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 populifolia, 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.
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 variation 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). Waterdeficit tolerance among birch genotypes was observed under controlled conditions (Ranney et al. 1991). Except for anecdotal 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 genotypes 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 [B. × ‘Royal Frost’ = B. populifolia ‘Whitespire’ × B. × ‘Crimson Frost’; B. בCrimson Frost’ = B. platyphylla var. szechuanica (Schneid.) Rehd × B. pendula ‘Purpurea’] has both North American and Euro-Asian heredity (Table 1). The 11 species typically grow in the range of USDA cold hardiness zone 2 to zone 6.
Characteristics and origin of 20 birch genotypes evaluated at Fayetteville and Hope, Arkansas.
One-year-old rooted cuttings or bare-root plants obtained from commercial nurseries were potted in 3.8 L (1 gal) pots with SunGro SB300 Universal Mix (Pine Bluff, AR) in Winter 2001. Three of the genotypes were obtained from two different nursery sources (B. nigra—Evergreen N. and J. F. Schmidt & Son Co.; B. nigra ‘Cully’ Heritage®—Heritage Seedlings Inc. and Forest Hills N.; B. pendula—Meadow Lake N. and J.F. Schmidt & Son Co.). Container plants were grown in an outdoor lathe house until they were planted in the field plots.
Trees were planted on 12 and 5 April 2002 at the Arkansas Agriculture Research and Extension Center, Fayetteville (latitude: 36.1N; longitude: 94.1W; altitude: 427 m/1400 ft; USDA cold hardiness zone 7; AHS heat zone 7) and Southwest Research and Extension Center, Hope (latitude: 33.7N; longitude: 93.6W; altitude: 106 m/350 ft; USDA cold hardiness zone 8; AHS heat zone 8), Arkansas, respectively. The soil type was Captina silt loam (pH = 6.2) at the Fayetteville site and Bowie fine sandy loam (pH = 5.5) at the Hope site. Trees were planted 2.5 m (8 ft) apart in a row and the distance between two rows of trees was 4.5 m (15 ft). After planting, rows were mulched with hardwood chips to a depth of 10 cm (4 in). Trees were fertilized with 10 g 15N–2P–8K fertilizer (Harrell’s Fertilizer, Lakeland, FL) with micronutrients after planting and with 10 g 45N–0P–0K (Oakley Fertilizer, North Little Rock, AR) annually from 2003 to 2005 as suggested by the soil analysis.
At Fayetteville, all trees were irrigated for 2 hours per day and 3 days per week from May to September using a drip system with Rainbird® EM-L20 SSP Lady Bug emitters (nominal flow rate = 2.0 L/hour−1; Rain Bird Corp., Glendora, CA) in 2002. There was one emitter for each tree and emitters were placed close to the tree trunk. Water was collected from randomly selected emitters and the average flow rate was 1.4 L/hour−1. In April 2003, mulch was removed and all rows were covered with 1.2 m (4 ft) wide plastic film (4 mil) to limit precipitation infiltration to the soil before being remulched with hardwood chips to a depth of 10 cm (4 in). In May 2003, soil tensiometers (Irrometer Company, Inc., Riverside, CA) were installed at 30 cm (12 in) depth close to the trunk of two randomly selected birch trees within each row at Fayetteville. Tensiometers were removed after each growing season. In April 2004, tensiometers were installed at 30 cm (12 in) depth at a distance of 30 cm (12 in) from the trunks of three randomly selected birch trees within each row. In April 2005, tensiometers were installed at 30 cm (12 in) depth at a distance of 50 cm (20 in) from the trunks of four randomly selected birch trees within each row. Tensiometer readings were recorded daily.
Two irrigation regimes were applied to the Fayetteville field plot from 2003 to 2005: (1) watered (WW): four rows of trees were watered to keep the average tensiometer readings between 0 and 10 KPa (10 cb); and (2) water-stressed (WS); the other four rows of trees were watered after the average tensiometer readings exceeded 40 KPa (40 cb).
At Hope, tree rows were not covered with plastic film but mulched and fertilized in a manner similar to Fayetteville. From 2002 to 2005, all trees were irrigated for 2 hours per day and 3 days per week from May to September, which was similar to the irrigation treatment for WW trees at Fayetteville.
