Ginkgo leaves in autumn

Ginkgo leaves in autumn

Cities are heating up because of a combination of climate change, the urban heat island effect, and a loss of urban tree canopy cover. We can mitigate some of these effects and increase the resilience of urban environments  if we plant more trees. The wrong choice of trees, though, can reduce urban biodiversity and may make cities less resilient.

There are few trees more glorious than ginkgo in the autumn. It is easy to overlook how abundant ginkgo trees have become in our cities until we see the blaze of yellow up and down the streets.

Ginkgo trees on an urban greenway

Ginkgo trees on an urban greenway

As most people know, ginkgo is an ancient tree, found worldwide in the fossil record but today only found in cities and in a tiny area of China, where its survival has probably depended on Chinese monks and botanists for thousands of years (See Peter Crane’s marvelous book Ginkgo: The Tree That Time Forgot for the whole story).

Over the last 150 years, ginkgo has found a place for itself in cities throughout the world’s temperate zones. It is tolerant of air pollution, which was probably the attribute that made it so popular. It also handles other urban stresses well, from soil compaction to excess salt. Ginkgo is almost entirely free from the insects and diseases that beset other trees in urban environments.

Ginkgo street trees

{/caption] Ginkgo street trees

And therein lies the conundrum of ginkgo – it seems to be such a perfect urban tree that we plant them by the millions.  In my city, Lexington Kentucky, we almost seem to have an obsession with ginkgo.  All the pictures on this page were taken within a few blocks of the center of town (click the pictures for a gallery).

If all we cared about was shade, ginkgo might be a good choice. But urban biodiversity is also important. Trees in urban areas can support many other species – birds, small mammals, insects. In fact, a highly diverse urban canopy can appear to many organisms as a forest.  Cooper’s hawks are forest birds that have become quite abundant in cities, and there are several nesting pairs in my urban neighborhood.

Fleshy seeds of female ginkgo

The fleshy seed of female ginkgo is not technically a fruit.

Ginkgo may not be a good neighbor for other species. I have carefully inspected a number of ginkgo trees in my neighborhood this summer. It is remarkably difficult to find insects on ginkgo trees. Douglas Tallamy, in his excellent book Bringing Nature Home, says that an urban oak may host over 500 species of caterpillars while ginkgo hosts only one.  Ginkgo seeds, with their strong odor that many people find offensive, are probably adapted to be distributed by carnivorous animals, but in urban area, only squirrels will eat ginkgo, and it is not a preferred species for them.  Acorns, hickory nuts and other native fruits are much preferred.

Not surprisingly, birds avoid ginkgo as well. Most resident birds spend time in trees where food is available. Since there are no insects in ginkgo, birds tend to avoid them. This summer, I only saw birds in ginkgo trees as casual visitors, flitting through on the way to somewhere else.

The genetic diversity of planted ginkgo trees is also low. Ginkgo in China appears to originate from only a few remnant populations, suggesting that the species has been through a genetic bottleneck of very small populations in only one or a few geographic areas.  In urban areas, the requirement for male trees, to avoid the offensive odor of females, means that only a few clones are planted, further reducing genetic diversity.  A city that contains thousands of ginkgo trees may in fact contain thousands of copies of a few individuals. While ginkgo is currently not troubled by pests and pathogens, having only a few clones is a risk for future problems.

I love ginkgo trees, as most of us do. But ginkgo is not helping to create diverse, resilient cities. Instead of endless planting of ginkgo, we urgently need to diversify our urban forests with diverse plantings of seedlings of many species.

We need to prepare our cities for climate change, and greatly increase not just our urban forest canopy, but our urban forest diversity.  We have more than enough ginkgo trees now. Let’s resolve to stop planting them.

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40 Responses

  1. Bill Fountain says:

    Thank you for your insight on avoiding the further use of ginkgo in the built environment. However, I must take exception with your position as stated. The urban environment is certainly less hospitable to both flora and fauna than native habitats. We plant trees in the urban environment for the multitude of human benefits, wildlife being only one. Urban biological systems are far more complex than simplistic statements will allow. Rather than avoiding the use of ginkgo in the urban environment, I continue to encourage the practice of matching the species to the site. Ginkgo is one of our toughest, most adaptable, most attractive and structurally stable species for sites where other species fail to thrive or fail structurally endangering human life and property. The absence of biological pests (e.g. aphids, scale, and mealy bugs) is a plus in parking areas where reflected light and heat is an issue as is dripping of honeydew and the subsequent formation of sooty mold on cars and other property. With limited municipal resources for urban tree care it makes economic sense to use this and other species that will allow us to stretch otherwise limited financial and personnel resources. With the alternative choice of having fewer trees and trees with increased potential for failure; my vote will be for the ginkgo every time. Rather than stopping planting ginkgoes we need to be more diligent about where we plant them and to avoid the use of monocultures of ginkgo or any other species. Rather than avoiding the use of ginkgo in the urban environment we should be reserving it for use in areas where we cannot tolerate diseases, insects, and the wildlife that are attracted to these food sources. It is more of a street tree than a park tree; a species for poor growing conditions where most of our beautiful and environmentally natives are unable to thrive.

