Arboriculture & Urban Forestry 39(1): January 2013 Arboriculture & Urban Forestry 2013. 39(1): 11–16 11 Effects of Emerald Ash Borer Infestation on the Structure and Material Properties of Ash Trees Anand B. Persad, John Siefer, Roy Montan, Scott Kirby, Oscar J. Rocha, Michael E. Redding, Christopher M. Ranger, and Andrew W. Jones Abstract. Emerald ash borer (EAB), an invasive insect borer on ash trees, currently occurs in the Untied States and Canada. In many regions, large popu- lations of ash trees are affected with many trees exhibiting partial to full canopy dieback. Several cases exist in northwest Ohio, U.S., where EAB infested ash branches or stems fail prematurely during deadwood pruning or whole tree removal. This study was initiated to resolve the effects of EAB on the material properties of ash branches and stems. Visually non-infested ash trees and trees with recent and advanced EAB activity were examined. The data from static loading tests on primary branches indicate that maximum bending stress at failure was not significantly lower in EAB infested trees compared to non-infested trees. Examination of the fracture zone, however, revealed that wood moisture was significantly lower and more cracking was observed in wood sections of branches taken from EAB infested trees. During static loading, branch failure at the union occurred only in the EAB infested trees. In a wood resistance evaluation of infested and non-infested ash stems, significantly lower resistance was observed in advanced EAB infested ash stems when drilled at the base compared to drill sites 1 m above. This was not observed at similar drill site heights in the visually non-infested ash stems. These data may help identify risk elements associated with structural and material degradation of ash wood as early as one to two years after infestation by EAB. Key Words. Anchor Points; Biomechanics; Branch Failure; Emerald Ash Borer; Resistance Drilling; Static Loading; Zone of Fracture. Emerald ash borer (EAB) (Agrilus planipennis Fairmaire), was identified in mainland North America in 2002 in Michigan and Ontario (Haack et al. 2002). Invasive borers such as EAB may not be suppressed by natural forces upon introduction into new territory and often exploit resources beyond the carrying capac- ity. Currently EAB has been recorded in 15 states in the United States, as well as in Ontario and Quebec in Canada. The Ohio Department of Natural Resources estimates that 3.8 billion ash trees with standing timber valued at more than USD $1 billion could be affected in Ohio. EAB also has been deemed to have the potential to virtually eliminate ash as a compo- nent of the North American forests, affecting ecosystem pro- cesses and plant and animal communities (Herms et al. 2004). In a study of ice storm damage in urban trees in Champaign, Illinois, U.S., Hauer et al. (1993) reported that 6.9% of 290 green ash trees suffered the highest severity ratings and ranked green ash seventh (category: susceptible) in decreasing order of damage severity out of 25 urban tree species. Green ash is often consid- ered as an intermediate landscape tree in terms of susceptibility to breakage; increased risks of ash tree failure associated with EAB infestation have become a cause for concern, especially as it pertains to tree worker safety in EAB infested areas. In spring 2009, an unusual number of EAB ash tree work-related incidents (Scott Kirby, pers. comm.) occurred in the greater To- ledo, Ohio, area. Most of the incidents involved do-it-yourself homeowners; at least one case involved a professional arborist. Static loading of primary branches (Study Part 1) and resistance drill measurements (Study Part 2) of stems of green ash trees com- prised the major techniques used to examine the effects of EAB on the material properties of ash trees. Trees were sourced in the great- er Toledo area, a region of Ohio where large tracts of ash trees were infested by EAB for several years. Visually un-infested ash trees and trees under infestation for varying duration were evaluated. MATERIALS AND METHODS The effects of EAB on the structure and material properties of branches and stems of green ash (Fraxinus pennsylvanica Marsh) were evaluated in this study using two standard tests: • Study Part 1: Static loading of branches. • Study Part 2: Resistance drill assessments of lower por- tions of the stem. Tree and Branch Selection Green ash trees with trunk diameter at breast height (DBH) ranging from 30 to 50 cm were selected in recreation park environments in and around the city of Perrysburg in northwest Ohio. All selected trees were 12- to 15-years-old, 10 to 14 m in height and measured 5 to 7 m in drip line diameter. Three groups of five trees each were selected based on age of EAB infestation, further described as: • Group I: Five ash trees that showed no visible signs of EAB infestation. • Group II: Five ash trees that were currently infested with EAB (within the last two years) and had at least two thirds of their canopies still intact. ©2013 International Society of Arboriculture
January 2013
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