80 relationship between wire baskets and: the girdling of buttress roots (Watson and Himelick 1997); root restrictions and injuries (Whitcomb 1987); restric- tions on vascular flow (Feucht 1986; Lumis and Struger 1988; Lumis 1990); tree growth and stability (Harris et al. 2004); and the increased stress on trees that can lead to decline and death (Sellers 1983; Lumis 1990; Watson and Himelick 1997). As noted, the research surrounding wire basket retention and removal is lim- ited. There is even less research focused on the long- term effects that wire baskets may have on the root systems of planted trees (Lumis and Struger 1988). When looking at the currently available research, none of the controlled studies have presented any results beyond three growing seasons. Goodwin and Lumis (1992) looked at the effects that simulated wire basket girdling had on the overall tree growth and root functions of 2-year-old green ash (Fraxinus pennsylvanica), hackberry (Celtis occidentalis), and poplar (Populus angulate × plantierensis) over the course of six months. The authors concluded that any resulting girdling of the roots had no effect on the growth of the tree. Similarly, Koeser et al. (2015) conducted a study on 30 Norway maple (Acer plata- noides) and on 30 honeylocust (Gleditsia triacanthos var. inermis ‘Skycole’) that assessed the impact wire basket retention and removal had on short-term growth and tree stress over a two- to three-year period. The results of these studies suggests that the wire baskets had little to no effect on tree caliper, twig elongation, or chlorophyll fluorescence. In contrast to these two earlier works, this research provides a controlled comparison of the longer-term (nine year) impacts of wire basket removal and reten- tion offering an assessment of growth and survival in fully established trees. In addition to the longer study timeframe, this work assesses a species (Fraxinus americana) not previously included in a controlled wire basket study. MATERIALS AND METHODS On November 29th and 30th, 2008, 45 3.8-cm (1.5- inch) field grown trees, Fraxinus americana ‘Autumn Purple,’ were mechanically harvested and trans- planted within the same nursery in Eagle, Nebraska, United States (USDA Hardiness Zone 5b; 40.8020° N, 96.4266° W). Soils at the planting site were pre- dominantly a silty clay loam (NRCS 2017). Each tree Klein et al: Impacts of Wire Basket Retention and Removal was randomly assigned one of three transplanting treatments: 1) transplanted by tree spade without burlap/ wire (spaded); 2) transplanted as balled-and-burlapped with only burlap and string removed (wire-intact); or 3) transplanted as balled-and-burlapped with all packag- ing materials (i.e., string, burlap, wire basket) removed (full-removal). Each treatment was replicated 15 times. All trees were mechanically harvested with a 71-cm (28-inch) skid steer-mounted hydraulic tree spade (Dutchman Industries, Brougham, Canada). Spaded trees were transplanted directly from their harvest location to their planting location without packaging their root balls in burlap and wire. Wire-intact and full-removal trees were balled, wrapped in bur- lap, and secured with wire baskets (NYP Corp., St. Louis, United States) and string before being moved to their planting location. At planting, the string was removed and burlap pulled down for the wire-intact trees. For the full-removal trees, the wire, burlap, and string surrounding the root ball was removed prior to planting. Trees were not staked, as it was not deemed necessary given their size. After planting, trees were mulched with a hard- wood mulch sourced locally. Mulch was applied as needed to maintain coverage across all trees (approx- imately 5 cm to 10 cm [2 to 4 in]). Drip irrigation emitters delivering 15 liters of water per hour (4 gal- lon per hour) were installed. Water was provided to trees (uniformly across all treatments) only when rainfall was deemed insufficient to meet moisture demands (as determined by nursery owner). Glypho- sate was used to control weeds growing in the mulch beds with care taken to avoid drift onto trunks. Prun- ing was limited to sucker removal and the removal of dead, crossing, or damaged branches (some wind damage was experience over the course of the exper- iment). Trunk caliper was measured annually at 15.2 cm (6 inches) from the soil line. Tree height was also measured annually. All measurements were conducted in the fall after leaf drop. The treated trees were arranged in a completely randomized design. After planting, treatments were coded and unknown to those managing the plots and conducting measurements during the nine-year trial. Data was analyzed as a repeated measures ANOVA using the nlme package in R (Pinheiro et al. 2014; R Core Team 2014). An α = 0.05 was adopted as a threshold for significance. ©2019 International Society of Arboriculture
May 2019
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