Pacific Island Ecosystems at Risk (PIER)

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Pyrus calleryana
Decne., Rosaceae
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Present on Pacific Islands?  no

Primarily a threat at high elevations?  no

Risk assessment results:  High risk; score: 9 (Hawaii-Pacific Weed Risk Assessment for Pyrus calleryana)

Other Latin names:  Pyrus kawakamii Hayata

Common name(s): [more details]

English: Bradford pear, callery pear

Habit:  tree

Description:  "Pyrus calleryana (Figure 1) is a tree 10-20 m tall, with a crown 8-15 m wide; the bark is light brown in younger plants, darkening with age to a deep grayish brown and becoming shallowly furrowed. The crown shape is variable, depending on the cultivar, ranging from broadly ovate to pyramidal to columnar (Haserodt and Sydnor 1983). While the species is thorny in its native habitat (Shen 1980), many cultivars are thornless (Fare et al. 1987b), though not all (Fare et al. 1987a). The branches range from glabrous to sometimes densely pubescent. Terminal buds of the species are densely pubescent and much larger than those of other Pyrus species, often reaching12-15 mm in length. Its leaves are alternate, on petioles 2.2-4.5 cm, broadly ovate to ovate or elliptical, 4-9 cm long, short-acuminate to attenuate at the apex, rounded to shallowly cordate at the base, with crenate margins; they are pubescent when young, quickly becoming glabrous and dark glossy green as they expand. The inflorescence is subumbellate or corymbose to short-racemose, containing 5-12 five-merous white, malodorous flowers on pedicels 1-3 cm long. The hypanthium is usually glabrous, with narrowly triangular sepals that are pubescent adaxially and are deciduous in fruit. The petals are broadly ovate to orbicular, and 6-7 mm wide and long. There are usually about 20 stamens, with anthers that range from pink to burgundy in color. There are 2 or 3 styles. The fruit is spherical to slightly oblong, 1-1.5 cm long, brown to yellow-brown, white to tan dotted, with 1-2(-4)" seeds. Flowering is in March and April, with the flowers opening as the first leaves begin to unfurl; there is sometimes also a second flowering in September-October, especially in drought or disease stressed trees (e.g., Tepe & Strittmatter 956 [MU]; Vincent 11337 [MU]). Fall leaf coloration is often very dramatic, varying from maroon to burgundy, occasionally yellow to orange and red. The species has a relatively short life-span of 25-30 or perhaps 50 years (Dirr 1990, Swearingen et al. 2002). There are documented chromosome numbers of n = 17, 2n=34 (Adati 1933, Nebel 1929, Zielinski and Thompson 1967)." (Vincent 2005, p. 23-24)

"Trees 5–8 m tall. Branchlets reddish brown when young, grayish brown when old, terete, initially tomentose, soon glabrescent, glabrous when old; buds triangular-ovoid, sparsely tomentose, apex shortly acuminate. Stipules caducous, linear-lanceolate, 4–7 cm, herbaceous, glabrous, margin entire, apex acuminate; petiole 2–4 cm, glabrous; leaf blade broadly ovate or ovate, rarely narrowly elliptic, 4–8 × 3.5–6 cm, glabrous, base rounded or broadly cuneate, margin obtusely serrate, apex acuminate, rarely acute. Raceme umbel-like, 6–12-flowered; peduncle glabrous; bracts caducous, linear-lanceolate, 0.8–1.3 cm, membranous, adaxially tomentose, margin initially glandular serrate, apex acuminate. Pedicel 1.5–3 cm; glabrous. Flowers 2–2.5 cm in diam. Hypanthium cupular, glabrous. Sepals lanceolate, ca. 5 mm, abaxially glabrous, adaxially tomentose, margin entire, apex acuminate. Petals white, ovate, ca. 1.3 × 1 cm, base shortly clawed, apex rounded. Stamens 20, slightly shorter than petals. Ovary 2(-4)-loculed, with 2 ovules per locule; styles 2(-4), nearly as long as stamens, glabrous basally. Pome blackish brown with pale dots, globose, ca. 1 cm in diam., 2(or 3)-loculed; sepals caducous; fruiting pedicel 1.5–3 cm, glabrous. Fl. Apr, fr. Aug–Sep. 2n = 34*." (Flora of China)

Habitat/ecology:  In China: "Slopes, plains, mixed valley forests, thickets; 100-1800 m." (Flora of China)

"Callery pear cultivars are known for their ability to tolerate a wide range of environmental conditions, including moisture, disease, and pollution. . . . 'One finds it [Pyrus calleryana] growing under all sorts of conditions; one time on dry, sterile mountain slopes; then again with its roots in standing water at the edge of a pond; sometimes in open pine forest, then again among scrub on blue-stone ledges in the burning sun; sometimes in low bamboo-jungle...and then again along the course of a fast flowing mountain stream or on the occasionally burned-over slope of a pebbly hill.'" (Culley & Hardiman 2007, p. 960)

In North America, where it is considered invasive, Pyrus calleryana is "[most] commonly found in disturbed woodlands, along roadsides, and in old fields. Trees can grow in a wide range of soil types. They spread most rapidly in temperate climates requiring some cold for seeds to germinate but not withstanding extremely cold temperatures." (A revision of Tibouchina, p. 115)

