David Sibley's name has become synonymous with birdwatching. The Sibley Guide to Birds
, The Sibley Field Guide to Birds of Western North America
, and The Sibley Guide to Bird Life and Behavior
, among many others, are some of the most respected and well-loved bird guides available today.
In his new work, which was eight years in the making, David Sibley focuses his authoritative eye on trees. Gorgeously illustrated and full of fascinating information, The Sibley Guide to Trees will dramatically change the way you look at your backyard, your neighborhood, and the larger botanical world.
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Jill Owens: How did you decide to focus on trees for this new book?
David Sibley: About seven or eight years ago, I was out on a book-signing tour promoting my newest bird guide, and I was thinking about what I wanted to do next. I decided that I really wanted to do another big book project. That's what I really like to do. I started searching around for what kind of species to cover in my next book; I didn't want to do another, more in-depth bird guide.
There were a couple of reasons that trees came to the top of the list. First, even while I was out there on the road traveling mostly in cities, I was seeing trees every day. Trees are so much a part of our everyday life, even more than birds. It seemed like knowing about trees would be something virtually anyone can put to use every day.
The other part of the decision was that I have always tried to be an all-around naturalist, and to learn as much as I could about other things besides birds. When I thought about field guides, I've always been a little frustrated with the tree guides, because they really work in a way that bird guides have advanced from many decades ago.
Tree identification makes sense because trees are so easy to approach. [Laughter] If you see a tree that looks interesting, you can walk up to it and pull out your 10-power or 20-power hand lens and study the really microscopic features, like the shape of the bud scale, or whether there are hairs on the underside of the leaf or not. There's no time limit; you can take as long as you need to identify it.
The tree guides have never really advanced beyond the stage where bird guides were 100 years ago, where you held the bird in your hand and you went through a key to figure out what it was. Modern bird guides work a lot more on simple pattern matching, just flipping the pages until you see a picture that matches. Gradually, as you use the book more and get more experienced, you internalize that, and one day you'll just look at a bird and know what it is, and not have to look it up in the book.
I wanted a tree guide that would work more in that way, having lots of illustrations and emphasizing the natural groupings and patterns of variation, so that if you're out on a walk and you saw an interesting leaf shape, or an odd fruit, or unusual bark, you could just pull out the book and flip through the pages until you found a picture that matched. I saw an opportunity to create a book that really would be something new, and would be a real contribution to advancing the hobby of tree identification through bringing in some of the advances in bird field guides that hadn't really trickled down to trees.
The way I thought of this field guide while I was working on it for the last seven years was as a tree field guide for birdwatchers. In a way, it sets up a kind of artificial hurdle; you pretend that you can only see the trees from a distance, and maybe that you’re only going to see them for a few seconds. You have to get your binoculars on them and identify them with the few clues you can view from a distance. That is kind of artificial because usually, you can walk right up to a tree and look at it, but if you can just be walking along a path with your binoculars and look at a tree from 50 yards away and identify it, it saves a lot of time.
Also in the same way, I'm imagining birdwatchers. You're looking at birds in your binoculars or telescopes, and most of the birds are sitting on trees. [Laughter] So if the bird flies away, or if you've identified it, you can turn your attention to the tree in the same view, without moving your binoculars or telescope, and have a whole new challenge of something to identify.
Jill: I hadn’t thought about it that way, but it makes a lot of sense; those kinds of identifications work well together.
You write in the introduction to the book, "Trees are not a well-defined biological group, like birds or insects." I found that oddly surprising. Why is that, and how are they defined instead?
Sibley: Yes. It was one of those things that was a little bit of a revelation to me when I started on the project, to realize that a field guide for trees is sort of the equivalent to a field guide to the large birds of North America. Trees are just plants that develop a certain growth form and get really big. There are species in the same genus, like the dogwood, the genus Cornus, where there are trees up to 60 feet tall, and another species in the same genus that's a little plant on the forest floor that never gets more than about four inches tall. Once you know that, you can see the similarities, if you look at the leaves, and the fruit, and the flowers. They're clearly closely related, but the growth form is completely different.
