Arboriculture & Urban Forestry 33(2): March 2007 85 side of the storm. For each neighborhood, all trees in front yards were observed along street transects. (If invited, we also measured trees in backyards.) Overall, we sampled 100 neighborhoods and 18,200 trees. (Branch loss measurements for Hurricanes Frances and Jeanne were combined and col- lected immediately after Hurricane Jeanne.) Each tree’s diameter at breast height (for dicots and coni- fers) or height (for palms) was measured (estimated for height) and then it was determined if the tree was standing, leaning, or had fallen. Leaning trees were those that were leaning as a result of the storm at less than a 45° angle. Fallen trees were either broken at the main stem or lying on the ground. All fallen trees were assessed as either broken or uprooted. Percent survival was calculated for each species using trees that were standing after the hurricane (Trees were considered not surviving if they had fallen or if they were leaning at less than a 45° angle.). Crowns of all standing trees were first assessed for percent branch loss and then for leaf loss from the hurricane. For palms, only percent leaf loss was assessed. Then for dicots and conifers, if a tree had 50% or greater branch loss from the hurricane, it was declared dead and a new second survival percentage was calculated. This is called the “recalculated survival” throughout this article. For each tree, we also estimated whether it had caused damage to property either from a falling branch or the entire tree. If it had damaged something, we recorded the type of property (for example, fence, power line, or house). To investigate the reasons why some trees are more wind- resistant than others, we looked at cluster plantings, wood density, defoliation, and tree crown attributes. To analyze cluster plantings, we assessed whether each tree was growing in a group with other trees or by itself. We defined a cluster as a group of five or more trees growing within 3 m (9.9 ft) of each other (but not in a row). To investigate the relation- ship between wind damage and wood characteristics, we ob- tained wood density, modulus of rupture, and modulus of elasticity for each of the tree species (Reyes et al. 1992; Forest Products Laboratory 1999). To relate crown characteristics to wind damage, we ob- tained information on crown density and growth form (ex- current versus decurrent) for each species. Crown density is an estimate of the openness of the crown or the ratio of positive and negative space within the crown (Hightshoe 1988; Gilman 2005). The growth form of a tree can be cat- egorized as excurrent or decurrent. Excurrent trees have strong apical dominance with the main trunk present through- out 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). We determined from the literature and observation the density class and growth form for each species and then compared open with moderate with dense crowns for branch loss and survival (Hightshoe 1988; Harris et al. 2004; Gilman 2005). Maximum sustained wind speeds for each hurricane were obtained from the National Oceanic and Atmospheric Ad- ministration National Hurricane Center web site (www.nhc. noaa.gov). The Survey After four hurricanes struck Florida in 2004, we concluded that urban forest professionals around Florida were a resource of knowledge about wind resistance. In June 2005, we sent out 240 surveys to arborists, urban foresters, and forest sci- entists who were members of either the International Society of Arboriculture (Florida chapter) or the Florida Urban For- estry Council or faculty at the University of Florida asking them to rank the wind resistance (high, medium, or low) of those urban tree species they observed after hurricanes. Eighty-five surveys (35%) were returned. We report these numbers and percentages in this publication and then use these ratings along with our measurements and analyses and the scientific literature to formulate wind resistance lists for tree species in urban areas. Statistical Analysis Data from all hurricanes were analyzed using the GLM, REG, LOGISTIC, and FREQ procedures of SAS. Only species with a sample size larger than or equal to 20 trees for each hurri- cane were included. PROC GLM was used for all survival and branch loss analyses. Species survival was modeled using species and neighborhoods with neighborhood considered a random effect. The error term used was the interaction of species and neighborhood. Multiple comparisons were used to compare survival means among species. For native versus exotic and cluster planting analyses, survival was modeled using them as a categorical variable and neighborhood was considered a random effect. The error term used was the interaction of the categorical variable and neighborhood. A t-test was used to compare survival with these variables. Fre- quency tables were used to describe if fallen trees were bro- ken or uprooted and to describe property damage by species. To analyze the relationship between leaf loss and survival, a logistic regression was conducted using the PROC LOGIS- TIC procedures in SAS with survival as the dependent vari- able and percentage of leaf loss as the explanatory variable. To determine if survival and branch damage were related to wood density, wood densities were grouped into four catego- ries using the GLM procedure in SAS. A multiple compari- son test was done for survival and branch damage between the categories. A 2 test was used to compare survival and excurrent ver- sus decurrent growth using the FREQ procedure in SAS. Branch damage was modeled using SAS GLM, and a t-test compared the two growth types. For crown density, 2 tests ©2007 International Society of Arboriculture
March 2007
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