130 ARBORICULTURAL ABSTRACTS INDEPENDENT AND CONTRASTING EFFECTS OF ELEVATED CO2 AND N-FERTILIZATION ON ROOT ARCHITECTURE IN PINUS PONDEROSA David T. Tingey, Mark G. Johnson, and Donald L. Phillips The effects of elevated CO2 and N-fertilization on the archi- tecture of Pinus ponderosa fine roots and their associated mycorrhizal symbionts were measured over a 4-year period using minirhizotron tubes. The study was conducted in open- top field-exposure chambers located near Placerville, Calif. A replicated (3 replicates),3×3 factorial experimental design with three CO2 concentrations [ambient air (354 mol mol–1), 525 mol mol–1, and 700 mol mol–1] and three rates of N-fertilization (0, 100, and 200 kg ha–1 year–1) was used. Elevated CO2 and N treatment had contrasting effects on the architecture of fine roots and their associated mycorrhizae. Elevated CO2 increased both fine root extensity (degree of soil exploration) and intensity (extent that roots use explored areas) but had no effect on mycorrhizae. In contrast, N- fertilization had no effect on fine root extensity or intensity but increased mycorrhizal extensity and intensity. To better understand and model the responses of systems to increasing CO2 concentrations and N deposition/fertilization it is neces- sary to consider these contrasting root architectural re- sponses. (Trees—Structure and Function 2005. 19(1):43–50) IMPACT OF THE LEAF MINER CAMERARIA OHRIDELLA ON WHOLE-PLANT PHOTOSYNTHETIC PRODUCTIVITY OF AESCULUS HIPPOCASTANUM: INSIGHTS FROM A MODEL Andrea Nardini, Fabio Raimondo, Mauro Scimone, and Sebastiano Salleo The leaf miner Cameraria ohridella causes premature defo- liation of Aesculus hippocastanum trees. In order to assess the whole-plant loss of productivity caused by the parasite, we monitored seasonal changes of leaf gas exchange and leaf area losses in horse chestnut trees freely infested or chemi- cally treated to prevent moth infestation (controls). Data were integrated in a model and the annual loss of net primary productivity (NPP) was calculated for infested trees with re- spect to controls. Measurements showed marked vertical stratification of C. ohridella attacks, with lower crown strata being more infested than higher ones. Leaf gas exchange was maximum between May and early June, but it strongly de- creased starting from mid-June even in controls. Model cal- culations showed that NPP loss of infested trees was about 30% on an annual basis (when the first moth attack is re- corded at the end of April). Model simulations showed that ©2006 International Society of Arboriculture postponing the start day of attack would have important posi- tive effects on plants NPP. For example, if the start day of attack was postponed to 20 May, the annual loss of NPP would be about 15%. Our study suggests that A. hippocasta- num trees attacked by C. ohridella are not facing serious risks of decline, especially if methods are adopted to postpone the start day of attack (e.g., removal of fallen leaves in autumn). Our data do not support the view that plants need to be totally protected from the parasite by application of insecticides. (Trees—Structure and Function 2004. 18(6):714–721) DEFINING THE SUSTAINABLE PARK: A FIFTH MODEL FOR URBAN PARKS Galen Cranz and Michael Boland How can parks contribute to the overarching project of help- ing cities become more ecologically sustainable? The history of urban parks in America reveals more concern with social problems than with ecological sustainability. Four types of city parks have been identified—the Pleasure Ground, the Reform Park, the Recreation Facility, and the Open Space System—and each of them respond to social issues, not eco- logical ones. Yet today, ecological problems are becoming one of our biggest social concerns, so a new urban park type focused on social solutions to ecological problems would be consistent with this pattern. Using the same social and physi- cal criteria that described the previous four models, Part I describes a fifth model, the Sustainable Park, which began to emerge in the late 1990s. Part II postulates three general attributes of this new kind of park: (1) self-sufficiency in regard to material resources and maintenance, (2) solving larger urban problems outside of park boundaries, and (3) creating new standards for aesthetics and landscape manage- ment in parks and other urban landscapes. It also explores policy implications of these attributes regarding park design and management, the practice of landscape architecture, citi- zen participation, and ecological education. (Landscape Jour- nal 2004. 23(2):102–120) A NON-INVASIVE ACOUSTIC TOOL REVEALING DECAY IN TREES D. Rioux A non-invasive sonic tomography apparatus was developed on the basis of the fact that waves produced by tapping sen- sors with a small hammer move more slowly through decayed or altered wood than through sound wood. Data were ana- lyzed using software that reconstitutes in two dimensions, the internal structure of the tree. Evaluations were made of 27 cross-sections from ten white oak (Quercus alba) and three
May 2006
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