Callery pear (Pyrus calleryana) was brought to the United States in the early 1900s for grafting onto fruit-producing european pear (Pyrus communis) trees to aid in fire blight management efforts (Culley and Hardiman, 2007). Although this objective was largely accomplished, one particular callery pear individual was marketed as the bradford pear tree and was once commonly planted. It is now nearly ubiquitous in lawns and other managed landscapes across much of the eastern (and parts of the western) United States. Bradford pear trees are self-incompatible, but cross-pollination can occur with other pear (Pyrus sp.) trees. This cross-pollination results in viable fruit that can be eaten by birds and other vertebrates, spread into new areas, and germinate (Culley, 2017; Culley and Hardiman, 2007).
Callery pear is now present across much of the eastern United States, growing in roadsides, old fields, vacant urban/suburban lots, and more recently encroaching into forested areas as shown in Fig. 1 (iNaturalist, 2021). Callery pear can grow in dense thickets and produce fruit in just a few years (Warrix et al., 2017), with seeds that can persist for more than a decade in the seedbank (Serota and Culley, 2019). Their growth form tends to be ramulose, and the many small branches are often covered in sharp thorn-like spur shoots (hereafter referred to as thorns), as shown in Fig. 2. Controlling callery pear requires sustained efforts, and several herbicides are effective (Flynn et al., 2015; Page et al., 2014; Vogt et al., 2020). However, lost in these control efforts is perhaps an equally urgent and practical question: what do land managers do about the thorns? Even after a callery pear tree has been killed with herbicide or cut down, the thorns remain sharp and dangerous. Many land managers and landowners have told the senior author (D.R.C.) about instances when callery pear thorns injured people and livestock, or punctured vehicle and wagon tires, as shown in Fig. 3. In some cases, hundreds to thousands of dollars and many work hours were lost because of equipment damage. How to avoid callery pear thorn damage is a common query from land managers and landowners involved with invasive species management.
Although prescribed fire is commonly used as a land management tool in the southern United States, fire alone is not a viable management option for callery pear (Warrix and Marshall, 2018). However, prescribed fire is being considered as part of a larger integrated pest management plan for callery pear, and knowing its effects on thorns may help land managers reduce damage to equipment and livestock. We hypothesized that fire would reduce the sharpness of thorns, while increasing their decomposition rate, thus resulting in a decreased probability of tire puncture.
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