Weather data were obtained from both Fayetteville and Hope locations from 2002 to 2005 (Tables 2 and 3). The average annual high and low temperatures during the 4 years were 20°C (68°F) and 9°C (48°F) at Fayetteville, which were 3°C (37°F) and 1°C (34°F) lower than those at Hope, respectively. The average annual precipitation during that period was 97.9 cm (39.2 in) at Fayetteville and 112.3 cm (44.9 in) at Hope. At Fayetteville, the number of frost-free days from 2002 to 2005 was 192, 225, 247, and 209, respectively. At Hope, the number of growing days from 2002 to 2005 was 239, 226, 298, and 222, respectively.
Monthly average high temperature and monthly average low temperature at Fayetteville and Hope, Arkansas, from 2002 to 2005.
Monthly precipitation at Fayetteville and Hope, Arkansas, from 2002 to 2005.
Tree height and trunk diameter were measured after planting in April 2002 at both locations and after the trees shed all leaves each fall (except 2005). Tree height was measured as the distance between the tallest bud on the tree and the soil surface. Trunk diameter was measured at 15 cm (6 in) above the soil surface using a caliper. Year-end measurements were taken at Fayetteville and Hope on 29 and 17 October 2002, on 4 December and 13 November 2003, on 16 and 28 November 2004, and on 13 and 4 October 2005, respectively. Annual change, presented as a percentage, is defined as the change in tree height or trunk diameter between the fall of the previous year and the fall of the current year divided by the same growth parameter at the end of the previous growing season. For 2002 data, the change in growth is divided by the initial value at planting. Survival of each birch genotype was recorded annually.
Two trial locations were treated as two separate experiments. The experimental design was a completely randomized design consisting of a two-factor factorial of 16 genotypes (B. albosinensis and B. pendula ‘Trost’s Dwarf’ did not survive through 2005, and B. ermanii and B. lenta were not included in statistical analysis as a result of excessive mortality) × two irrigation regimes with seven to 15 replications at Fayetteville and a completely randomized design consisting of one factor of 13 genotypes with four to 12 replications at Hope (seven of 20 genotypes did not survive through 2005). Data were subjected to analysis of variance (ANOVA) in a General Linear Model using SAS software (version 9.1, 2004; SAS Institute Inc., Cary, NC). Means were considered significantly different if P value was less than 0.05 or 0.1 as determined by ANOVA.
RESULTS
Fayetteville
The overall tree survival was 62% (Table 4). The average survival for WW trees and WS trees was 64% and 59%, respectively. Survival after four growing seasons ranged from 100% (B. × ‘Royal Frost’) to 0% (B. albosinensis and B. pendula ‘Trost’s Dwarf’). Genotypes, which had greater than 90% survival, also included B. nigra ‘BNMTF’ Dura-Heat™ (93%), B. nigra ‘Cully’ (94%), B. pendula ‘Laciniata’ (93%), and B. populifolia (93%).
Survival of 20 birch genotypes evaluated at Fayettevillez and Hopey, Arkansas, in 2005.
There was an interaction between genotype and irrigation on the tree height in 2005 (Table 5). Main effects of genotype and irrigation treatment were significant. The WS treatment reduced tree height (data not shown). Of those genotypes that survived, B. nigra ‘Cully’, B. nigra ‘BNMTF’, B. × ‘Royal Frost’, B. nigra, and B. pendula ‘Laciniata’ were among the tallest trees in the plot (Figure 1). Only B. nigra was among the genotypes with the greatest annual change in tree height during every growing season from 2002 to 2005 (data not shown). In both 2004 and 2005, B. davurica was also among the genotypes with the greatest annual change in tree height. Betula utilis var. jacquemontii was the shortest tree and had the lowest annual change in tree height in both 2004 and 2005. The overall average annual change in height was 169%, 117%, 59%, and 23% from 2002 to 2005.
Statistical significance from analysis of variance of genotype and irrigation treatment on the initial and final tree height and trunk diameter of birch trees planted in Spring 2002 at Fayetteville and Hope, Arkansas.z
Tree height of birch trees at Fayetteville, Arkansas, from 2002 to 2005. Bars represent standard error of genotype on the final tree height (Tukey’s adjusted test; P ≤ 0.05).
