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Maackia amurensis Rupr. & Maxim. is a leguminous tree with potential for increased use in urban landscapes. Information on the nutrition of M. amurensis is limited. To our knowledge, modulation and N2 fixation have not been reported. Our objective was to examine M. amurensis for nodulation and N2 fixation. Soil samples were collected near legume trees at arboreta throughout the United States, with additional samples from Canada and China. Seedlings were grown for six weeks in a low-N, sterile medium and inoculated with soil samples. Upon harvest, small white nodules were found on the lateral and upper portions of the root systems. Bacteria were isolated from the larger nodules, subculture, and used to inoculate seedlings. Inoculated plants nodulated and fixed N2 as determined by the acetylene reduction assay. We conclude M. amurensis forms N2-fixing symbioses with Rhizobium.

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There is broad consensus that we need a greater understanding of the interaction between trees and urban planting sites. This study was conducted to correlate annual increment growth with different street-tree planting specifications, with a primary emphasis on effective rooting volume of soil. The primary site of analysis was Pennsylvania Avenue in Washington, D. C., with four outlying sites chosen for comparison. From a cohort of 450, a randomly generated sample of 60 Pennsylvania Avenue willow oaks was chosen and increment cores taken at diameter breast height. A total of 60 cores was taken from willow oaks at the comparison sites. The annual incremental growth was measured using a microscope equipped with a computerized stage micrometer. The incremental growth per year in the nursery ranged between 6 and 8 mm and transplant shock generally lasted for 2 to 3 years, until growth regained or exceeded pretransplant levels.

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Honey locust (Gleditsia triacanthos var. inermis Wind.) and tree-of-heaven Ailanthus altissima (Mill.) Swingle] sometimes are exposed to high root-zone temperatures in urban microclimates. The objective of this study was to test the hypothesis that seedlings of these species differ in how elevated root-zone temperature affects growth, leaf water relations, and root hydraulic properties. Shoot extension, leaf area, root: shoot ratio, and root and shoot dry weights were less for tree-of-heaven grown with the root zone at 34C than for those with root zones at 24C. Tree-of-heaven with roots at 34C had a lower mean transpiration rate (E) than those grown at 24C, but leaf water potential (ψ1) was similar at both temperatures. In contrast, shoot extension of seedlings of honey locust grown with roots at 34C was greater than honey locust at 24C, E was similar at both temperatures, and ψ1 was reduced at 34C. Hydraulic properties of root systems grown at both temperatures were determined during exposure to pressure in solution held at 24 or 34C. For each species at both solution temperatures, water flux through root systems (Jv) grown at 34C was less than for roots grown at 24C. Roots of tree-of-heaven grown at 34C had lower hydraulic conductivity coefficients (Lp) than those grown at 24C, but Lp of roots of honey locust grown at the two temperatures was similar.

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A community tree planting project was conducted on the border of an urban Nashville, Tenn., neighborhood in Autumn 1994. In Jan. 2000, a written survey was developed to assess residents' perception of this site. Responses were gathered voluntarily and anonymously following a community meeting. Photographs of the site taken before the planting and again recently were available to respondents. Descriptions of the site's appearance prior to planting (turf only) included barren, boring, and lacking character. Comments regarding the site with trees suggest that trees provide cover and shade, are aesthetically pleasing, and represent positive human involvement. The average rating of the site's appearance prior to planting was “fair,” while its recent appearance was rated “very good.” Among three tree species included in the planting, Southern magnolia was strongly preferred over Canadian (Eastern) hemlock and Eastern redbud. Respondents valued magnolia's size, unique flowers and leaves, and evergreen nature. Most respondents did not use the area for any specific purpose. Despite that fact, respondents stated that they benefitted from the soothing aesthetics of the landscaped site, and that the site added value to the neighborhood and implied the qualities of belonging and leadership. An unintended outcome of the survey was its educational aspect. Nearly two-thirds of respondents did not live in the area when this site was landscaped, and most of them were not aware that the neighborhood had conducted the project. Nearly one-half of all respondents expressed interest in additional landscaping at this site or nearby high-visibility, high-use sites.

