ARBORICULTURE ARBORICULTU URBAN FORESTRY Volume 31, Issue 3, May 2005 & CONTENTS Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) www.isa-arbor.com Scott Cullen TREES AND WIND: A PRACTICAL CONSIDERATION OF THE DRAG EQUATION VELOCITY EXPONENT FOR URBAN TREE RISK MANAGEMENT ........................................ 101 Abstract. Arborists and urban foresters are increasingly concerned with tree risk management. The aerodynamic drag equation is a potentially useful management tool. Some sources question the form of equation—specifically, the velocity exponent— that should be applied to trees. For the tree risk manager, concerned with public safety and legal liability, this is more than an academic curiosity. Uncer- tainty about the appropriate exponent questions the reliability of the conventional form. This paper reviews the literature, reports on modeling of both equation forms, and concludes that the conventional form—velocity squared—is appropriate for trees. Detailed analysis is presented for the researcher or advance practitioner. A summary explanation is provided for the typical practitioner. Key Words. Aerodynamics; Biomechanics; Drag Equation; Trees and Wind; Tree Risk Management; Velocity Exponent; Wind. Thomas B. Randrup DEVELOPMENT OF A DANISH MODEL FOR PLANT APPRAISAL ...................................................................... 114 Abstract. Inspired by the American Council of Tree and Landscape Appraisers, the Danish Tree Care Association (ISA’s Den- mark Chapter) init ated a group of national experts, representing various green-industry associations, in order to develop a com- mon tree valuation model of specific relevance for Danish climate, culture, and traditions. The model (VAT03) has four primary fac- tors: (1) a basis value, (2) health condition of the tree, (3) location of the tree, and (4) tree age. The new model establishes a value that is approximately 10 times higher than was past practice. However, tree values using this model are presumably lower than what can be assessed by other models. The model was introduced in 2003 and has already been used in several, and very different, court cases. Key Words. Urban Trees; Value; Appraisal; Denmark. Richard H. Yahner and Russell J. Hutnik PLANT SPECIES RICHNESS ON AN ELECTRIC TRANSMISSION RIGHT-OF–WAY USING INTEGRATED VEGETATION MANAGEMENT ...............................................................124 Abstract. The State Game Lands (SGL) 33 Research and Demonstration Area, Centre County, Pennsylvania, U.S., has been studied each year since 1953, making this 52-year old project extremely valuable as a source of information on the effects of mechanical and herbicidal maintenance on flora and fauna along an electric transmission right-of-way (ROW). A desired objective of integrated vegetation manage- ment on the SGL 33 Research and Demonstration Area is to create a diversity of plant species. In this paper, our objective was to document plant species richness among treatment units and in relation to wire and border zones on the SGL 33 Research and Demonstration Area. We noted the presence of plant species from late May through mid-August in both 2003 and 2004 and observed 125 vascular plant spe- cies in the 15 treatment units. The total number of species per unit ranged from a low of 35 species in a mowing unit to a high of 63 spe- cies in a basal lowvolume spray unit. Of the total number of plant species found on the right-of-way, 95 (76%) and 110 (88%) occurred in wire and border zones, respectively. In wire zones, the average number of plant species ranged from 31 in mowing units to 41 in stem–foli- age spray units. In border zones, the average number of plant species varied from a low of 34 in mowing units to a high of 41 in handcut units. The proportion of exotic species did not vary appreciably between wire and border zones (19% and 22% of total, respectively) on the ROW. However, the three units adjacent to unpaved state forest roads with high rates vehicular traffic not only had the highest number of total species in the unit (55 to 63 species) but also the highest number of exotic species (13 to 16 species). Hence, vehicular traffic and road- side management may be responsible in part for the invasion of seeds or other means of plant dispersal to these units. Because units rela- tively isolated from state forest roads tended to have fewer exotic species, these sections of the ROW can serve as refugia for native flora. Key Words. Exotic Species; Herbicides; Integrated Vegetation Management; Rights-of-Way; Species Richness; Tree Control; Vegetation. ©2005 | International Society of Arboriculture | ISSN:1935-5297
May 2005
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