192 Arboricultural Abstracts ARBORICULTURAL ABSTRACTS CARBON SEQUESTRATION BY QUERCUS ILEX L. AND QUERCUS PUBESCENS WILLD. AND THEIR CONTRIBUTION TO DECREASING AIR TEMPERATURE IN ROME Loretta Gratani and Laura Varone Carbon sequestration capability by Quercus ilex L. and Q. pubescens Willd., widely distributed in the city of Rome, and their contribution to decreasing air temperature were inves- tigated. Crown volume is the most significant (P < 0.01) variable explaining variation of air temperature below the tree crown. Quercus pubescens gives a higher contribution to de- creasing air temperature during the hottest months, due to its inherent larger crown volume than Q. ilex (252 ± 19 and 533±52m3, respectively, for the large size). Moreover, our results show the existence of a strong urban carbon dioxide dome with a peak CO2 concentration (on an average 432 ± 37 ppm) at polluted sites, 16% greater than at control sites. Total carbon sequestration is 84 ± 12 and 111 ± 9 kg/yr of CO2 for the small Q. ilex and Q. pubescens tree size, respec- tively, and 151 ± 10 and 185 ± 7 kg/yr of CO2 for the large Q. ilex and Q. pubescens tree size, respectively. Quercus pubescens, by its higher total photosynthetic leaf surface area (39% higher than Q. ilex) and its higher mean yearly photo- synthetic rates (48% higher than Q. ilex) seems to have a greater role than Q. ilex. However, taking into account the leaf longevity (i.e., 12 ± 3 months for Q. ilex and4± 2 months for Q. pubescens), the evergreen species, by its continuous photosynthetic activity, contributes to reduce CO2 throughout the year, and in particular during the winter months, when traffic volume has a pick, than Q. pubescens. (Urban Ecosystems 2006. 9:27–37) SIMULATING LANDSCAPE-LEVEL EFFECTS OF CONSTRAINTS TO PUBLIC FOREST REGENERATION HARVESTS DUE TO ADJACENT RESIDENTIAL DEVELOPMENT IN NORTHERN WISCONSIN Brendan C. Ward, David J. Mladenoff, and Robert M. Scheller Residential development in rural forests is currently one of the most prominent land use changes in the United States. Such development can have important effects on ecosystem processes and landscape patterns. It can also constrain forest management on public lands, influencing tree species com- position and age structure at the landscape scale. We used the forest landscape simulation model LANDIS-II to analyze changes to the landscape patterns of tree species composition, age structure, windthrow disturbance, and aboveground live biomass across a range of constraints to public forest timber ©2006 International Society of Arboriculture harvests on a northern Wisconsin landscape. Our results dem- onstrate that decreasing harvest area through the use of buff- ers reduces the dominance of early-successional species in- creases the dominance of mid- to later-successional species, and shifts the stand age distribution within the landscape toward older forests. These buffers increase the spatial het- erogeneity of dominant species and age structure at the land- scape scale, and lead to more windthrow disturbance. We believe that our study can inform policymakers, forest man- agers, and scientists about potential long-term landscape- level effects of interaction between residential development and forest management. (Forest Science 2005. 51(6):616– 632) SHEAR EFFECTS ON FAILURE OF HOLLOW TREES C. Mattheck, K. Bethge, and I. Tesari It is shown that bending stresses in a non-cracked, hollow trunk can never explain failure. Consequently, stem breakage due to bending stress cannot be primary failure. It is shown by field studies and simple theoretical assessments that the initiation of a longitudinal shear crack is primarily respon- sible for failure. Due to cracking, the bending stresses in- crease and failure by bending happens as secondary failure. As a result, bending theory of a non-cracked, closed, circular pipe is inappropriate to describe failure of hollow trees. (Trees—Structure and Function 2006. 20(3):329–333) FOURIER TRANSFORM-INFRARED SPECTROSCOPY AS A NEW METHOD FOR EVALUATING HOST RESISTANCE IN THE DUTCH ELM DISEASE COMPLEX J.A. Martín, A. Solla, S. Woodward, and L. Gil Resistance of elms (Ulmus spp.) to the pathogenic fungus Ophiostoma novo-ulmi Brasier depends on chemical and ana- tomical factors that confine the spread of the pathogen in the vascular system of the host. This study focused on detecting chemical differences in 4-year-old Ulmus minor Mill. seed- lings before and after inoculation with a virulent O. novo- ulmi isolate. According to symptom development over 60 days, the trees were divided into resistant (0% to 33% wilt- ing) and susceptible (67% to 100% wilting) groups. Histo- chemical tests and Fourier transform-infrared (FT-IR) spec- troscopy analysis were performed on transverse sections of 2-year-old twigs, 2 days before and 40 days after inoculation. Although histochemical tests did not clearly discriminate sus- ceptible from resistant elms, chemical differences between resistant, susceptible and control trees were detected by FT- IR. The average spectrum for resistant tree samples had
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