  2. Tom Kimmerer says:

    Thanks for your comments, Bill (for other readers, I should point out that Bill and I live in the same city, Lexington, KY).

    Your comments about my "simplistic statements" are a perfect illustration of what is wrong with industrial horticulture. I will have a column soon about the difference between urban forestry and horticulture. Suffice it to say for now that forestry strives to increase biodiversity, while horticulture strives to decrease it.

    We can look at the many tales of woe that industrial horticulture has visited on our cities:
    – Endless duplication of a small number of clones, so that, rather than having thousands of genotypes from planting seedlings, we have a huge number of copies of few genotypes.
    – A long-term proclivity for introducing large numbers of poorly-behaved species, such as callery pear, bush honeysuckle, wintercreeper- the list is practically endless.
    – A failure to learn from past mistakes. The devastation of Dutch elm disease in cities with too many elms should have taught us the benefits of diversity, but instead, cities repeated the same mistakes over and over – pin oak being just one example. There is an old comedy routine where a man is asked if he has learned from his mistakes and he replies "I have learned from my mistakes and believe I can repeat them exactly." That is modern horticulture.

    You say that we should plant more ginkgo because the urban environment is inhospitable to other species. The answer is to make our planting sites more hospitable. You praise the virtue of ginkgo for having no insect pests, but in fact it has no insects period. I encourage you and your horticulture colleagues to pay head to Doug Tallamy's fine book Bringing Nature Home. Instead of making our cities less diverse and less hospitable to wildlife, we should be inviting wildlife, including insects, into our cities by planting appropriate trees. An oak (whether native or not) can host up to 500 species of insects, and therefore attract birds and small mammals. A ginkgo is a biological desert that happens to provide some shade.

    If we stop planting ginkgo trees, or greatly reduce the frequency with which we plant them, there will still be plenty of them because of our current overplanting. Rather than avoiding natives because it is inconvenient to find a niche for them, we should use the urban landscape to make conditions more hospitable to beneficial trees.

    • J. Ayers says:

      This article is spot on. Any ginkgoes are too many in North America. Humans’ endless urban sprawl and intensifying agriculture mean every tree planted needs to be a native species with high wildlife value, period.

      If you want a plastic tree instead then plant one of those. Don’t pretend it’s about green space, though. It’s purely about vacuous self-defeating convenience.

    • Bonnie List says:

      Tom Kimmerer I agree with you completely.

  3. Troy says:

    You honestly think gingko trees are over-planted in Lexington? Oaks, young & old, everywhere I look…maples galore…gingko, a rarity. If you are referring to the relatively young gingko trees planted in downtown Lexington….give the city two or three years and they will cut them all down (likely at your advice) and plant something new. I too believe diversity is the key, but I feel we have room for a quite a few more hundred gingko trees in our beautiful city…I personally pray that
    many of them survive to maturity, better yet, old age.

    • Troy, while I can’t fault you for your aesthetic preferences, I’m afraid this attitude reveals a basic misunderstanding of what Dr. Kimmerer is saying. Ginkgos, lovely though they may be, are not conducive to a healthy biome in this part of the world. Personally, I’m a big fan of lush, green grass, but here in LA that is a serious waste of water. We can’t continue planting it and watering it because we do not have the climate (or the water) to support it.

    • Tom Kimmerer says:

      Troy, thank you for your comment. I suggest that you look in the area around Rose Street/Elm Tree Lane and adjacent streets. The city has planted several hundred ginkgo trees. That makes this area essentially a biological desert, inhospitable to lepidopterans (moths and butterflies) and other insects, and also for birds. The more we create such low-diversity areas within our cities, the more the total biodiversity of the city declines. So it is not really a question of the total number of ginkgo trees in the city, but of their distribution. By the way, you may want to check your spelling – it is ginkgo.

