Dendrology Library

The best tool for a tree-watcher is a good tree book.

I've got a few, most of them featured in the photo above.

The majority of them are guides, each one just different enough to add it to my collection. Why would you need different guides for trees? I mean, it's not like one book is arguing with another book about the identity of the tree in question. No. Guides differ in two areas.  They differ in the way they organize the trees and they differ in the way they make you see.  It's those two differences that compel me to buy another guide.

You'll need a healthy mix of field guides and tree guides.


You'll need one field guide that is just a key. I've got two or three. A tree key often reads like a Choose-Your-Own-Adventure book. It's really just a list of yes and no questions that will lead you to the correct identification. Normally, the first questions of any tree key are:
  • does the tree bear cones and are its leaves needle-shaped, scale-like or linear
  • does the tree bear seeds in an ovary and are its leaves broad-shaped
Depending on how you answer, the key will direct you to a new page with a new set of questions, like "are the needles growing in clusters of five" or "does the tree have opposite or alternate branches" or even "is this an evergreen or deciduous tree."

And on and on the adventure of yes and no questions continue until you get to something like:
  • leaves with small rounded teeth; buds slender and shiny as if varnished, or 
  • leaves with larger sharper teeth, buds slightly white-downy
...and that's how you know if the tree in front of you is a quaking aspen or a bigtooth aspen.  

When you finally get to the end of the questions, hopefully there will be a picture of a typical leaf, fruit, bark or bud to compare. If the picture doesn't match what you're looking at, you normally just have to start at the beginning.

A good tree key book will also have a separate winter key that asks you questions about the bark or the buds on the leafless branches. A key book without a winter key is normally not worth buying. Once you get to the right tree, a good field guide should list the common name, scientific name, regional names, distinguishing characteristics, its range and a good picture of a leaf, fruit or seed, bark or flower. I prefer illustrations over photographs but that's me.

There's one other sign to tell whether the field guide is bunk. 

Does it warn you right away about poison ivy and poison sumac?
Illustrations by Arthur Harmount Graves
That's why I champion, and trust, the Illustrated Guide to Trees and Shrubs by Arthur Harmount Graves. He writes in the opening paragraph: Before trying to identify a plant we should make sure that the plant in question is neither Poison-ivy nor Poison-sumac...These poisonous plants will be found illustrated on Plate XXV, 1 and 2, and described on pp 163 and 165. He even provides pictures of these plants as they appear in winter without leaves. Good looking out, Arthur Harmount Graves.


Other than field guides, you'll also need some tree guides. These books require a beginner's knowledge of identification. In these tree guides, the author is free to organize the trees in his own way. 

For example, The Book of Forest and Thicket: Trees, Shrubs and Wildflowers of Eastern North America, by John Eastman, is a fantastic guide, one of my favorite books. 

Each plant is researched at an exhaustive level. You get the names, the distinguishing characteristics and the ranges. 

Then, you get to read about its lifestyle, how it propagates, how it grows, how it dies. You get a little tree history and folklore too.

Eastman goes on to explain the plant's close associates, what other vegetation might be growing nearby, what insects or birds are common users of this tree, even what mushrooms might tend to grow in the ground near this particular tree. 

Each entry is encyclopedic but there's one big problem.  It's arranged alphabetically. 

A great tree guide but, if you're trying to use it for identification, good luck.

That's an unusual organization, though, for a tree guide.  

Usually, the author will arrange the trees along a botanical, taxonomic or evolutionary line.  

In most books, the gymnosperms, the oldest types of trees, usually come before angiosperms, their broadleaf descendants.  Yews come before pines and pines come before firs and spruces and the book goes right down the line to the cedars, junipers, cypresses and the California Bigtree we call sequoia.  

Then, the author usually tackles the angiosperms, probably starting with the magnolias and laurels and ending with catalpa and holly.

Somewhere in the book, the author has to squeeze in the palm trees, the cyads, the ginkgo, the joshua tree and the saguaro cactus.


The Sibley Guide to Trees, by David Allen Sibley, deserves special mention here.  The book is spectacular.  I mean, it's truly a spectacle.  Every picture in the book is hand-painted and it's just beautiful to behold, even beautiful to flip the pages.  You don't really read it.  You watch it. 

Sibley arranges his book right down the taxonomic line, from yew to holly, throwing in the muskroot at the end just to be obstinate.  Yet, he very clearly wants the readers to use this as a field guide.  

A field guide without a question key?

I saw him speak once.  He said that the problem with keys is that it puts too much emphasis on the differences between trees.  The questions that a key asks are obsessed with the way one tree is different from another.

Is it deciduous or evergreen?  Is it alternate or opposite?  Does it have smooth or plated bark? 

By the time you get to the very end of the adventure, your choice of trees might look similar but they are actually separated by a wide gulf of geologic time, families are spread out unevenly throughout the book and you might discover that the tree is part of, say, the Fagus family but why?  Why are oaks and beech and chestnuts in the same family?  A regular key guide won't ever answer that question.

Sibley's organization forces the reader to identify trees by noticing the similarities, especially the patterns that repeat themselves down the family line.  It's a revolutionary way of writing a tree field guide and it works.  It's not for beginners though.  It's hard to identify a tree using this book, but his holistic approach is a success.

