Arboriculture & Urban Forestry 32(5): September 2006 Arboriculture & Urban Forestry 2006. 32(5):253–254. 253 ARBORICULTURAL ABSTRACTS SCREENING EUROPEAN ELMS FOR RESISTANCE TO OPHIOSTOMA NOVO-ULMI Alejandro Solla, Jürgen Bohnens, Eric Collin, Stephanos Diamandis, Albrecht Franke, Luis Gil, Margarita Burón, Alberto Santini, Lorenzo Mittempergher, Jean Pinon, and An Vanden Broeck Resistance breeding of the native elms against Dutch elm disease, caused by the fungus Ophiostoma novo-ulmi Brasier, is a major objective in Europe for the conservation of this tree species. More than 2,500 cuttings of 324 elm clones (Ulmus minor Miller, U. glabra Huds., U. laevis Pall., U. pumila L., U. minor x U. glabra, and U. minor x U. pumila) from eight European countries, planted in several randomized two-block designed plots, were inoculated with various O. novo-ulmi strains. Crown wilting and dieback were recorded during the first year after inoculation. The wilting of the control trees varied among the plots, making the results difficult to com- pare, but analysis of variance (ANOVA) within each plot showed significant differences in disease severity among the clones tested, allowing study of the variation of the response among elm taxa. Results showed that 19 European inoculated clones recovered from O. novo-ulmi attack, giving hope for the reestablishment of native elms in countryside hedges and forests. (Forest Science 2005. 51(2):134–141) MODELING XYLEM AND PHLOEM WATER FLOWS IN TREES ACCORDING TO COHESION THEORY AND MÜNCH HYPOTHESIS T. Hölttä, T. Vesala, S. Sevanto, M. Perämäki, and E. Nikinmaa Water and solute flows in the coupled system of xylem and phloem were modeled together with predictions for xylem and whole-stem diameter changes. With the model, we could produce water circulation between xylem and phloem as pre- sented by the Münch hypothesis. Viscosity was modeled as an explicit function of solute concentration, and this was found to vary the resistance of the phloem sap flow by many orders of magnitude in the possible physiological range of sap concentrations. Also, the sensitivity of the predicted phloem translocation to changes in the boundary conditions and pa- rameters such as sugar loading, transpiration, and hydraulic conductivity were studied. The system was found to be quite sensitive to the sugar-loading rate, as too high sugar concen- tration (approximately 7 MPa) would cause phloem translo- cation to be irreversibly hindered and soon totally blocked due to accumulation of sugar at the top of the phloem and the consequent rise in the viscosity of the phloem sap. A too-low sugar-loading rate, on the other hand, would not induce a sufficient axial water pressure gradient. The model also re- vealed the existence of Münch “counter flow,” i.e., xylem water flow in the absence of transpiration resulting from wa- ter circulation between the xylem and phloem. Modeled di- ameter changes of the stem were found to be compatible with actual stem diameter measurements from earlier studies. The diurnal diameter variation of the whole stem was approxi- mately 0.1 mm, of which the xylem constituted approximately one-third. (Trees—Structure and Function 2006. 20(1):67–78) STRATEGY USE AND CHALLENGES OF ECOLOGICAL DESIGN IN LANDSCAPE ARCHITECTURE Meg Calkins Despite growing interest, rhetoric, and research on ecological design in landscape architecture, practitioners in the United States are not implementing as many ecological design strat- egies as might be expected. To better understand this phe- nomenon, the Green Building Practice Survey (GBPS) was carried out among landscape architects practicing varying de- grees of ecological design to determine (1) the frequency of use of common ecological design landscape strategies; (2) the obstacles and challenges that contribute to non-use; (3) sig- nificant characteristics of the firms; and (4) methods of proj- ect delivery. Phase I of the Green Building Practice Study, an on-line survey undertaken in association with the American Society of Landscape Architects, measured ecological design strategy use, identified unique characteristics of U.S. ecologi- cal design practice in landscape architecture, and quantita- tively revealed many challenges and constraints that practi- tioners face as they try to implement strategies. Phase II of the study, discussed in a separate publication, targeted a rep- resentative sample of 44 respondents with standard- questionnaire phone interviews to elucidate methods and techniques of ecological design practice. The study revealed high-frequency use of native plants, local materials, and site protection strategies; while use of green roofs, on-site waste- water treatment, and material life-cycle analysis was quite low among the respondents. Commonly cited challenges were issues of cost; lack of information, testing and data on performance of strategies; time available for research; and resistance by project stakeholders, other consultants, and code officials. The results of this study highlight a strong ©2006 International Society of Arboriculture
September 2006
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