2012 USDA Cold Hardiness Zone map cascading racemes of golden-yellow flowers. Book Review (USDA, 2012). What made this particular cultivar especially The authors added two criteria not listed memorable was its location: a 2 ft. wide road in the 2009 Manual: ‘‘street tree use’’ and ‘‘in verge (a.k.a. hellstrip)—the area between the the trade.’’ While the discussion of street- sidewalk and street, that will prove challeng- The Tree Book: Superior Selections for scape adaptability lacks the detail and depth ing to cultivars of callery pear (Pyrus · Landscapes, Streetscapes, and Gar- of other print and digital resources, it brings calleryana Decne.) and Chinese elm (Ulmus dens. Michael A. Dirr and Keith S. attention to the inhospitable, crucible-like parvifolia Jacq.) Interestingly, Dirr and War- Warren. 2019. Timber Press, Inc., Port- conditions of the urban environment. Street ren do not recommend golden chain trees for land, OR. 900 pages incl. photo credits, tree selection often relies on a Darwinian street tree use for a number of valid reasons. index (scientific and common names), survival-of-the-fittest approach—the arbori- A trivial comment is that some of the text color photographs. $79.95 (U.S.), hard- cultural equivalent of The Hunger Games— might have benefitted from additional infor- cover (ISBN: 9781604697148). Digital that results in a pared-down list of a few, mation. In discussing the development of book (ISBN: 9781604699180). overused but resilient taxa. chestnut blight-resistant hybrids, the authors Their ‘‘In the trade’’ comments address did not mention Phytophthora cinnamomi The Tree Book, co-authored by two re- the commercial availability of the taxa, Rands, the second most lethal pathogen of nowned plantsmen, who have collaborated which ranges from ‘‘rare’’ to ‘‘omnipresent.’’ American chestnut and its hybrids, which has for more than 30 years and introduced 66 Rare or uncommon species, such as Henry hampered their establishment in the wild, patented and trademarked plants between Wilson tree (Sinowilsonia henryi Hemsl.), primarily in the Piedmont regions of the them, resembles the layout of Dirr’s Ency- receive the ‘‘BIO’’ designation: botanical southeastern U.S.A. Their recommended list clopedia of Trees and Shrubs (Dirr, 2011). garden interest only. Additionally, some en- of pecan cultivars might have included their An introductory section is followed by an tries include information about how the taxa Type I and Type II dichogamy. Additionally, alphabetical listing of taxa arranged by sci- are sold (seeds or clones) and propagated, the authors parenthetically provide defini- entific name. The Tree Book focuses on trees provenance, and opinions and anecdotes tions of terms when a glossary and an index and palms—‘‘trees’’ broadly defined as from a pair of legendary nursery insiders. of terms would have enhanced comprehen- plants greater than 15 ft. in height—adapted Compared to Dirr’s Encyclopedia of sion of the botanical jargon. to temperate regions of the northern hemi- Trees and Shrubs (2011), Dirr and Warren Some readers will question the inclusion sphere. included more than 150 additional species of some taxa and the exclusion of others. I In the 33-page Introduction, Dirr and and cultivars. As they state in the Introduc- wonder why Dirr and Warren included the Warren explain their reasons for writing the tion: ‘‘We included the good and the bad.’’ invasive glossy privet (Ligustrum lucidum book, share insights regarding the breeding, They discuss a plethora of good—I dare say, W. T. Aiton) but not Japanese privet (Ligus- selection, and evaluation of trees, and men- great—species that offer multiseason inter- trum japonicum Thunb.). The authors write tion the cultural ecosystem services provided est, enjoy widespread availability, and per- that L. lucidum is ‘‘a suitable urban tree only by urban trees. They allude to a number of form reliably in landscapes or streetscapes. if rendered sterile via modern breeding tech- studies but do not cite references. The attrac- They also introduce the reader to a number of niques’’ and has only ‘‘limited’’ commercial tive photographs in this section complement species that deserve recognition and evalua- availability. Ligustrum japonicum and its the text, but the staccato captions (e.g., tion before they become mainstream plants. cultivars, which are widely available, well ‘‘Ulmus americana, Princeton, looking Dirr and Warren expose ‘‘bad’’ taxa, such behaved, and considered by Dirr (2011) to be good.’’) and punctuation errors, such as the as salt-cedar (Tamarix chinensis Lour.): ‘‘an absolute building block of southern and incorrect use of single quotes with a trade- ‘‘Our advice is simple: don’t plant it.’’ Other West Coast landscapes,’’ was not included. marked name (Lagerstroemia ‘TWILIGHT ornamentals considered invasive or endowed Ligustrum japonicum possesses the same MAGIC’) instead of L. ‘PIILAG-VIII’) an- with invasive traits, such as Russian-olive growth habit and tolerance to limbing-up as noy, rather than distract, the reader. (Elaeagnus angustifolia L.), Chinese parasol other species addressed in The Tree Book The ‘‘Origins of new shade and ornamen- tree (Firmiana simplex W. Wight), china- (e.g., Chilean myrtle [Luma apiculata (DC.) tal trees: The roles of serendipity and breed- berry (Melia azedarach L.), and princess tree Burret], staghorn sumac [Rhus typhina L.] ing’’ fascinated and enlightened me. The (Paulownia tomentosa Steud.) receive en- nannyberry [Viburnum lentago L.] and yel- section on ‘‘Provenance’’ offers the reader dorsements for breeding or genetically engi- lowhorn [Xanthoceras sorbifolium Bunge]). parallel viewpoints: one extolling the impor- neering sterile cultivars. They include In presenting the attributes of Acer tance of locally sourced seed-propagated caveats with some species, such as recom- rubrum and its widespread popularity, the shade and ornamental trees to improve bio- mending only male Chinese pistache (Pista- authors might have mentioned the existence diversity and urban resilience and the other cia chinensis Bunge) cultivars. of wet- and dry-site ecotypes and the inability supporting the use of clones because of their An outstanding feature that makes this of red maples to cope with the physical, availability, predictability, and reliability. book stand out are the photographs— chemical, and biological adversities of the The A-Z index that follows the Introduc- closeups and wide shots of foliage, flowers, urban environment. Recent investigations tion includes more than 2,400 species and and forms—that range from so-so to sublime. have documented the stress imposed by cultivars, according to the publisher. Dirr and Their inclusion of seasonal images of a urban heat islands, which increases suscepti- Warren introduce the reader to each taxon particular species or cultivar showcases its bility of red maples to pests, viz., gloomy with an opening paragraph that summarizes multiseason interest. scale (Melanaspis tenebricosa Comstock). noteworthy characteristics, which include The authors annotated the plant images Other investigators recommend special ac- mature height and spread, form, growth rate, with either a cultivar or trademarked name. commodations for city-grown red maples by texture, and ornamental features. Perhaps in subsequent editions the authors reducing impervious surface area to mini- Included in The Tree Book, but absent in will include image locations to answer the mize infestations and improve their perfor- the Encyclopedia,areaseriesofcriteria oft-asked question: ‘‘Will it grow around mance and longevity in this anthropocentric reminiscent of Dirr’s magnum opus, Manual here?’’ Only one photograph in the entire space. of Woody Landscape Plants (2009): ‘‘fo- book lists a location: the U.S. National Although I disagree with the authors’ liage,’’ ‘‘flowers/seeds/fruits/cones,’’ Arboretum. contention that this 7.5 lb. book is portable ‘‘adaptability’’ (origin and habitat), and Many of the stunning photographs of (digital alternatives are available in online, ‘‘landscape use.’’ The authors define only flowering trees justify their place in The Tree downloadable PDF, or ePub formats), I agree mature height and spread in the introduction, Book. They included many outstanding im- with their statement: ‘‘A computer is great for so the reader must assume the hardiness ages, such as the one of Laburnum · watereri seeking out very specific information, but we zones used in The Tree Book refer to the (Wettst.) Dippel ‘Vossii’ in full bloom with believe in the power of a book to encompass a
1650 HORTSCIENCE VOL. 54(9) SEPTEMBER 2019 subject within a framework of the authors’ marked names, accommodating genetic di- to plant a tree was 20 years ago. The second knowledge.’’ Tree-selection decisions, how- versity in a built environment that requires best time is now.’’ ever, are difficult to make with The Tree uniformity and symmetry, or whether the Dirr, M. A. 2009. Manual of Woody Book. Unlike Dirr’s Encyclopedia with its Tsuga hybrids that are resistant to hemlock Landscape Plants. 2009. 6th ed. Stipes 28-page section titled ‘‘Selecting Plants for woolly adelgid can still be considered natives Pub., Champaign, IL. Specific Characteristics or Purposes’’ where because of their Asian parentage. Dirr, M. 2011. Dirr’s Encyclopedia of the taxa are organized into 15 categories, The In summary, The Tree Book serves as an Trees and Shrubs. Timber Press, Portland, OR. Tree Book lacks features to select appropriate entree to a diverse collection of taxa with USDA Plant Hardiness Zone Map, 2012. plants for particular purposes and designs. foundational information that must be aug- Agricultural Research Service, U.S. Depart- Instructors of college-level woody plant mented by the knowledge and experience of ment of Agriculture. 12 June 2019.
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