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  • Author or Editor: Edward L. McWilliams x
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Hurricanes strike the Gulf Coast of the United States every few years. We briefly describe generalized hurricane tracks for the Gulf Coast and vegetation damage using NDVI satellite imagery as well as slides of damaged urban trees in Florida. The impact of recent hurricanes on both pecan defoliation and production and on initial damage and subsequent recovery of various ornamental trees is described. Pecan harvests were greatly reduced by hurricanes that struck late in the season in both Alabama and Texas. Varieties of pecans varied in their susceptibility to various stresses. Pine forests were sometimes devastated by certain hurricanes while live oaks, various shrubs, and important insects often survived the same storms with little damage. Many exotic ornamental plants including Chinese tallow are either adventive or invasive along the Gulf Coast. Species escape from cultivation over a long period of time and exhibit different invasion lag phases. In Texas and Louisiana, hurricane damage to native trees allowed Chinese tallow seedlings and saplings to subsequently dominate some areas as a result of the disturbance. One delayed ecological response to hurricanes and typhoons is an acceleration of ongoing exotic plant invasions.

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Controversy over regional climatic change (RCC) and the direction of RCC continues. Models that predict how local plants would respond to defined regional climatic warming (RCW) would be useful.

The urban heat island intensity (UHII) has been documented in a number of cities including Houston, Texas, Phoenix, Arizona, St. Louis, Missouri, and Gainesville, Florida. We studies the phenological response of selected horticultural plants growing along urban/rural thermal gradients in several cities where the UHII had previously been defined. Deciduous plants flowered earlier in the spring and retained their leaves longer in the fall in warmer urban areas than they did in adjacent rural areas.

The phenological response of local plants to known thermal gradients appears to be a useful model of the phenological effects of potential RCW.

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Urban areas have average annual temperatures 2–3°C warmer than surrounding rural areas, with daily differences of 5–6°C common. A suggested reason for this temperature difference is the extensive use of concrete, asphalt, and other building materials in the urban environment. Vegetation can moderate these temperatures by intercepting incoming radiation. The influence of vegetation patterns on the magnitude of urban and micro-urban “heat islands” (UHI and MUHI, respectively) is compared for several cities including Houston, Austin, College Station, and Ft. Worth, Texas; Huntsville, Ala.; and Gainesville, Fla. Temperatures for all cities studied were greatest in the built-up areas and dropped off in suburban areas and adjacent rural areas. In Houston, surrounding rice fields were 3–5°C cooler than urban areas. Heavily built-up areas of Austin were 2–4°C warmer than parks and fields outside of the city. In all of the cities, large parks were typically 2–3°C cooler than adjacent built-up areas. Large shopping malls varied in nocturnal winter and summer temperature, with winter temperatures near door openings 2–3°C warmer, and summer daytime temperatures as much as 17°C cooler beneath trees. This effect seemed to persist at the microclimatic scale. Areas beneath evergreen trees and shrubs were warmer in the winter than surrounding grass covered areas. Video thermography indicated that the lower surfaces of limbs in deciduous trees were warmer than the upper surfaces. Overall, vegetation played a significant role, both at the local and microscale, in temperature moderation.

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As the World Wide Web (WWW) expands, information is rapidly becoming more accessible. Using satellite data previously required high-end computers running complex imaging software, sophisticated downloading equipment, and high monetary support. Satellite data is now available on the internet for little or no cost and can be handled on standard desktop computers using common software programs. The purpose of our project was to determine the availability and cost of different types of data and how this data may benefit horticultural instruction. Satellite data currently is archived at NASA, NOAA, the Department of Defense, the US Geological Survey, and various meteorological departments throughout the world. Satellite data such as large-scale thermal imagery can be used to determine microclimate effects within urban areas, including the cooling effects of urban plants. Natural Density Vegetation Index (NDVI) imagery can indicate changes in vegetational cover or give general indications of plant health in large areas. NASA photographic imagery can show the effects of erosion on a large scale. Higher resolution imagery can give indications of plant stresses in large plantings such as orchards or vegetable plots.

