Table of Contents Hanns Christof Spatz and Jochen Pfisterer Mechanical Properties of Green Wood and Their Relevance for Tree Risk Assessment ................218 Abstract. In a biological context, the mechanical properties as elasticity and strength of green wood, particularly as measured in the axial direc- tion, influence the stability of trees against static loads (e.g., snow, ice, rain) and dynamic loads (i.e., wind). Extensive collections of data on mechanical properties are listed in three different catalogs edited in Canada, Great Britain, and the United States. A statistical analysis shows that the density of the wood is a major predictor for the mechanical properties as measured in axial direction. In this respect, conifers from temperate zones and deciduous trees both from temperate and tropical zones do not differ significantly from each other. A common, nearly linear relation between the modulus of elasticity and the density at 50% moisture content is found. Relationships between strengths in bend- ing, compression, and shear and green wood density have ordinary least squares scaling exponents around 1.2, but can almost equally well be approximated by linear functions of wood density. Therefore, if the density of stem wood of a given tree is known from direct measure- ment and differs from the tabulated value, the values tabulated for mechanical properties can be corrected for by a simple rule of proportion. Pulling tests as tools for tree control are discussed with emphasis on how the method is based on the knowledge of the mechanical properties of green wood, and how wood density is measured. Key Words. Conifers; Deciduous trees; Elasticity; Green wood; Pulling Tests; Strength; Wood density. Munna Singh, Aradhna Kumari, and Krishan Kumar Verma Physiological, Growth, and Biomass Attributes in Populus deltoides L. (clones G-48 and Kranti) Influenced by Water Stress ............................................................................................... 226 Abstract. Six-week-old uniform cottonwood seedlings (clones G-48 and Kranti) were raised from stem cuttings and subjected under two dif- ferent water regimes (full and half field capacity) up to 60 days under open field conditions. The higher and lower regulations of physi- ological responses were triggered in case these seedlings irrigated up to their full and half-field capacities. The enhanced A value was observed from 13–19 and 12–14 µmol m-2 s-1 quently, the study reveals that irrigation to the level of half field capacity for a period of 60 days impaired agronomic traits viz., plant height, number of leaves, leaf area expansion, specific leaf area, relative water content, biomass, and harvest index, significantly. It also concludes susceptibility of clones G-48 and Kranti toward drought in relation to plant performance (i.e., CO2 tem II photochemistry (Fv/ Fm) and CO2 assimilation, Fv/Fm, and biomass yield). Key Words. Biomass; Cottonwood; Drought; Fv/Fm; Photosynthesis; Populus deltoides L.; Transpiration. Adrianna Szczepaniec, Brian B. Raupp, and Michael J. Raupp Effects of Dinotefuran and Imidacloprid on Target and Non-target Arthropods on American Elm .......................................................................................................................... 231 Abstract. Neonicotinoid insecticides are a relatively new class of compounds with excellent efficacy against a broad assemblage of key insect pests of woody plants. Unfortunately, the use of one neonicotinoid, imidacloprid, has been linked to secondary outbreaks of several species of spider mites on different trees and shrubs. Dinotefuran is another neonicotinoid insecticide now widely used by arborists to manage insects, includ- ing egregious borers like emerald ash borer. Researchers tested a hypothesis that applications of dinotefuran to American elms (Ulmus americana) elevated populations of a spider mite, Tetranychus schoenei, and rust mites in the family Diptilomiopidae, and found no indication that dinotefuran elevated densities of either mite. Applications of imidacloprid elevated densities of T. schoenei, but not Diptilomiopidae. Both neonicotinoids were highly efficacious in reducing abundances of European elm scale, Eriococcus spuria, and elm cockscomb gall aphid, Colopha ulmicola. Key Words. Cockscomb Gall Aphid; Colopha ulmicola; Diptilomiopidae; Dinotefuran; Eriococcus spuria; European Elm Scale; Imidacloprid; Rust Mites; Secondary Pest Outbreak; Spider Mites; Tetranychus schoenei; Ulmus americana. in clones G-48 and Kranti aſter subjecting them under irrigation to the level of full field capac- ity. The withdrawal of irrigation to the level of half field capacity could reduce these values (≤50%), significantly. The decreased CO2 assimi- assimilation was found to be correlated with the loss in transpiration in both these clones. Conse- lation during drought stress was found to be correlated with decline in transpiration, largely regulated by stomatal dynamics to restrict CO2 diffusion, which also impaired carboxylation. Upon experiencing drought, the progressive loss in maximum quantum yield of photosys- ©2013 | International Society of Arboriculture | ISSN:1935-5297
September 2013
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