Arboriculture & Urban Forestry 33(2): March 2007 103 59% uprooted; royal, 100%; sabal, 67%; and queen [Syagrus romanzoffiana], 81% uprooted). Property Damage In Hurricanes Jeanne and Charley, only 3% and 4% of the trees that fell damaged property. In Jeanne, all of this damage was to major property (houses, power lines, or docks), and the only two species with more than 3% of their fallen trees causing damage were sand and south Florida slash pines. In Charley, half of the damage (2% out of a total of 4% of the fallen trees) was to major property (houses or power lines) and there were no dominant species causing damage. Eleven percent of the trees that fell damaged property in Hurricane Georges. Of these, 27% damaged major property (houses, power lines, screened enclosures, automobiles, and so on) and 73% damaged minor property (fences, sheds, side- walks). The only tree species that caused more than 3% dam- age was swamp mahogany. With 20%, 21%, and 8% of the trees that fell causing property damage in Hurricanes Ivan, Erin, and Opal, respectively, it appears that falling trees cause more damage in these north Florida hurricanes than in south Florida (Duryea 1997; Duryea et al. 2007); this could be attributable to the increased urban forest canopy in north Florida and the poor health and aged condition of trees such as laurel oaks, water oaks, and pecans. Direction of Fall To investigate the direction that trees fell in Hurricane An- drew, we conducted a 2 analysis using species with sample sizes larger than 20 trees (n318 trees). We found that most trees fell to the west (48%) followed by south (21%) and the southwest (15%). These three directions totaled 83% of the fallen trees and were significantly different than the total of all the other directions, which encompassed 17% of the trees (P 0.0001). What Makes a Tree More Wind-Resistant? The goal of this research project is to attempt to determine what biological and cultural factors make trees more or less wind-resistant. By evaluating these factors, we can better un- derstand the differences between species (i.e., whether they have dense wood or defoliate quickly in wind) and between certain practices (such as rooting space or planting trees in groups compared with individual tree plantings), which could result in a healthier and more wind-resistant urban forest. Defoliation In a logistic regression with survival as the response variable and leaves (percent lost) as the explanatory variable, leaf loss had no relationship with survival in Hurricanes Jeanne, Char- ley, or Georges. This is in contrast to Hurricane Ivan in which southeastern coastal plain tree species that lost more leaves also survived better (Duryea et al. 2007). Losing leaves and Figure 3. Survival of native trees compared with exotic trees for Hurricanes Georges (Puerto Rico), Jeanne, Char- ley, and Andrew (south Florida). (N.S. means survival of native trees is not significantly different than exotic trees for Georges; **** means survival is significantly different for native trees compared with exotic trees at the P < 0.0001 level.) ©2007 International Society of Arboriculture reducing the wind drag or resistance from the crown may be a strategy for some species and not for others. Native and Exotic Species Native tree species survived better in Hurricanes Jeanne, Charley, and Andrew but not in Hurricane Georges (Fig- ure 3). Native species also lost fewer branches than exotic species in Jeanne (21% versus 36%, P0.0001) and Char- ley (36% versus 39%, P 0.0001). Some of the exotic species with low survival were melaleuca, Australian pine, and queen palm and these can be compared with native spe- cies with high survival: live oak, gumbo limbo, and sabal palm. In their extensive review of hurricanes and forest dam- age, Everham and Brokaw (1996) summarize that there is a trend toward more damage in exotic forest plantations, al- though they also point out that these exotic forests are often monocultures. Of the 35 tree species measured after Hurri- cane Georges in Puerto Rico (n 20), only four were native trees to Puerto Rico: Santa Maria, black olive, white cedar, and common calabash tree (Crescentia cujete). Santa Maria survived very well (93%) but the other three had 84%, 83%, and 67%, not surviving better than many of the exotic species (Table 2). Branch loss of exotics and natives in Puerto Rico, too, appeared to be equal (31% for exotics versus 27%, not significant). With few exotic species in the urban forest popu- lation, natives also did not survive better in the southeastern United States Coastal Plain during Hurricane Ivan (Duryea et al. 2007). Trees Growing in Groups We asked the question whether trees growing in groups or clusters, as compared with singly, might survive hurricane
March 2007
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
