ARBORICULTURE ARBORICULTU & CONTENTS Brian Kane URBAN FORESTRY Volume 38, Issue 1, January 2012 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) www.isa-arbor.com Breaking Load of Hitches and Ropes Used in Rigging ....................................................................1 Abstract. The incorporation of hardware like blocks into the rigging system has prompted a change in the types of ropes used as slings to attach blocks to trees. Since large forces can be generated while rigging trees, it is important to determine the breaking load of hitches used to attach a sling to a tree or the rigging rope to a piece of wood. Breaking load and specific strength (the ratio of breaking strength to linear density of the rope) were mea- sured for four common hitches and seven ropes oſten used in arboricultural rigging. Hitches were tied around a utility pole to sim ulate field condi- tions, and tested with a gradually increasing load. Breaking load was similar between all hitches, but varied widely among ropes, while spe- cific strength differed between ropes and hitches. Tying hitches around the utility pole mimicked the arboricultural application of hitches and ropes, but the static application of the load, which did not reflect dynamic loads oſten generated during rigging, was an important limitation. Key Words. Breaking Load; Hitch; Rigging; Rope; Specific Strength. Bruce R. Roberts, R. Scott Linder, Charles R. Krause, and Ryan Harmanis Humectants as Post-plant Soil Amendments: Effects on Growth and Physiological Activity of Drought-stressed, Container-grown Tree Seedlings ....................................................................6 Abstract. One-year-old seedlings of red maple (Acer rubrum L.) and yellow poplar (Liriodendron tulipifera L.) were treated with Hydretain ES™(HydES) or EcoSential™(EcoS) applied as a soil drench. A progressive drought cycle was imposed aſter treatment, and as each seedling wilted, the leaves and roots were harvested. Foliar growth was unaffected by HydES or EcoS, but root growth (roots < 1 mm diameter) was significantly less for seedlings grown in the humectant-treated media. These data, along with measurements of substrate moisture content taken during a similar dry down period, suggest that drought-induced fine root growth in humectant-treated media was slower because there was less need for these roots to extend and proliferate in search of addition al soil moisture supplies. In studies conducted the following year, HydES or EcoS were applied as a soil drench to one-year-old seedlings of red maple and river birch (Betula nigra L.) prior to withholding irrigation. In these studies, measurements of chlorophyll fluorescence, leaf gas exchange, and xylem wa ter potential indicate that physiological activity was greater for drought-stressed seedlings grown in HydES-treated media compared to similar seedlings grown in EcoS-treated media, a condition attributed to lower levels of plant-water stress (higher xylem water potentials) in the HydES-treated seedlings. Key Words. Acer rubrum; Chlorophyll Fluorescence; CO2 Exchange; Liriodendron tulipifera; Organic Amendments; Production Type; Red Maple; River Birch; Root Zone Moisture Management; Yellow Poplar. Gary W. Watson and Angela M. Hewitt The Relationship Between Structural Root Depth and Vigor of Urban Trees .................................13 Abstract. The prevalence of deep root systems on urban trees has been well documented, but the consequences are not well understood. The re lationship between structural root depth and vigor of street trees was investigated in Greensboro, North Carolina; Snoqualmie, Washington; and Glen Ellyn, Illinois, United States. Regression analysis was used to explore the relationship between root depth and crown vigor, trunk diameter growth, and trunk condition as indicators of tree performance. The average depth of structural roots for most species was less than three centime- ters. However, in 10 of the 14 species included in the study, the structural roots of 20%–60% of the individual trees were more than eight centime- ters deep. Regression analysis showed a significant relationship between root depth and indicators of tree performance for Acer rubrum, Quercus bicolor, Fraxinus oxycarpa, and Tilia cordata, but no relationship was identified for other species measured. Root depth explained less than half of the reduction in tree performance of these species, however, and is apparently only one of several factors affecting the growth of street trees. Key Words. Buried Roots; Deep Planting; Root Architecture. ©2012 | International Society of Arboriculture | ISSN:1935-5297
January 2012
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