  4. Lee S says:

    I am no expert, but I tend to agree with Bill. I am aware of a considerable number of ginkgo trees in the Ashland Park area (1 street, in particular) going back over 75 years. But outside of downtown Lexington, I don’t see near as many gingkos as I do oaks (particularly pin oaks) and maples. Now I admit, I do not claim to know what trees have been planted in downtown in recent years in areas of rebuilding. But if there has been a resurgence of the gingko in recent years, I say, good!
    Depending on the subdivision, it’s age and location, I would wager there are several types of trees that have been overused much more heavily than gingkos. If you live in the Chevy Chase area, you must be aware of all the pin oaks! Then during baby boom years, when middle income homes were spreading like wildfire, so was the use of silver “water” maples. Many homeowners replaced these over the years with red maples and sugar maples. There were also a lot of locust trees around the same time.
    Then there was the trend of planting flowering crabs and other flowering trees, plums and, of course, the Bradford pears– so desirable for awhile for there shape and blossoms– until they started splitting! Another unfortunate trend was planting magnolia trees, also spruce trees, right up against houses with no allowance for root growth.
    But I digress… Mainly I wanted to point out that I feel the pin-oaks and maples have been used much more than the gingko, and many are currently struggling. I don’t know if they suffer from a common disease or if it is a combination of age and stress, but we are in danger of losing a lot of our 50+ year old trees, If there has been a resurgence of the gingko, it may be because of its lack of problems. I know in my area, we are currently needing to replace some of our trees. It would be helpful if, rather than merely criticize the gingko, you could make suggestions of suitable replacements on your opinion.
    Your suggestions are most welcome!

    • Tom Kimmerer says:

      I don’t disagree with anything you say. However, I think you somewhat miss the point of the article. The problem with ginkgo is that, as a non-native tree in a genus unrelated to any North American trees, it is not hospitable to all the organisms that live on and in trees and thereby increase biodiversity in our urban forest. All the other trees you mention, regardless of their other failings, are of native species and genera, and therefore can support thousands of species that live on and in them. Even callery pear (also called Bradford), while not native to North America, is in a native genus, Pyrus.

      The choice of replacement trees depends very much on site conditions. You would not want to put a bur oak between the street and sidewalk because it will be too big. LFUCG has a recommended species list available, which may provide a good starting point.

  5. I notice that gingko is on the list that you linked to.

  6. Arnold says:

    Thank you for the excellent discussion. At risk of over simplification, it seems this is primarily an argument of native vs non native. And designing the overarching goals of a sustainable urban forest. As a city planner, this is a tough one. Most cities have precious few dollars to devote to trees. The choices must be well thought out and planned. Survivability, limiting your maintenance costs, promoting ecological diversity, aesthetics all factor into the equation. I always lean towards natives, ecological diversity and avoiding monoculture installations along a single street. However, a quaint neighborhood street lined with Ginkgos in the fall sure is beautiful!

    • Tom Kimmerer says:

      As I said in my article, I certainly agree that a street lined with ginkgo trees is lovely, but having all streets lined with genetically identical trees is not. In spite of huge efforts and expense to improve urban forests, the majority of cities are losing canopy cover. In most cities, street trees don’t survive long enough to pay, in environmental benefits, for their planting costs.

  7. Dave P. says:

    Is it possible to plant a vine on the Ginkgo trees to bring some bio-diversity? If so, what kind of vines won’t take over/strangle it?

    • Tom Kimmerer says:

      It is not a good idea. Plants that climb trees are often harmful to the tree. They add weight to the tree as they climb, and that weight can eventually cause the tree to fail.

  8. Jim says:

    OK then what SHOULD I plant, and looking for a tree that will be about 10 feet from my house?

    • Tom Kimmerer says:

      I can’t make a generic recommendation. I suggest you consult your city or states urban forestry program, which will often provide lists of recommended trees of different sizes.

  9. Cynthia says:

    Great article. I saw an article titled, “would you want a 70 foot statue in your yard?” How about the same statue lining your street? A ginkgo tree in North America is like growing a 70 foot concrete statue instead of a tree. Might be lovely but it might as well be made of concrete.

    • Tom Kimmerer says:

      This is a great observation. Ginkgo trees are slightly better than statues – they photosynthesize, store carbon, provide shade, and reduce stormwater runoff. From a biodiversity standpoint, though, you are correct.

  10. Cynthia says:

    Dave P. I like the vine idea-my city (Seattle) planted two on the planting/parking strip in front of my house.

    It’s true-I have a bird sanctuary -with so many birds, but not a bird ever on my ginkgo trees.

