Pyrus calleryana is a medium sized, deciduous ornamental tree with an upright conical form, sometimes spreading with maturity, reaching 10 to 20 meters in height. Leaves are alternate, simple, heart shaped to ovate or broad ovate with crenate margins; glossy and dark green in color on top, paler light green on bottom; leathery and glabrous with an acuminate tip and finely serrated margins. Flowers appear in large clusters about 7.5 centimeters in diameter, before or with leaves in spring, white in color and very attractive. Fruit consists of small pome about 1.5 centimeters in diameter, olive-brown to tan in color speckled with tiny russet dots; resembles a tiny pear, very bitter. Each fruit typically contains 2-6 seeds. Twigs are reddish-brown to grey with large, ovate, fuzzy terminal buds about 0.5 to 1.5 centimeters in length on branch tips and spur shoots. Bark is light brown to reddish-brown and smooth with lenticels when adolescent becoming greyish-brown with slight furrows and scaly ridges with maturity (Brand, 2001; Ohio State University, 2008; Seiler et al. 2008).
There are an increasing number of cultivars of Pyrus calleryana. Some of the most common commercially available cultivars are Aristocrat, Autumn Blaze, Bradford, Redspire and Cleveland Select which is also known as Chanticleer, Select, or Stone Hill. Characteristics of individual cultivars are often predictable, such as expected fruit set and seed viability, but crosses of these cultivars produce trees that reveal traits not characteristic of the individual cultivars they were derived from, such as forming dense thorny thickets (Ohio State University, 2008; Culley & Hardiman, 2007).
Pyrus calleryana is a short to medium lived species, often living to age 25 to 30 if pruned correctly and reaching sexual maturity around age 3. Fruits take months to mature, staying on the tree until autumn. Seeds need a period of cold stratification for viability. Seeds exhibit secondary dormancy if exposed to warm temperatures in late winter, making seed banks more viable (Culley & Hardiman, 2007; Swearingen et al. 2002; USDA NRCS, 2008).
Since commercial introduction in 1962, Pyrus calleryana is one of the most commonly planted ornamentals in the United States. It is prized for its early spring flowers, rapid growth and fall color (Culley and Hardiman 2007), P. calleryana is also used as graft stock, and as a pollen donor for commercial pear production. P. calleryana was originally brought to the United States to fight fire blight in the common pear (Culley & Hardiman, 2007; USDA ARS, 2008; Vincent, 2005).
While Pyrus calleryana prefers full sunlight with moist, well drained soils, it can tolerate partial shade in poor soils of variable pH, drought, heat, pollution and restricted or shallow rooting zones and is highly disease and pest tollerant. Pyrus calleryana has a low shade tolerance, rarely being found in the understory in the wild and can not survive temperatures below -28 degrees Celsius; recommended for USDA hardiness zones 5-9 (Culley & Hardiman, 2007; Ohio State University, 2008; Swearingen et al. 2002).
Pyrus calleryana is a perennial tree that starts to flower around age 3. Flower buds are produced in early spring in clusters of 6 to 12 flowers per inflorescence. Each flower can produce a maximum of 10 seeds, however 2 to 6 seeds per flower is more likely. Flowers are highly attractive to insect pollinators. Many cultivars will not often self pollinate, exhibiting gametophytic self incompatibility to a certain degree. In isolation, the cultivar Bradford pear will set fruit at a very low rate and is incompatible with the cultivar Hansen pear and P. communis.
Planting more than 1 cultivar of any P. calleryana species in an area will often greatly increase fruit set (Culley & Hardiman, 2007; Swearingen et al. 2002; Vincent, 2005).
Although it varies between cultivars, Pyrus calleryana generally has a medium C:N ratio, a medium fertility requirement, a low CaCO3 tolerance, no anaerobic tolerance, a pH range of 5 to 7.5, and requires a minimum of 35 inches of rain per year (USDA NRCS, 2008).
Principal source: Culley, T.M. and Hardiman, N.A., 2007. The Beginning of a New Invasive Plant: A History of the Ornamental Callery Pear in the United States. BioScience: Vol. 57, No. 11, pp.956-964. American Institute of Biological Sciences, 2007. (doi:10.1641/B571108)
Vincent, M.A., 2005. On the spread and current distribution of Pyrus calleryana in the United States. Castanea 70: 20–31.
Swearingen, J. and Reshetiloff, K. and Slattery, B. and Zwicker, S. 2002. Plant Invaders of Mid-Atlantic Natural Areas. National Park Service and U.S. Fish & Wildlife Service, Washington, D.C. pp. 82.
Compiler: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Review: Theresa M. Culley, Assistant Professor Department of Biological Sciences University of Cincinnati, Ohio USA
Publication date: 2008-06-05
Recommended citation: Global Invasive Species Database (2017) Species profile: Pyrus calleryana. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=1389 on 29-03-2017.
As an ornamental, Pyrus calleryana is one of the most widely planted trees in the United States. Also known as Callery pear, this tree often has structural problems, becoming prone to breakage around age 20. Until recently the species was considered unable to escape from cultivation because of self-incompatibility, vegetative propagation and rare fruit production (Gilman and Watson 1994 in Culley and Hardiman 2008).
However due to increased number of cultivars planted in close proximity in urban landscapes, cross pollination has caused\r\nP. calleryana cultivars to hybridize. It is well known that intra-specific hybridization can be an important stimulus of invasiveness, allowing hybrids to expand ecological tolerance and invade new niche environments (Culley & Hardiman 2009). Hybridization has allowed P. calleryana to produce fruits with viable seed, which subsequently are dispersed by European starlings and other wildlife. As a consequence increasing numbers of wild individuals in natural areas are being found (Culley and Hardiman 2007).\r\nPyrus calleryana often invade disturbed areas and can disrupt the establishment of middle to late successional species, sometimes forming dense thorny thickets that are impenetrable to humans (Culley & Hardiman, 2007; Vincent, 2005).
: Swearingen et al
. (2002) recommend not planting Pyrus calleryana
. The root stock of grafted plants can sprout and reproduce by crossing with the upper scion. Sucker growth should be promptly removed to prevent possible cross pollination with the scion (Culley & Hardiman, 2007).
Physical: Pull up seedlings by hand or with a gardening tool which helps capture the roots. Cut down trees and immediately treat entire surface area of cut stump with a systemic herbicide such as concentrated glyphosate or triclopyr, following all labeling instructions, to prevent resprouting. Adult trees can be girdled in spring or summer by cutting through the bark around the entire circumference of the tree at the base of the tree. Mowing is not effective because of likelihood of resprouting (Swearingen et al. 2002).
Chemical: Treat entire surface area of any cut stumps immediately with a systemic herbicide such as concentrated glyphosate or triclopyr, following all labeling instructions, to prevent resprouting. To prevent fruiting of adult trees, spray with ethephon during full bloom; only 95% effective (Culley & Hardiman, 2007).