Abstract
Sources of eastern redcedar (Juniperus virginiana L.) were established as a provenance test near Colby, Kansas, U.S. in 1980. Height, diameter, number of stems, crown density, branch angle, and general vigor were evaluated with ANOVA, cluster analysis, simple correlation, and regression analysis techniques. Clear source and cluster differences were found. Total height at 23 years ranged from 3.6 to 5.4 m (11.8 to 17.7 ft), dbh (diameter at breast height) ranged from 2.5 to 14.4 cm (1 to 5.7 in), and mean survival rate was 78%. Sources from the central plains grew best. Selection of fast-growing sources may begin at five years after field planting.
Eastern redcedar (Juniperus virginiana L.) is the most widely distributed conifer tree in the eastern United States (Burns and Honkaka 1990). The species range extends into southern Canada, and has been naturalized into the western Great Plains by natural regeneration from planted trees. Eastern redcedar is a small- to medium-sized, slow-growing intolerant tree (Harlow et al. 1979). There have been numerous taxonomical studies on this tree (Fassett 1944; Comer et al 1982; Adams 1983; Schaefer 1995). Cunningham and King (2000) identified genetic variation of various major traits for 10-year-old plantings, and seed source selection zones, for the Great Plains area.
This test is a part of a larger regional study initiated in 1973 by the now disbanded Technical Committee of the Great Plains Agricultural Council. The objectives were to determine the genetic variation of major traits and to identify the best sources of seed for windbreak applications. This paper presents the portion of the study established in Colby, Kansas after 23 years of growth in the field.
MATERIALS AND METHODS
A complete description of the methodology used for this greater study can be found in Van Haverbeke and King (1990). Seed cones were collected from 140 trees in natural stands and windbreaks across the Great Plains. Seed trees that had desirable windbreak characteristics (e.g., abundant branches, dense foliage) were selected. Seed lots were sown in the USDA Forest Service Bessey Nursery near Halsey, Nebraska in 1977 and were out-planted at 12 test sites in 1980. This study reports on the Colby site (39.38°N and 101.07°W), located in the central geographic region of zones established by Van Haverbeke (1968). Soil is from the Keith series loam (e.g., fine-silty, mixed, mesic Aridic Haplustolls) and Richfield silty clay loam (e.g., fine, montmorillonitic, mesic Aridic Haplustolls). A randomized complete-block with five replications of 4-tree, linear plots was established having 20 trees maximum for each source. A total of 2320 trees were planted, along with 520 Rocky Mountain juniper (Juniperus scopulorum L.). Spacings in the plantation were 2.4 m (8 ft) within rows and 3.6 m (12 ft) between rows. A single border row was planted on all sides. Clean cultivation was maintained for five years. Growth evaluations were made at age 5, 10, and 23 years.
Statistical analyses were performed with SAS software (Statistical Analysis System, SAS Institute Inc., Cary, NC). Data were analyzed via the analysis of variance procedure, and the Duncan’s means test was used for mean separation. Cluster analysis (Ward’s minimum variance) were used to identify seed sources with similar performance characteristics. Variables usse in said analyses were survival rate, total height, dbh (diameter at breast height), number of stems, crown density, branch angle, vigor, latitude, longitude, and elevation.
If trees had multiple stems, then only the largest was evaluated for height and diameter. Simple Pearson correlations were computed among seed sources of individual trees for each trait. The correlation of each trait with latitude and longitude was also examined. Least squares regression models of differences in latitude, longitude, and elevation between source locations and the Colby plantation were run to find the extent of the geographic area from which seed may be collected to give good tree growth performance in western Kansas. To determine the reliability of early seed source selection, age/age correlations were computed for survival and height of source means at age 10 and age 23.
RESULTS
Significant differences among seed sources existed for survival, height, dbh, number of stems, crown density, branch angle, and vigor. Each is discussed separately, but we also chose to identify more general patterns of variation by using cluster analysis.
Survival
Seed sources were significantly different at P < 0.01 (analysis of variance) in survival rates through age 23, with a range of 10 to 100%. The mean survival was 78%. The best sources were from the central part of the range, while the poorest surviving sources were from southern Texas which was 30%.
Height
Seed sources were significantly different in height at the P < 0.01 (analysis of variance) through age 23 (Table 1). The mean height for all of the trees was 5.3 m (17.5 ft), ranging from 3.1 to 6.2 m (10.2 to 20.3 ft). Specific patterns were found geographically for total height. The tallest trees (10) had high survival (100%) and were also generally in the upper 10% of dbh [12.9 cm (5.1 in)]. The shortest 10% of the sources were from Texas [4.2 m (13.9 ft)].
