Margaret Livingston

Effects of Three Landscape Treatments on Residential Energy and Water Use in Tucson, Arizona*

Abstract Vegetation can reduce the cooling loads of buildings in hot arid climates by modifying air temperature, solar heat gain, longwave heat gain, and heat loss by convection. However, savings from reduced mechanical cooling may be offset by increased irrigation water costs. In this study, three similar 1 4 -scale model buildings were constructed and surrounded with different landscapes: turf, rock mulch with a foundation planting of shrubs, and rock mulch with no plants. Irrigation water use and electricity required to power the three room-sized air conditioners and interior lights were measured for two approximately week-long periods. Electrical energy consumed for air-conditioning by the rock model was 20 – 30% more than for the turf and shade models. Factors accounting for these differences in energy performance include dense shade that substantially reduced solar heat gain for the shaded model, a 16% difference in longwave radiation flux between the rock and turf treatments, and a maximum drybulb depression of 4 °C over the turf compared with the rock. Air-conditioning savings exceeded water costs for shade treatments that were simulated to receive moderate and low amounts of irrigation water. These preliminary findings suggest that the localized effects of vegetation on building microclimate may be more significant than boundary layer effects in hot arid regions.

A model for assessing wildlife habitats in urban landscapes of eastern Pima County, Arizona (USA)

The loss of large natural areas due to development has increased interest for and use of vegetated areas in urban and suburban areas for wildlife habitats. The goal of this study was to quantify vegetation characteristics for each type of land cover found in the greater Tucson, Arizona area, thereby providing a predictive tool for wildlife management and other land management issues. This research was based on and is a continuation of a pilot study that developed a method associating land cover categories to aerial photographs in eastern Pima County, including the City of Tucson. Aggregation of land cover categories used by Tucson and Pima County and verifications of any uncertain classifications of land cover with field evaluations produced a consistent land cover classification system and database. Natural open space was the largest land cover category within our study area, comprising 52% of the total land cover. Riparian areas, low-density housing and natural open space areas had the highest percentage of native vegetation and escape cover. Golf and neighborhood parks ranked much lower than these land covers relative to native vegetation and escape cover (vegetation with foliage/stems at ground level). The most structurally diverse plant communities were associated with medium density residential areas and zoos that contain a relatively high number of exotic species. Results from the wildlife habitats index indicated riparian areas as the most valuable habitats in eastern Pima County (the county where Tucson is located), followed by low-density housing (≤1 residence/acre), natural open space, and federal/state parks and forests.

Surface soil water loss after summer rainfall in a semidesert grassland

Surface soil water contents were analyzed for bare and litter‐ or gravel‐covered soils for 20 drying periods after summer rainfall in southeastern Arizona. Water contents were measured every minute by fiberglass cells calibrated for the sandy‐loam soil, and 30‐ to 60‐min averages were stored by microloggers. Water loss to equivalent matric potentials of ‐1.5 MPa for bare surface soils (1–3 cm) was fast (1.2 ± 0.5 days), moderate (2.6 ± 0.9 days), or slow (5.9 ± 1.4 days) when the upper 15 cm of soil at the start of the drying period had 13.3, 27.1, and 36.1 cm of water, respectively. Those water contents are near saturation and near field capacity for slow and moderate drying rates, respectively. For fast drying rates, water content was near field capacity at 1–3 cm but dry below 8 cm. Litter or gravel mulches increased the time of surface soil water availability by 0.7 to 1.9 days for fast and moderate drying periods, respectively. Drying from the surface down into the soil profile averaged 3.6 cm day‐1....

Vegetative characteristics of urban land covers in metropolitan Tucson

In this study we developed a methodology that associated land cover categories to aerial photographs. We selected 4, 42-mile (10 km2) study sites within metropolitan Tucson, Arizona for our pilot study. Land uses within these sites covered the range of landscapes found within Pima County, Arizona, although not necessarily in proportions representative of the metropolitan area. We designated land cover categories within the pilot sites based on recent (March, 1990) aerial photographs and developed a geographical information system (GIS) database of these land cover categories. We measured vegetation attributes on randomly selected samples within each land cover category and classified vegetation occurring on specific land cover categories according to the Brown et al. (1979) system. Our land cover classification system was nominal with a hierarchical structure, facilitating organization and providing flexibility for adding new categories.Our results showed that although neighborhood parks contained the greatest vegetated areas within our four study plots, very low density housing (≥4 acres/house), rivers whose banks were partially stabilized, naturally occurring washes (with no bank stabilization), and natural open space contained the highest percentage of native vegetation. Within our four study sites, low density housing (≥4 acres/house), rivers with partially stabilized banks, naturally occurring washes (no bank stabilization), and natural open space land cover categories contained the most area that was covered with vegetation providing escape cover.

