Arboriculture & Urban Forestry 41(1): January 2015 they may be girdled by persisting burlap (Watson and Himelick 2013). When the long-term stage of this study is completed and trees are evaluated for differ- ences in whole-tree stability, the root systems will be excavated and inspected for signs of past girdling. The removal of ropes to prevent stem girdling has long been recommended (Gouin 1983). In the current study, the rope was leſt to prevent root ball breakage from wind during the first year. Despite being constructed of natural material, the ropes at both sites were still very much intact and removed before the second growing season. While researchers failed to note significant differ- ences in growth rates among the three treatments, dramatic differences were witnessed in tree stability for the Norway maple three weeks aſter planting at the Minnesota site. A late spring windstorm toppled two of the partial and three of the full removal treat- ments. The remaining trees for these two treatments had visible leans. All trees were straightened and the soil was re-tamped around each. With frequent rains in the area, growing conditions at the site remained favorable aſter the storm, and the trees survived with no noticeable impact to growth and health. This experience highlights the potential need for tree staking or guying materials for the two levels of wire-basket removal and is one of the arguments used by those advocating that wire and burlap be leſt intact (Appleton and Floyd 2004; Marshall undated). If leaving the wire basket intact is truly sufficient to prevent newly planted trees from top- pling in winds, consumers would be spared a 2013 industry average of $41.50 for staking costs in areas where wind is a concern (RSMeans 2013). Interestingly, site did not significantly impact final caliper measurements, despite the difference in the number of seasons in the ground. The study authors believe this reflects the difference in each site’s first growing season. When the Wisconsin trees were planted in 2011, the area was experiencing notably dry conditions. In contrast, when the Minnesota trees were planted in 2012, they experienced moist soil conditions characterized by frequent rain events. This research serves as yet another indication that wire baskets do not pose significant stress to newly transplanted trees (for the species and environ- mental condition tested). The authors acknowledge that while this is not in contrast with past research (Lumis and Struger 1988; Goodwin and Lumis 23 1992), it does go counter to some of the personal experiences and accounts offered by professional arborists. It seems plausible that in some cases of transplant failure, minimally-degraded wire bas- kets and natural burlap materials were blamed for the death of the tree when in fact their presence was merely an indication of poor planting sites. The decay organisms that ultimately break down burlap coverings are influenced by compaction, excess/limiting soil moisture, pH, and other soil factors that also influence tree survival. Oxidation is similarly linked to water and air availability and, noting this, researchers have used corrosion levels on steel rods as a means of gauging long-term underground growing conditions (Hodge 1994). In less than ideal soil conditions, wire from baskets can persist for years with minimal loss of strength (Lumis 1990a; Lumis 1990b). As such, at many urban planting sites, roots may partially girdle as they grow into the remain- ing wire. While past observation has shown trees can recover from this potential stress, no con- trolled experiments have compared the growth of these trees to similar specimens not hindered by wire. Similarly, the impact of wire growth on tree stability is unknown. This population of trees will remain in the research plots for future testing in an attempt to address these questions. SUMMARY While this study does not end the debate regarding the removal of wire baskets and burlap aſter plant- ing, the findings do offer further considerations for the best management practices of tree planting. Similarly, this work offers an estimate of planting time differences for various levels of wire-basket removal, which can be incorporated into bid pro- posals. Staking of trees following the removal of a wire basket is recommended as a precaution in areas where toppling from wind loading is a concern. Removal of packing materials did cause minor to moderate cracking of the root ball. However, this did not translate into reduced growth or greater stress. Acknowledgments. This study was supported by the Tree Research and Education Endowment Fund (TREE Fund) and the Wisconsin Arborist Association, with in-kind donations from Silver Creek Nurseries, Inc., and Hardwood Creek Nurseries, Inc. ©2015 International Society of Arboriculture
January 2015
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