  11. Jim, for a tree 10 feet from your house, I recommend serviceberry. Ostrya virginiana and Carpinus caroliniana are underused smaller native trees that I like, too. A dogwood or a crabapple would work, also.

    • J. Ayers says:

      Bradford pears drive me crazy. They’re useless for pollinators, not particularly attractive, invasive, and like to split. Of course, developers in my area just adore them.

      Industrial contractor mindset = plant the least-worthy species, with only vacuous decoration in mind — never wildlife value. Who needs nature when you can grow corn and soy, right?

  12. JR in Raleigh says:

    Negative and not helpful. Instead of trashing useful and popular ginkgo trees, why don’t you offer an alternative that stands up to the stresses nearly as well?

  13. Dena lentz says:

    Now I’m depressed
    I want a ginkgo
    My favorite tree

    My least favorite is a pin oak

  14. Lee Ann says:

    Despite this discussion, I am planting a Ginkgo today, a sapling, so I have no idea of sex but I have always wanted one. I am in a rural area, lots of trees so I am not going to worry about a thing and just enjoy.

  15. Dena, no reason for depression. There are more trees than gingko and pin oaks. If I had to pick a favorite it would be southern magnolia. Those gorgeous leaves! Those fabulous flowers with a scent to die for! Regal! White oaks are also magnificent. The honey locust outside my former house was a migration stop for a zebra warbler, who stayed for at least three weeks before moving on. Sugar maples, river birch, willow oak, sweet gum, sour gum… those last two have great fall color. We have many, many beautiful native trees.

  16. Sherri Bourdage says:

    Any suggestions on what to do with the ginko fruit from the trees? They may not be suitable to hanging over sidewalks as the fruit drops and is slippery and public safety hazard. Are there recipies for ginko?

    • Tom Kimmerer says:

      You should not handle ginkgo fruits. Although the nut at the center is edible, and prized in Chinese cuisine, the pulp on the outside can cause severe skin irritation, causing a rash like poison ivy. It is best to pick them up with a shovel and dispose of them, or let them rot in place.

  17. The fruits don’t seem to be good for much. From the Washington Post:

    Larger than pistachios but with thinner shells, the nuts are high in niacin, starch and protein, but low in fat. However, they also contain toxins.

    Cooking them will break down bitter-tasting cyanogenic glycosides, but the nuts will retain the heat-resistant compound 4-methoxypyridoxine, which depletes vitamin B6. Children are especially susceptible to the toxin.

    Roasted nuts are a translucent jade green with a soft, dense texture. They taste like a combination of edamame, potato and pine nut. Some people say they’re reminiscent of chestnuts.

    East Asians consider the nut a delicacy and use them in desserts, soups and with meats; but the Hong Kong government’s Centre for Food Safety cautions people about the nut’s toxicity, advising them “not to consume more than a few seeds at one time.”

  18. Patrick says:

    My grandparents had a female gingko tree. Picking up the fruits was a task often delegated to grandchildren, and we picked them up with our hands, not shovels. Never got a rash, though we did wash our hands afterwards.

    It is a beautiful tree now, lovely in all seasons. I’d take this column’s advice of planting something else if I was planting an entire subdivision, but then a whole subdivision should not be planted in just one kind of tree anyway.

  19. Al VanB says:

    One might consider planting a Japanese Maple, at 20 years pls is a 20’ majestic try with grey branches and beautiful burgundy leaves.
    I also have the Ginko a Sumac and a Tulip tree.

  20. Cary Opteris says:

    In Raleigh, NC, I’ve only noticed ginkgoes planted at one gas station, and not along any roads. They are a columnar variety. I prefer to avoid planting the same tree in a row because with most trees it makes them vulnerable to disease. Even without that risk, it is a missed opportunity to provide for wildlife. I would like to see serviceberry trees and black gum (not more sweet gums!). Some sassafras trees would be nice, although I hear they are not long-lived.

  21. Riesah Prock says:

    In my small town, they have planted far too many female green ash trees, which produce millions of seeds that are highly invasive, difficult to root out once they’ve above 5″ tall, roots are hard and hold on tight, thicken like the trunk of the tree. I must have pulled well over a thousand seedlings looking to root in my back yard alone. Green ash is one of the hardest woods. I don’t recommend it, unless you’re in the country, far from urban settings.

