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D.A. Devitt, M. Berkowitz, P.J. Schulte, and R.L. Morris

We compared transpiration estimates of three common desert landscape tree species using stem-flow gauges and lysimetry. Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill., seedling selection) were subjected to three irrigation regimes. Leaching fractions of +0.25, 0.00, and -0.25 were imposed for 2 years. During the summer of the second year, we conducted a comparative transpiration study. Trees growing in 190-liter plastic containers had a highly linear correlation (r = 0.98, P = 0.001) between transpiration estimated by stem-flow gauges and lysimetry. An average 18% error was measured between paired data (total runs of 14 to 72.5 hours) of stem-flow gauge and lysimetry transpiration estimates. However, a lower error was correlated significantly with longer run times (r = -0.37, P = 0.05). Based on field measurements taken in this experiment, run times would have to be >68 hours to maintain an associated error below 10%. Higher cumulative transpiration also was associated with longer run times (r = 0.80, P = 0.001). These results suggest that the stem-flow gauge can be used to estimate transpiration accurately to schedule irrigation for woody ornamental trees in an arid environment, provided that irrigation predictions are not based on short-term stem-flow gauge estimates (<68 hours).

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Phillip A. Wadl, Robert N. Trigiano, Dennis J. Werner, Margaret R. Pooler, and Timothy A. Rinehart

There are 11 recognized Cercis L. species, but identification is problematic using morphological characters, which are largely quantitative and continuous. Previous studies have combined morphological and molecular data to resolve taxonomic questions about geographic distribution of Cercis species, identifying botanical varieties, and associations between morphological variation and the environment. Three species have been used in ornamental plant breeding in the United States, including three botanical varieties of C. canadensis L. from North America and two Asian species, C. chingii Chun and C. chinensis Bunge. In this article, 51 taxa were sampled comprising eight species of Cercis and a closely related species, Bauhinia faberi Oliv. Sixty-eight polymorphic simple sequence repeat markers were used to assess genetic relationships between species and cultivars. For all samples the number of alleles detected ranged from two to 20 and 10 or more alleles were detected at 22 loci. Average polymorphic information content was 0.57 and values ranged from 0.06 to 0.91 with 44 loci 0.50 or greater. Cross-species transfer within Cercis was extremely high with 55 loci that amplified at 100%. Results support previously reported phylogenetic relationships of the North American and western Eurasian species and indicate suitability of these markers for mapping studies involving C. canadensis and C. chinensis. Results also support known pedigrees from ornamental tree breeding programs for the widely cultivated C. canadensis and C. chinensis species, which comprised the majority of the samples analyzed.

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C. Richer-Leclerc and J.-A. Rioux

159 WORKSHOP 25 Contributions of Canadian Agriculture to the Introduction, Evaluation, and Testing of Woody Ornamental Trees and Shrubs for Use in Plant Breed Programs

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Chris A. Martin and Linda B. Stabler

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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Charles R. Hall, Alan W. Hodges, and John J. Haydu

The United States environmental horticulture industry, also known as the Green Industry, is comprised of wholesale nursery and sod growers; landscape architects, designers/builders, contractors, and maintenance firms; retail garden centers, home centers, and mass merchandisers with lawn and garden departments; and marketing intermediaries such as brokers and horticultural distribution centers (re-wholesalers). Environmental horticulture is one of the fastest growing segments of the nation's agricultural economy. In spite of the magnitude and recent growth in the Green Industry, there is surprisingly little information regarding its economic impact. Thus, the objective of this study was to estimate the economic impacts of the Green Industry at the national level. Economic impacts for the U.S. Green Industry in 2002 were estimated at $147.8 billion in output, 1,964,339 jobs, $95.1 billion in value added, $64.3 billion in labor income, and $6.9 billion in indirect business taxes, with these values expressed in 2004 dollars. In addition, this study evaluated the value and role of urban forest trees (woody ornamental trees); the total output of tree production and care services was valued at $14.55 billion, which translated into $21.02 billion in total output impacts, 259,224 jobs, and $14.12 billion in value added.

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D.A. Devitt, R.L. Morris, and D.S. Neuman

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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Brian E. Jackson, Robert D. Wright, and Michael C. Barnes

387 400 Jones R.K. Benson D.M. Diseases of woody ornamental trees in nurseries APS Press St. Paul, MN Boodley, J.W. Sheldrake R. Jr 1964 Cornell peat-lite mixes for commercial plant growing

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Tamara Wynne and Dale Devitt

fractions of irrigated desert turfgrass systems Agron. J. 84 717 723 Devitt, D.A. Berkowitz, M. Schulte, P.J. Morris, R.L. 1993 Estimating transpiration for three woody ornamental tree species using stem-flow gauges and lysimetry HortScience 28 320 322