Arboriculture & Urban Forestry 36(1): January 2010 in excess of the 10-20-30 rule (Santamour 1990). For example, maples constituted 50% of the street trees in Toledo, Ohio, and 37% of the trees representing 56% of the canopy cover in Xenia, Ohio (Sydnor and Subburayalu 2008a; Sydnor and Subburayalu 2008b). Based on the 10-20-30 guidelines, it would not be recom- mended to plant maples in Ohio’s public spaces unless or until community stocking levels are reduced below 20% to reduce the potential risk of an introduced exotic pest such as the Asian long- horned beetle that might attack maples (Fater 2008). In another study, when demand was expressed as percent market share, the demand for maples by urban foresters was expected to decline by almost two percentage-points from 2005 to 2010 (Sydnor 2008). The Cornaceae, Hamamelidaceae, and Pinaceae families tended to be available in excess of quantities demanded by urban foresters. Pines and spruce are rarely used as street trees in Ohio, but commonly available due to demand for landscape plant- ings. Likewise, many plants in the dogwood family are forest understory plants and infrequently used on community streets. Plants in the Betulaceae, Eucommiaceae, Fagaceae, Leguminosaea, Oleaceae, Platanaceae, Tiliaceae, and Ulmaceae families generally are lacking in availability. Seed sources are important for plants in the beech family, thus making propagation more difficult. For example, pin oak, a member of Fagaceae, is native and adaptable if grown from local seed sources in the higher pH of central Ohioan soils, but is prone to develop an iron deficiency if grown from seed plants adapted to an acidic soil region of the United States. Genus and Species Level When considering species, Acer palmatum (Japanese), A. platanoides (Norway), A. saccharum (sugar), A. × Freemanii (Freeman), and A. rubrum (red) maples demonstrated excess availability for both 2005 and 2010 (Table 2). Conversely, Acer campestre and A. truncatum maples were deficient in availability for 2005 and 2010, while A. buergeranum and A. ginnala maples supplies appeared to fall short of anticipated demand for 2010. The projected lack of downy serviceberry may simply be a no- menclatural problem as Amelanchiers are often sold under more than one scientific name. Most cultivars seen in the nursery trade are Amelanchier × grandiflora but are sold under a variety of names. Carpinus betulus (European hornbeam) was projected to be in limited supply for both 2005 and 2010. Interestingly, this plant has not done well in Ohio except in the colder areas (Sydnor et al. 1999). The senior author has observed this plan doing well north of Ohio. Hornbeam borer attacks plants in the warmer areas of Ohio. Crataegus (hawthorns) establish but perform poorly in stressful urban sites, such as tree lawns, in Ohio (Sydnor et al. 1999), and now tend to be used in less stressful lawn panels or plant beds. Hawthorn hybrids were or are projected to be lacking in availability. Crataegus viridis, C. punctata, C. Phaenopyrum, and C. crus-galli inermis hawthorns are also utilized in landscape plantings with green and thornless cockspur hawthorn being available in excess of demand. Ash (Fraxinus spp.) was an interesting situation with a warning as to the importance of taxonomic diversity. In Feb- ruary 2003, EAB was discovered in Lucas County, Ohio. In spring 2004, the landscape market for ash collapsed. Ohio com- munities planted few ash trees to fill in plantings or for spe- cial requests in 2005, and none were requested for 2010. The plant was not listed in the 2008 Ohio Nursery Stock Survey. 49 Gleditsia triacanthos inermis (thornless honeylocust) was de- ficient in availability for 2005 but in excess for 2010. Communi- ties have been reducing the use of honeylocust as a street tree as it frequently damages sidewalks but performs well and rarely exceeds 10% of an Ohio community’s urban forest. If properly sited, this tree could be used more frequently. Some communities substitute Gymnocladus dioicus (Kentucky coffeetree), for hon- eylocust. This leguminous tree grows slowly in nursery produc- tion and has an open, irregular canopy making it unpopular with many growers thus explaining its limited availability in 2010. Parrotia persica (Persian parrotia) and Phellodendron amurense (Amur corktree) are projected as deficient in availability for 2010 despite urban forester’s lack of ex- perience with this tree. Communities looking for great- er diversity are seeking these plants. This may repre- sent a possible marketing opportunity for producers. Platanus spp. were deficient in availability in 2005 and are pro- jected to be so in 2010 as well. Communities favor London plane- tree (P. × acerifolia) for planting despite its being marginally cold hardy because of resistance to sycamore anthracnose, a common cosmetic disease. Sycamore (P. occidentalis), in contrast, has been variably sensitive to the cosmetic disease but resistant to canker- stain (often fatal to London planetrees in Ohio). Interestingly, if demand were expressed as an expected change in percent market share from 2005 to 2010, sycamore would be increasing slightly while London planetree would be diminishing (Sydnor 2008). Prunus sp. (cherries and plums) were variable with some shortages in flowering cherries as communities seek alterna- tives to crabapples and pears. When considered as percent market share, cherries are generally decreasing in community demand (Sydnor 2008). Plums and cherries are more com- monly seen in private landscapes rather than streetscapes. Quercus spp. (oaks) are variable but generally lacking in availability, especially for 2010. Many nursery profession- als prefer to grow clones and many oaks are difficult to propa- gate asexually. Additionally, many oaks take additional time to grow which adds to a nursery’s costs. Despite these chal- lenges, oaks appear to be a real opportunity for nursery pro- ducers given the increasing interest from urban foresters. Pekin (Syringa pekinensis) and Japanese (S. amurensis) tree lilacs are deficient in availability and increasing in demand as a percent market share (Sydnor 2008). They are being used as flow- ering trees but are small in stature and slow growing in tree lawns. Lindens (Tilia sp.) are generally undersupplied with American (T. americana) and silver (T. tomentosa) be- ing in highest demand. ture in this genus may factor in the results shown. Elms (Ulmus sp.) are generally lacking in availabil- ity. Fast growth and urban tolerance are among the as- sets for elm species. Disease resistance has been identified for many serious problems, but some cosmetic concerns are present. Interestingly, lacebark elm (U. parvifolia) was one of the few elms decreasing in demand when ex- pressed as change in percent market share (Sydnor 2008). Overall, availability fell short in this study for 2005 and 2010. Elm seems poised to be among the most popular species for landscape applications in another ten years. Again inaccurate nomencla- ©2010 International Society of Arboriculture
January 2010
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