96 lowing extreme wind events (Kane 2008). The influence of slen- derness in affecting damage is consistent with analysis follow- ing Hurricane Juan, which was the most recent hurricane to hit at northern latitudes (albeit in a more temperate/Acadian forest zone). Here, slenderness and stand density were found to be the only significant predictors of stand damage (Cameron 2004). Unlike some studies in the tropics that showed different dam- age patterns for native/non-native species in some storms (Asner and Goldstein 1997; Duryea et al. 2007a; Duryea et al. 2007b), tree category did not appear to affect susceptibility to tree fall. Other factors that have been shown to influence tree fall in the topics include the degree to which trees are clumped (Duryea et al. 2007a; Duryea et al. 2007b). In the current study, researchers measured the distance from each fallen tree to the nearest stand- ing tree, but this was not a significant predictor. This metric is not necessarily a useful predictor of spatial patterns of clumping, and the pair-wise sampling design employed did not enable individ- uals to examine larger scale patterns of tree fall across the greater St. John’s area as a function of spatial patterns of tree aggregations. Francis (2000) and Duryea et al. (2007a; 2007b) suggested the soil and rooting properties were significant predictors of tree fall in tropical and subtropical urban areas. While soil types are not homogenous across the current study area (Heringa 1981), soils in the province are generally very thin and rocky. Root pro- files of those trees that were uprooted were mostly wide diameter and shallow depth. The authors did not have root profiles for the trees that snapped or remained standing, and were unable to as- sess whether these were different from those trees that were up- rooted. The high amount of rainfall immediately preceding the hurricane-force winds, coupled with the thin soil and poor drain- age of the entire island, resulted in highly saturated soils during the storm. Thus, shallow-rooted trees may have been more sus- ceptible to blow down due to weakened soil cohesion in saturated conditions. However, uprooting was not related to species, so if root profiles are species-specific, then this hypothesis is likely not supported. Nonetheless, if localized soil patterns are such that they contribute to shallow rooting, then this may have contrib- uted to patterns of tree fall. Because of the nature of the pair-wise sampling, the authors were unable to statistically test this hypoth- esis. An analysis of tree fall in high wind events in Minnesota (Webb 1989) showed that high rainfall/wet soil confounded re- sults when looking for patterns in tree properties. Similarly, Ever- ham and Brokaw (1996), in a review of a large suite of papers on wind damage, showed that in many studies, rainfall amounts influenced damage rates, and Fan and Su (2008) demonstrated how soil saturation affects shear strength of soils in Taiwan. Whether a tree was a conifer or deciduous did not affect whether it was damaged, or if damaged, whether it was snapped or uprooted. Hurricane Igor hit while the leaves were still on the trees. If the storm had been later in the season (i.e., post- leaf drop), then different results may have been expected (Kane 2008). Many studies (see summary in Everham and Brokaw 1996) have shown no difference in damage rates between de- ciduous and coniferous trees, and coniferous trees in Nova Scotia were not more resilient to uprooting following Hurri- cane Juan (Cameron 2004). Moreover, whether a tree was na- tive to the island of Newfoundland or not did not affect whether it was damaged, or if damaged, if it was uprooted or snapped. This is consistent with some (but not all) observations of native/ non-native species in Florida across different hurricane events ©2012 International Society of Arboriculture Wiersma et al.: Factors Influencing Tree Fall in an Urban Setting (Duryea et al. 2007a; Duryea et al. 2007b), but is inconsistent with observations from Hawaii (Asner and Goldstein 1997). Overall, it appears that at very localized scales (i.e., be- tween adjacent trees subjected to the same wind patterns), those that were larger in diameter (but not height) were more likely to be uprooted or snapped by Hurricane Igor, and that this pattern did not differ between coniferous and deciduous species or between native and non-native species. Across the region, high rainfall immediately preceding the storm satur- ated the soils, which may have been a contributing factor in up- rooting events (Everham and Brokaw 1996; Fan and Su 2008). CONCLUSION Hurricane Igor was a rare Category 1 hurricane event for the island of Newfoundland. While much larger and more frequent storms are not unexpected at more southern latitudes, trees in more northern latitudes have not had a chance to evolve in response to hurricane-force winds. The rarity of the storm afforded a unique opportunity to assess factors affecting tree fall in an urban setting situated within a boreal ecozone. Consistent with the dominant pattern across a range of studies from the tropics, subtropics, and temperate zones the size of trees (measured as DBH) was the best predictor of whether an individual tree was snapped or uprooted. Given that there were no clear patterns of different species be- ing more or less susceptible to snapping/uprooting, coupled with the rarity of the storm, recommendations for planting to avoid wind damage [such as those provided by Duryea et al. (2007a) and Duryea et al. (2007b)] cannot be made at this time. The intense rain and soil saturation was likely a major factor in the amount of damage, and those trees with more shallow roots simply fell over in the wet, shallow soils. Due to the island’s location in the North Atlantic, any future hurricane events are likely to be preceded by high rainfall. Thus the only planting strategy that might avoid dam- age to infrastructure is to make sure large trees are not adjacent to infrastructure (e.g., buildings, power lines), especially when those trees are on particularly shallow, rocky, or poorly drained soils. However, damage to trees and forest ecosystems will like- ly be unavoidable in future hurricane events in Newfoundland. Acknowledgments. Thanks to Linda Morrissey and Gary Collins for timely assistance with equipment. Troy L. Davis thanks Dave Schneider for statistical advice. Ashley Quirke was funded by a Memorial Univer- sity Career Employment Placement granted to Yolanda F. Wiersma. This project was also supported through a Natural Science and Engineering Research Council Discovery Grant to Yolanda F. Wiersma. LITERATURE CITED Achim, A., J.-C. Ruel, B.A. Gardiner, G. Laflamme, and S. Meunier. 2005. Modelling the vulnerability of balsam fir forests to wind dam- age. Forest Ecology and Management 204:35–50. Asner, G.P., and G. Goldstein. 1997. Correlating stem biomechanical properties of Hawaiian canopy trees with hurricane wind damage. Biotropica 29:145–150. Boose, E.R., D.R. Foster, and M. Fluet. 1994. Hurricane impacts to tropical and temperate forest landscapes. Ecological Monographs 64:369–400. Boose, E.R., K.E. Chamberlin, D.R. Foster. 2001. Landscape and region- al impacts of hurricanes in New England. Ecological Monographs 71:27–48.
May 2012
| 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
