Girdled and Topped Trees
Looking around the garden, you might think we don’t like trees. NOTHING could be further from the truth. All of these trees were American Ash, and are either dead or well on their way. They were all infested with a tiny, but deadly, insect from Northern Asia, the Emerald Ash Borer (EAB).
EAB was inadvertently imported, but the Asian predators and pathogens which keep it in check, were not. This lack of biocontrol is one of the main factors in exotic species success. Entomologists often try to find these absent control species, but they had no luck in the case of EAB.
Once a tree is infested, little can be done. If caught early, injecting the tree with a pesticide, using the Mauget injection technique, will buy it some years. Unfortunately, the pesticide the trees are injected with is not species specific, and so, it is contrary to our goal of maximizing biodiversity.
That leaves us with minimizing the damage and replacing trees!
Dying ash trees rarely just topple over. Usually they fall apart, piece by piece. In a densely planted or woodland landscape, a least harm solution is to let them do just that. Trees that are girdled are unable to move water to upper branches. When those branches fall, they should be lighter and cause less harm. Trees that had valuable “targets”, like Umbrella pines, under or near them, were topped. Topping is less expensive than removal, and the remaining trunk is valuable as food and habitat to birds, small mammals and insects.
A much happier topic is tree replacement. This is a great opportunity to really increase the diversity, and therefore, the resilience of our canopy. We’re transplanting, or adding, native and a few regionally native species. These include Red Elm, American Linden, Yellow Birch, Shagbark Hickory, Butternut, Box Elder and Kentucky Coffee Tree, to name a few. Obviously, it will be more than a few years until these new trees are adding much shade. But in the long term, EAB, just may, benefit the gardens.