Q. I have heard recently that flowering pear trees are invasive. Is this true?
A. There is increasing evidence that flowering pear tree seedlings are spreading rampantly into wild disturbed areas. Many states on the East Coast list this tree as invasive, while many other states such as Indiana have it on their invasive watch lists.
Flowering pear was initially brought to the United States in the early 1900s to combat fire blight (a devastating bacterial disease) in the common edible pear. Scientists and plant explorers were sent to China, Taiwan and Japan to collect seed from trees growing in their native habitat to be used for rootstocks in common pear. Seedling trees were planted in various locations in Oregon. By 1950, there were still a few flowering pears at the USDA Plant Introduction Station in Oregon. In 1952, plant breeders at the station noticed one particular vigorous, thornless tree. Clones of this tree were planted in a nearby subdivision.
After eight years, the cultivar Bradford was born in honor of a horticulturalist at the station. Bradford was prized for its white spring flowers, rapid growth, adaptability to a wide variety of soil and weather conditions, compact form and glossy, dark green leaves. It was widely and extensively planted in landscapes and street plantings. Many nurseries began developing and releasing their own cultivars. Aristocrat was selected in 1969 from seedlings growing at a nursery near Independence, Ky. Chanticleer was cloned from a street tree in Cleveland.
Over time, Bradford was found to have issues. The narrow crotch angles of the branches eventually caused individual trees to split under their own weight after about 15 to 20 years of growth. Aristocrat and Chanticleer were planted more extensively. Ornamental pear trees planted in urban areas are now a mix of different cultivars.
This doesnt seem like a problem, but this diversity in flowering pear has contributed to its invasive nature. Flowering pears are mostly self-incompatible and produce little – if any – fruit. More recently, however, abundant fruit set has been detected in many cultivars growing in urban areas.
Why? If the rootstock of a flowering pear is allowed to develop, it may cross with another pear that is genetically different. Numerous fruits are also produced by crosses between cultivars that have different Chinese ancestry.
Flowering pear seedlings have now begun to aggressively appear in many natural areas. These sun loving trees are taking over native habitat. When native habitat is replaced by exotic species, then the birds, insects, and other creatures which depend on that native habitat also disappear.
Because of their increasing invasiveness, susceptibility to fire blight, and poor branching habit; flowering pears are becoming a poor choice for urban landscapes. Homeowners and landscape professionals should prevent suckering of existing flowering pears and replace flowering pears with other species such as serviceberry and fringe tree whenever possible.
Wild pears that have escaped to natural areas should be removed.