250 Walker and Dahle: Likelihood of Failure of Trees Along Utility Rights-of-Way trenching at a distance less than twice the trunk diam- eter reduced anchorage strength by more than 15%, and if lateral roots were severed at the trunk base, the anchorage strength was reduced by roughly 35%. Furthermore, during static pull tests, trees were observed to not return to upright if inclined past 1° to 2.5° at the tree’s base (Sinn 1990), and afterwards the stiffness of the root-soil plate was found to be decreased (Rodgers et al. 1995; Vanomsen 2006; Lundström et al. 2009). Figure 3. An asymmetrical crown resulting from line-clearance operations. ground-to-sky trimming techniques (Gaffrey and Kniemeyer 2002). Furthermore, Kane (2008) found that pruning did not reduce a tree’s overall likelihood of failure. The literature does suggest that the time of year or season can account for up to a 40% difference in probability of failure, particularly in deciduous trees, due to differences of leaf-off and leaf-on wind, snow, and ice-load interception (Ciftci et al. 2014a). Addi- tionally, thinning of an individual tree may help pre- vent snow and/or ice damage to that tree, but in turn may change wind regimens and make wind-induced failure of neighboring trees more likely (Peltola et al. 1999; Kane 2008; Peterson and Claassen 2013). Root Systems Tree stability depends upon a tree’s root spread, root architecture, and root-plate development (Dahle et al. 2017). Yet the most important region of a tree’s root system, in regard to tree failure, appears to be the soil- root plate (Ji et al. 2006; Dupuy et al. 2007; Tobin et al. 2007; Ghani et al. 2009). Smiley (2008) found that ©2022 International Society of Arboriculture The soil-root plate of younger trees was found to have a greater degree of rotation at maximum resis- tance, and the degree of rotation at maximum resis- tance is expected to vary with tree-age class, root architecture, and soil structure (Crook and Ennos 1996; Stokes 1999). As trees grow, their root-system strength increases, and root shape may be altered in response to loading (Stokes et al. 1998; Stokes 1999). This adaptive growth may decrease the likelihood of overturning (Dahle et al. 2017). When trees do uproot, a consistent relationship between tree diameter and the size or volume of the root pits and mounds has been observed (Peterson 2007). Root failures were observed to be more likely at sites where nearby trees had been removed prior to storms (Kane 2008). Yet, it is difficult to determine how the interactions of neigh- boring tree removal, the associated wind regimen change, hypothesized elevated stress levels at the soil-root plate of the remaining tree, soil properties at that location and time, and likelihood of tree failure relate to one another. Multiple findings have suggested greater vulnera- bility of conifers and early successional species, but the support is weak (Peterson 2007; Kabir et al. 2018). When a species tends to possess traits for both deep rooting and strong wood, they are generally resistant to windthrow: for example, Acer saccharum (Peterson 2007). In addition, wood strength was observed to have some influence on the risk of final failure and the mode of failure but was generally not significant on its own (Putz et al. 1983; Asner and Goldstein 1997; Gardiner et al. 2000; Peterson 2007). Furthermore, wood strength seems more indicative of the mode of failure, where trees with stronger wood are more likely to experience uprooting and trees with weaker wood are more likely to experience stem breakage (Peterson 2007). This relationship could explain how a variable for “tree species” may par- tially capture that particular species’ general wood
July 2022
| Title Name |
Pages |
Delete |
Url |
| Empty |
Ai generated response may be inaccurate.
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.
Downloading PDF
Generating your PDF, please wait...
This process might take longer please wait