Propagation:  Propagates by seed. (Vincent 2005, p. 20)

In North America, where it is considered invasive, Pyrus calleryana "spread[s] most rapidly in temperate climates requiring some cold for seeds to germinate but not withstanding extremely cold temperatures." (Kaufman & Kaufman 2007, p. 115)

"Reproduction. Pyrus calleryana is a perennial tree that begins flowering at approximately three years of age. It is one of the first trees to leaf out in the early spring and one of the last to retain its leaves in late autumn. Flower buds of this species are produced in early spring before leaf formation, and typically appear grouped together in approximately 6 to 12 flowers per inflorescence (Cuizhi and Spongberg 2003). Individual flowers are protandrous, about 2 to 2.5 centimeters (cm) in diameter, and consist of five sepals, five petals, two sets of 10 anthers each that differentially dehisce, and two to five carpels (Cuizhi and Spongberg 2003) with two ovules per locule. This produces a maximum seed number of 10, although the actual number is usually between 2 and 6. The flowers are strongly malodiferous and are highly attractive to insect pollinators, including generalist honeybees (Apis mellifera L.), bumblebees (Bombus terrestris L.), other introduced bees, and hoverflies (Syrphidae) (Farkas et al. 2002). Fruits take several months to develop and remain on the tree until they mature in early to late autumn (August to October). The fruits are consumed and the seeds dispersed in late fall by a variety of animals, such as European starlings and American robins (Gilman and Watson 1994, Swearingen et al. 2002). A prominent seed bank is likely for P. calleryana because its seeds possess secondary dormancy if exposed to warm temperatures in late winter (Huxley 1999). The species is diploid (2n = 34; Zielinski and Thompson 1967, Cuizhi and Spongberg 2003). ¶Self-incompatibility. Self-incompatibility. ¶Like other members of the Rosaceae, P. calleryana is self-incompatible (Zielinski 1965) and thus cannot produce fruits through self-pollination." (Culley & Hardiman 2007, p. 959)

Native range:  The native range of Pyrus calleryana Decne. (Rosaceae) includes China, Taiwan, Korea, Vietnam, (GRIN), and Japan (Flora of China).

Impacts and invaded habitats:  "Dense, often thorny thickets of callery pear prevent colonization by native species. . . . Trees can produce fruits after only 3 years of growth. Birds and small mammals. . .disperse the seeds. Although cultivars are self-sterile . . . enough other cultivars are now widely planted that viable seeds are frequently produced." (Kaufman & Kaufman 2007, p. 115)

"Invasive problem in several areas in the US." (CAL-IPC)

"Pyrus calleryana, a very commonly planted ornamental tree species, is documented as an escape from cultivation in the District of Columbia and 152 counties or parishes in 25 states, and is reported as new to California, Michigan, Missouri, New Jersey, and West Virginia. . . .the species is rapidly becoming invasive in much of its horticultural range in at least the eastern United States. . . . Callery pear often produces thorny thickets as it escapes into marginal and disturbed areas, and appears to be reproducing readily in the wild." (Vincent 2005, p. 20)

"Concerns about the invasive potential of callery pear began to surface in the literature in the late 1990’s, and, by the turn of the century, were being expressed with increasing frequency (Reshetiloff 2002, Rowan 2002, Southeast Exotic Pest Plant Council 2001, Stewart 1999, Thompson 1999). The species has been shown to be escaping (see publications of numerous state records listed below), though the extent to which it has been doing so is only now becoming apparent. In fact, some authors (e.g., Mohlenbrock 1986) describe the species as "rarely escaping." Callery pears are precocious, having a very short juvenile period, and 19states:Alabama(Diamond 2003, Kartesz and Meacham 1999), Arkansas (Smith 1988, Sundell 1986, Sundell et al. 1999), Florida (Wunderlin 1998), Georgia (Kartesz and Meacham 1999), Illinois (Mohlenbrock 1986, Swink and Wilhelm 1994), Indiana (Kartesz and Meacham 1999), Kansas (Freeman et al. 2003), Kentucky (Clark and Bauer 2001, Weckmanet al. 2003), Maryland (Santamour and McArdle 1983, Stewart 1999), Mississippi (Kartesz and Meacham 1999), New York (Anonymous2002a),NorthCarolina(Nesom2000a), Ohio (Vincent and Cusick 1998, Cooperrider et al. 2001), Oklahoma (Taylor et al. 1996), Pennsylvania (Rhoads and Block 2000), South Carolina (Kartesz and Meacham 1999), Tennessee (Tennessee Exotic Pest Plant Council 2001), Texas (Jones et al. 1997), and Virginia (Kartesz and Meacham 1999). . . . ¶Pyrus calleryana can now be described as escaping and adventive, becoming widely naturalized (Nesom 2000b). It seems unquestionable that this species is becoming invasive, as defined in other studies (Lehtonen 2001, Reichard and White 2001, Swearingen et al. 2002). Callery pear is developing self-sustaining populations in many areas as it escapes and spreads. It is beginning to cover larger and larger areas, due in large part to the fact that it is so widely planted, perhaps even over-planted, throughout the United States. It seems to have few, if any, natural controls. Indeed, callery pear seems almost ideally suited to become an invasive species: it is tolerant of a wide range of growing conditions (Gilman and Watson 1994a,1994b,1994c), is attacked by few pests (Bell 1990), grows rapidly, reaches sexual maturity at a young age (Bell and Zimmerman 1990), and has bird-dispersed seeds that are produced in frequent large fruit set (Fare et al. 1987b; Gilman and Watson 1994a, 1994b, 1994c). Pyrus calleryana seems almost a textbook example of a plant designed for invasion (Reichard 2001, Reichard et al. 2001, Reichard and Hamilton 1997, Rejmanek 2001). While callery pear was introduced with the best of intentions, it now seems that a plague is truly upon us. Touted by some as a sterile plant and promoted widely, it has become proof that one can indeed have too much of a good thing. Dirr (1990) was correct in more ways than he realized when he voiced his concern that the tree was approaching "epidemic proportions"! It seems quite evident that callery pear will continue to spread from cultivation anywhere in the United States where it is not limited by extreme cold, or extreme drought, or extreme heat." (Vincent 2005, pp. 20-23)