Survival, height, and dbh rankings of top and bottom 10 eastern redcedar seed sources at 23 years.
Diameter
Seed sources (Table 1) were significantly different at the P < 0.01 (analysis of variance). The mean dbh was 10.9 cm (4.3 in) with a range of 2.5 to 14.5 cm (5.7 in). Specific patterns were found, geographically, for diameter measurements. The largest diameter trees were from Iowa [14 cm (5.5 in)]. Sources from the central plains were generally the largest; mean survival was approximately 85%.
Other Variables
The mean value of the number of stems per tree for the entire planting was 1.6, with a range of 1 to 3.3 stems per tree. Nearly 15% of the sources showed a consistent trend toward a single-stem habit. No geographic pattern was recognized. Crown density was good for most sources planted, with ratings ranging from medium to dense for windbreak characteristics. However, Southern Texas sources were found to have sparse to very sparse crowns. Over 90% of the sources had branch angles between 45 and 90°. All sources had good vigor and were generally healthy showing minimal crown damage.
Cluster Analysis
Cluster analysis included all 140 sources. The analysis differentiated 3, 4, and 5 clusters for height, with a significance that was P < 0.01 for height, survival, and dbh. The other variables listed were deleted in the analysis because of similar values. General patterns of variation were identified by using this analysis. Distinct geographic patterns were shown in the all of the clusters evaluated. The 5-cluster analysis was selected as it most clearly indicated geographic source patterns of variation (Figure 1). A similar arrangement was found in South Dakota for 10-year-old eastern redcedar (Schaefer 1995), with the exception that Texas sources were not considered. Cluster values are shown in Table 2. The height values for first through fifth clusters were 5.8, 5.4, 4.9, 4.2, and 3.5 m (18.9, 17.6, 16.1, 13.9, and 11.4 ft), dbh values were 13, 11.7, 9.7, 7.4, and 4.6 cm (5.1, 4.6, 3.8, 2.9, and 1.8 in). The two Texas sources were the shortest.
Performance clusters of eastern redcedar seed sources representing natural stands based upon Ward’s method. The plus sign indicates the location of test plantation.
Mean growth values of 5 ERC clusters
Correlations
Age/age correlations between height and dbh, were particularly high. Height growth at 5 years (Table 3) predicted the tallest trees at 10 years (Pearson correlation coefficient = 0.960). Height at 10 years (Table 3) predicted height at 23 years (0.945). Five-year data was not available for determining 23-year relationships, but one could assume that the correlations would be high. The tallest trees had the largest diameters (correlation = 0.930). The other major variables and the geographic traits did not provide any significantly high correlations to predict growth (Table 3).
Correlations of height and dbh of eastern red cedar with age and geographic traits.
Regression Analysis
The reliability of the regression model to predict the 23-year height from the 10-year height data gave an R-square value of 0.8939 and was significant at the 1% level.
The regression model to predict 23-year old growth and survival using a combination of geographic variables as differences from the Colby plantation gave R-square values of 0.6426 (height), 0.6404 (dbh), and 0.4435 (survival) for values significant at the 1% level. Sources north and east of the Colby plantation produced taller and larger diameter trees with higher survival.
DISCUSSION AND CONCLUSIONS
In an earlier study comparing eastern redcedar to Rocky Mountain juniper in the Great Plains Region (Cunningham and King 2000), tree survival did not differ significantly. Eastern redcedar were taller, and had wider crowns than did Rocky Mountain juniper at 10 years of age, but Rocky Mountain juniper has better crown density for wind reduction than redcedar.
Our findings showed growth at 10 years predicted superior growth at 23 years, and in agreement with our previously reported study for Rocky mountain juniper (Geyer et al. 2007), Schafer (1995) and Van Haverbeke and King (1990), for five-year and ten-year relationships.
In our Kansas study, we identified at 23 years of age the best area to collect eastern redcedar seed for production of seedlings for Kansas was from an area bounded by eastern and central Nebraska, central and northern Kansas, and south eastern South Dakota. Two southern clusters from southern Oklahoma and eastern Texas were much shorter in height. Trees from these sources are not recommended for windbreak plantings in western Kansas.
Thus, the general good health, dense crown, and many stems of eastern redcedar from the preferred sources would provide excellent structure, and this species should be selected for use in establishing new windbreaks in western Kansas and nearby areas in central and western Nebraska. This study suggests use of a seed source from within 482.8 km (300 mi) of the planting site would provide the best results for windbreak plantings in the Great Plains.
Acknowledgements
This is contribution no. 08-397-J from the Kansas Agricultural Experiment Station, Manhattan, Kansas.
- Copyright © 2009, International Society of Arboriculture. All rights reserved.
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