The ginkgo
Jessica Quinton
2020-07-20
This week’s tree has been consistently planted along the streets of Halifax for years. Although these recently-planted trees are still quite small, you can find larger well-established specimens in the Public Gardens (photo below, left) or on the King’s College campus (photo below, right). Its bi-lobed, fan-shaped leaves are incredibly distinctive, making this species easy to identify. In the autumn, you can see these unique leaves turn a beautiful golden yellow before falling to the ground.
Ginkgo biloba L., otherwise known as the Ginkgo tree or the Maidenhair tree, is a unique species with an interesting (and long) history. The name “Ginkgo” appears to have originated by mistake, when a German botanist misspelled “ginkjo”, a Japanese word meaning ‘silver apricot’. Ginkgo fruit does look similar to an apricot, with a grey (or silver) seed inside. Due to the way it’s pronounced, people often misspell the name as “Gingko”. The other name for this species, the Maidenhair tree, is due to the similarity of the leaves of this tree with the leaves of the maidenhair fern. However, the Ginkgo is not closely related to the maidenhair fern.
Ginkgo is often referred to as a ‘living fossil’ with a fossil record of at least 200 million years, meaning this tree species existed alongside dinosaurs. The fossils indicate that the Ginkgo has changed very little since the Jurassic era. While the leaves make Ginkgo easy to pick out in a crowd, its identification is also made easier by its lack of living relatives. No need to agonize over miniscule differences in leaf size, shape, or texture to distinguish between species (I’m looking at you, lindens!), as Ginkgo biloba is the only remaining species of Ginkgo. Its closest living relatives are the cycads, a group of trees that are often mistaken for palms and thus look very different from Ginkgo.
Is there somewhere else you may have seen these unique fan-shaped leaves? On a bottle of supplements. Ginkgo has a history in traditional Chinese medicine dating back to the 15th century. There have been many purported benefits of Ginkgo, which today are mainly derived from preparations of leaf extracts. The focus of research into the medicinal benefits of Ginkgo has largely emphasized improved cognitive function but has also examined inflammation, heart health, vision, mental illness, and respiratory ailments. However, the current body of research is inconsistent regarding the benefits (and side effects) of Ginkgo supplements and further study is needed.
Ginkgo is native to China but has been introduced around the world. It shows up time and time again on the Halifax tree-planting species list (see photo, left). If you’re wondering how a non-native species has gotten such resounding approval from our urban foresters, consider the following factors. The Ginkgo tolerates a wide range of soil types and is fairly drought-resistant, especially at maturity. It can also tolerate salt and air pollution and grow in confined spaces. Its tolerance to these conditions makes it well suited to establishment and growth in tough urban environments. Furthermore, although they are sparsely branched when younger, Ginkgos can grow to be 20-35 m in height, with a pyramidal shape that works well as a shade tree.
Ginkgo is also a relatively long-lived species and can live more than a thousand years. Their longevity has been credited to the production of an array of defensive and immune-supporting chemicals. Six specimens of this tree species even managed to survive the bombing of Hiroshima—how’s that for resilience? Ginkgos also have relatively few pests or diseases and have not been ravaged by anything similar to Dutch Elm Disease or the Emerald Ash Borer. Another checkmark for them is their low potential to become invasive, so there’s no worry about it becoming the next Norway maple.
The Ginkgo is a dioecious tree, meaning there are separate male and female trees. The males produce pollen while females produce seeds and, eventually, fruit. Beware the female Ginkgo, however. As the flesh-covered seeds drop to the ground in autumn, the decay of the outer portion releases a foul-smelling odour, often likened to that of vomit. For this reason, the city of Halifax plants only male Ginkgos.
Perhaps one of the downsides to planting Ginkgo is one common to non-native tree species: the lack of support they provide for urban biodiversity. Due to co-evolution, native tree species can provide food and habitat and other resources for a wide variety of native insects, birds, and mammals. The same is not true of non-native species, as they are typically able to support far fewer other species. However, planting Ginkgo does diversify the urban forest of Halifax itself, which is important for maintaining canopy cover in the future. The key is to avoid over-reliance on one species when planting trees in an urban environment, to prevent large losses from climate change, pests and diseases, etc., in the future.