If you are a resident of a city in the Midwest or Southern USA, have a look to the roadsides or empty lots as you take a drive on the outskirts of town this spring. At this time of year, there’s a good chance you’ll see bunches of dense, bright white flowers on some of the mid-sized trees, as in the photo below. Where I am, in eastern Tennessee, this first flowering tree (just before dogwoods and apple trees) sometimes occurs in clusters so thick it looks like a newly fallen snow. Though they are admittedly pretty against the mostly still brown backdrop of spring, these are problematic invaders- commonly referred to as “Bradford” pear tree, an ornamental introduced from China, whose official name is Callery pear (Pyrus calleryana, distinct from Asian pear, Pyrus pyrifolia).
Pear trees invading roadside habitat. Creative commons license from Britt Slattery, US Fish and Wildlife Service, Bugwood.org, via invasive.org
Callery pears (called Bradford pears in common usage because one of the most popular cultivated varieties is “Bradford”) were first introduced as an ornamental tree in the 1960s, though were previously grown as early as 1900 as a rootstock. They were assumed to pose a low threat of invasion due to self-incompatibility in which a given cultivar could not pollinate any trees of the same cultivar. However, as the number of cultivars have grown to several dozen, and as the tree has been planted more commonly, the genetically differentiated cultivars can cross pollinate and bear fruit with viable seeds. Unfortunately, it is now so common that it is almost a tree of choice in new suburbs due to its fast growth, attractive flowers and tidy cone shape. Birds eat the now abundant tiny pears and spread the seeds far and wide, so that Bradford pears are increasingly found along roadsides and in open fields. (For those interested, the distance between trees along the interstate gives a pretty good idea of the seed dispersal distances, with large clusters and then some lone trees hundreds of meters down the road.)
The pear trees cause numerous problems for those in the suburb and beyond. In addition to the overwhelming floral scent that some (like me!) find noxious, the trees have extremely weak wood and are prone to limb breakage, which can damage cars, homes and powerlines (see photo below). In dense stands, the pear tree also outcompete native trees. They are quite tolerant to many soil types and shade, and are reported as established outside cultivation in at least two dozen states. Their abundant fruit set and wide dispersal capabilities means that one escaped tree will soon become many!
Broken pear tree in residential area. Creative commons license from David J. Moorhead, University of Georgia, Bugwood.org, via invasive.org.
But invasivores may take heart because the fruits are reportedly edible and can be made into jams or wine! Pear wood is also a beautiful fine wood for carving or furniture. In addition to removing the fruit and the trees themselves, you can help by choosing native species that also have high ornamental value for their beautiful blooms this time of year, including redbud and dogwood. Read more about those native trees here!