280 Gu et al.: Early Landscape Performance of Field-Grown Birch was 276%, 181%, 52%, and 29%, respectively, from 2002 to 2005. Hope The tree survival by the end of 2005 was 30% (Table 4). Seven of 20 birch genotypes (B. albosinensis, B. alleghanien- sis, B. ermanii, B. papyrifera ‘Renci’ Renaissance Reflec- tion™, B. pendula ‘Trost’s Dwarf’, B. pendula ‘Laciniata’, and B. utilis var. jacquemontii) did not survive through four growing seasons. Six of 13 survived birch genotypes died back in 2002 (Figure 3). Survival of the 13 genotypes ranged from 17% (B. davurica, B. maximowicziana, B. nigra, B. pendula, and B. platyphylla ‘Fargo’) to 100% (B. nigra ‘BNMTF’). Betula nigra ‘Cully’ (94%) was the only other genotype, which had greater than 90% survival. There were significant differences for final tree height, final trunk caliper, and annual annual change among geno- types (Table 5). Of the 13 surviving genotypes, B. nigra ‘Cully’, B. nigra ‘BNMTF’, B. בRoyal Frost’, B. pendula, and B. papyrifera were significantly taller than B. papyrifera ‘Uenci’, B. populifolia ‘Whitespire’, B. maximowicziana, and B. lenta after four growing seasons (Figure 3). In both 2004 and 2005, B. papyrifera was among trees with the highest annual change in tree height, and one of its selections, ‘Uenci’, had the lowest annual change in tree height (data not shown). The overall average annual change in height was 56%, 151%, 40%, and 26% from 2002 to 2005. Betula nigra ‘Cully’, B. nigra ‘BNMTF’, and B. pendula had greater final trunk diameter than B. papyrifera ‘Uenci’, B. populifolia ‘Whitespire’, B. nigra, B. maximowicziana, and B. lenta (Figure 4). In 2004, B. davurica and B. papyri- fera had the highest annual change in trunk diameter and B. papyrifera ‘Uenci’ had the lowest annual change (data not shown). In 2005, annual change in trunk diameter was not significant among the birch genotypes (Table 5). The overall Figure 4. Trunk diameter of birch trees at Hope, Arkansas, from 2002 to 2005. Bars represent standard error of geno- type on the final trunk diameter (Tukey’s adjusted test; P ≤ 0.05). average annual change in trunk diameter was 169%, 196%, 79%, and 31% from 2002 to 2005. DISCUSSION Hope is located at a lower latitude and lower elevation than Fayetteville and in a different USDA cold hardiness zone and AHS heat zone. Both monthly average high temperatures and monthly average low temperatures were higher at Hope than Fayetteville from 2002 to 2005 (Table 1). The warmer tem- perature at Hope may account for the lower overall survival compared with Fayetteville (Table 4). Only 41% of birch trees survived through the first growing season at Hope com- pared with 86% at Fayetteville. The warmer temperature may also increase transpiration, which exceeded water uptake ca- pacity from the establishing root system and led to shoot dieback in six birch genotypes at Hope in 2002. The survival changed slightly after 2003, which could be attributed by initial screening in the first 2 years and the established root systems in survived trees. In 2003 and 2004, most birch trees had greater growth in Figure 3. Tree height of birch trees at Hope, Arkansas, from 2002 to 2005. Bars represent standard error of geno- type on the final tree height (Tukey’s adjusted test; P ≤ 0.05). ©2007 International Society of Arboriculture both height and trunk caliper at two locations than in 2002 (Figures 1–4), which could be attributed to more established roots. Although there was more rainfall in 2004, the relatively cool summer in Fayetteville could result in less growth in trunk diameter (Figure 2). Betula pendula ‘Trost’s Dwarf’, B. ermanii, and B. al- bosinensis had the lowest survival at both locations in Ar- kansas after four growing seasons (Table 4). Dirr (1998) found that Betula pendula ‘Trost’s Dwarf’ did not perform as well in the landscapes as indicated by articles, and B. ermanii was rarely seen in the eastern United States as a result of high temperature. Betula populifolia, B. nigra ‘BNMTF’, B. nigra ‘Cully’, and B. בRoyal Frost’ had greater survival than the other birch genotypes investigated at both locations. One un- expected results was the low survival of B. nigra at both
July 2007
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