City Trees

Prior to accepting the position of Horticulturist for the City of Clemson four years ago, I worked for 25 years in the private landscaping sector. In the early 1990s a lot of the Bradford pears were just reaching that point of maturity when they start to self-destruct due to their poor branching habit. My first encounter with the Callery pear was in 1993 on the grounds of a local technical college. Our crew was removing the tree for a construction project and thinking it was a regular old Bradford; I started whacking away at the branches and quickly discovered that this particular "Bradford" had a sharp end to it! After getting ripped to shreds trying to remove the tree I asked the grounds superintendent, what on earth is this thing? He informed me that I was dealing with a parent of the Bradford pear as this specimen was reverting (by way of bud sport) back to its thorny parentage. Fast forward twenty years to 2013 and I was a month into my new position with the City of Clemson. The transitional vacancy in leadership had left a lot of areas unkempt and my new crew and I spent a lot of that first year on reclamation. When we started clearing—and getting scratched by—a dense thicket of vegetation beside a parking lot at City Hall, I realized the thicket was my old nemesis, the Callery pear. It had reached a shocking size and dominance. In the last four years we have removed many of these nasty pear volunteers. Callery pear has now joined privet (Ligustrum sinese) and thorny olive (Elaeagnus pungens) on our "public enemy #1" invasive plant list. I would discourage the sale and use of this public pest! —Tony Tidwell, Horticulturist, City of Clemson Parks and Recreation, Clemson, South Carolina Americorps volunteers clearing rogue Callery pear hybrids from natural areas in Columbia, Missouri. Photo by Brett O'Brien unparalleled toughness including tolerance to drought and resistance to fire blight, a devastating bacterial disease that injures and kills edible pears. Back in 1963, Bradford pear appeared to be the perfect ornamental street tree but its Achilles' heel turned out to be its production of closely spaced, upright branches. As these poorly attached branches grew and expanded in gir th, the crown tended to split apar t during snow-, ice-, and wind- storms. It often happened to unpruned or poorly pruned trees when they reached 15 to 20 years of age. To overcome this structural flaw, cultivars were developed that offered improved branching habits, such as 'Aristocrat' and 'Chanticleer'; the latter was the SMA 2005 Urban Tree of the Year. Other cultivars were developed with narrower forms, such as 'Capital', a U. S. National Arboretum release, that embodied the aesthetic and urban-tolerant traits of Bradford but offered applications in tight, confined locations. This profusion of Callery pear cultivars eventually led to another problem that had ecological consequences. In the past, Bradford pear rarely produced viable fruit because it's self-infer tile, but with the widespread planting of cultivars that differed slightly genetically, the barrier to fer tility and subsequent fruit production was overcome. Fur ther, in some cases the Callery pear understock of a Bradford pear would sprout, flower, and provide viable pollen. The Callery pear fruits were consumed and dispersed by birds and other ani- mals to open, disturbed habitats where the progeny formed dense thickets. These naturalized Callery pears mature early—flowering star t- ing at three years of age—and are one of the first trees to bloom in early spring. They're also one of the last trees to lose their leaves in fall. Callery pears are resistant to insects and diseases and their thorny stems and branches discour- age deer-browsing. Interestingly, the "Survivor Tree" at the 9/11 Memorial is a Callery pear that survived the September 11, 2001 terror attacks at the World Trade Center. In the context of the Memorial, it serves as a symbol of survival, recovery, and resilience. Some states in the Mid-Atlantic, Southeast, and Midwest regions of the U.S. have declared Callery pear to be an inva- sive, self-sustaining species that dominates and disrupts native flora. Here in South Carolina, Callery pear is on the invasive watch list. In the past, I encouraged Bradford pear owners in our state to selectively prune the branches. Now that I have witnessed large tracts of land throughout our state covered like a white fog in early spring, I encourage them to prune Callery pears at soil level. –Bob Polomski www.urban-forestry.com 17

• Cover