No interaction between birch genotypes and irrigation regimes was observed for the final trunk diameter (Table 5). Main effects of genotype and irrigation treatment were significant for final trunk diameter. The WS treatment reduced trunk diameter in birch trees (data not shown). Of the surviving birch genotypes, B. nigra and its two selections, ‘BNMTF’ and ‘Cully’, had greater final trunk diameter than B. utilis var. jacquemontii, B. populifolia ‘Whitespire’, B. papyrifera ‘Uenci’ Renaissance Upright™, B. papyrifera, B. platyphylla ‘Fargo’ Dakota Pinnacle™, B. alleghaniensis, and B. maximowicziana (Figure 2). In 2005, B. nigra, B. nigra ‘BNMTF’, B. davurica, and B. platyphylla ‘Fargo’ had the greatest annual change in trunk diameter, and B papyrifera ‘Uenci’, B. pendula ‘Laciniata’, and B. × ‘Royal Frost’ had the lowest annual change in trunk diameter (data not shown). The overall average annual change in trunk diameter was 276%, 181%, 52%, and 29%, respectively, from 2002 to 2005.
Trunk diameter of birch trees at Fayetteville, Arkansas, from 2002 to 2005. Bars represent standard error of genotype on the final trunk diameter (Tukey’s adjusted test; P ≤ 0.05).
Hope
The tree survival by the end of 2005 was 30% (Table 4). Seven of 20 birch genotypes (B. albosinensis, B. alleghaniensis, B. ermanii, B. papyrifera ‘Renci’ Renaissance Reflection™, 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.
Tree height of birch trees at Hope, Arkansas, from 2002 to 2005. Bars represent standard error of genotype on the final tree height (Tukey’s adjusted test; P ≤ 0.05).
There were significant differences for final tree height, final trunk caliper, and annual annual change among genotypes (Table 5). Of the 13 surviving genotypes, B. nigra ‘Cully’, B. nigra ‘BNMTF’, B. × ‘Royal 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. papyrifera 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 average annual change in trunk diameter was 169%, 196%, 79%, and 31% from 2002 to 2005.
Trunk diameter of birch trees at Hope, Arkansas, from 2002 to 2005. Bars represent standard error of genotype on the final trunk diameter (Tukey’s adjusted test; P ≤ 0.05).
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 temperature 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 compared with 86% at Fayetteville. The warmer temperature may also increase transpiration, which exceeded water uptake capacity 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 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. albosinensis had the lowest survival at both locations in Arkansas 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. × ‘Royal Frost’ had greater survival than the other birch genotypes investigated at both locations. One unexpected results was the low survival of B. nigra at both locations. One possible explanation is the provenance sources for the seed-grown B. nigra seedlings.
Experiments under controlled conditions indicated that water-deficit stress reduced tree height of birch genotypes (Fort et al. 1998; Pääkkönen et al. 1998; Wang et al. 1998). Similar reductions were observed for most birch trees investigated under the field conditions at Fayetteville (data not shown). Betula populifolia ‘Whitespire’ was reported to be better adapted to dry sites than B. nigra, B. maximowicziana, B. papyrifera, B. pendula, and B. populifolia in a study under controlled conditions (Ranney et al. 1991). However, its growth was among the lowest at Fayetteville (Figures 1 and 2), and the difference between the growth of WW plants and WS plants was not significant (data not shown). Dirr’s (1998) observation at a nursery indicated that ‘Cully’ was superior in every aspect when compared with ‘Whitespire’.
CONCLUSION
Based on the tree survival, growth, and annual change of the 20 birch genotypes, B. nigra ‘Cully’, B. × ‘Royal Frost’, B. pendula, B. nigra ‘BNMTF’, B. davurica, and B. papyrifera could survive and be used for landscape use in the southern United States. Betula pendula ‘Trost’s Dwarf’, B. ermanii, B. albosinensis, B. populifolia ‘Whitespire’, B. papyrifera ‘Uenci’, B. lenta, B. maximowicziana, B. utilis var. jacquemontii, and B. alleghaniensis would not perform well in landscapes in the southern United States.
Of the six birch genotypes recommended for the southern United States, Betula nigra ‘Cully’, B. nigra ‘BNMTF’, and B. davurica have creamy white to reddish brown peeling bark. Betula × ‘Royal Frost’, B. pendula, and B. papyrifera have distinguished white bark. Leaves on B. × ‘Royal Frost’ are burgundy red in spring and the color fades off slightly during summer, and turned to red or orange–red in the fall. The other five genotypes have yellow fall foliage. All six genotypes have pyramidal habit and could be used as specimen or shade tree in the landscape.
Acknowledgments
We thank Manjula Carter for technical assistance at the Southwest Research and Extension Center, Hope, AR, and for financial assistance from the Research Incentive Grant Program at the University of Arkansas.
- © 2007, International Society of Arboriculture. All rights reserved.
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