Presence:

Pacific Rim
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
Asia
Asia (Pacific rim)
Korea native
U.S. National Plant Germplasm System (year unknown)
accessed 20180122
Australia
Australia (continental)
New South Wales introduced
California Invasive Plant Council (CAL-IPC) (2016)
established ("naturalized")
Australia
Australia (continental)
Australia (continental) introduced
California Invasive Plant Council (CAL-IPC) (2016)
established ("naturalized") in South Australia and New South Wales
China
China
China (People's Republic of) native
U.S. National Plant Germplasm System (year unknown)
accessed 20180122
China
China
China (People's Republic of) native
Vincent, Michael A. (2005) (p. 20)
"native to eastern and southern China...."
China
China
China (People's Republic of) native (presumably)
Flora of China (year unknown)
PIER assumes that range given in document is native; it's not stated explicitly (but it conforms to other references)
Japan
Japan
Japan (country) native (presumably)
Flora of China (year unknown)
PIER assumes that range given in document is native; it's not stated explicitly (but it conforms to other references)
Taiwan
Taiwan Island
Taiwan Island native
U.S. National Plant Germplasm System (year unknown)
accessed 20180122
Taiwan
Taiwan Island
Taiwan Island native
Vincent, Michael A. (2005) (p. 20)
United States (west coast)
United States (west coast states)
USA (California) introduced
U.S. National Plant Germplasm System (year unknown)
established ("naturalized")
Vietnam
Vietnam
Vietnam (Socialist Republic of) native
U.S. National Plant Germplasm System (year unknown)
accessed 20180122
Vietnam
Vietnam
Vietnam (Socialist Republic of) native (presumably)
Flora of China (year unknown)
PIER assumes that range given in document is native; it's not stated explicitly (but it conforms to other references)
Also reported from
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
Europe
Europe
Europe introduced
California Invasive Plant Council (CAL-IPC) (2016)
established ("naturalized")
South Africa
South Africa
South Africa (Republic of) introduced
California Invasive Plant Council (CAL-IPC) (2016)
established ("naturalized")
United States of America
United States
United States introduced
cultivated
U.S. National Plant Germplasm System (year unknown)
established ("naturalized")
United States of America
United States
United States introduced
invasive
cultivated
Vincent, Michael A. (2005) (p. 20)
accessed 20180122
United States (continental except west coast)
United States (other states)
United States (other states) introduced
invasive
cultivated
Kaufman, Sylvan Ramsey/Kaufman, Wallace (2007) (p. 114)
"Found from New York south to Florida and west to Kansas and Indiana." ) (p. 114)
"They spread most rapidly in temperate climates requiring some cold for seeds to germinate but not withstanding extremely cold temperatures." (p.&nbnsp;115)

Comments:  For other references to Pyrus calleryana as an "environmental weed, naturalised, weed," see the Global Compendium of Weeds.

Control:  "Removal and control. There are few documented management strategies for the Callery pear. The most effective control practice for wild trees is complete removal (Swearingen et al. 2002). For large trees that have been cut down, an appropriate systemic herbicide, such as concentrated glyphosate or triclopyr, must be applied immediately to all parts of the freshly cut trunk to prevent regrowth (Swearingen et al. 2002). Trees can also be girdled about 15 cm above the ground during spring and summer, if complete removal is not possible. Mowing of saplings and small trees is ineffective, because the species readily sprouts from any existing trunk or root system. Seedlings and shallow-rooted plants can be pulled up with care if the soil is moist (Swearingen et al. 2002)." (Culley & Hardiman 2007, p. 961)

"Seedlings can be hand pulled. Saplings can be pulled out using tools like a weed wrench. Larter trees can be girdled or cut down. Resprouts can be sprayed with glyphosate or triclopyr." (Kaufman & Kaufman 2007, p. 116)


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This page was created on 12 SEP 2017 and was last updated on 21 MAY 2018.