Arboriculture & Urban Forestry 33(4): July 2007 Arboriculture & Urban Forestry 2007. 33(4):275–282. 275 Early Landscape Performance of 20 Field-Grown Birch Genotypes at Two Locations in Arkansas, U.S. and Response to Irrigation Mengmeng Gu, James A. Robbins, and Curt R. Rom Abstract. Twenty birch genotypes were planted in the field in April 2002 to evaluate their survival and growth at Fayetteville and Hope, Arkansas, U.S., and to evaluate their response to two irrigation regimes at Fayetteville. After four growing seasons, the overall tree survival was 62% and 30% at Fayetteville and Hope, respectively. Betula pendula ‘Trost’s Dwarf’, B. ermanii, and B. albosinensis were among genotypes with the lowest survival at both locations. Betula popu- lifolia, B. nigra ‘BNMTF’, B. nigra ‘Cully’, and B. × ‘Royal Frost’ had greater survival after four growing seasons than the other birch genotypes investigated. Betula nigra ‘BNMTF’ and B. nigra ‘Cully’ were taller and had greater trunk diameter than the other surviving birch genotypes at both locations after four growing seasons. At the end of 2005, B. utilis var. jacquemontii was the shortest and had the smallest trunk diameter among the 18 surviving genotypes at Fayetteville, and B. papyrifera ‘Uenci’, B. populifolia ‘Whitespire’, B. maximowicziana, and B. lenta were the shortest and had the smallest trunk diameter among the 13 surviving genotypes at Hope. At Fayetteville, B. nigra and B. davurica had the greatest annual change in tree height in both 2004 and 2005, and B. davurica was among genotypes having the greatest annual change in trunk diameter in 2002, 2004, and 2005. At Hope, B. papyrifera had the greatest annual change in tree height in both 2004 and 2005, and B. davurica had the greatest annual change in trunk diameter in 2004. In 2005, annual change was not significant among birch genotypes at Hope. At Fayetteville, water-stress treatment reduced final tree height and trunk diameter in birch trees. Key Words. Growth; irrigation regime; survival. The birches (Betula L.), especially white-barked genotypes, are popular woody plants. Their ornamental characteristics include pendulous catkins, yellow fall foliage, and peeling bark featuring colors from reddish brown to white (Furlow 1990). The origins of most birch genotypes are the temperate, boreal, and arctic zones of North America, Europe, and Asia (Krussmann 1984; Furlow 1990; Atkinson 1992; Farrar 1995). High air temperatures are often a limiting factor in a plant’s adaptability and productivity and there is considerable varia- tion in high temperature tolerance among birch genotypes (Ranney and Peet 1994). Water deficit often limits tree growth in urban landscapes (Zwack and Graves 1998; Ladjal et al. 2000). Bronze birch borer, Agrilus anxius Gory, is a major problem causing birch dieback in urban landscapes (Santamour 1999). In many birch species under water stress, rhododendrol hydrolyzed from rhododendrin may act as a stimulant to its oviposition (Santamour et al. 1997). Water- deficit tolerance among birch genotypes was observed under controlled conditions (Ranney et al. 1991). Except for anec- dotal observations, no research data are available on field performance of birch genotypes or the effect of irrigation regimes on field-grown birch genotypes in the southern United States. Intensive landscape evaluation of birch geno- types in the southern United States would provide useful information for the ornamental industry and homeowners. The objectives of this study were to evaluate survival and growth of 20 birch genotypes at two locations in Arkansas representing two USDA cold hardiness zones and two AHS heat zones, Fayetteville (USDA cold hardiness zone 7; AHS heat zone 7) and Hope (USDA cold hardiness zone 8; AHS heat zone 8), and to evaluate their response to two irrigation regimes at Fayetteville. The hypothesis was that the survival and growth of birch genotypes under higher temperature and nonirrigation conditions would not be as good as under cooler and irrigated conditions. MATERIALS AND METHODS Of the 20 birch genotypes evaluated in the study, 10 are native North American species or their selections, nine are Euro-Asian origin species or their selections, and one hybrid ©2007 International Society of Arboriculture
July 2007
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