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Tom Kimmerer, PhD

@tomkimmerer.bsky.social

41K followers 5.3K following 8.5K posts

I am a tree scientist and botanist writing about relationships between trees and humans including climate change. A Fulbright Scholar, Author of Venerable Trees and more books in progress. Read about trees here: ourtrees.substack.com.

Posts Replies Media

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 27/09/2026

Joshua trees are uncommon, with a limited range, and threatened by climate change. Read what scientists are doing to stabilize the species.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 26/09/2026

This old bur oak, Quercus macrocarpa, on the University of Kentucky campus is one of my favorites for its fine form. It predates the existence of the university by several hundred years. Unfortunately, that building behind the tree was filling with people and the parking lot was jammed.

An ancient bur oak in front of a building on the University of Kentucky Campus. Photo by Tom Kimmerer

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 07/09/2026

Autumn is arriving and trees are preparing for the cold. This is not a simple response of trees to changing weather, but a complex series of physiologic events in trees that begins in early spring. Have a look at Our Trees.

Trees End Their Season

A complex series of events prepare trees for cold

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 03/09/2026

Wendell is no longer physically with us, but his writings and his influence on our society will continue. The threats to our planet are severe, but, inspired by Wendell, we will push back and care for our Earth.

ourtrees.substack.com

Wendell Will Be With Us

I first encountered Wendell Berry’s writing when I was 19.

Reposted by Tom Kimmerer, PhD

Brian J. Enquist @bjenquist.bsky.social · 31/08/2026

Thrilled to announce that my department - Ecology and Evolutionary Biology - at the U of Arizona will likely be hiring for a tenure-track position in "Population and Community Ecology" this fall. Watch this space for more details and official announcements coming soon ... #Ecology #EcologyJobs 🌐🌾🧪

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 25/08/2026

At Our Trees, we are discussing pawpaw, which has become very popular in recent years. Are you a pawpaw fan? Read the story and take the quiz.

ourtrees.substack.com

The PawPaws Ripen

The rise of America’s largest native fruit

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 24/08/2026

It’s the anniversary of my major career change that connected me to trees for life. Read about it at Our Trees.

Tom Kimmerer (@tomkimmerer)

This is the anniversary date of a decision that changed my path in life. It is the day that I chose to spend the rest of my life learning from trees. I made a start in college that did not work, then...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 21/08/2026

Here is an exciting postdoc opportunity.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 20/08/2026

This is a wonderful opportunity!

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 12/08/2026

Climate, Lightning, and Trees Lightning is a major cause of death of large trees and the climate crisis is increasing lightning frequency. Read more about what lightning does to trees at Our Trees.

ourtrees.substack.com

Climate, Lightning, and Trees

Climate change is increasing the rate of lightning strikes on trees, many of which are fatal. We describe the causes of death and injury to trees from lightning.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 09/08/2026

In a seminar when I was a grad student, the lecturer said "When digging for potatoes, it is not so important to dig like hell as it is to dig where the potatoes are." That has been the guiding principle of my work in science ever since. It is written on the first page of each of my notebooks.

People digging for potatoes in a field.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 31/07/2026

This amazing basswood, Tilia americana, came up in a discussion, and I thought you might enjoy it. Despite its setting, this is not a planted tree and greatly predates this cemetery. I hope you enjoy it.

Tom Kimmerer (@tomkimmerer)

Yesterday’s basswood leaf prompted a comment from Alder Burns regarding this amazing species, American basswood, Tilia americana. Basswood is a species of linden. Here is a picture of the tree that ga...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 27/07/2026

Looking closely at a tree can be quite rewarding. The white flower of this flowering dogwood is not really a flower, but a complex inflorescence containing dozens of tiny green flowers. The tree does this not to trick us, but to attract pollinators to its tiny flowers. Have a look.

Tom Kimmerer (@tomkimmerer)

Trees can be tricky at times. Look, for example, at the beautiful white flower of flowering dogwood, Cornus florida. In common parlance, it is a flower. But in the reproductive life of this tree, the ...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 26/07/2026

Here is a brief story about the cover of my first book Venerable Trees and why the blue ash tree on the cover is significant.

Tom Kimmerer (@tomkimmerer)

This is the cover of my first book, Venerable Trees. The book designer did a wonderful job, selecting this picture from several dozen that I provided. This is a large blue ash, Fraxinus quadrangulata...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 24/07/2026

I visited my local bison herd this morning. It is good to remind ourselves that bison are not strictly western animals. They were the dominant herbivore of the Bluegrass and created our woodland pasture ecosystem. More at Our Trees.

