92 Duryea et al.: Hurricanes and the Urban Forest, I Table 5. Results of the survey of arborists, scientists, and urban foresters in Florida with their rankings for wind resistance of southeastern United States coastal plain tree speciesz High Scientific name Quercus laurifolia Quercus michauxii Quercus myrtifolia Quercus nigra Quercus phellos Quercus shumardii Quercus stellata Quercus virginiana Salix × sepulcralis Taxodium distichum Taxodium ascendens Tilia americana Ulmus alata Ulmus americana Ulmus parvifolia Vaccinium arboreum Palms Butia capitata Phoenix canariensis Phoenix dactylifera Sabal palmetto Washingtonia robusta Common name Laurel oak Swamp chestnut oak Myrtle oak Water oak Willow oak Shumard oak Post oak Live oak Weeping willow Baldcypress Pondcypress Basswood Winged elm American elm Chinese elm Sparkleberry Pindo, jelly Cabbage, sabal palm Washington fan palm n 3 8 50 13 76 3 1 .(continued) Wind resistance Medium Percent n 4 8 8 13 52 5 33 64 89 2 12 59 91 41 91 5 38 15 53 6 30 7 23 11 85 Canary Island date palm 49 89 Date palm 34 79 33 94 71 99 29 54 Percent n 27 39 8 50 4 24 14 36 8 67 10 40 10 67 8 11 8 50 6 4 Low Percent 39 57 0 0 0 0 22 56 3 25 2 0 0 9 9 4 31 12 43 12 60 11 35 2 15 7 16 4 2 1 7 6 1 16 29 (P > 0.05). yCaution: may be used but manage to prevent escape because of possible invasiveness (Fox et al. 2005). to be spared. Our results did agree with the literature for branch damage; tree species with dense crowns lost more branches (24% branch loss) than those with moderate and open crowns (19% and 18%) (P < 0.0001). Some of the dense-crown species are live oak, sand live oak, laurel oak, American holly, and Bradford pear. Red maple (Acer ru- brum), dogwood, crapemyrtle, sweetgum, southern magnolia, water oak, and red oak have moderately dense crowns. Ex- amples of open crowns are the pines, pecan, southern redce- dar, and wax myrtle. The growth form of a tree can be categorized as excurrent or decurrent. Excurrent trees have strong apical dominance with the main trunk present throughout the life of the tree (giving rise to cone-shaped crowns with a central trunk). Decurrent trees have lateral branches that grow as rapidly as the central trunk; they have no dominant main leader (Harris et al. 2004). Decurrent trees had significantly higher survival (80%) compared with excurrent trees (69%). Recalculated survival (excluding those with heavy branch loss) of decur- rent species was less different than excurrent trees but it was still significant (72% versus 64%, P 0.0005). However, ©2007 International Society of Arboriculture decurrent species experienced more branch damage than ex- current (22% versus 17%, P < 0.0001). Examples of decur- rent trees in the southeastern coastal plain are pecan, dog- wood, crapemyrtle, oaks, and wax myrtle. Excurrent trees include pines, American holly, sweetgum, southern redcedar, tulip poplar, and southern magnolia. Trees Growing in Groups We hypothesized that trees growing in groups or clusters might survive hurricane force winds better. A group was defined as five or more trees each growing within 3 m of another tree (but not in a row). Trees growing in groups had 80% survival during Hurricane Ivan compared with 70% for those growing as individual trees (P0.0002). Trees grow- ing in groups also lost significantly more leaves than indi- vidual trees (63% leaf loss versus 55%, P0.0001). Branch loss, however, was the same for trees in groups and individu- als (19% and 20%, NS). The Survey Arborists’ and urban foresters’ ratings of wind resistance for coastal plain species show a strong agreement with our mea- 8 0 0 6 38 0 0 0 0 4 31 1 4 2 10 13 42 0 2 2 0 0 0 5 4 0 0 9 17 P value 0.0001 NS 0.0290 0.0009 0.0388 0.0207 NS 0.0001 NS 0.0001 0.0001 NS 0.0030 0.0224 NS 0.0126 0.0001 0.0001 0.0001 0.0001 0.0033 Total n 69 16 17 39 12 25 15 72 16 65 45 13 28 20 31 13 43 55 35 72 54 zn is the number of respondents for each species out of a total of 85 experts. P values from the 2 test for equal proportions indicate the significance level for one or more of the categories being different from the others; NS means that there is no significant difference between the categories of high, medium, and low
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