Repository logo

Browsing by Author "Klett, James, advisor"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Drought stress and recovery in green ash (Fraxinus pennsylvanica Marsh.)
    (Colorado State University. Libraries, 2009) Litus, Gregory, author; Klett, James, advisor
    Throughout the Front Range of Colorado, municipalities have developed urban forest management plans that focus on preserving the health of landscape trees and promoting an increase in the canopy cover as an offset to carbon dioxide emissions through carbon sequestration. However, drought in recent years has prompted a concerted effort to conserve water used for landscape irrigation. The combined drought and reductions in irrigation have the potentials to increase water stress in shade trees and lessen the amount of carbon sequestered. To assess the effects of drought stress on growth, photosynthesis and long term health of established green ash (Fraxinus pennsylvanica Marsh.), a record dry 2005-2006 winter was exploited so that severe drought stress could be induced. Early season drought reduced spring leaf growth by 25 percent compared to controls. As drought progressed through the growing season, the stressed trees increased intrinsic water use efficiency by controlling stomatal conductance, based on threshold water potentials, while maintaining photosynthesis. After irrigation was applied in late summer, tree water potentials, stomatal conductance and photosynthesis recovered to near pre-drought levels. The decreased photosynthesis contributed to the reduction in tree growth for the season but did not alter total non-structural carbohydrates concentrations or produce a carbohydrate deficit that would dramatically hinder growth in subsequent years. The extended drought stress followed by irrigation did not affect dormancy and cold hardiness was maintained to -50 °C. Potted green ash trees were used to determine the extent of drought stress tolerated by green ash. At a predawn leaf water potential of -5.28 MPa, stomatal conductance and photosynthesis were reduced but still measurable. Established trees exposed to severe drought conditions did not experience predawn leaf water potentials below -3.14 MPa. Considering the range of drought stress tolerated by green ash and the unlikelihood of those conditions occurring in a managed landscape, negative effects of drought stress are minimized as long as late season irrigation can be applied. However, in green ash, the timing of drought stress can permanently restrict growth in any single year and significantly reduce the total carbon sequestered through photosynthesis.
  • Thumbnail Image
    ItemOpen Access
    Extensive green roofs in Colorado: plant species performance, growing media modifications, and species response to growing media dry down
    (Colorado State University. Libraries, 2010) Bousselot, Jennifer McGuire, author; Klett, James, advisor; Kelaidis, Panayoti, committee member; Barbarick, Kenneth, committee member; Koski, Anthony, committee member
    To view the abstract, please see the full text of the document.
  • Thumbnail Image
    ItemOpen Access
    Multi-site trial of woody plants: 2006 planting and evaluation of differences in drought tolerance of three Amelanchier species
    (Colorado State University. Libraries, 2012) Hammond, Eric, author; Klett, James, advisor; Jacobi, William, committee member; Hughes, Harrison, committee member
    CHAPTER 1: MULTI-SITE WOODY PLANT EVALUATION IN COLORADO A multi-site trial of several woody plants plant species and cultivars was conducted to determine their potential for landscape use in the state of Colorado. The trial was conducted with the input and cooperation for the Colorado Nursery Research and Education Foundation and Plant Select®. Data was collected from 2006-2010 at five sites with different soils, climates and cultural practices. Plants were evaluated based on size, growth, survival, aesthetics and heath. The taxa evaluated were: Acer monspessulanum, Juniperus scopulorum 'Woodward', Larix decidua, Prunus serotina (of central Texas providence), Pyrus ussuriensis 'Burgundy', Quercus polymorpha and, Quercus × pauciloba. Researchers recommend Juniperus scopulorum 'Woodward', Prunus serotina and, Quercus × pauciloba for widespread use in the state. Quercus polymorpha did not prove adapted to any of the sites and is not recommended. Larix decidua and Pyrus ussuriensis 'Burgundy' did not perform well at all sites and are only recommended for use in the state in some situations. CHAPTER 2: EVALUATION OF DIFFERENCES IN DROUGHT TOLERANCE OF THREE AMELANCHIER SPECIES In the summer and fall of 2010, research was conducted to evaluate the drought tolerance of Amelanchier alnifolia, Amelanchier canadensis, and Amelanchier utahensis. Potted plants of each species were subjected to three increasingly long periods without watering (dry downs) in a greenhouse. Predawn leaf water potential and soil volumetric water content (measured by time domain reflectometry) were measured for each plant and compared. The third dry down was allowed to continue until plants went dormant or died. Results show that in a greenhouse, potted, Amelanchier utahensis is more tolerant of low water conditions than the other species. The differences in drought tolerance between the Amelanchier canadensis and Amelanchier alnifolia are not as clear and may require more research to understand.