Arboriculture & Urban Forestry 33(2): March 2007 99 The objectives of this study were to analyze the effects of three hurricanes on urban tree species growing in tropical and subtropical regions: (1) to determine if there was species- specific damage over the varied wind speeds, and (2) to de- termine if damage was related to tree attributes (such as size, leaf loss, wood density, and crown) and site characteristics (rooting space and grouped plantings). We then combined these results with previous results from Hurricane Andrew (Duryea et al. 1996), a survey of arborists, urban foresters, and scientists, and the scientific literature to develop wind- resistant lists and cultural recommendations for tropical and subtropical species. METHODS Urban Tree Measurements Urban tree damage was measured after (within 3 to 10 days) the three hurricanes that struck Florida (Charley and Jeanne 2004) and Puerto Rico (Georges 1998) (Duryea et al. 2007). We also include the hurricane response of some tropical/ subtropical species such as live oak (Quercus virginiana) and sabal palm (Sabal palmetto) that occur throughout Florida and were impacted by Hurricanes Erin (1995), Opal (1995), and Ivan (2004) in the Florida panhandle. Hurricane Andrew measurements involved a survey of 128 homeowners in Dade County, Florida, who measured and reported to us about each tree in their yards (Duryea et al. 1996). The methodology for the other hurricanes was the same and is as follows: neigh- borhoods at the point of landfall of the hurricane were ran- domly chosen. For each neighborhood, all trees were ob- served along street transects. For each of the three hurricanes, we sampled 26 neighborhoods and 3,678 trees (Georges), 17 neighborhoods and 2272 trees (Charley), and 7 neighbor- hoods and 1642 trees (Jeanne). (Branch loss measurements for Hurricanes Frances [2005] and Jeanne were combined and made immediately after Hurricane Jeanne.) The urban tree measurement methods, the survey methods and the statistical analyses conducted are described in Duryea et al. (2007). RESULTS AND DISCUSSION Overall Urban Forest Loss The percent urban forest loss for these three hurricanes ranged from 13% for Georges to 16% for Jeanne to 18% for Charley. To evaluate tree survival and responses, we divided the species into four categories: palms, dicots, conifers, and Puerto Rico species. Tree Survival and Branch Loss Palms Of the palms, sabal palm along with the smaller palms such as areca (Chrysalidocarpus lutescens), Manila (Veitchia mer- rilii), and pigmy date (Phoenix roebelenii) had 89% or greater survival (Table 1). In Hurricane Charley, palm sur- vival was 88% compared with 77% for all other tree species (P 0.0001). In Hurricane Jeanne, palm survival was 86% versus 76% for all other tree species (P < 0.0001). When compared with dicots, palms have often been observed to be more resistant to winds (Frangi and Lugo 1991; Francis and Gillespie 1993). Zimmerman et al. (1994) conclude that palms are wind-resistant because they are able to lose all their leaves without losing their terminal meristem. Coconut palm (Cocos nucifera), which survived poorly in Hurricane An- drew (Duryea et al. 1996), exhibited intermediate survival in both Charley’s and Georges’ winds (77% survival) (Table 1). Royal palm (Roystonea elata) with only 63% survival in Andrew had improved survival (87%) in Hurricane Charley on the deeper soils of the Gulf Coast. Washington palm (Washingtonia robusta) survived well in Charley’s 233 km/h (145 mph) winds (92%) but less well in Jeanne’s winds of 193 km/h (120 mph) (80%). This was perplexing to us until we looked at the height comparisons of the two populations. Washington palms in the Ft. Pierce area that experienced Hurricane Jeanne averaged 11 m (36.3 ft) in height with 42% of the palms above 10 m (33 ft) compared with an average of 4 m (13.2 ft) and only 7% over 10 m (33 ft) for Charley; perhaps when Washington palms acquire their heights of 20 m (66 ft) and above, their wind resistance starts to plummet. Dicots Of the dicot tree species, the poorest surviving species were seen in Hurricane Charley’s survival figures with melaleuca (Melaleuca quinquenervia), Australian pine (Casuarina equi- sitifolia), and black olive (Bucida buceras) (Figures 1A and B). Dicots with highest survival were camphor (Cinnamo- mum camphora), gumbo limbo (Bursera simarouba), sea grape (Coccoloba uvifera), strangler fig (Ficus aurea), live oak, and laurel oak (Quercus laurifolia). Some species such as camphor, strangler fig, laurel oak, and live oak may con- tinue to stand in hurricane force winds but at the same time lose large branches, especially at the 233 km/h (145 mph) winds of Charley (Figure 2). After intermediate survival in Hurricane Andrew, West Indian mahogany (Swietenia ma- hagoni) and white cedar (Tabebuia heterophylla) exhibited higher survival in Hurricane Georges at 177 km/h (110 mph). After relatively poor survival in Andrew, 94% of the royal poinciana (Delonix regia) survived the relatively lighter winds of Hurricane Georges. In a study of 24 species of urban trees in San Juan, Puerto Rico, after Hurricane Georges, spe- cies with the highest survival (lowest failed stems) were West Indian mahogany (100%), mango (Mangifera indica) (98%), queen’s crapemyrtle (Lagerstroemia speciosa) (98%), and royal poinciana (98%) (Francis 2000). Species with the poor- est survival were African tuliptree (Spathodea campanulata) (66%) and weeping banyan (Ficus benjamina) (70%) (Fran- cis 2000). Studies summarized in Everham and Brokaw’s ©2007 International Society of Arboriculture
March 2007
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