We all know a tree when we see one, but trying to put some actual strict definition to it — it's always a bit fuzzy around the edges. I write quite a bit about that in the introduction of the book. There is no perfect definition of a tree, but at the same time, if you show somebody a plant, and ask them if it's a tree or not, there's usually not much ambiguity there. You can look at an individual plant and say, Yes, that's a tree or that's not. But in the very beginning, when I started working on the project, that was one of the real revelations that made me realize just how different this was going to be from the bird guide.
Jill: I like the summation you used that if you can walk under it, it's a tree, and if you have to walk around it, it's not.
You compare an interest in tree identification to learning a new language, in the introduction, which seems accurate in two ways: I was unfamiliar with several of the actual terms (pinnate, mesic, and inflorescence, for example), and it's also almost like learning to "read" the organism itself, using its own language.
Sibley: Yes. I think, just to carry the comparison out a little more, say you're learning a new language. You're going to learn the vocabulary, the verb conjugations, and assemble it piece by piece, so that you can hear a phrase or read a phrase and pick it apart and figure it out. Gradually, over time, you develop a more intuitive understanding of it, so that as you hear the language more or read the language more, and you get more accustomed to using it, things just become ingrained in your mind and subconsciously you start to understand it. At the same time, as you reach each level of understanding and comprehension, your ability to distinguish subtleties increases.
With trees, as you learn a few species to begin with, you can get to know some of the common species. Then one day, you'll be traveling along on the same path or road that you've been down many times before, marking the trees that you know really well as they pass, and all of a sudden, one that's a little different will catch your eye. For six months you've been walking past it every day and you haven't even noticed it, and suddenly, something about the leaves or the bark or just the way it's shaped makes you think, "What's that one?" What starts out as a sea of green leaves when you begin tree-watching gradually, over many years, resolves itself into more detail and more and more subtlety as your brain gets more accustomed to picking out those little details.
Jill: With trees or birds or anything in nature, it seems to be about paying attention and changing the way that we see. I wonder if that actually changes our brains to some degree.
Sibley: I wouldn't be surprised. You’re training your brain to make these distinctions, to see these subtleties, and the more you look for, the more you see. I think it's sort of the same way that people talk about drawing or painting changing the way they see the world. You look at things differently and focus on different details. You start to pick out all sorts of little minor variations and differences that earlier you wouldn't have been capable of seeing because you hadn’t fine-tuned your perception that much to be able to notice them.
Jill: I will say it's really addictive. I identified some of the trees in my immediate neighborhood yesterday, and then later, as I was driving, I caught myself watching the trees as they went by, trying to pick out the species that I knew.
Sibley: Yes! It is. [Laughter]
Jill: You say in the book to start local and start small. What are some other good tips for beginners at tree identification?
Sibley: The same advice I give to beginning birdwatchers. First, spend some time at home with the field guide, just flipping through the pages. Read little bits here and there, look at the pictures, and get a feeling for how much variation there is, how each group of related species is similar and different. Without even trying, just by browsing the pages of the book, you'll get a sense of what makes a maple a maple and what makes an alder an alder, and how those are different from other genera. The more you can build up that familiarity with the groupings in the book, then you'll find that you get out in the field and notice something. You'll think, "I don't know what its name is, but I know I've seen it in the book." Then you're halfway there. You can just flip through the pages; you've already recognized it, you just have to find the name.
Another bit of advice is that when you're really just starting out, it can be a bit confusing and frustrating. You can get sort of lost in the possibilities, not trusting that what looks like a match in the book is really a match, so maybe you think you still haven't identified it. It can be helpful, then, to go to a local nature center, botanical garden, park, or sanctuary, someplace that has a nature trail where some species are labeled. A lot of places also offer guided walks. Going out with someone who can point to these species and say, "Yes, that's a Douglas Fir and that's an Engelmann Spruce." You can get these common species sorted out with complete confidence, and really get that foundation. The first 30 species are the hardest ones, and once you've got that kind of a head start, it becomes much easier to use the book on your own and add a few more species each week or each month to your own repertoire. But in getting those first 30 species under your belt, it's really helpful to have some guidance.