Tom Kimmerer (@tomkimmerer)

I took advantage of today’s fine weather to visit my local bison. You may think of bison as western animals, but they were first seen by European settlers in what is now downtown Washington DC and onc...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 21/07/2026

One of the most beautiful small trees in our flora is staghorn sumac. It grows in dense clusters in woodland edges and bears beautiful and useful red fruit from late summer through winter.

open.substack.com

Staghorn sumac is a beautiful small tree that forms dense thickets in woodland edges. The fruit makes delicious drinks and a popular spice.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 11/07/2026

On my morning walks, I often see trees, especially black walnuts, covered in mistletoe, Phoradendron leucarpum. Mistletoe is abundant in the Bluegrass on many trees, especially black walnut.

Tom Kimmerer (@tomkimmerer)

On my morning wanderings, I often see black walnuts covered in mistletoe, Phoradendron leucarpum. It is common on walnuts and other hardwoods, especially in the Bluegrass. Mistletoe leaves are green a...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 11/07/2026

Professor Joyce Onyenedum is a skilled botanist, a professor at NYU, and a great storyteller. If you are looking for more well-told stories about plants, you want to visit her YouTube channel. Check her out!

Professor Joyce Onyenedum

Welcome! This channel is dedicated to sharing my love of plants with anyone who will listen. My name is Dr. Joyce G. Onyenedum, and I am a Botany Professor at New York University in New York City. ...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 10/07/2026

Our wet summer is allowing many trees wo produce late flushes of growth, often with pale leaves. This is quite unusual in chinkapin oak, a slow-growing tree. Here is a huge chinkapin oak in a woodland pasture in the Bluegrass, and a second flush of growth with pale leaves.

Tom Kimmerer (@tomkimmerer)

In my part of the world, The Bluegrass, this is an extraordinary summer to be a tree. I don’t recall a summer with such frequent rain, and the trees take advantage of wet summers like this produce flu...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 08/07/2026

This is the oldest known painting of a tree. It is on a rock wall in Serra di Capivara National Park in Brazil. The painting is at least 20,000 years old. Learn more at Our Trees.

Tom Kimmerer (@tomkimmerer)

Given the long and essential relationship between trees and hominins (humans and their ancestors), and the wide use of trees in art, here is a surprise: cave paintings and rock art is ancient but gene...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 06/07/2026

Encouraging news came this week of a reinvigorated program to restore blight-resistant American chestnut. If successful, this would be the biggest news for our eastern forests since the chestnuts were wiped out before 1950. This is reason for optimism.

Tom Kimmerer (@tomkimmerer)

The Return of American Chestnut? American chestnuts have been a part of my life since I was a kid. We would buy fresh roasted chestnuts from street vendors in Baltimore. I didn’t know it but by the t...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 05/07/2026

The Trump regime wants to destroy American science. One big step to maintain our strong science just happened, as Dr. Neil Shubin became President of the US National Academy of Sciences. Shubin is an important paleontologist and an equally important interpreter of science for the lay public.

Tom Kimmerer (@tomkimmerer)

The Trump regime is working hard to destroy American science, corrupt our science institutions, steal our natural resources, and drag medicine back by a century or more. The good news is that American...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 05/07/2026

On a warm, breezy morning before the rains come, we like to hang the kids out to dry.

Tom Kimmerer (@tomkimmerer)

It will rain for much of this week, but for now the warm breeze is allowing us to hang the kids out to dry. Photo by Tom Kimmerer

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 04/07/2026

The Indonesian volcano Gunung Merapi is seen just after midnight on July 4 2026, in celebration of the natural world, instead of our political world.

Tom Kimmerer (@tomkimmerer)

Last night, at the stroke of midnight on the 4th of July, my favorite volcano,* Gunung Merapi in Java, Indonesia, decided to celebrate with a huge lava flow, shown live all over the world. I think o...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 02/07/2026

Here is a magnificent kingnut, Carya laciniosa. Kingnut was the original English name, but it was later called shellbark hickory. The original name is far more appropriate. This is an exceptionally large and elegant specimen in a woodland pasture, with a blue ash behind it.

Tom Kimmerer (@tomkimmerer)

Let’s have a look at another uncommon tree. Kingnut, Carya laciniosa, is an uncommon tree in the midwest, especially on limestone. It is a spectacular tree that is large in all its aspects. The tree i...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 01/07/2026

Here is some late evening Bluesky for you, along with a blue ash tree and a moon. Enjoy!

