Journal of Arboriculture 31(2): March 2005 83 IRRIGATION EFFECTS ON THE GROWTH OF NEWLY PLANTED OAKS (QUERCUS SPP.) By Laurence R. Costello1 , Katherine S. Jones2 Abstract. The effect of irrigation on the growth of container- grown oaks was investigated over a 4-year period. Quercus lobata, Q. agrifolia, and Q. douglasii were irrigated at three levels of reference evapotranspiration (0, 0.25, and 0.5 ET0 ) after being established for 1 year at the University of California Bay Area Research and Extension Center in Santa Clara, California, U.S. Although no significant differences were found in trunk diameter growth for irrigation treatments after 4 years, growth of Q. agrifolia was significantly greater than Q. lobata and Q. douglasii. Root mass, shoot mass, and root distribution were measured for Q. agrifolia, and mean shoot:root ratio was found to be 2.6 to 1. Many roots of Q. agrifolia were found to develop with a stronger vertical than horizontal orientation, and root distribution was not signifi- cantly affected by irrigation treatments. Key Words. Irrigation; Quercus; planting. , and Douglas D. McCreary3 Although native oaks are considered highly desirable species in California, U.S., oak populations have declined in both wildland and urban areas over the past century (Pavlik et al. 1992). In wildland areas, substantial efforts have been made to restore populations, and new stands have been established in the past 20 years (McCreary 1993, 2001; Swiecki and Bernhardt 1993; Standiford 1999). In urban areas, however, many mature oaks have declined or been removed to make room for residential or commercial developments and replaced with non-native species. Native oaks are often replaced with non-native species because native oaks have been characterized as being slow- growing: they are viewed as requiring much more time to achieve a desirable size than “fast-growing” landscape species. This characterization likely resulted from observa- tions of oaks in their native habitat and may not be an accurate assessment of their actual performance in urban landscapes. Because many urban landscapes in California are irrigated, and the growth rate of many woody species is enhanced by irrigation, it was hypothesized that the growth rate of native oaks also may be enhanced by irrigation. Previous reports have provided evidence of a positive response of Quercus spp. to irrigation during the establish- ment period. In a study evaluating irrigation volume and frequency on the establishment of container-grown Q. virginiana, Gilman et al. (1998) reported that frequent irrigation during the first growing season after transplanting (76 L [20 gal] every day for 6 months) promoted greater survival and establishment than infrequent irrigation (76 L [20 gal] every 2 or 3 days for 3 months) for southern live oak planted in a sandy soil in Florida. It was noted that “it was more important to irrigate transplanted trees frequently that it was to apply a large volume of water.” In a follow-up study evaluating nursery production methods, irrigation, and inoculation with mycorrhizae-forming fungi on the establishment of Q. virginiana, Gilman (2001) found that irrigation during the first summer after transplanting resulted in higher survival rates for all nursery production types tested (container- and field-grown stock). During the irrigation treatment period (for 6 months after transplant- ing), trunk diameter growth rate for all nursery production types was greater for irrigated than for nonirrigated trees. In the 2-year period following the cessation of irrigation, however, trunk diameter growth rate was equivalent whether trees were initially irrigated or not. These results provide evidence that irrigation during the first year after transplanting can have a measurable and positive effect on the survival and growth of transplanted container- and field- grown trees. Although previous studies support the need for irriga- tion during the first year after transplanting for southern live oak, irrigation effects on the growth of California native oaks (Quercus spp.) following a 1-year establishment period have not been evaluated. This study was conducted to (1) evaluate the influence of irrigation volume on trunk diameter growth of three California oak species over a 4- year period, (2) quantify differences in irrigation response among species, and (3) describe root distribution and quantify shoot:root ratio for coast live oak (Q. agrifolia). METHODS This study was conducted at the University of California Bay Area Research and Extension Center (BAREC) in Santa Clara, California, from spring 1997 to fall 2001. Prior to planting, a field plot measuring 33 m (100 ft) wide and 41 m (125 ft) long was cultivated approximately 0.82 m (2.5 ft) deep to create uniform root zone soil conditions. Soil analysis indicated that soil pH (6.8) and salt content (electrical conductivity = 0.91 dS/m) were not limiting (Craul 1999). Soil texture was classified as loam (47% sand, 38% silt, and 15% clay), and mean bulk density was 1.48 g/cc (range = 1.41 to 1.59 g/cc) for three depths (0.33, 1, and 2 m [1, 3, and 6 ft]) and three locations across the plot. Growth- ©2005 International Society of Arboriculture
March 2005
| 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
