Callery Pear

Description:

Plant: 30-50 ft. tall, 20-30 ft. wide; young trees may be thorny. Leaves: deciduous, alternate, simple, broad-ovate to ovate, 1½-3 in. long; shiny dark green and leathery, small round-toothed margins; scarlet, mahogany, purple hues in fall. Flowers, fruits and seeds: flowers in early spring before the leaves, white with five petals, about 1 in. across; fruits mature in fall and are small, hard, brown, and almost woody. Spreads: by seeds that are dispersed to new locations by starlings and other birds that eat the fruits.

Habitat:

While beautiful in spring, these Callery Pear have invaded some of the Corps of Engineer land along the Lewisville Lake shore, forming dense groves that push out native plants.

Notes:

In the past, the potential for self-fruiting had generally been minimal because cultivars of Pyrus calleryanna were considered to be self-incompatible, unable to self-pollinate or produce fertile fruit from a genetically identical cultivar. However, by the late 1990's, it had become apparent in communities with large numbers of ornamental pear trees that many cultivars had unexpectedly begun to interbreed fairly readily. The hybrid fruit is eaten by starlings and other birds. The seeds are then dispersed into nearby fields, right-of-ways, parks or other natural open areas. Highly variable, many of the seedlings show characteristics such as thorniness that had been purposely bred out of their parent cultivar. The Callery pear progeny are now aggressively invading fields and other open areas, much like other introduced exotic plant species, such as Amur honeysuckle. The following consequences can occur as a result of this interbreeding: Ecological damage caused by displacing native plant communities Increased economic costs due to vegetation management problems near transportation corridors or under power line right-of-ways. Potential threat to electrical and transportation services from falling branches or toppled trees because of these notoriously fast-growing, weak-wooded trees. Callery pear was imported multiple times to the U.S., including the first introduction in 1909 to the Arnold Arboretum and an introduction in 1916 by the U.S. Department of Agriculture for development of fire blight resistance in the common pear (Pyrus communis), which was devastating the commercial pear industry. It was widely planted as a rootstock for common pear long before it gained interest as an ornamental. Around 1950, the ornamental value and hardiness of Callery pear were recognized, leading to the development of a number of cultivars, including ‘Bradford.’ Cultivars in the U.S. originated from China and represent different genotypes. While some genotypes are self-incompatible, meaning they require cross pollination from another genotype in order to set seed, others can pollinate themselves. Different genotypes growing near each other (e.g., within about 300 ft.) can cross-pollinate and produce fruit with viable seed. Also, cultivars are often grafted onto seed-grown rootstocks with varying genotypes; if the plant produces shoots from the rootstock (which it often does), then these shoots and the graft can pollinate one another. Thus, the Bradford pear cultivar is one of several cultivars (varieties) of Callery pear capable of spreading and being invasive. Pyrus calleryana ‘Bradford’ is one genotype. It is propagated asexually (by grafting and cuttings) and does not change over time. Any plant resulting from a seed produced by Pyrus calleryana ‘Bradford’ is a different genotype of Pyrus calleryana and not a member of any cultivar (unless somebody propagates that seedling and names it as a new cultivar). The plants that spread in natural areas are not cultivars. They are sexually reproducing populations consisting of multiple genotypes that recombine every generation. Distribution and Habitat Callery pear occurs throughout the eastern U.S. from New Jersey to Illinois and south to Texas. It grows best in full sun but will tolerate some shading and drought. Ecological Threat Once established Callery pear forms dense thickets that push out other plants including native species that can’t tolerate the deep shade or compete with pear for water, soil and space. A single tree can spread rapidly by seed and vegetative means forming a sizeable patch within several years. Its success as an invader results from its capacity to produce copious amounts of seed that is dispersed by birds and possibly small mammals, seedlings that germinate and grow rapidly in disturbed areas and a general lack of natural controls like insects and diseases, with the exception of fire blight.