Table of Contents Jacopo Mori, Alessio Fini, Gianluca Burchi, and Francesco Ferrini Carbon Uptake and Air Pollution Mitigation of Different Evergreen Shrub Species ................... 329 Abstract. Three independent experiments assessed CO2 (Exp. 1) under optimal water availability and in 2012 (Exp. 2) under drought on potted plants. A third experiment (Exp. 3) mea- sured seasonal leaf depositions of Cd, Cu, Ni, Pb, and Zn in 2011 on plants transplanted in proximity of a four-lane road. E. × ebbingei showed the highest CO2 (Arbutus unedo L., Elaeagnus × ebbingei L., Laurus nobilis L., Ligustrum japonicum Thunb., Photinia × fraseri Dress., Viburnum tinus subsp. lucidum L., and Viburnum tinus subsp. tinus L.). CO2 assimilation and metals leaf deposition of seven evergreen shrub species assimilation and carbon allocation were determined in 2011 In Experiment 3, E. × ebbingei showed the highest metal deposition, mainly due to its greater leaf area. Greater rainfall and RH% decreased metal depositions, whilst greater wind velocity and air temperature increased leaf depositions. Species which drasti- cally reduce CO2 1, 2). Conversely, P. × fraseri had intermediate CO2 lution mitigation (Exp. 3) of widely used shrubs for application in urban areas and planning of roadside greening in southern Europe. Key Words. Arbutus unedo L.; CO2 prone environments, where drought-tolerant “mesic” species (P. × fraseri), should be preferred. E. × ebbingei could be used to optimize deposition of metals. The three experiments provide useful insights especially about CO2 cum Thunb.; Meteorological Parameters; Photinia × fraseri Dress.; Relative Growth Rate; Seasonal Trend; Shrub; Trace Metals; Traffic Pollution; Viburnum tinus subsp. lucidum L.; Viburnum tinus subsp. tinus L. Richard W. Harper and Paul A. Weston Potential of Alternative Tsuga spp. as Landscape Replacements for T. canadensis: Longer-Term Evaluation and Propagation of T. chinensis ............................................................. 346 Abstract. Seven species of hemlock (Tsuga spp.)—four from North America and three from Asia—were evaluated in replicated plots in Katonah, New York, United States (USDA Plant Hardiness Zone 6b) as potential replacements for eastern hemlock (Tsuga canadensis), which is gradually being extirpated from landscapes in the eastern United States. by the invasive hemlock woolly adelgid (Adelges tsugae). Trends reported in an earlier study (Weston and Harper 2009) continued but were exaggerated aſter an additional three years of obser- vation. For example, Chinese hemlock (T. chinensis) continued to show the greatest potential as a replacement for T. canadensis as mor- tality was very low, overall plant health was exceptional, and tolerance to A. tsugae was robust. Early indicators suggest that T. chinen- sis may also be readily propagated from hardwood cuttings under appropriate greenhouse conditions. These characteristics suggest that T. chinensis may indeed become a viable replacement for T. canadensis, and a valuable addition to landscapes in the eastern U.S. Key Words. Elongate Hemlock Scale; Hemlock; Hemlock Woolly Adelgid; Host Resistance; Tsuga canadensis; Tsuga caroliniana; Tsuga chinen- sis; Tsuga diversifolia; Tsuga heterophylla; Tsuga mertensiana; Tsuga sieboldii. Duncan Slater and A. Roland Ennos An Assessment of the Remodeling of Bifurcations in Hazel (Corylus avellana L.) in Response to Bracing, Drilling, and Splitting ............................................................................ 355 Abstract. The ability of trees to remodel their woody structure aſter injury or strain to outer tissues greatly assists in their survival; how- ever, this remodeling process is complex because it is influenced by many factors. The speed and extent of remodeling of branch junctions in trees around a mechanical flaw, such as included bark, will dictate to what extent and for how long the junction is mechanically weakened. In this study, 100 normally formed bifurcations in semi-mature hazel (Corylus avellana L.) were artificially modified by being rod- braced, drilled through the apex or split, and then leſt to grow in situ. Two further groups were identified as controls: 120 normally formed bifurcations and 70 bark-included bifurcations. Aſter two to four years, these bifurcations were harvested and underwent tests of their bend- ing strength. The bifurcations rigidly braced over three growing seasons developed adverse taper in their branches and had only 70.5% of the bending strength of the normally formed bifurcations. Bifurcations with the central 20% of the xylem drilled out of them were capa- ble of recovering fully from this defect; in contrast, split bifurcations were found to be highly vulnerable to failure during wind-loading events. This study concludes that a bifurcation may be considered compromised in its bending strength if its apex is compromised, but that semi-mature bifurcations in hazel do exhibit a good ability to remodel aſter injury. The role of thigmomorphogenesis in this remodel- ing process is assessed with reference to the rod-braced specimens that suffered no significant mechanical perturbation at their apices. Key Words. Bark Inclusion; Bifurcation; Biomechanics; Bracing; Corylus avellana L.; England; Hazel; Lancashire; Remodeling; Thigmomorpho- genesis; Tree Crotch; Tree Fork. Assimilation; Drought; Elaeagnus × ebbingei L.; Italy; Laurus nobilis L.; Leaf Deposition; Ligustrum japoni- assimilation under drought (V. tinus subsp. lucidum, L. japonicum, E. × ebbingei) are not recommended in drought- assimilation (Exp. 1, 2) and air pol- assimilation under optimal water availability but one of the lowest under drought (Exp. assimilation but it declined less during drought compared to the other species. ©2016 | International Society of Arboriculture | ISSN:1935-5297
September 2016
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