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urban landscapes. Although this study only included one species, other commonly used landscape species that transplant as BR stock may perform similarly, with smaller 25-mm caliper trees preferable to larger 40-mm caliper trees where stress is

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genetic and phenotypic diversity. In another study, traits such as tree height/diameter, flower arrangement, fruit development and morphology, and pollen morphology were assessed in different accessions of M . sieversii populations from diverse regions

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A 2-year study was conducted to quantify the actual evapotranspiration (ETa) of three woody ornamental trees placed under three different leaching fractions (LFs). Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (Cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill.) (nursery seedling selection) were planted as 3.8-, 18.9-, or 56.8-liter container nursery stock outdoors in 190-liter plastic lysimeters in which weekly hydrologic balances were maintained. Weekly storage changes were measured with a portable hoist-load cell apparatus. Irrigations were applied to maintain LFs of +0.25, 0.00, or -0.25 (theoretical) based on the equation irrigation (I) = ETa/(1 - LF). Tree height, trunk diameter, canopy volume, leaf area index, total leaf area (oak only) and dry weight were monitored during the experiment or measured at final harvest. Average yearly ETa was significantly influenced by planting size (oak and willow, P ≤ 0.001) and leaching fraction imposed (P ≤ 0.001). Multiple regressions accounting for the variability in average yearly ETa were comprised of different growth and water management variables depending on the species. LF, trunk diameter, and canopy volume accounted for 92% (P ≤ 0.001) of the variability in the average yearly ETa of oak. Monthly ETa data were also evaluated, with multiple regressions based on data from nonwater-deficit trees, such that LF could be ignored. In the case of desert willow, monthly potential ET and trunk diameter accounted for 88% (P ≤ 0.001) of the variability in the monthly ETa. Results suggest that irrigators could apply water to arid urban landscapes more efficiently if irrigations were scheduled based on such information.

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Field-grown (FG) trees lose a significant portion of their root system ( Gilman and Beeson, 1996 ) and when transplanted are subjected to great stress. Water deficits often develop ( Montague et al., 2000a ) because the natural balance between

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shrubs for different climates and growing conditions in nature widens their use potential for urban environments compared with trees, indicating a need for site-related research of shrubs in urban environments. Moreover, recent research of shrubs and

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Landscape trees are becoming increasingly important in urban and suburban environments as a result of the values and benefits they provide by virtue of their aesthetic nature, ability to purify ambient air, use in providing shade, and service as

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climate parameters HortScience 47 907 916 Gilman, E.F. Masters, F. Grabosky, J.C. 2008 Pruning affects tree movement in hurricane force wind Arboric. Urban For. 34 20 28 Hellkvist, J. Richards, G.P. Jamis, P.G. 1974 Vertical gradients of water potential

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Amur maackia (Maackia amurensis Rupr. & Maxim.) has potential for use in small, urban, or cold landscapes. Although Amur maackia is becoming increasingly popular, plants are currently grown from open-pollinated seed populations, and there has been no selection of cultivars. We have addressed the effects of climate on growth and have begun field trials for selection of horticulturally superior genotypes. In May 1995, a field trial near Ames was begun with 337 plants. These were selected from more than 2000 greenhouse-grown seedlings to represent 32 half-sibling seed groups from 16 arboreta across North America. After two growing seasons, the increase in stem length among seed groups ranged from 3% to 75%. Survival rate did not vary with seed group. In a related study, 30 plants from six half-sibling groups have been established at each of 10 sites in the U.S. and four in Canada to assess effects of location on survival and growth. The influence of seed group on survival after 1 year varied with the trial site location. Survival among combinations of half-sibling group and trial location ranged from 0% to 100% (mean = 54%). Half-sibling group and trial location affected growth without interaction. The greatest growth across locations, an 83% increase in stem length, was shown by seeds that originated from a tree at the Arnold Arboretum. At the 14 locations, changes in stem length over half-sibling groups varied from <0% in Ithaca, N.Y., to 179% in Puyallup, Wash.

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State University, and Masami Yamaguchi, National Institute of Fruit Tree Science of Japan, for providing plant materials.

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Shredded and chipped wood mulches are used for weed suppression in perennial fruit crops, in urban landscapes, and occasionally in vegetable crops. Wood chip mulches with weed-suppressing allelochemicals may be more effective for weed control, especially under sustainable and organic production systems, than mulches without such properties. The objective of this study was to test for the presence of water-soluble allelochemicals in wood chips derived from tree species, often found in wood resource recovery operations in the southeastern US. Presence of allelochemicals in water eluates of woodchips and leaves was evaluated in a lettuce bioassay. Eluates of wood chips from red maple (Acer rubrum L.), swamp chestnut oak (Quercus michauxii Nutt.), red cedar (Juniperus silicicola L.H. Bailey), neem (Azadirachta indica A. Juss.), and magnolia (Magnolia grandiflora L.) highly inhibited germinating lettuce seeds, as assessed by inhibition of hypocotyl and radicle growth. The effects of wood chip eluates from these five species were more than that found for eluates from wood chips of black walnut (Juglans nigra L.,) a species previously identified to have weed-suppressing allelochemicals. Tests on red cedar, red maple, and neem showed that water-soluble allelochemicals were present not only in the wood but also in the leaves. In greenhouse trials, red cedar wood chip mulch significantly inhibited the growth of florida beggarweed (Desmodium tortuosum DC.), compared to the gravel-mulched and no-mulch controls.

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