ARBORICULTURE ARBORICULTU URBAN FORESTRY Volume 33, Issue 1, January 2007 & CONTENTS Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) www.isa-arbor.com E. Gregory McPherson Benefit-Based Tree Valuation ...................................................................................................................................1 Abstract. Benefit-based tree valuation provides alternative estimates of the fair and reasonable value of trees while illustrating the relative contr bution of different benefit types. This study compared estimates of tree value obtained using cost- and benefit-based approaches. The cost-based approach used the Council of Landscape and Tree Appraisers trunk formula method, and the benefit-based approach calculated the net present value (NPV, total future benefits minus costs discounted to the present) of future benefits and costs using tree growth data and numerical models. In a hypothetical example, the value of a 40 year old green ash (Fraxinus pennsylvanica) was $5,807 using the cost-based approach and either $3,102 (for a tree grow- ing in Fort Collins, CO, U.S.) or $5,022 (for a tree growing in Boulder, CO) using the benefit-based approach. This example, however, did not con- sider planting and management costs. In a multitree example, 15 years aſter planting five pistache (Pistacia chinesis) street trees in Davis, California, the trunk formula (cost-based) value was $8,756, whereas the benefit-based value NPV of benefits was neg tive at discount rates ranging from 0% to 10%. Negative NPVs occurred because future sidewalk repair costs were projected to be in excess of benefits, a relationship not fully captured in the cost-based approach to valuation. Removing and replacing the five pistache street trees was not cost-effective at 7% and 10% discount rates, primarily because high future sidewalk repair costs associated with retaining the trees were heavily discounted. Planting the five pistache trees in their current location was not an economically sound decision, but planting the same trees in a nearby shrub bed would have saved an estimated $1,102 (10%) to $12,460 (0%) over 40 years. These examples illustrate the use of the benefit based approach as a decision support tool for design and management. Key Words. Tree Appraisal; Tree Benefits; Tree Value; Trunk Formula Method. Joseph J. Doccola, Eric J. Bristol, Samantha D. Sifleet, Joseph Lojko, and Peter M. Wild Efficacy and Duration of Trunk-Injected Imidacloprid in the Management of Hemlock Woolly Adelgid (Adelges tsugae) .....................................................................12 Abstract. Hemlock woolly adelgid (Adelges tsugae) (HWA) is an introduced piercing, sucking insect that affects hemlocks (Tsuga spp.) by extract- ing carbohydrates from the xylem ray parenchyma cells. Leſt untreated, HWA will result in reduced shoot growth, branch dieback, and ulti- mately tree death. In this study, the insecticide IMA-jet (5% imidacloprid w/w) was applied by trunk microinjection with the Arborjet Tree I.V. using the VIPER method. Sixteen randomly selected HWAinfested hemlocks were treated in 2002 and 2003 and eight trees were selected as untreated controls. Eight infested branch samples per tree were cut each year (2003, 2004, and 2005) and assessed. Four parameters were used to assess the efficacy and duration of treatments. These were percent HWA mortality, total and live HWA per linear centimeter shoot growth, and current-year shoot growth. The eastern hemlock (T. canadensis) in this study had high initial HWA pressure. In the 3 years of the study, winter low temperatures were insufficient to cause an appreciable or sustainable reduction in infestation levels. In the controls, HWA increased and hemlock growth decreased. Treatment with stem-injected imidacloprid did not provide a quick knockdown of the HWA; rather, it required time (i.e., at least 1 year). In the year aſter a second treatment, we observed sufficiently high HWA mortality for hemlock to resume growth. We have a high degree of confidence that a repeat treatment increased the levels of imidacloprid for the duration of efficacy observed. We rec- ommend a 2× dosage (e.g., for trees in the 30 to 59 cm [12 to 23.6 in] size class, increase from 0.08 g A.I. to 0.16 gm A.I./cm trunk diam- eter at breast height [dbh]) for an increased level of efficacy to extend the injection interval (to once every 2 years) and to limit the number of wounds a tree receives to centimeters dbh/5 (dbh in/2). The new rate recommendations are reflected on the IMA-jet label amended in 2006. These results demonstrate that hemlock with high HWA pressure can be successfully treated using IMA-jet and the Arborjet Tree I.V. system. Key Words. Arborplug; Hemlock; Hemlock Woolly Adelgid; IMA-Jet; Imidacloprid; Micro-Infusion; Plant Health; Systemic Injection; Tree I.V.; Trunk Injection; VIPER; Wound Response. ©2007 | International Society of Arboriculture | ISSN:1935-5297
January 2007
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