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Research was conducted to investigate how energy balance of bark mulch and turf surfaces influence gas exchange and growth of recently transplanted trees. On several occasions over a 3-year period, stomatal conductance and leaf temperature were measured throughout the day on `Emerald Queen' Norway maple (Acer platanoides L.) and `Greenspire' littleleaf linden (Tilia cordata Mill.) trees growing over each surface. Tree water loss was estimated using a general transport flux equation applied to the tree crown apportioned between sunlit and shade layers. Microclimate variables were measured over each surface with a permanent weather station. Tree growth data were collected at the end of each growing season. Soil heat flux data revealed that a greater portion of incoming radiation was prevented from entering the soil below mulch than below turf. Due to this insulating effect, and consequent lack of evaporative cooling, mulch surface temperature was greater, and emitted more longwave radiation, than turf. Leaves over mulch intercepted more longwave radiation, had greater leaf temperature, and greater leaf-to-air vapor pressure difference than leaves over turf. As a result, leaves over mulch had greater stomatal closure than leaves over turf. Estimated tree water loss varied between surface treatments and with climatic conditions. Trees over turf had greater shoot elongation and leaf area than trees over mulch. These data suggest that gas exchange and growth of recently transplanted trees in an arid climate may be reduced if planted over nonvegetative, urban surfaces.

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Auburn Univ.'s shade tree evaluation is an ongoing study comparing a moderately diverse range of species, varieties and cultivars of larger-growing trees. Initiated in 1980, there were 250 tree selections planted in three replications located at the Piedmont Substation near Camp Hill, Ala. Among the published “fruits” of the evaluation have been critical comparisons of 10 Acer rubrum selections with respect to growth and fall color characteristics; growth rate and aesthetic characteristics of fourteen Quercus selections; growth and fireblight susceptibility of 10 Pyrus calleryana selections; and the best performing trees overall in the first 12 years of the study. The shade tree evaluation has served as an important precedent for initiation of six additional landscape tree tests in Alabama. Besides its benefits as a research project, the shade tree evaluation has provided a living laboratory for a wide range of educational audiences including landscape and nursery professionals, county extension agents, urban foresters, Master Gardeners, garden club members, and horticulture students. Knowledge gained from the shade tree evaluation has also been shared through presentations at many meetings and conferences.

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The Auburn University Shade Tree Evaluation is an ongoing trial of a moderately diverse range of species, and varieties of larger-growing trees. The study was initiated in 1980 with the planting of 250 selections in three replications of three trees each, located at the Alabama Agricultural Experiment Station, Piedmont Substation in east-central Alabama. Among the fruit of the investigation have been an evaluation of 10 red maple (Acer rubrum) selections with respect to growth and fall color characteristics; a comparison of growth rate and aesthetic characteristics of 14 oak (Quercus) selections; a comparison of the growth and fireblight (Erwinia amylovora) susceptibility of 10 callery pear (Pyrus calleryana) selections; and a 12-year evaluation of the overall best performing trees. The Shade Tree Evaluation has served as a precedent for six additional landscape tree evaluations in Alabama. It has provided a living laboratory for a wide range of educational audiences including landscape and nursery professionals, county extension agents, urban foresters, Master Gardeners, garden club members, and horticulture students. Knowledge gained from the Shade Tree Evaluation has been shared through presentations at meetings and conferences.

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Mulches applied to landscape surfaces can moderate soil temperatures by changing the surface heat energy balance and conserve soil water by reducing evaporation rates. In the Southwest, decomposing granite is commonly used as landscape mulch. However, organic mulches, such as pine residue mulch and shredded tree trimmings, are becoming more available as industry by-products. Recent impetus toward water conservation and recycling forest and urban tree waste into urban landscapes has increased the need to better understand how such mulch types effect the temperature, moisture. and light quality of drip-irrigated landscapes typically found in the Southwest. We compared effects of three mulches, two organic (composted ponderosa pine residue and shredded urban tree trimmings) and one inorganic (Red Mountain Coral decomposing granite), turf grass, and bare soil applied to 14 drip-irrigated landscape research plots on below-ground soil temperatures at depths of 5 cm and 30 cm, temperatures at the mulch-soil interface, mulch surface temperatures, diel mulch surface net radiation, and albedo. Below-ground soil temperatures were more buffered by organic mulches, and mulch-soil interface temperatures were lower under organic mulch than inorganic mulches. Inorganic mulch daytime surface temperatures were lower than organic mulch surface temperatures. Nighttime net radiation values were less negative over organic mulches than inorganic mulches and albedo was significantly higher for the inorganic mulch and bare soil treatments. These results provide evidence to show that organic surface mulches have higher resistances to heat transfer than inorganic mulches, which could improve landscape plant water and nutrient use efficiencies by lowering high summer root zone temperatures.

