288 Rathjens et al.: Evaluating Root Crown Excavation for Deeply-Planted Landscape Trees Table 1. Description of the Ohio root crown excavation experimental sites. Location Planting area Cincinnati Cincinnati Dublin Dublin Dublin Strongsville Strongsville Strongsville Street median strip Street tree Park Park Park Parking lot island Street tree Street tree SD = Standard Deviation. ered excessive by both nursery and green industry standards (American National Standards Institute 2004; Watson 2005). The name and the taxonomic class for the soil in each of the sites is provided in Table 2. The soil at the Dublin location was a silt loam soil (Soil Survey Staff 2009). The remainder of the locations con- tained highly disturbed soils typical of many urban tree plantings. The experiment was conducted in cooperation with munici- pal arborists or horticulturalists. During the experimental peri- od, municipal arborists maintained the trees. All trees received applications of mulch every 1–2 years. In addition, some trees, including the Cincinnati shingle oak and the Strongsville hon- eylocust, received periodic fertilizer and/or pesticide treatments as determined by the municipality. Approximately 1.5 years after the initiation of the treatment, the excavated areas were inspected. At this time, soil, fallen tree leaves, and grass clip- pings were removed from the excavated area using hand tools. Tree mortality during the experiment was low with the excep- tion of two sites. Eighteen percent of the Cincinnati shingle oak and 20% of the hedge maple trees in Strongsville died or were re- moved due to automobile accidents, construction, or poor health. Planting area Soil name ROOT CROWN EXCAVATION For most of the sites, the RCE was performed in the ear- ly spring of 2004. The only exception was in Cincin- nati, where the trees were excavated in the autumn of 2003. Local commercial arborists performed the RCE treatment using air excavation. Either an Air Knife® (Easy Use Air Tools Inc., Allison Park, PA) or an Air-Spade® (Air-Spade, Guardair Corp., Chicopee, MA) air excavation tool was used, the brand varying with the provider. Excess soil was removed from the root flare and in a 45.7 cm (18 in) radius outward from the trunk. The goal of the treatment, was to remove enough soil so the top of root system, or the highest main lateral roots were at the soil surface while minimizing the disruption to the appear- ance and function of the landscape. The area was kept as bare ground for the entire experimental period following the excava- tion. Control trees did not receive RCE and were left untreated. Immediately following the RCE, potential girdling roots were removed from the trees. Generally, only one to two roots per tree were removed using hand pruners. Remov- al of potential girdling roots was only necessary for the Table 2. Name and taxonomic class of the soils in the Ohio root crown excavation experiment. Location Cincinnati Cincinnati Dublin Strongsville Strongsville Street median strip Street tree Park Parking lot island, Hedge maple street tree Honeylocust street tree Urban land-Martinsville complex Urban land-Stonelick complex Crosby silt loam Mahoning-Urban land complex Udorthents, loamy Taxonomic class Fine-loamy, mixed, active, mesic Typic Hapludalfs Coarse-loamy, mixed, superactive, calcareous, mesic Typic Udifluvents Fine, mixed, active, mesic Aeric Epiaqualfs Fine, illitic, mesic Aeric Epiaqualfs Loamy, mixed, mesic Typic Udorthents Tree species Shingle oak (Quercus imbricaria Michx.) Lacebark elm (Ulmus parvifolia Jacq.) Ash species (Fraxinus spp.) Maple species (Acer spp.) Blue spruce (Picea pungens Engelm.) Honeylocust (Gleditsia triacanthos L. var. inermis (L.) Zab.) Honeylocust (Gleditsia triacanthos) Hedge maple (Acer campestre L.) 20 40 5 1 11.6 (3.3) 17.7 (4.5) Number of trees 30 20 40 40 40 20 Age of planting years 2 9 0.5 0.5 0.5 6 Plant depth cm Mean (SD) 8.8 (3.5) 6.8 (3.5) 16.2 (4.5) 20.3 (6.0) 10.1 (6.0) 13.7 (3.8) ©2009 International Society of Arboriculture
November 2009
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