Mechanical pollarding as a means to increase rubber yields in guayule (Parthenium argentatum, Asteraceae)

Guayule (Parthenium argentatum Gray, Asteraceae) is a potential domestic source of natural rubber, but is presently not competitive economically with imported Hevea rubber. Guayule can become competitive by either increasing rubber yield or reducing the costs of cultural practices, or both. Pollarding, harvesting the branches by cutting leaving the root-crown to regrow new branches, can potentially increase both rubber yields and reduce the costs of stand establishment. The objective of this study was to determine the efficiency of mechanical-pollarding, and to determine if there were increased rubber yields one year after pollarding. A mechanical clipper was used to pollard shrub (accession N396), planted at the standard density of 36.650 plants ha. 17 and 29 months after stand establishment. Mechanical pollarding at 17 months left 19% of the branches unclipped on both a fresh and dry weight basis, representing 16% of the potential resin and rubber yield. After regrowth for one year (29 months), pollarded plants had increased fresh weight, dry weight and resin yield over non-pollarded plants of 25, 24 and 15%, respectively. However, rubber yield increased by only 3%, due mainly to the low rubber content in the regrowth. After a single pollarding (17 months) 98% of the plants survived and regenerated new growth. Plants pollarded two consecutive years (17 and 29 months) had only a 66% survival rate. The low rubber yield in the regrowth after one year, and the reduced survival rate of plants pollarded two consecutive years, suggests that a clipping interval of two years may be optimal for line N396.

Comparison of three stability measures in guayule

Guayule (Parthenium argentatum Gray), a desert shrub native to the Chihuahuan desert of North America, is being domesticated as a potential rubber source. Two Uniform Regional Guayule Variety Trials were conducted in eleven locations using a total of twelve entries. Data from each of these trials were used to compute stability coefficients using the methods of Finlay and Wilkinson (1963), Eberhart and Russell (1966) and Zhang and Geng (1986). Results and interpretations of these methods were compared. Zhang and Gengs method was the most useful because it allowed comparison of entries grown in the two different yield trials. Using this method, the following conclusions were reached: Arizona breeding line AZ101 was significantly less stable than average in biomass and resin yield, ‘11605’ was less stable than average for percent rubber, and ‘Cal-6’ and ‘Cal-7’ were less stable than average for rubber yield. Six entries (‘N565’, ‘N576’, ‘11591’, ‘11605’, ‘11619’ and ‘12229’) were significantly more stable than average for biomass yield, resin yield and rubber yield. Germplasm line N396 was also more stable than average for resin yield and percent resin. AZ101 was more stable than average for rubber percentage and rubber yield. Over all entries, there was a negative correlation between stability and yields of resin and rubber.

Design Concept of a Reverse Osmosis Reject Irrigated Landscape: Connecting Source to Sabkha

Feasibility studies in Arizona (U.S.A.) have determined that ocean delivery is a viable disposal option for saline waste water when sourced from near coastline regions. Use of open canals to transport waste water and use of evaporation ponds to reduce waste water volume are standard engineering practices. Engineered designs tend to focus on practicality and efficiency without regard to principles of landscape ecology. The concept of a saline ecosystem with landscape pattern incorporated as the vehicle for an evapotranspiration induced sequence of ecotopes along a directional saline gradient is proposed. This model will serve as a constructive, ecologically-based method to reduce reverse osmosis concentrate waste volume while increasing salinity during transport from source (RO facility) to sink (sabkha). In the process, biota is allowed to self-organize into marsh habitat and the system of pattern creates potential for plant and microbial crops. Potential for research use of the ecosystem is illustrated in light of a conceptual plan for the Santa Clara Slough, located at the northern end of the Sea of Cortez in the Gulf of California.