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Abstract

Twenty species of ornamental trees were grown for 12-16 months in 50 cm diameter (“20 gallon”) containers. Six individuals of each species were irrigated with tap water from a public potable water supply and 6 with secondary treated sewage effluent from a wastewater treatment facility. Three individuals within each irrigation treatment received controlled-release fertilizer applications and 3 received no supplemental fertilization. The effluent irrigation significantly accelerated growth in 4 species: orchid tree (Bauhinia variegata L.), baldcypress (Taxodium distichum (L.) L. Rich), coconut palm (Cocos nucifera L.), and black iron wood (Krugiodendron ferreum [Vahl] Urban). The addition of supplemental fertilization accelerated growth in 7 species: orchid tree, ficus (Ficus benjamina L.), black olive (Bucida buceras L.), satin leaf (Chrysophyllum oliviforme L.), royal poinciana (Delonix regia [Bojer] Raf.), silver buttonwood (Conocarpus erectus var. sericeus Fors. ex DC.), and blolly (Pisonia discolor Spreng.). A significant interaction occurred between irrigation and fertilization in 3 species: orchid tree, red cedar (Juniperus silicicola [Small] L. H. Bailey), and lignum vitae (Guaicum sanctum L.). The remaining 8 species grew at rates that were not significantly influenced, one way or another, by either source of irrigation or supplemental fertilization.

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Urban horticulture is an emerging area of interest to the researcher, teacher, landscape architect, city planner, forester, nurseryman, and the public. In today's society, demands are made on plants and man which are often above and beyond anything that could be considered normal for the species. The human animal is expected to work efficiently and effectively amidst austere surroundings of glass and concrete of major cities and to “relax” in busy, often sunless streets. In order to improve this working environment, planners and architects recommend a greater use of plants, the benefits of which have been provided for us by many of the early researchers in design and greenspace architecture. Trees and other woody plants improve the urban environment by screening unwanted views, by reducing noise and air pollution, and by generally improving the well-being of the individuals who come in contact with them. However, we often fall short of success in our search for suitable plants for use in the urban environment.

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Urban sprawl of the greater Phoenix metropolitan area is rapidly replacing agricultural and non-irrigated desert vegetation with an irrigated urban forest comprised of a mixture of woody ornamental plant materials. Our objective was to estimate and compare the carbon acquisition potential (CAP) of residential landscape plants to the dominate plant species found in adjacent agricultural and desert sites. Maximum shoot and leaf gas exchange measurements were made at monthly intervals for one year (Aug. 1998 to July 1999) using a portable photo-synthesis system. Concurrent diel gas exchange measurements were made seasonally. Gas exchange measurements were made on alfalfa at agricultural sites, blue palo verde, creosote bush and bur sage at desert sites, and on a mixture of 19 different woody ornamental tree, shrub and ground cover species at residential sites. A trapezoidal integration model was used to estimate daily CAP at each site based on maximum assimilation flux values and seasonally adjusted diel assimilation patterns. Annual landscape CAP was then calculated as the summation of estimates of daily CAP. Calculated annual CAP was highest at agricultural sites (159.0 mol/m2 per year), lowest at desert sites (35.3 mol/m2 per year), and intermediate at residential landscape sites (99.3 mol/m2 per year).

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Growing southern highbush blueberries in milled pine bark beds ≈15 cm deep has become a popular fruit production system in Georgia and Florida. One of the primary limiting economic factors in this system is the cost of the growing media, which can exceed $10,000 U.S. per ha. In an effort to discover low-cost substitutes for milled pine bark, available waste or low-cost organic materials were screened for there suitability as growing media for southern highbush blueberries. Cotton gin waste, pecan shells, hardwood “flume” dirt, milled composted urban yard waste, composted urban tree trimmings, pine telephone pole peelings, and pine fence post peelings were evaluated. Only pine derived materials had a suitable pH (<5.3). Fresh pine telephone pole peelings (≈25% bark to 75% elongated fibers of cambial wood) and pine fence post peelings (≈75% bark to 25% elongated fibers of cambial wood) were evaluated for several seasons in containers and field trials. The growth index of blueberries in these materials was slightly less or equal to milled pine bark. Surprisingly, nitrogen deficiency was slight or not a problem. The results indicate that pine pole and post peelings may offer an excellent, low-cost substitute for milled pine bark for blueberry production.

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Abstract

Chinese elm (Ulmus parvifolia Jacq.) is an attractive, medium-sized ornamental tree with excellent urban-hardiness and pest resistance. Introduced into cultivation in the late 1700s, this species is commonly grown in parks, lawns, and streetside locations in the southern United States and California. There have been only three Chinese elm cultivars selected in this country (1, 2). Nurserymen have expressed their desire to find a Chinese elm with an increased level of cold hardiness so that the species could be used in cities in the northern United States. The ‘Aross Central Park’ Chinese elm is cold hardy to zone 6 (Arnold Arboretum hardiness zones) and will grow in protected areas in zone 5. Thus, it is the most cold hardy Chinese elm available.

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Rural-Urban Task Force, The Ohio State University, College of Food, Agriculture, and Environmental Sciences.

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