  22. WeThemYou says:

    Cypress are nice as long as they aren’t planted next to drainage or septic areas. Large, long lived and loved by birds and squirrels. As for Ginkgo trees in the city. I get what you are saying but no city I have seen or lived in has the budget dedicated to “make areas more hospitable” for planting your coveted trees. Ginkgo are usually planted and survive giving at least something back. I have watched the city plant trees with no support and 50% of the oaks or whatever die just because of careless planting practices. (Dead of summer 95+ temps) The cities don’t care about what you want done. They just want something green in a hole. Unless you are willing to use your magic resources to change their mind it is best to have something that will live as long as possible. Better to have a grove of ginkgo than a street with 10 oaks, spaced 2 or 3 spaces apart because they don’t bother to replace the ones that were cut down. And 6 of the remaining ones are marked to be cut down because of disease and are a hazard. Your idea of native trees and diversity is good, it really is the problem is that the city isn’t going to till up the soil and amend it with lovely loam and manure to make it hospitable for the natives. They……don’t……care…… Your turn, I’m sure you will quote for me to read some study that the cities obviously aren’t going to read. If you can’t force them to supplement the soil then Ginkgo it what you will get. That or Myrtle. Jeez that’s all we have, Ginkgo and Myrtle.

  23. VSM says:

    I actually live on Catalpa Road in Lexington, KY–ironically, lined with Ginkgo trees…I was pleased to have participated in this project (see link below) that uses the Ginkgo leaves to study climate change. I am thankful that I have been able to glance out my windows for 30+ years to see these amazing trees (50+ years if you count the view from my childhood home). While the Gingkoes are in abundance on my street, I am also fortunate to have 7 other species of trees on my lot alone–the surrounding neighbors have the same. I am glad to read that others are mindful of planting a variety of trees, for all the reasons mentioned in the posts above. I would also never give up my Gingko, ‘stink bomb’ seeds and all!

  24. ALICE I ALLEN, says:

    I have searched for an answer to this question and cannot find. Is the fruit of the ginko harmful to cattle? We have a tree in back yard and was loaded with fruit. What to do with the fruit? Can we put in the pasture where there is cattle till it can be burned? Will it harm the cattle if they decide to eat some?
    Thanks for any help you can give me.

    • Tom Kimmerer says:

      There are two factors that suggest that you should not expose your cattle to ginkgo fruits. While ingesting a few ginkgoes is harmless, large quantities could be toxic. The strong odor of ginkgo comes from butyric acid, the same chemical that creates the smell of dirty sweat socks. Butyric acid can also form in improperly stored silage, and veterinarians recommend against feeding cattle with contaminated silage. Ingestion of more than 50g of butyric acid per day is considered hazardous to cattle.

      The second factor is less well understood. Contact with ginkgo fruit causes contact dermatitis in many people after repeated exposure. This is similar to the effect of poison ivy. I don’t know what the chemical agent is, or whether it affects cattle.

      Taken together, I don’t think a little casual exposure of your cattle to ginkgo is harmful, but I would not dump the excess fruit in their pasture. I have raised cattle and know that exposing them to a novel food is often not a good idea. If you have a compost bin, you could compost the ginkgo and use it as fertilizer. Otherwise, you could just let it rot in place.

  25. ALICE I ALLEN, says:

    Thank you so much for taking the time to answer my question. We dumped the fruit along with the leaves on a large brush pile. My husband intends to burn the brush pile and thinks it will burn the fruit up. Meanwhile we are keeping the cattle out of that lot. We just had a 50 ft. dead tree cut down, so have a rather large brush pile along with trimming from other trees as well.

    • Tom Kimmerer says:

      I recommend not standing downwind from the burn pile. I don’t know for sure, but a lot of people have strong reactions to ginkgo seeds, and the smoke may be problematic. I know people who have been severely injured by smoke from burning poison ivy, so caution may be a good idea.

      If you are on Facebook, you might want to friend me. There are a number of excellent Facebook groups about trees that you may find interesting.

  26. Doug Meadows says:

    Thank you for the well written article with new ecological insight! I read the encyclopedia-like book “Ginkgo” but don’t recall the biodiversity aspect being covered. (Only indirectly, by its reference to no insect “problems”.)

    I applaud industrial horticulturalists and their contributions to out landscapes in our imperfect world. Imagine what our neighborhoods and cities would be like without them?

    Here in Fort Collins I have planted way over 1000 trees and shrubs of watered by two miles of drip irrigation . . . which is still inadequate. I am quite envious of Lexington rainfall!

    I will soon plant my first ginkgo from a whip I potted February 2020 and it and grew it outside (but overwintered it in the garage). I am planning to plant it on the side of our road drainage ditch to take advantage of the extra rain and snow.

    I now understand but accept that planting a ginkgo is mostly an aesthetic indulgence . . . but one that comes with arguably the most unique genetic legacy.

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