92 Wiersma et al.: Factors Influencing Tree Fall in an Urban Setting Arboriculture & Urban Forestry 2012. 38(3): 92–98 Hurricane Igor Impacts at Northern Latitudes: Factors Influencing Tree Fall in an Urban Setting Yolanda F. Wiersma, Troy L. Davis, Elizabeth C. Eberendu, Ian Gidge, Maria Jewison, Hiliary C. Martin, Kaylah C. Parsons, Heidi Patterson, and Ashley Quirke Abstract. Hurricane Igor was a Category 1 hurricane when it passed the island of Newfoundland, Canada, causing extensive damage. Hurricanes are un- common at northern latitudes, and boreal species are not adapted to hurricane-force winds. Moreover, much of the storm damage was in the urban area of the City of St. John’s, where there are also numerous non-native trees. This research tested whether there were attributes of trees (e.g., height, diameter at breast height, slenderness, species, age, or distance to nearest tree) that may have influenced whether a tree fell or was left standing. The study authors sampled 70 trees and found that DBH was a significant predictor of tree fall (snapping or uprooting). Conifers were no more or less likely to fall in the storm than decidu- ous trees, nor were native trees more or less susceptible to wind damage than non-natives. These results suggest that for a boreal, urban ecosystem, there are no target species available that could be planted strategically to minimize risk of tree fall in a major wind event. Thus, to minimize storm damage to human- built infrastructure in regions where hurricanes are rare, the best strategy would be to avoid having large trees located in close proximity to infrastructure. Key Words. Abies balsamea; Acer platanoides; Acer pseudoplatanus; Betula papyrifera; Boreal Forest; Hurricane; Picea mariana; Tilia americana; Tree Damage; Urban Forest; Wind Damage. Severe wind storms, in particular hurricanes, can have dramatic impacts on urban forests and trees. Although disturbance is a natural ecological phenomenon, wind disturbance of trees in urban areas often impacts built infrastructure (e.g., buildings, power lines) and can cause temporary road closures as well as a reduction of landscape aesthetics. Tropical and sub-tropical re- gions are exposed to hurricanes on a relatively frequent basis, and research on the susceptibility of trees to hurricane damage in these areas is well studied (e.g., Lugo et al. 1983; Gresham et al. 1991; Walker 1991; Zimmerman et al. 1994; Asner and Goldstein 1997; Weaver 1999; Boose et al. 2004; Canham et al. 2010). However, most of this research is outside of urban areas. Research on the impacts of hurricanes on trees in urban areas within tropical and sub-tropical regions is limited to a few stud- ies in San Juan, Puerto Rico (Francis 2000; Boose et al. 2004; Duryea et al. 2007a) and cities in Florida, U.S. (Duryea et al. 1996; Duryea et al. 2007a; Duryea et al. 2007b). There is even less research on the impacts of hurricanes in more northern lati- tudes, in part due to the infrequency of hurricane-force storms in these areas. Research in northern forests has focused more on wind damage generally (e.g., Webb 1989; Peterson 2000; Peter- son 2007; Ulanova 2000; Kane 2008; Zeng et al. 2009) and not on hurricanes specifically. Work on hurricane effects on trees in temperate and more northerly latitudes is limited; there has been some work following Hurricane Juan in Nova Scotia, Canada (Cameron 2004; Burley et al. 2008), and research to develop historical reconstructions of the 1938 New England hurricane (Boose et al. 1994; Busby et al. 2009). Moreover, most of the research on wind damage in more northerly latitudes is focused ©2012 International Society of Arboriculture away from urban areas. The last hurricane event to affect an urban area in Atlantic Canada was Hurricane Juan, which struck Nova Scotia in 2003. The provincial Department of Natural Resources investigated factors that might have made commercial forest stands more susceptible to damage (reported in Cameron 2004); other research following Hurricane Juan has focused on mitigat- ing damage to power lines (Kochanoff 2004) and forest recov- ery/restoration two years after the hurricane (Burley et al. 2008). Hurricane Igor presented a unique opportunity to study the impacts of a hurricane in an urban setting located within a boreal ecozone. On September 21, 2010, Hurricane Igor passed very close to the island of Newfoundland, on the northeast coast of Canada (Figure 1). With winds of 120 to 130 km/h, and gusting from 150 to165 km/h, this Category 1 hurricane was a once in 75–100 year event for the region (Environment Canada 2010; Pasch and Kimberlain 2011; World Meteorological Organi- zation 2011). The storm caused more than CAD $200 million in damage, and included the toppling of many trees as well as bridge and road washouts and damage to buildings (Pasch and Kimberlain 2011). Storm records for the greater St. John’s ur- ban area, consisting of the City of St. John’s and surrounding municipalities, showed that the area was hit rather hard, with wind gusts of 137 km/h recorded at the airport meteorological station, with sustained speeds of 92 km/h over 10 minute in- tervals (Environment Canada 2010). The high winds were pre- ceded by 120–134 mm of rainfall in the St. John’s area over an interval of a few hours (Environment Canada 2010; Pasch and Kimberlain 2011). It was estimated that approximately 1200 public trees within the city limits (excluding surrounding
May 2012
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