Arboriculture & Urban Forestry 37(5): September 2011 Table 6. Results of comparisons of symptoms for all sampled trees with and without stabilization systems (Wilcoxon rank sum test, P = 0.05, n = 488). Symptom Overall health Crown dieback Girdled trunk Swelling Pest/disease Leaf scorch Wilting Stunted growth Suckering z y x P value 0.0072 z 0.2878 0.0158y <0.0001y <0.0001z 0.0637 <0.0001 y 0.0581 x 0.2330 Significantly (P = 0.05) less severe on trees observed with a tree stabilization system. Significantly (P = 0.05) more severe on trees observed with a tree stabilization system. Significantly (P = 0.06) more severe on trees observed with a tree stabilization system. DISCUSSION Across the entire data set, it was found that trees with a TSSs had significantly fewer symptoms of pests/diseases and diminished overall health; stunted growth was (marginally significantly) re- duced. These results indicate that TSSs are associated with im- proved tree health during the establishment and early post-estab- lishment period in Guelph. The added stability might be helping to compensate for the root loss due to transplanting practices, thus reducing the risk of transplant shock and associated symptoms, which might explain why stunted growth, pests/diseases, and di- minished overall health are less common for trees with a TSS in Guelph (conforms to Alvey et al. 2009; Struve 2009). These results concur with those of others regarding the positive effects associated with TSSs relating to tree health by providing added stability to trees in sites that are windy or have unstable soils (Appleton et al. 2008; Eckstein and Gilman 2008; Urban 2008; Alvey et al. 2009). Because newly planted trees on windy sites may be more susceptible to blowing over in strong winds, a TSS can help anchor the root ball while structural roots are still estab- lishing (Appleton et al. 2008). Unstable soil can cause the root ball to shift and can even uproot the tree (Rahardjo et al. 2009). Negative health symptoms have also been connected with the use of a TSS. Girdling of the trunk, swelling above the point of constriction, and wilting were observed to be worse on trees with a TSS in this research. These are common, vivid symp- toms associated with TSSs, especially those not removed as the trees grow. The same symptoms were also found by Appleton (2006) and Glenn (1965). Glenn (1965) also found scratches and discolouration of the bark as a result of staking materials. Aboveground systems that are attached to the trunk with stiff metal wire prevent the natural increase in trunk diameter as the tree grows (Costello et al. 2003; Harris et al. 2004). The results are indentations in the trunk as the tree attempts to overcome the obstruction. Swelling results as the nutrients transported by the phloem are restricted and build up above the metal attach- ment (Johnson 1997; Costello et al. 2003; Harris et al. 2004). TSSs were more strongly associated with good tree health on public property compared to those on private property. Public trees expressed fewer symptoms of diminished overall health, crown dieback, pests/diseases, stunted growth, and suckering than did trees on private property. Notably they did not suffer significantly more girdling or swelling even though they had a 223 TSS. Conversely, trees on private land observed with a TSS ex- pressed severe swelling and girdling on their trunks, along with more crown dieback, than publicly owned trees with a TSS. These results indicate that land ownership (a cultural factor; Corry and Nassauer 2002) affects the susceptibility of trees to TSS effects and should be an added consideration for planting specifications. The cause of differences might be due to man- agement practices on public and private lands. Trees on public lands are examined by City of Guelph staff approximately two years after transplant at a warranty inspection. They are in- spected for tree health and establishment with the TSS removed prior to this inspection. Management and inspection of private lands with diverse land owners is unknown and no warranty inspection is known (none is required for site plan approval). The authors conducted a deeper examination of the data to determine if management or location was the factor chang- ing the susceptibility to TSS effects on public and private lands. Trees planted on public lands had a tendency to be in parks and stormwater management facilities, while trees on private property were often found in parking lots medians or located in close proximity to busy roads. Species composi- tion was generally similar and appropriate to the planting loca- tions, yet the variable conditions of the settings (medians ver- sus water management facilities) complicates the interpretation of the results. The additional stress of the location of private trees may also increase the tree’s susceptibility to TSS effects. To consider land ownership and use and planting location ef- fects (e.g., medians to stormwater management facilities), the study authors compared the health symptom scores of trees on public land with private institutional land. Private institutional land ownership/use had the most similar site characteristics to the public landscapes observed. Private institutional land uses were most like the public parks and storm water management sites in terms of openness and relatively undisturbed soil and drainage conditions; species selection was similar for private institutional and public sites. The two most common genera among public sites were Acer and Quercus (40% of all trees). For private institutional sites, Acer and Quercus constituted 46% of all trees. However, Syringa and Pyrus were each 10% of pri- vate institutional trees and were not observed on public lands. Trees with TSSs on private institutional land had lower health scores than those on public lands, indicating that management appears to be an important factor causing an increased suscepti- bility of trees to TSS effects. This has implications for ensuring the removal of TSSs as part of the construction documentation. Results from current research seem to suggest that stabilization systems benefit tree establishment and reduce transplant shock for symptoms of overall health and pest/disease. However, nega- tive effects of TSSs are known to occur when TSSs remain on the tree after it has established in the landscape, exhibiting symp- toms of a girdled trunk, trunk swelling, and wilting (Table 7). These symptoms worsen and impact the overall health of the tree. Management plays an important role in tree susceptibility to TSS effects and should be mandated with the installation of TSS. Appleton (2006) found symptoms of girdling on tree trunks when TSSs were left on for two years; however, no significant damage was observed on trees with TSSs for one year. The cur- rent research also observed trunk damage on many trees when the TSS was apparently left on too long. While exact planting dates are not known (but inferred from site plan approval dates or war- ©2011 International Society of Arboriculture
September 2011
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