Casey Trees

The genus Ginkgo has been around for 200 million years, but Ginkgo biloba is the only surviving member of that line. Its resistance to pests (insects, diseases, etc.) accounts, at least in part, for its longevity.

Ginkgo Fruit

The Ginkgo is closely associated with its foul-smelling fruit. Ginkgos can fruit heavily and litter the ground in large amounts if not harvested. The unpleasant smell is due to the presence of two volatile compounds in the fruiting structure – butanoic and hexanoic acids (butyric acid is a constituent of vomit). This has earned the tree nicknames like “stinkbomb tree” in the West.

The fruit also contains gingkoic acid, and contact with this compound can cause severe allergic reaction or contact dermatitis in some people.

However, the tree has been long cultivated in the East for these same fruits, which are highly valued as a delicacy and key to long life. More recently, researchers have found that the amino acid ginkgolin, found in both the nuts and leaves of the plant, increase blood flow to the brain and enhance memory function. This has led to increased cultivation of this plant for commercial purposes.

Gender Selection

Though trees and reproductive structures on trees are thought of as male and female, they actually are more complex than a “this or that” description suggests. Populations of plants have evolved to survive over time, and can change sex as needed to ensure continued propagation of the species by ensuring an appropriate ratio of male:female plants.

Because of this phenomenon, removing all female ginkgoes and replacing them with males is likely an unsuccessful long-term strategy made more difficult to manage as there is no way to predict which trees in the population may begin to bear fruit or when that may occur.

Chemical Control of Reproduction

There are chemicals sold for the purpose of preventing or inhibiting fruit formation in landscape trees. Widespread application of pesticides to trees in public space may create unnecessary public concern and risk. Additionally, these materials have been shown to produce unreliable results here in Washington, D.C. on ginkgoes.

Recommendations

Diversity is the key to a healthy urban forest. All trees present some potential social negatives regarding leaf litter, fruit litter, conflicts with hardscape, or other issues. Ginkgo biloba is a good shade tree and should be one component of the DC tree population.

Removing all female ginkgoes and replacing them with all male ginkgoes is an expensive and unreliable strategy to manage fruit litter issues. Pesticide application to prevent fruit growth is similarly expensive and unreliable.

A program to maintain ginkgo populations where they are desired by the community, coupled with programs to remove trees in places where they cause documented health problems for adjacent residents will optimally balance social and ecological concerns.

All Arbor Issues:

• Ginkgo trees
• Powerlines
• Sidewalks
• Storm damage
• Streetcars

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