Tom Kimmerer (@tomkimmerer)

A blue ash tree at night. Blue ash, Fraxinus quadrangulata, is common on limestone uplands throughout the midwest, especially in the Bluegrass. The tree is named for the blue dye that can be extracted...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 26/06/2026

If you were making beer in Kentucky in 1779, you did not have access to the ingredients we use now. Instead, settlers used honeylocust and persimmon fruit. I have made beer according to the recipe in the linked story and it was quite good. Check out the story at Our Trees.

Tom Kimmerer (@tomkimmerer)

Making beer in 1779 In the early days of colonial settlement of Kentucky, two precious beverages were coffee and beer. Coffee was an important trade item brought by traders coming across the mountain...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 25/06/2026

For your enjoyment, here is an ancient bur oak, Quercus macrocarpa, under a full moon on the University of Kentucky campus. Photo by Tom Kimmerer

Tom Kimmerer (@tomkimmerer)

An ancient bur oak, Quercus macrocarpa, under a full moon on the University of Kentucky campus.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 24/06/2026

Late season flushes of growth in trees, leading to pale yellow-green foliage, used to be an uncommon late summer phenomenon. Now, it is happening every year, a result of climate change. Read about it at Our Trees.

open.substack.com

Climate Change and the Summer Flush in Trees

Trees sometimes produce a second flush of growth, which is often pale compared with the first flush. This used to be a rare phenomenon but now occurs every year, probably due to climate change.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 21/06/2026

The summer solstice is not just a calendar entry. It is a signal to all the trees in temperate zones in the north to begin preparation to survive the winter cold. Yes, today, the growing season ends for most trees. Have a look at the trees you walk by. Most of them have probably already set buds.

Tom Kimmerer (@tomkimmerer)

Today is the summer solstice. Perhaps it is just a date on your calendar, but it is a signal occasion to temperate trees: the growing season has ended. From now until next spring, most trees are doing...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 20/06/2026

Here is the current global warming stripe for the US. We are making progress toward renewable energy, but the fossil fuel oligarchy and its minions in the trump regime are doing everything they can to slow the adoption of renewables. They will fail, but every day of delay makes the crisis worse.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 09/06/2026

This is Gunung Merapi (Fire Mountain) near Yogyakarta, Indonesia from a live camera tonight. The Special Region of Yogyakarta is one of the most fascinating, beautiful places on Earth. I taught at Universitas Gadjah Madah and had the pleasure of climbing Gunung Merapi. I hope it settles down soon.

Mt. Merapi, Java, Indonesia at 2 am local time June 10 on a clear, starry night with lava flowing down the volcano. Source: https://www.youtube.com/live/z1kLiiWvm4U?si=A3nHY8eINnxoCJ6L

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 06/06/2026

The fruit flies in my kitchen always remind me of the great biologist Tom Morgan, who grew up down the street from where I live. Read about him here.

Tom Kimmerer (@tomkimmerer)

This morning, my kitchen was filled with fruit flies, Drosophila melanogaster. This is not surprising as I keep a lot of tropical fruit on hand. Fruit flies always remind me of science. As an underg...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 03/06/2026

A true story of the cobra under my desk.

Tom Kimmerer (@tomkimmerer)

The Cobra Under My Desk The morning I was late to my lab in Borneo was the morning that a king cobra took up residence under my desk. It may well be why I am still alive so I have to thank Deborah, m...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 31/05/2026

Sassafras is an important tree both for its stunning beauty and for its long history in cuisine and medicine. Have a look at Our Trees.

Tom Kimmerer (@tomkimmerer)

Sassafras, Sassafras albidum, is a tree that is deeply embedded in our culture not only for its beauty but for its long-term medicinal and culinary uses. Is there any tree more spectacular than sassa...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 29/05/2026

Baldcypress is a glorious tree in southeastern wetlands, the longest-lived eastern tree and one of the largest. It is increasingly common in urban landscapes. Do you know this tree? Take a look at Our Trees.

Tom Kimmerer (@tomkimmerer)

We have been discussing trees that have close relationships with humans. Here is one with an increasingly close association with our landscapes. Baldcypress, Taxodium distichum, is a huge, unusual tre...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 27/05/2026

I have seen many stories on Substack and elswhere claiming that almonds are a good choice for our health. This is true, but there are better choices for our planet, and the best choice is pecans.

open.substack.com

Pecans or Almonds? The choice is clear

Both are nutritious, but pecans are a better choice for our planet

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 26/05/2026

Here is another tree with a history tied to us. Catalpa is a gorgeous tree, but its native range is tiny. Due to a 19th century craze in planting this tree for railroad ties, it is now everywhere. It made lousy railroad ties, but it sure is nice to have in our landscapes. Read more at Our Trees.

