94 Luley et al.: Trunk Decay in Street Tree Maples Arboriculture & Urban Forestry 2009. 35(2): 94–99 Frequency and Severity of Trunk Decay in Street Tree Maples in Four New York Cities Christopher J. Luley, David J. Nowak, and Eric J. Greenfield Abstract. A proportional random selection of street tree Norway, silver, and sugar maples, and other species among four diameter classes were surveyed in the U.S.’ New York cities of Albany, Buffalo, Rochester, and Syracuse for decay incidence and severity. Decay was determined by drilling sampled trees with a Resistograph and calculating the ratio of sound wood to radius. Overall, 58.3% of the sampled trees had some amount of decay and incidence was highest in sugar maples and in the largest size class trees. However, decay incidence was high (53.2%) even in the smallest diameter tree size class (30.5–45.7cm (12–18 in). Decay severity was greatest in silver maple and in the largest diameter trees, although only 3.2% of the trees sampled had serious decay. The study shows that decay is common in street trees but is seldom severe. It also suggests that decay becomes established early in the life of street trees but is most severe in larger diameter trees and in trees that compartmentalize decay poorly such as silver maple. The frequency and severity of decay in the cities studied indicates that they need to continue to identify and manage trees with decay. Key Words. Decay; Resistograph; street trees; maples; hazard trees; carbon loss Little is known about the frequency and severity of decay in urban trees. Tate (1984; Tate 1986) quantified the incidence of decay in trees using an increment borer, and found that it ranged from 13% in street trees in New Jersey to 16% in Cen- tral Park, New York City. The development of a number of commercially available decay detecting tools, such as the Re- sistograph, Picus tomography, tree radar, and others (Nico- lotti and Miglietta 1998; Gilbert and Smiley 2004) now allow a more extensive investigation of both the incidence and sever- ity of decay in trees using minimally invasive testing methods. In New York State, maples species frequently dominate the street tree population, and it is common for Norway (Acer pla- tanoides), silver (A. saccharinum), sugar (A. saccharum), red (A. rubrum), and other maples to comprise over 50% of the popula- tion in both small communities and larger cities (Manion 1981a; Jaenson et al. 1992; Sisinni et al. 1995). In some cases, Norway maple alone may comprise over 50% of the planted street trees (Manion 1981a). Many of these maples were replacements for the American elms (Ulmus americana) that were lost as a re- sult of the Dutch elm disease epidemic that started in the 1930’s (Nowak and Rowntree 1990). Therefore, a significant portion of this maple population is mature; and the health, structural stabil- ity, and carbon storage as affected by wood decay, is in ques- tion. Furthermore, the upstate New York maple population is threatened by the presence and potential northern and western spread of the Asian Longhorned Beetle currently known to in- fest parts of New York City, Long Island, Massachusetts and New Jersey. This insect has potential to seriously impact the health and structural stability of maples and other species in New York. This research was initiated to determine the incidence and severity of wood decay in street tree maples and other species in Albany, Buffalo, Rochester, and Syracuse, New York. It used a Resistograph, visual evaluation, and sounding evaluation with a mallet to estimate decay frequency and amounts. The Resis- tograph allows for rapid decay testing and has been used in a ©2009 International Society of Arboriculture variety of testing environments including decay in trees (Cos- tello and Quarles 1999; Bethge et al. 1996; Mattheck et al. 1997), wood in service (Brashaw et al. 2005), and assessment of wood density of genetic crosses (Isik and Li 2003). This pa- per reveals the first set of results from this research on the fre- quency of decay and severity of decay in street tree trunks among four cities, four tree species classes, and four diameter classes. MATERIALS AND METHODS Sample Selection The sample for the study was taken from street tree inventory data of trees greater than 30.5 cm (12 in) in diameter provided by the cities of Albany, Buffalo, Rochester, and Syracuse, New York. The inventories in each city were complete except for Al- bany where outlying portions of the city had yet to be invento- ried. The initial sample was comprised of a random selection of 480 trees per city, and included thirty Norway, silver, and sugar maple, and “other” species (random selection from all other spe- cies present in the city) in each of four diameter-at-breast-height (DBH; diameter at 1.37 m (4.5 ft) classes. The random selec- tion of trees was made in each selection class (diameter and spe- cies) by pooling all the trees from the inventory for each city individually and then selecting from that pool of species. Other species included in the sample, starting with the most frequent were, Tilia cordata, Gleditsia triacanthos, Platanus x acerifo- lia, Fraxinus pennsylvanica, Acer rubrum, Aeculus hippocasta- num, Quercus rubra, F. americana, Ulmus spp., Q. palustris, T. americana, Zelkova serrata, P. occidentalis, Acer negundo, Celtis occidentalis, and Liquidambar styraciflua, and 39 other species that comprised the remaining 15% of the sample. The four DBH classes were 30.5–45.7 cm (12-18 in), 45.7–61 cm (18–24 in), 61–76.2 cm (24–30 in), and greater than 76.2 cm (30 in). Field data were collected from June to October, 2007.
March 2009
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