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Abstract

Since the urban population of American elms (Ulmus americana L.) was ravaged by Dutch elm disease fungus [Ceratocystis ulmi Buism. (C. Moreau)], attention has focused on the development of disease resistant elm hybrids. The cultivars ‘Sapporo Autumn Gold’, ‘Urban’, and ‘Regal’ are highly resistant to Dutch elm disease (7, 8, 9); however, they are extremely susceptible to the elm leaf beetle, (Pyrrhalta luteola Muller), because the susceptible Siberian elm Ulmus pumila L.) is a common parent (10). On the other hand, Ulmus parvifolia Jacq. (syn. U. sempervirens), U. chinensis Pers., sometimes listed incorrectly as the lacebark elm (syn. leatherleaf elm, Chinese elm) is highly resistant to Dutch elm disease and the elm leaf beetle (1, 2, 4, 10). Lacebark elm is native to central China, Japan, and Korea, is drought tolerant, and withstands the severe conditions often associated with urban sites (10). Like most other members of the genus Ulmus, lacebark elm is propagated by seed collected in the fall; however, Schopmeyer (6) indicated that less than 50% of the seeds are viable, and only 5% to 12% of the viable seed sown can be expected to produce saleable trees. Four asexually produced cultivars, ‘Sempervirens’, ‘Drake’, ‘True Green’, and ‘Dynasty’ (5), currently sold provide improved consistency and quality.

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about the booming urban horticulture scene in Asia, teaching urban permaculture to students in Virginia, and training small farmers in Tajikistan and Kyrgyzstan how to prune their fruit trees. In the current series, we feature urban horticulture in Iran

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In 1992, Hurricane Andrew destroyed over 1000 mature trees in the City of North Miami, located 50 mi north of the storm center. The cleanup cost over $1,000.000. Most of the tree failures were caused by structural faults: co-dominant leaders, narrow limb attachment, included bark, over-lifting, hatracking, poor vertical limb placement, crown imbalance, overly-dense crowns, crossing and in-growing branches. All could have been corrected with proper pruning. Action was taken to reduce future damage. The city arborist made a complete, computerized inventory of all trees on public property, creating a data-base with all structural problems identified. These were prioritized so the worst could be addressed first. After any pruning work was done on a city tree, a follow-up evaluation was made, and any additional pruning needed was scheduled. Pruning followed the recommendations of state specialists and three county extension agents with the University of Florida Cooperative Extension Service. City workers were taught using lectures, demonstrations, site visits, CES publications, and individualized instruction. In addition, all new trees purchased were grades FL Fancy or FL no. 1, based on Grades and Standards for Nursery Plants; such trees require little or no corrective pruning at planting and mature as structurally-sound trees which resist wind damage. Two later storms (1993, 1999) produced winds in North Miami similar to those of Hurricane Andrew. Together they destroyed only 35 trees which cost $35,000 to remove. These data demonstrate that following CES pruning recommendations reduces storm damage to trees, saving money and preserving the urban forest canopy.

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In many sectors of agriculture, precision irrigation, applying only what water is needed for a given small area, has become a familiar term. Irrigation in most woody ornamental nurseries, though, has changed little since the 1960s. In many areas of the U.S., irrigation volumes required for nursery production have come under scrutiny due to projected, or real, competition for water with urban populations, or concerns over nursery runoff. Modeling of woody ornamental water use, and subsequent irrigation requirements, has been limited and focused mostly on trees. Previous research for modeling of non-tree water use is reviewed as an introduction to current efforts to develop models for precision irrigation of woody ornamentals. Pitfalls and limitations in current modeling efforts, along with suggestions for standardizing future research is emphasized. The latest model derived from recent research is presented.

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Landscape trees are frequently planted in heavily compacted soils, such as around newly constructed buildings or in urban areas. Under such conditions, trees frequently die, or decline prematurely. Techniques for ameliorating these conditions were studied: vertical drainage mat panels, gravel-filled sumps, soil trenching and peat-amended backfill. Acer saccharum Marsh. `Seneca Chief, ` a species sensitive to compaction stresses, and the less sensitive Pyrus calleryana Decne. `Red Spire' were planted in a compacted clay loam. Shoot growth, root distribution and soil oxygen levels were measured over two growing seasons. Oxygen levels varied with treatment, but were not limiting to root growth. Shoot growth of pears was greatest for soil trenches. Except for the gravel-filled sumps, all other treatments also showed increased shoot growth compared to controls. Maple mortality was generally high and inversely correlated with field drainage.

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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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