Jill: That's good to know, because it did take me a long time to identify one particular tree in my yard yesterday. I'm pretty sure it's a California Laurel, but getting there required lots of page-flipping.
The families are interesting; I didn't know that cherries and apples belong to the rose family, or that sumacs and pistachios are members of the cashew family. Do you have a favorite family of trees?
Sibley: That's a good question. Most people ask me if I have a favorite tree, and I don't. I guess my answer would be that I couldn't really pick a favorite family, but the legumes, the bean family, is right up there as one of my favorites. I've always enjoyed seeing them; it's really a tropical family, with just a few species that make it up north into the temperate part of the United States. So I associate those legumes like acacias and mesquites and the Southwestern species with some really interesting places and fun experiences that I've had in the Southwest. There's a lot of diversity in that family, and lot of really distinctive species. Some great flowers — everything from redbuds, with their bright pink flowers that show up before the leaves in the spring, to Black Locust or yellowwoods that have these really incredible displays of white flowers in the early summer. If I had to live on an island with just one family of trees to look at, the legumes would be a good choice.
Jill: I found it interesting that ginkgo is so unique that it gets it own division.
Sibley: Yes. I guess there's some debate about that now. A lot of the DNA work is still showing that it's very distinctive, but it might fit in with the other gymnosperms more closely than was thought before. No matter what, it's a very distinctive tree, and it's really all alone; there’s really nothing else like it in so many ways.
You brought up that it's interesting to you to know which species are related in each family and to know how distinctive something like ginkgo is. I found all that fascinating, too, because a lot of this was new for me as I've been working on the book over the last seven years. It's not like the bird guide where I learned everything and then sat down to do the book. With the trees, I was learning as I went, and I kept finding out all these interesting tidbits of information and jotting notes, and thinking, "Wow, that's great! I'll have to make sure I put that in."
Jill: Like the tree records that you include. That amazing system of quaking aspens in Utah that are 80,000 years old.
Sibley: Or something like that. [Laughter]
Jill: Are those protected?
Sibley: A lot of them are on National Forest land or in National Parks in the mountains, but I don't know if there are any real specific efforts to protect those individual plants, the oldest ones.
Jill: Are tree ranges or other behaviors changing because of climate change?
Sibley: Yes. There have been big shifts. There was a study done here in Massachusetts a few years ago gathering old historic photos from the late 1800s and early 1900s. The researchers went back to the same places on the same dates now and took matching photographs. They found that the time of leaf emergence in these trees had advanced in the spring by several weeks.
There was one really dramatic photograph of a cemetery in the town of Lowell, north of Boston, on Memorial Day weekend in 1890 or so. They went back the same date in 2005 to take another photograph. Some of the same trees were in the photograph. The trees have gotten bigger, but they're still there. The difference was just incredible. In the 1800s photo, it looked like what you would expect to see on April 30, now, with the branches mostly bare and the leaves just beginning to emerge from the buds on May 25th. Now, on May 25th, the spring is over. The trees are completely leafed out; you can't see the twigs. It's just a solid canopy of green.
That's really good documentation that, at least in the northeast, spring has advanced by several weeks because of warmer temperatures. Other than that, I'm not aware of other studies that show changes that are directly linked to changes in the climate. Some of the droughts in the West over the last ten years or so, whether they’re related to climate change or other cycles, have been really devastating to a lot of trees. If it keeps up, if it's not just a blip in the long-term pattern, if this is the beginning of a new pattern of drier summers or drier climates throughout the West, it will mean tremendous changes in tree distribution.
Jill: You write that perhaps no other group of organisms has been as affected by humans as trees, which seems absolutely true, but it's not something that you think of that way initially.
Sibley: Also, so much of the natural world is based on trees. Once you change the trees, you're changing the insects and the birds and the plants in the understory. So I guess that's one way to say it. Trees have been more directly affected by humans, but then they're having direct effects on everything else down the line.
