The Trees of Western North America is the companion title to the eastern edition that was released in the same year and previously reviewed in these columns (RR 2016/130). This book is part of the renowned Princeton Field Guide series, which presents information on plants, animals, ecology and conservation in a format accessible to scientists and amateur naturalists while in the field. Focusing on the western half of North America, this region is defined as the area from the eastern base of the Rocky Mountains to the Pacific Ocean, or more specifically west of the 100th meridian line. Coverage includes 630 native and introduced species of trees, which is significantly more than the main competitors to this book, the National Audubon Society Field Guide to North American Trees, Western Region (Little, 1980) and A Field Guide to Western Trees (Petrides, 1998).
Organization of the book is by species, grouped into two sections: gymnosperm (e.g. conifers) and angiosperms (flowering plants). Gymnosperms come first, preceded by angiosperms. The angiosperms are further subdivided into monocots and dicots. Within each group, trees are organized by family, genus and finally species. Family groupings are differentiated by coloured headers at the top of each page, allowing for quick browsing. Each family, genus and species has its own description, unless there is only one species representing a genus, in which case they are combined. The primary finding aid to individual species is a leaf and twig key at the beginning of the book. However, because the paintings of individual leaves and twigs are so small, it is difficult to assess details that are important for identification.
Species’ descriptions vary in length based on their cultural or ecological significance, or the extent of their geographic range. However, most species are described within one page. All native species, and some non-native, are headed by a Quick ID statement to provide key identification characteristics. Following is a more detailed description of habitat, bark, twigs, foliage, flowers and fruit. Coloured paintings of the overall tree, leaves, fruit, flowers and bark provide important visual ques. Range maps are also included at the end of each entry. Other features include a nine-page section on tree biology and a brief description of forest structure. A five-page glossary helps define terms mentioned in the book, and there is a complete index of species names, including common names.
Compared to the National Audubon Society Field Guide to North American Trees, Western Region the Princeton Field Guide provides more detailed descriptions of identification features such as bark, twigs and flowers, often differentiating between young forms and more mature trees. Also, in the Trees of Western North America, coloured paintings are on the same page as the descriptions. Although the National Audubon guide has coloured photographs for leaves, flowers and fruit, they are located in a separate section of the book. One nice feature of the National Audubon guide is the brief cultural, historical or natural history tidbits provided in the species descriptions. This type of information is not as common in the Trees of Western North America.
In contrast to the previous books, A Field Guide to Western Trees uses a more sophisticated key to identify species. The key at the beginning of the book helps differentiate whether a species for identification has needle, scale-like or broadleaf leaves, and then further refines the search by categorizing the needles/leaves by length, number per cluster, opposite or alternative branching and simple or compound. From here, users are directed to plates that provide colour pictures of the leaves/needles, fruits and stems of like-appearing trees. Although the key is sophisticated, it is mainly text-based and can be confusing or off-putting to people who want quick identification. Species descriptions in the A Field Guide to Western Trees are similar to those in the Trees of Western North America, but the only images included in a species description is a profile of the entire tree and a range map. As mentioned already, leaf, fruit and twig images are located in a different part of the book, making access to all identification features as inconvenient as with the National Audubon guide. A feature of the A Field Guide to Western Trees is that leaf, fruit and twig dimensions, along with overall tree height, are in inches and feet, not metric units.
Another detailed, key-based book is Identifying Trees: An All-season Guide to Western North America (DeMarco and Mengel, 2015). This book improves upon the system in the National Audubon Society Field Guide to North American Trees, Western Region by providing a better understanding of how to use the key and including photographs to help clarify identification features (ex. compound leaves). However, the descriptions of individual species are not as complete, nor do they consistently provide dimensions of features such as leaves or fruits. Coloured pictures aid in identification, but unlike Princeton’s Trees of Western North America, they do not always include fruit, flowers or twigs, often focusing on leaves and bark instead.
My concluding recommendations are congruent with those made in my earlier review of Princeton’s Trees of Eastern North America. The Trees of Western North America is one of the better field guides for the region. More species are covered in this guide than others, and it has an abundance of coloured paintings and detailed descriptions. However, finding a particular tree via the twig and leaf key is not as helpful as with other sources. A more complete solution is to combine the Trees of Western North America with a better key-based book like Identifying Trees: An All-season Guide to Western North America. That way you have an effective means for narrowing down a tree to a family or genus and can use images in Princeton’s Trees of Western North America for final identification and description. Recommended for all libraries.
