowth after cutting and less severe in black locust than in tree-of-heaven in the same habitat (Hoshino et al. 2021).
Girdling is also impractical on multi-stemmed species.
Thin-barked species can be frilled using a machete or hatchet. Frilling of dense-wooded species should not be attempted for safety reasons (Stelzer 2006). Thicker barked species can be girdled using a hatchet or a single-bladed axe to make the cuts and a chisel to pry off the bark. It is less labor intensive to girdle thick-barked species by making the ringed cuts using a chainsaw (Stelzer 2006).
A team from the U.S. Forest Service’s Technology and Development Program evaluated girdling trees of varying size with a hand axe, a chainsaw, a specialized hand tool, and a specialized power tool. Overall, the laborers preferred the chainsaw for making cuts and the specialized hand tool for removing bark between chainsaw cuts. The chainsaw was most efficient for larger trees. The specialized power tool was most efficient for smaller trees, despite being more difficult to use. The hand axe was considered the least efficient and the most dangerous tool evaluated (Kilroy and Windell 1999). Operators should follow OSHA training and personal protective equipment recommendations for chainsaw use.
If invasive plant seeds are likely present on site (e.g., the plants being girdled are fruiting or have fruited previously), all equipment and operator clothing and footwear should be cleaned before leaving the site to prevent spreading invasive plant seeds to new locations.
Any invasive species treatment needs to be monitored in the years following treatment. Regrowth below the girdle should be anticipated following the girdling of any woody invasive species.
- Hoshino, Y., Fukamachi, A. & Hasegawa, N. 2021. Girdling of young Robinia pseudoacacia trees on the Tama River terrace, central Japan. Landscape Ecology and Engineering, 17: 85–93.
- Kilroy, B, and K Windell. 1999. Tree girdling tools: Part 1, Part 2, Part 3. United States Department of Agriculture, Forest Service, Technology and Development Program.
- Stelzer, H. 2006. Removing unwanted trees from your woodland: Part 1, Part 2. Green Horizons, University of Missouri Extension 10 (1 & 2).
Header Photo: Stephen Packard via Vestal Grove blogspot.com