As I flip the pages, I literally can see the trees evolve into each other.  His approach also helps make sense of the odd ducks inside a particular family, like the Box Elder Maple with its compound leaves.  It's the only field guide I know that consistently shows the whole shape of a typical tree, instead of concentrating so much on the tiny details of leaf points, needle clusters and terminal buds.  Before his book, I never used the shapes and branch structures for identification.  Now, out in the field, out on the hunt, I can look at the tree in front of me, look at Sibley's page, look back and see everything at once: its shape, its branch structure, its leaves, fruit and bark.  Sibley makes me look at the whole tree. For field guides, it's a paradigm shift.  

The rumor is that Sibley's next book will be about insects or moths. Can't wait.


Eventually, all tree-watchers discover Donald Culross Peattie.  He wrote the definitive tome, A Natural History of North American Trees.

He writes in a style that is completely outdated, naive and romantic and it is lovely.   

The Tamarack, he writes, goes further north than any other tree in North America, and at the farthest limits of its distribution it grows in summer by the light of the midnight sun.  At that season it is one of the most tenderly beautiful of all native trees, with its pale green needles like a rime of life and light.  But in winter it is the deadest-looking vegetation on the globe.  Many a tenderfoot has been horrified, coming upon a Tamarack swamp...that selection was found at random.

No tree gets the slight in his book.  He loves to quote from Whitman, Thoreau, Emerson, Bartram, Muir or from any colonial diary that's survived the centuries.  This is not a guide that will help you identify a tree but, after each article, you'll know the tree. 

He has an enormous knowledge of regional uses and traditions.  He is very fond of explaining how some trees played a role in Native American life.  In a side valley of the Grand Canyon today lives the small tribe of Havasupai, a people of the Yuman stock.  In the life of the Havasupai the Utah Juniper figures from babyhood to grave.  When the child is born he is covered with Juniper bark...and he continues explaining the campfires made from the juniper branches, the marriage bed made from juniper bark, and the way the family retreats from the grave of a loved one, sweeping their tracks with Juniper boughs.  

For Donald Culross Peattie, trees are intertwined with American history.  He writes about the sweet locust: Down in Florida this tree is still sometimes called by the obsolete name of Confederate Pintree, because its formidable spines were used to pin together the tattered uniforms of the Southern hosts in the war of the Blue and Gray.  

Donald Culross Peattie
He also gives equal attention to the lumber and timber industry.  In the early days of the automobile industry in Michigan, when much wood was going into car construction, large quantities of Cork Elm were used for hubs and spokes and in other places which had to take great strain...during the era when most kitchen furniture, including refrigerators, was wooden, this was a favorite...

Wooden refrigerators?  Beds made of juniper bark? Uniforms stitched together with locust thorns?  When you read Donald Culross Peattie, the world stops being blue and green.  It becomes wood.   


Field guides.  Tree guides.  Those are really the two types of tree books.  There are also nature books, and I do read a lot of nature books.  Some of the nature books concentrate on trees or woods or forests, but they're not going to help you find, identify and watch the trees that surround you, the purpose of this blog, after all.

Besides field guides and tree guides, I'd recommend picking up maps of local woods and forests, hiking grounds, nature preserves, state parks if you got any, and cemeteries.  In the city, cemeteries are a tree-watcher's haunt.  

Not a lot of cities have local tree maps.  Philadelphia is lucky. There's a website called PA Big Trees,, which lists the locations of champion trees within the entire state.  We also have a small, thin, rare booklet published in 1969, prepared for the International Shade Tree Convention of 1967, entitled Some Trees Notable for Size and/or Rarity in the Philadelphia Area.  It is the pride of my collection.

It looks like a book report, stapled together, obviously written on a typewriter, originally sold for 50 cents.  Compiled by John Swartley of Temple University and Joseph Hayden of the Shade Tree Bureau of Lower Merion, it is literally an index of notable trees and their locations.  To me, it reads like a treasure map and it will be one of my most useful tools for this blog.


There is one other kind of tree book, I suppose.  Coffee table books.  Here are some distinguishing characteristics of coffee table tree books: big, expensive, can't be taken outside, can't fit in a backpack, every picture and every tree is pristine and perfect.  It rarely has any organizational pattern, so an African baobab is just a page away from a New England birch right next to a English countryside yew.  It has no keys, no value, no worth and isn't any help.

Coffee table books about trees?  I got a big problem with them and it comes down to this.  They take up too much room and, out in the wild, here in the city, there is one rule and one rule only: you only take up as much room as you need. 

Jon Spruce.


  1. I agree, tree shape is such a key indicator. I'm surprised most field ID books don't use it. I think Dirr's Manual of Woody Plants uses it. That book is more of a planting guide than a field guide, but definitely worth checking out. I just saw that he has an app now too.

  2. Another wonderful tree book is "The Lives of the Trees, An Uncommon History" by Diana Wells. It isn't limited to North American trees, but it gives you all sort of "lore" on each tree e.g. Ginko Biloba: are the leaves one leaf being pulled apart or two leaves fused together?

    Miriam Fisher, Chestnut Hill