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John F. Karlik and Arthur M. Winer

More than 70 biogenic hydrocarbon (BHC) compounds are known to be emitted by plants, but only a few are emitted in relatively large quantities. The magnitude of BHC emissions from individual trees is affected by ambient light and temperature, species-specific emissions rates, and leafmass. Like other volatile organic compounds (VOC), BHC emissions react with oxides of nitrogen (NOx) to form ozone and, thus, can contribute to urban air pollution. On average, BHC emissions are as reactive or more reactive than the VOC emissions from automobiles and can have higher ozone-forming potential. An accurate estimate of the overall magnitude of BHC contributions is important in formulating strategies to reduce peak ozone concentrations because an effective strategy will take into account the relative strengths of NOx and VOC emissions. The choice between NOx and VOC controls is crucial since an incorrect emphasis may result in non-attainment of ozone-reduction goals and control measures for either NOx or VOC involve enormous costs. As part of a program to develop a reliable BHC emission inventory for the Central Valley of California, a quantitative investigation of the leafmass of urban trees was conducted. Twenty-one trees in Bakersfield, Calif., were harvested and leaves removed, dried, and weighed. Leaf masses per tree ranged from 1.5 to 89.6 kg. Leaf mass densities (dry leaf mass per area of crown projection) ranged from 150 to 3200 g·m-2, as much as eight times greater than leaf mass densities for deciduous forests and more than twice those for coniferous forests. These data suggest the BHC contributions of urban trees may be underestimated if their foliar masses are calculated using forest-based leaf mass density data.

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Patricia R. Knight, D. Joseph Eakes, and Charles H. Gilliam

Two inch caliper Acer rubrum, Quercus phellos, and Platanus occidentalis were planted March 26, 1990, into 8' × 8' planting holes that were lined with either Typar Biobarrier, Dewitt Pro-5 Weed Barrier or left unlined as a control. There has been little or no root penetration beyond the Biobarrier for the 3 tree species during the first 3 years of this study. At the end of 1990, the control and the Dewitt Pro-5 had similar root penetration numbers. By the end of 1991, the Dewitt Pro-5 had greater root penetration than did the control for A. rubrun. Root penetration of Dewitt Pro-5 and the control treatment was similar for Q. phellos and P. occidentalis. There were no differences in root penetration for Dewitt Pro-5 and the control in 1992 for any species. There were no differences in height for any tree species following the 1990 or 1991 growing seasons and no difference following the 1992 growing season for A. rubrum and Q. phellos. The control treatment had the grearest height for P. occidentalis in 1992. There were no differences in caliper due to root control treatment for the 3 species during the first 3 years of this study.

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Ghazal Tarar, Coleman L. Etheredge, Amy McFarland, Amy Snelgrove, Tina M. Waliczek, and Jayne M. Zajicek

exam viewed plants, their positive feelings increased, while fear and anger decreased ( Ulrich, 1979 ). Even brief visual contact with plants, such as urban tree plantings or office parks, might be valuable in restoration from mild daily stress. Views

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Edward F. Gilman

This computer program, delivered-on a CD-ROM disc, develops a list of tree species and cultivars suited for a specific planting site. It requires little previous computer experience or tree knowledge to operate. Using multiple choice questions, the program automatically brings the user through above ground and below ground site analysis. This includes all the considerations known to influence proper species section for a planting site. Using C++ programming and the NASA-developed expert system shell called CUPS, a list of facts is generated as the user answers the questions. At the press of a button, the program finds trees that match the attributes the expert system placed on the facts list. The list can be further modified by choosing among ornamental and other tree attributes that might be of interest to the user. The tree list can be printed in several seconds. A typical run through the expert system takes 2 to 4 minutes to answer about 20 to 25 questions. The program contains data on 681 trees, more than 1,800 color photographs, and a 4-page fact sheet including 3 line drawings for each tree totaling more than 2,000 pages. The program can also be used as a reference by paging through the tree records to find information about specific trees. Each tree record lists on the computer monitor a large variety of data for the tree, allows you to view text about the tree, displays a line drawing of the entire tree, and displays up to seven photographs of each tree. The program will be distributed nationwide as a tool to help landscape architects, horticulturists and others select the right tree for the right place.

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D.M. Lauderdale, C.H. Gilliam, D.J. Eakes, and G.J. Keever

Two tree species, Acer rubrum `October Glory' (October Glory red maple) and Quercus phellos (willow oak) were planted in Columbus, GA and Mobile, AL. Variables evaluated were location (park vs residential) and tree size (1.5 vs 3.0 inch caliper). Greater shoot elongation occurred with 1.5 inch red maples and willow oaks than with 3.0 inch caliper trees. First year growth differences were not related to photosynthesis, night respiration, leaf water potential, or foliar nitrogen levels. Little height or caliper change occurred with either species. Red maple shoot elongation was greater in Mobile than into Columbus. Growth was not affected by location within either city.

