Introduction One of my earliest memories is of standing on a vast emerald lawn shaded by dozens of towering American elm. The sense I had of being in a living green cathedral is not much of an exaggeration. Many people have similar memories. I was also just old enough to witness the final rapid decline and disappearance of this majestic tree from the public spaces of this continent. The experience taught me that even such wonder and beauty as they had provided could end. I have been a lover of trees ever since. Whether in my formal studies in botany and environmental studies, or in my work in landscape design and teaching, trees have never been far out of my sight or mind. It has always been important to me to promote a positive response not just to trees themselves but also to how they and their environments are integral, mutually defining and endlessly dynamic. This environment includes not only other plants, animals, soil, and climate, but also people, in increasing numbers. This is an ecological theme. People have a relationship to trees. We derive food and shelter from them, and use them to create a huge variety of products. We also employ them to grace our surroundings, and buffer our impact upon the land and climate. In the process, we destroy vast numbers of them, and set up conditions that favor their decline. If we are to continue to enjoy their bounty, it is necessary to know what they are, their diversity of kind, the specific environments within which they develop and which they themselves help to shape, and how they are used by people and other animals as well. In writing this book I intended to address in a small way this necessity. Specifically I have attempted to do several things. The first objective of this book is to present as many tree species native to North America as are currently recognized. To some extent this is a subjective exercise; it involves defining what is meant by "tree" and what constitutes a species. These definitions are not always as easy to come by as the layperson might think or wish. Generally, as presented here, a tree is any primarily woody plant of one to several perennial stems arising from the ground and living for 20 or more years, and attaining a height of at least 10 feet (3 m). Others definitions vary somewhat from this, but not significantly so. Connected to this is the issue of distinguishing trees from shrubs. In cultivation, some species of shrubs are preferentially pruned into tree-like forms; and in nature, many woody plants straddle the conceptual boundary between shrub and tree. This book deals primarily with those woody plants that assume at maturity a tree form on optimal sites in their natural habitats. Such a distinction cannot hope to please everyone. There will be plants that some consider trees which do not appear here; equally there are some plants discussed that could be considered shrubs. On the one hand, I have felt impelled by love to include a few small trees, such as Alternate-leaved Dogwood, which are more often than not shrub-like, and conventionally treated as such. I cannot rationalize such inclusions, and make no effort to do so. Those who know such plants, or come to know them, will understand why I have succumbed to mere affection. On the other hand, academic perversity has led me to include a very few species, such as Engelmann Oak, which are often encountered as shrubs. In these very few exceptional instances, I have felt it necessary to include these plants, in part, because they represent one end of a continuum in form of the genus to which they belong. Engelmann Oak, for instance, is one of a number of Oaks, some wholly shrubby, that are characteristic of the dry, fire-dependent chaparral habitats in California. It seems to me worthwhile highlighting this, so that the reader does not go away with the idea that all the Oaks are Mighty Trees. The question of what constitutes a species is not cut and dried either. All life forms ultimately defy human attempts at categorization, and plants particularly so. Species are described by an authority (occasionally two people working together) who delineates the boundaries, most often features physically intrinsic to the group that separate it from all others, and set it in what is termed its phylogenetic relationship to all other plants. These boundaries are not always universally agreed to, and over time arguments are put forward for recognizing as a species a group that was formerly included as a variety or subspecies within another species. Some species in some genera are very much in contention; species in the genus Crataegus, the Hawthorns, are a case in point. Over time, the arguments lead, we hope, to a more thorough understanding of the group in question, and general agreement is reached as to the group's status. One of the consequences of this activity, however, is that several names will arise and be used either simultaneously or consecutively for a particular group of plants. For instance, American Basswood has in the past been known as Tilia neglecta, but is currently called Tilia americans. In some instances the confusion in species status, and hence in naming, is bewildering. It is important, however, not to consider this seeming uncertainty a "bad thing." In dealing with this situation, a useful adjunct to the species-name itself is the name of the authority who has described and named it. Such names are provided in this book, as in many others, in small letters immediately after the botanical species- name. Most often the authority name is abbreviated, but not always. The addition of the authority names flags to the reader that, in some cases, the species was formerly considered under another botanical name. The reader can then, if interested, seek additional information under the former name, also known as a synonym. In the end this is not a book on taxonomy. Some species considered here are dealt with by others as varieties or subspecies of other species. Some authors also split single species discussed here into two or more. This is an enduring legacy of taxonomy. The second specific objective of this book is to provide, for each tree, a brief description, supported by one or two photographs, of what the tree looks like in its most salient features, i.e. overall size, habit, trunk, crown, bark, leaf, flower, fruit and root, as far as any of these are particularly notable or useful to an interested reader. In some cases flowers are so inconspicuous as to go unnoticed, and have not been described in the same level of detail as those on trees that have highly conspicuous and showy flowers. For some trees, root structure is not well documented in the literature, or is inconsistently described; consequently, I have either not discussed it or noted the varying opinions. Keeping in mind that the book is intended to be used by non-specialists, the descriptions concentrate more on what is easily observable and understandable, rather than on the taxonomically fine features. The third goal of the book is to describe, as briefly as possible, the natural environment of each tree, including its natural range, the various habitats within which it is usually found, the trees with which it commonly associates, the topography, in some cases the climatic regime, and the soil types on which it is found, noting those conditions under which optimal growth occurs. I have usually provided in this description the tolerance of each species to shade and/or drought, and/or flooding, and attempted to relate this to life-span and the very broad successional/climax habitat that the species seems most often to inhabit. This information is of particular use to the avid gardener or naturalist, who realizes that the more a plant and its siting are brought into consonance, the better the plant will fare, the greater the degree of predictability in behavior and the less intervention should be required. The fourth objective is to highlight, for each species, some of its more important and interesting uses and values, not only in landscaping, human economy and ethnobotany, but also within the context of the natural environment, i.e. in restoration, watershed management and wildlife habitat. There is an enormous amount of information available in this area. Those interested in knowing more about the specific uses of a particular tree will find an abundance of information in a simple search of the literature. Finally, in the hope that the reader will feel moved to act upon what is presented here, several sections have been added at the end, on USDA zone hardiness, further reading, and places and organizations to contact. I hope the reader finds some favorite native trees here, as well as discovers and rediscovers many others. Each one is worthy of consideration and praise. Excerpted from The Encyclopedia of North American Trees by Sam Benvie All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.