That was another thing that struck me almost as soon as I started working on this project and looking carefully at trees. In the Northeast, which is region that I mostly travel in, including New England, New York, and New Jersey, nearly every single tree you look at is less than 100 years old, and a lot of the trees that I see every day have been planted, which is the ultimate in human intervention. It's very different from birds, which you can imagine are still living their lives migrating and nesting and singing and doing their thing regardless of humans.
Jill: Which trees are in your yard?
Sibley: We've lived in this house now for about eight years, and it's in the woods. It's surrounded by about four species of oaks, three species of maples, Black Cherry, a hickory or two. There's a chestnut tree that sprouts and dies back the way chestnuts do now. Black Locust and White Pine. We've planted a few shrubs, but mostly we're surrounded by trees, so we haven't really touched the trees much in the yard. It's a really good variety.
Jill: Is there another group of plants you're interested in writing about?
Sibley: I don't think so. I'm not sure what my next project will be, but I think I've gotten my fill of big projects for awhile. I don't feel the same way I did eight years ago when I decided that I really wanted to do another big project. Trees really caught my attention because they're so conspicuous and so much a part of our everyday lives, and the number of species in North America is about 700, depending on how you define a tree. It was a manageable number of species. I think the estimate is 27,000 species of plants in North America. A lot of those are grasses and sedges and other inconspicuous small plants, but even a guide to wildflowers of a small region would quickly get up over 1,000 species, and I don't think I have the time or energy. [Laughter]
I’m not sure what my next project will be, but I think it'll be a smaller project. I may go back to birds for a while.
Jill: What are you reading lately?
Sibley: I've been reading a couple of books about Irish history. My wife's grandparents are from Ireland, and we just took a trip there this summer to track down her family roots. So I've been reading a book called The Great Hunger, about the potato famine in the late 1800s. It's really a fantastic book. It's older, but it's a great history book.
I also just started rereading Jonathan Rosen's book The Life of the Skies, about birds and birdwatching. I read it a year or so ago, when it first came out, but I was distracted by my work on the tree book, though I really liked it. So I just started rereading that, and I think it's an incredible book. So many times reading through the pages I say, "He's right. Yes, that's exactly what it's about, that's what it's like. That's why we like birdwatching. That's why it's so compelling."
Jill: What has been one of the most memorable or remarkable moments you’ve had with birds?
Sibley: There's a story that I have told at some of my lectures that I think summarizes part of the appeal of birdwatching. I was leading a bird walk in Central Park in New York City in late October. It was gray, overcast, with a little drizzle, a cold late October day. But there were a lot of migrating birds in the park, little songbirds heading south. Somebody in the group of people that I was with looked up and saw a flock of birds in a V formation way up overhead, higher than the buildings that were surrounding us in the park. I looked at them with my binoculars and recognized that they were brants. A brant is a small goose that nests in the Arctic and winters along the sea coast. Some of them winter on the shore of Long Island, a few miles away from where we were in Central Park. You could see that these birds were flying south on a line towards the Jamaica Bay National Wildlife Refuge, where a lot of them winter. You could see that they were in their V formation, and they'd set their wings and they were gliding, making their descent towards that salt marsh habitat.
The direction that they were coming from was 600 or 800 miles to James Bay, which would be the nearest place you'd expect to find a brant. That realization, that moment of seeing those birds dropping down towards their winter home, and realizing that they must be just finishing maybe 14 or 18 hours of nonstop flight, coming from Hudson Bay or James Bay, traveling all night following the Hudson River, and then finally just at that moment catching a glimpse of the salt marsh where they’re gong to spend the winter and dropping down… It was really a magical moment.
You get the sense that the city is something new and those brant, their ancestors have been migrating the same way for thousands of years. These concrete boxes have just sprung up in the last hundred or hundred and fifty years. Something Jonathan Rosen talks about in his book that I was just rereading last night is that we tend to think of birds as ephemeral, as just barely there spirits of the wind, and that we think of our cities and skyscrapers as concrete and permanent. In that sort of moment, you see it as just the opposite. The city is temporary; it's this very new structure that just for the last few generations has marked the end of the journey for these brant, which have been making this trip for thousands of years.
I spoke to David Sibley on September 7, 2009.