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Urban areas are typically 2 to 3°C warmer than surrounding rural areas throughout the year. Winter minimum temperatures are often 4 to 5 °C warmer in the city and, during extreme episodes may exhibit differences of 12 to 13°C. Because the USDA Hardiness Maps compile readings from individual stations in an area, temperature differences may not be apparent at the local scale. This study was conducted to compare ornamental plant damage during Winter 1995–96 in Fort Worth, Texas. AVHRR 1-km thermal satellite imagery was used to determine the warmest and coolest portions in Fort Worth, Texas. Each temperature area was divided into five 0.5-km blocks on the basis of similar landscape features and plant types. During Mar. 1996, these areas were evaluated on the basis of plant damage to several species. Asian jasmine (Trachelospermum asiaticum), indian hawthorn (Raphiolepis indica), St. augustine turf (Stenotaphrum secundatum), southern magnolia (Magnolia grandiflora), and Live Oak (Quercus virginiana) were the primary species damaged. Asian jasmine and St. Augustine turf were either completely killed or severely damaged in the coldest areas but suffered only moderate or light damage in the warmest areas. Indian hawthorn, live oak, and southern magnolia suffered leaf and stem damage in the coldest areas but little to no damage in the warmer areas.

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Abstract

Exposure to low temperature (4.5°C) for 4 days killed Scindapsus pictus Hassk. and resulted in a 49.2% reduction in dry weight of Maranta leuconeura E. Moor. Var. erythroneura Bunting. Aphelandra squarrosa Ness. cv. Louisae exhibited an 8.5% reduction in dry weight and leaf abscission after 6 or more days of chilling. Each of the chilling sensitive species displayed unique and distinctive symptoms. Pilea cadierei Gagnep. and Guillanum showed no chilling damage. The species studied exhibited a decreasing sensitivity to chilling in the following order: 1) S. pictus, 2) M. leuconeura, 3) A. squarrosa, 4) P. cadierei.

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Abstract

Amorpha fruticosa L. has a national distribution from the American west coast to the east coast and from Wyoming to Sonora, Mexico (Correll and Johnston, 1970). There has been much confusion, due to the large amount of variation that exists, as to the correct botanical nomenclature of the species. A tentative nomenclature change would leave A. fruticosa with at least 16 synonyms (Kartesz and Kartesz, 1980). The cultivar discussed would be listed by some authors under A. fruticosa L. var. angustifolia Pursh. (Correll and Johnston, 1970; Shinners, 1972). ‘Dark Lance’ was selected for its beauty of spring flowering, being literally covered with dense spikes of violet flowers with yellow-orange anthers in late April. This floral display is apparent for 7 to 14 days, depending on weather conditions. This is a desirable landscape plant with low requirements of fertilizer and maintenance, and apparent freedom from disease and insect pests. However, it is the first Texas A&M Univ. resource-efficient plant released to the Texas and southwestern nursery industry that does not have strong drought tolerance.

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Abstract

Several species of Leucophyllum are widely used in Texas and the southwestern United States (Arizona, California, Nevada, New Mexico) for amenity plantings. These taxa are among the most ornamental of all native Texas plants (8). Leucophyllum candidum I. M. Johnst. (2, 7) grows on arid sites in northern Mexico and in southern Brewster Co., Texas, and is usually found on caliche, gravelly hillsides (11). The low requirements for nutrients, water, pest control, and general maintenance make the use of ‘Thunder Cloud’ a pragmatic choice for water and energy conservation in the arid to semi-arid southwest (12).

Open Access

Abstract

Desert willow [Chilopsis linearis (Cav.) Sweet.] (7, 12) is a facultative phreatophyte (a plant whose roots will extract water from underground streams, a water table, or perched sources, or the strata immediately above these sources, but which can also function well in the absence of these water supplies). It is a tall shrub to a small tree (2, 3) and is native to the American southwest, from Baja California, southern California, southern Nevada, Arizona, and New Mexico to southwestern Texas and northern Mexico (8, 9).

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The combination of concrete and asphalt surfaces, large buildings, lack of surface water, and anthropogenic heat inputs result in urban temperatures warmer than surrounding rural areas. This effect is often most pronounced with winter minimum temperatures and may cause changes in local plant hardiness zones. Local minimum temperatures were obtained for the years 1974-96 from the National Climatic Data Center and the Office of the State Climatologist of Texas for all recording stations within the Dallas-Fort Worth, Texas metropolitan area. Data were averaged and analyzed in two groups: 1974-86 and 1987-96. Contour maps were created using Surfer software. The 1974-86 local map had only one major difference from the 1990 USDA Plant Hardiness Zone map, which was the inclusion of 8a temperatures in more western portions of the metroplex. The inclusion of the years 1987-96 resulted in the westward expansion of 8a and a new 8b zone near downtown Dallas. These changes mimic the expansion of suburban development and increased urbanization over the last decade. We propose an updated plant hardiness zone map for this metropolitan area, which should more accurately reflect changes that have occurred since publication of the USDA Plant Hardiness Zone map.

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