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Mitchell W. Goyne and Michael A. Arnold

Growth responses during nursery production in 2.2- and 11.4-liter plastic containers to conventional and alternative media of four species of small trees of limited availability for potential use in urban sites in the southwest United States (Acacia wrightii, Chilopsis linearis, × Chitalpa tashkentensis, and Rhus lanceolata) were compared to that of a commercially available small tree (Fraxinus velutina). Four media combinations, at 3:1 (v/v) of bark: sand (conventional), bark: coconut coir pith, kenaf stalk core: peatmoss, and kenaf: coir, with three fertilizer concentrations (3.6, 7.2, and 10.7 kg·m–3 of 18N–2.6P–10K Osmocote) were tested with each species. All species exhibited commercially acceptable growth (80 to 167 cm mean heights in 11.4-liter containers in 240 days) with near 100% survival in most media and fertilizer combinations with the following exceptions: shoot extension of Rhus lanceolata was reduced by 20 to 30 cm and survival by 20% to 50% in kenaf media with high fertility rates; and Acacia wrightii had acceptable shoot extension but exhibited poor trunk diameter growth across media relative to the other species. Slightreductions in growth of some species were noted with kenaf media and slight increases with coconut coir, but differences were not likely of commercial significance. Kenaf media was significantly lighter (20% to 80%) than bark media, but had elevated initial electrical conductivity (EC) and shrank to 60% to 70% of its initial volume after 240 days. Kenaf: peatmoss media had a slightly lower mean pH (6.34) compared to the other media (pH 6.41–6.49).

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William R. Graves and Anthony S. Aiello

Information on the heat resistance of silver maple (Acer saccharinum L.) could help develop stress-resistant Freeman maples (Acer ×freemanii E. Murray). Our first objective was to determine how 26, 30, 32, 34, and 36 °C in the root zone affect growth and water relations of plants from rooted cuttings of a silver maple clone indigenous to Mississippi (33.3 °N latitude). Fresh mass increased over time for plants at all temperatures and was highest for plants with root zones at 30 °C. Quadratic regression functions predicted maximal plant dry mass, leaf surface area, and stomatal conductance at 29, 29, and 28 °C, respectively. Stem xylem water potential (ψ) during the photoperiod decreased linearly with increasing root-zone temperature from -0.83 MPa at 26 °C to -1.05 MPa at 36 °C. Our second objective was to compare six clones of silver maple from the Mississippi location with six clones from 44.4 °N latitude in Minnesota for effects of 35 °C in the root zone on plant growth, stomatal conductance, and stem ψ. Provenance and temperature main effects were significant for most dependent variables, but there were no provenance × temperature interactions. Over both provenances, plant fresh and dry mass, leaf surface area, stomatal conductance, and stem ψ during the photoperiod were higher at 29 than 35 °C. Over both temperatures, plants from Minnesota clones had higher fresh and dry mass and more leaf surface area than plants from Mississippi clones. The lack of temperature × provenance interactions suggests that ecotypic or clinal variation in heat resistance is minimal and will not be useful for identifying superior genotypes for use in interspecific crosses with red maple (Acer rubrum L.).

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Roger Kjelgren, Yongyut Trisurat, Ladawan Puangchit, Nestor Baguinon, and Puay Tan Yok

TROPICAL URBAN TREES Urban trees are an increasingly important quality of life issue in tropical cities as economic growth swells increasingly affluent urban populations ( Nilsson, 2005 ). The understanding and management of urban trees in tropical

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W. Todd Watson

Studies have demonstrated that the size of transplanted trees has a measurable impact on establishment rates in the landscape. Larger trees require a longer period of time than smaller trees to produce a root system comparable in spatial distribution to similar sized non-transplanted trees. This lag in redevelopment of root system architecture results in reduced growth that increases with transplant size. Research has demonstrated that smaller transplanted trees become established more quickly and ultimately result in larger trees in the landscape in a few years. Additional studies dispute these findings. This paper provides a review of current research on the effect of tree size on transplant establishment.

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Miles Schwartz Sax, Nina Bassuk, and Mark Bridgen

A tissue culture system was developed to clonally propagate a series of hybrid white oaks (Quercus L.) at the plant breeding program of the Urban Horticulture Institute (UHI), Cornell University. From 2014 through 2018, 34 genotypes and 1966 individual explants of UHI hybrid white oaks were trialed to determine their capacity to establish, multiply, and root in a tissue culture environment. UHI hybrid oak genotypes were selected based on their known tolerance to stresses common in the urban environment (drought, alkaline soils, pests, and diseases) and their ornamental qualities. Individual genotype was the single largest factor affecting successful establishment, multiplication, stabilization, and rooting of hybrid oaks in vitro. Thirteen clones of hybrid oaks were identified as having the capacity to stabilize and grow continuously in the multiplication phase. Multiplication efficiency rates were dependent on individual genotype. Stabilized genotypes showed the capacity to be re-established during successive years. The tissue culture process was simplified and refined to make the protocols less labor intensive for laboratory technicians using these methods. This study presents a preliminary and promising method for the clonal propagation of oak species and provides a path for cultivar development for plants belonging to the genus Quercus.