Tom Kimmerer (@tomkimmerer)

Catalpa is another tree that has benefited from its relationships with humans. Originally native to very small areas in the southern US, several enthusiasts began mailing seeds to anyone who wanted t...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 25/05/2026

Osage-orange, or hedge-apple, is a tree very familiar to those of us in the Bluegrass, where it was widely planted for natural fencing and hedges. Do you find this tree where you live?

Tom Kimmerer (@tomkimmerer)

Here is another tree whose abundance and distribution is due to its close relationship with us. Osage-orange, Maclura pomifera, is certainly one such tree. Once found in a small area of Texas and adja...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 24/05/2026

Black locust is a very successful tree in our human-dominated world. It is spectacular in flower and produces exceptionally fine honey. Learn more about this amazing tree at Our Trees.

Tom Kimmerer (@tomkimmerer)

Black locust, Robinia pseudoacacia, is one of the most successful species in our modern landscape. Increased disturbance - forest clearing, farming, surface mining - favors this amazing tree. It seeds...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 22/05/2026

Do you know this spectacular little tree? It is fringetree, Chionanthus virginicus, and is one of the most beautiful flowering trees. It common in lowland forests of the Atlantic and Gulf coastal plains, but is abundant along the Rockcastle River in Kentucky. It is a wonderful native ornamental.

Tom Kimmerer (@tomkimmerer)

Tree flowers are usually not as showy as garden flowers, but some are quite spectacular. Here is fringetree, Chionanthus virginicus. Each small tree is decked with thousands of very simple flowers wit...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 21/05/2026

This is the view from the front porch of my home in Borneo. Now, back in Kentucky, I am thoroughly enjoying a week of rainy days, which should end our spring drought. Do you love rainy days?

View from the porch of a house on a rainy day in Indonesian Borneo. Photo by Tom Kimmerer

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 20/05/2026

People say they are allergic to showy flowers like the black locust on the left. They are looking at the wrong trees. Showy flowers are animal pollinated and their pollen is too large to cause allergies. It is nearby dull flowers like the oak on the right, wind-pollinated, that deserve the blame.

Showy flowers (left) have large pollen carried by animals and do not cause allergies in people, and are labelled Not Allergenic. Flowers with dull colors like this oak (right) have small pollen, are wind-pollinated, and may cuase allergies.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 12/05/2026

One of the highlights of life in Malaysia and Indonesia is the pasar malam, or night market. It is the vibrant social center of many communities, and is a major source of food, way better than the super market. Read about it at Our Trees (free).

Tom Kimmerer (@tomkimmerer)

Among the many joys of living in Indonesia or Malaysia (I lived in both) is shopping at the pasar malam, the night market. This is an open-air market where people, often entire families, set up a tabl...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 01/05/2026

It is Derby Weekend in Kentucky. See how horse agriculture benefits the preservation of open space, and especially of the rare woodland pasture ecosystem of the Bluegrass.

Tom Kimmerer (@tomkimmerer)

It is Kentucky Derby Weekend here in the Bluegrass, when the place goes a bit nuts. The races are in Louisville, not here in Lexington, but the Bluegrass counties of central Kentucky are where many of...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 29/04/2026

Tree sex is beautiful, complex, and intricate. Here is the first of our series on tree sex.

Tom Kimmerer (@tomkimmerer)

Tree sex is beautiful, complicated, intricate. It is also far more complicated than human sex. Here is the start of our series on tree sex.

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 29/04/2026

Red maple is one of the dominant trees of eastern forests and of urban areas everywhere. They are now coming into the season when winged seeds will fly everywhere. Have a look.

Tom Kimmerer (@tomkimmerer)

Red maple (Acer rubrum) trees have finished flowering in much of their range and are now making these amazing samaras - winged seeds. Red maple is certainly the most successful North American tree sin...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 28/04/2026

The rain has passed, the trees are growing furiously, and it's a perfect time to get out in your local park for play, like these two small guys who have recruited their dads for kite flying.

Tom Kimmerer (@tomkimmerer)

The rain has passed and it is a perfect time to get out into our local parks. These boys have enlisted their dads to get kites in the air. The boy on the left has gathered excellent sticks for his act...

Tom Kimmerer, PhD @tomkimmerer.bsky.social · 24/04/2026

Yellow-poplar or tulip tree, Liriodendron tulipifera, is one of the most dramatic trees in our flora, especially in spring. Have a look at Our Trees.

Tom Kimmerer (@tomkimmerer)

One of the most spectacular trees in our flora is Liriodendron tulipifera, which means tulip-bearing lyre tree. My botany prof said that the name tulip-tree is from the resemblance of the leaf shape t...