86 Duryea et al.: Hurricanes and the Urban Forest, I were used to compare survival. Branch damage was modeled using the GLM procedure in SAS with the particular crown density, and t-tests were used to compare branch damage. After comparing survival of palms and nonpalms, palms were removed from these analyses. RESULTS AND DISCUSSION Overall Urban Forest Loss The percent of urban forest loss (mortality) was positively correlated with wind speed (Figure 2). Francis and Gillespie (1993) also related wind speed to urban tree damage from Hurricane Hugo in Puerto Rico and found that at 50 km/h (31 mph), there was no damage compared with 80% damage at 125 km/h (78 mph) and 90% to 100% damage at 200 km/h (124 mph). Some of the other factors that could explain the variation of tree loss include the speed that the hurricane moved through the area, soil conditions including soil depth and moisture, and the overall tree canopy and its health. Hur- ricane damage in natural forest ecosystems in the Caribbean has been found to be dependent on four factors: (1) the hur- ricane intensity including rainfall, (2) the storm size, (3) to- pography, and (4) the susceptibility of the ecosystem to dam- age (Tanner et al. 1991). Tree Survival and Branch Loss Tree species in the Southeastern Coastal Plain respond dif- ferently to hurricanes. Response of species to Hurricane Ivan in 2004 illustrates differences at 209 km/h (130 mph) wind speeds (Figure 3). Tree species demonstrating the highest survival in these winds were sand live oak (Quercus gemi- nata), American holly (Ilex opaca), southern magnolia (Mag- nolia grandiflora), live oak, wax myrtle (Myrica cerifera), sweetgum (Liquidambar styraciflua), crapemyrtle (Lager- Figure 3. Survival (percent of trees standing after the hur- ricane) of tree species in Hurricane Ivan, which struck at 209 km/h (130 mph). The least significant difference is at the 0.05 level. stroemia indica), dogwood (Cornus florida), and sabal palm. Dogwood, live oak, sabal palm, sand live oak, and southern magnolia were also the best survivors in Hurricanes Erin and Opal in 1995 (Duryea 1997). A more detailed look at live oak and sabal palm demonstrates their repeated resilience to hur- ricane force winds (Table 1). However, it can also be seen that in south Florida, when the winds reached 233 and 265 km/h (145 and 165 mph) in Hurricanes Charley and Andrew, survival of live oak decreased to 78%. In a statistical com- parison of sand live oak, live oak, and laurel oak, laurel oak had poorer overall survival than both live oak and sand live oak in four panhandle Florida hurricanes (P < 0.001) (Figure 4). In several publications, live oak, sabal palm, baldcypress (Taxodium distichum), and pondcypress (Taxodium ascen- dens) have been ranked at the top of lists for hurricane-related wind resistance (Touliatos and Roth 1971; Swain 1979; Barry et al. 1993). Branch loss in hurricanes may also be an important mea- Figure 2. Urban forest loss (%) increased with wind speed. A polynomial relationship with R2 hurricanes. ©2007 International Society of Arboriculture = 0.80 includes eight sure of their resilience (Figure 5). In Hurricane Ivan, southern redcedar (Juniperus virginiana var. silicicola), sycamore (Platanus occidentalis), southern red oak (Quercus falcata), and laurel oak lost on average over 25% of their branches. Sweetgum, silver maple (Acer saccharinum), sycamore, and southern redcedar were species losing the most branches in Hurricanes Erin and Opal (Duryea 1997). Species with 10% or less branch loss were crapemyrtle, loblolly pine (Pinus taeda), American holly, and tulip poplar (Liriodendron tulip- ifera). When we looked at tree diameter and branch loss, large trees (100 to 200 cm [40 to 80 in] diameter) lost the most branches (30%), then medium-sized trees (50 to 99 cm
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