336 2004) when compared to woody plants growing over vegetative surfaces. Kjelgren and Clark (1993) found morning-to-evening gs of sweetgum (Liquid- ambar styraciflua) trees in an urban plaza in Seattle, Washington, U.S., was lower when compared to gs for sweetgum trees in a nearby park. Montague et al. (1998; 2000; 2004) found containerized shrubs (Euonymus kiautschovicus ‘Manhattan’ and Cornus sericea), containerized trees (Acer platanoides ‘Crim- son King’, Salix matsudana ‘Navajo’ and Platanus occidentalis), and balled and burlapped Acer plat- anoides ‘Emerald Queen’ and Tilia cordata ‘Green- spire’ trees grown over pine bark mulch had greater leaf temperature, were exposed to greater VPD, had lower gs, and less water loss when compared to shrubs and trees growing over established turf. Cregg and Dix (2001) monitored crown air tem- perature, leaf water potential, and gas exchange (gs and A) of mature (15–30 year old) trees (Fraxi- nus pennsylvanica ‘Marshall’s Seedless’, Quercus rubra, and Pinus nigra) growing in an urban and a rural college campus site. They reported greater air temperature and VPD for trees in the urban site. In addition, tree crown air temperature and pre-dawn leaf water potential (ψl ) were lower, and gas exchange was greater for Q. rubra and F. pennsylvanica ‘Marshall’s Seedless’ trees grow- ing at the rural college campus location. For P. nigra, differences between sites was minimal. Additionally, Zajicek and Heilman (1991) indi- cate containerized crapemyrtle (Lagerstroemia indica) cultivars (‘Hope’, ‘Seminole’, ‘Victor’, and ‘Carolina Beauty’) placed over pine bark mulch had greater water loss when compared to plants grown over turf, or bare soil. Transpiration rates for hon- eylocust (Gleditsia triacanthos inermis) and green ash (Fraxinus pennsylvanica) trees grown over non- vegetative surfaces in urban settings were also greater when compared to transpiration rates for trees grown over vegetative surfaces in rural sites (Potts and Herrington 1982; Whitlow and Bassuk 1988). Because water deficits oſten develop in urban landscapes, more information is needed to estab- lish irrigation requirements for urban trees. An ideal method to schedule irrigation would be to estimate water requirements, and replenish the root system with the required volume (Mathers et al. 2005). However, because irrigation require- ments of many landscape tree species are not well ©2015 International Society of Arboriculture Montague and Bates: Response of Maple to Reduced Irrigation known, and vary with climate (Montague et al. 2004; Kjelgren et al. 2005), nursery and landscape irrigation managers are oſten unsure of the vol- ume of water that landscape trees require (Beeson 2005). In fact, because of the lack of information regarding tree irrigation requirements, land- scape and nursery trees are frequently irrigated in excess (which may result in waterlogged soil, poor plant growth, increased irrigation runoff, leached nutrients, increased water bills, and misuse of irrigation water) or deficit amounts (which may result in poor plant growth, poor plant aesthetics, and plant death) (Kjelgren et al. 2000; Montague et al. 2004; Mathers et al. 2005). In either case, performance of ornamental tree species will not meet production or landscape expectations. A robust approach to estimate the water needs of plants is to define plant water loss factors by a constant, standardized measure of reference water loss that is a function of climatic factors (Levitt et al. 1995). The American Society of Civil Engi- neers Penman-Monteith (ASCE-PM) equation has defined reference evapotranspiration (ETo) as the rate of evapotranspiration from a short, cool-season reference grass surface (Allen et al. 2005), and variables needed to calculate ETo (wind speed, air temperature, humidity, incoming shortwave solar radiation) are readily available from automated weather stations. The ASCE-PM approach determines plant water loss by param- eterizing empirically measured plant evapotrans- piration (Ec) as a function of ETo using a Plant Factor (PF). The dimensionless PF is computed as: [1] PF = (Ec) / (ETo) where both Ec and ETo have units of depth of water evaporated (mm) / (unit time). Water loss of turf- grass is closely related to ETo. Therefore, PF values have been developed for many turf species (Car- row 1995; Ervin and Koski 1998). However, due to the difficulty of quantifying values (Kjelgren et al. 2000), the great diversity of species (Sun et al. 2012), and the reality that PF values determined in one climate may not translate to another climate (Kjelgren et al. 2005), there are a limited number of PF values reported for landscape tree species (Levitt et al. 1995; Montague et al. 2004; Niu et al. 2006; Fox and Montague 2009; Costello 2013).
November 2015
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
