Evaluation of Ponderosa Pine Seed Sources for the Eastern Great Plains

Methods

Ponderosa pine seedlings were grown for two years in a nursery bed and one year in a transplant bed at the U.S.D.A. Forest Service Bessy Nursery in Halsy, Nebraska, then planted on a sandy loam soil in spring 1968 at a spacing of 8 by 12 feet. The site is near Junction City, Kansas, approximately 125 miles west of Kansas City, Kansas. Seventy-seven geographic sources were represented, including 1 from Arizona, 11 from Colorado, 1 from Idaho, 20 from Montana, 13 from South Dakota, 1 from Washington, and 14 from Wyoming. The plantation was established as a randomized complete block design with every source represented by a four-tree linear plot in each of 15 blocks. Weeds were controlled by Simazine application and mowing as necessary, with frequency of control decreasing as trees began to shade weeds.

Survival and height were recorded for every tree in May 1983, 15 years after establishment. Chi-square contingency analysis was employed to determine if seed sources differed with respect to survival. Analysis of variance was employed to determine if heights differed among seed sources. Mean heights at age 15 were correlated with those at ages 5 and 10 to estimate the youngest age at which reliable selections are possible.

Foliage color and retention were evaluated in June, 1986. Needles on 1984 and 1985 branch nodes were rated by the following system:

• 1. = nearly all needles were green over their entire length and more than one third of the node supported foliage;

• 2. = 50% or more of the needles were green for greater than half their length and more than one third of the node supported foliage;

• 3. = fewer than 50% of the needles were green for greater than half their length and more than one third of the node supported foliage;

• 4. = less than one third of the node supported foliage.

Current year’s growth was not included in the analysis because it was healthy on every tree examined. Three branches were sampled from the lower third of the crown on the southern half of trees from three blocks. Two nodes per branch were sampled and their scores were combined to yield branch totals. These were averaged to obtain an overall tree score; the potential range in tree scores was 2.00 (best) to 8.00 (poorest). Analysis of variance was employed to determine if differences in foliar characteristics existed among sources. A Spearman’s rank correlation test was used to determine if height and foliar characteristics were correlated.

Results

The mean survival percentage by sources at age 15 was 77.5% with a range of 33.3% to 91.6% (Table 1); differences were statistically significant (P=0.005). Sources from Montana, Nebraska, South Dakota, and Wyoming survived the best; those from south of Kansas or west of the continental divide survived the poorest.

Height was significantly different (P=0.0001) among seed sources. Means ranged from 5.8 feet to 16.0 feet (Table 1). Eight sources exceeded the mean plantation height (8.8 feet) by at least one standard deviation (1.9 feet); these were from Montana, Nebraska, and South Dakota (Figure 1). Those from south of Kansas or west of the continental divide generally were shortest. Six sources (720, 721, 754, 757, 825, and 853) were at least one standard deviation taller than the plantation mean and had a survival rate as high or higher than the plantation mean (Figure 2). The correlation between height at age 5 and at age 15 was moderate (r² = 0.51), however, heights at age 10 and at age 15 were highly correlated (r² = 0.95). Damage by western pine tip moth was severe on many sources.

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Figure 1.

Mean heights of the ten tallest ponderosa pine sources at age 15.

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Figure 2.

Mean survival of the ten tallest ponderosa pine sources.

Foliar characteristic scores were significantly different (P=0.0001) among seed sources, ranging from 2.74 to 7.94 (Table 1). Spearman’s rank correlation test suggested a close relationship between foliar characteristics and height growth (Spearman’s rank correlation coefficient = 0.49; P = 0.0001). Six sources (720, 721, 754, 757, 825, and 855) were ranked among the top ten with respect to height and foliar characteristics; five of these had survival percentages above the mean.

Discussion

Ponderosa pine from north-central Nebraska (sources 720, 721, 853, and 855), south-central South Dakota (sources 757 and 854) and several locations in Montana (sources 754, 822, and 825) are better suited to the eastern Great Plains because of superior survival, height growth, and foliar characteristics compared with those from south of Kansas or west of the continental divide. Those from Colorado and southern Wyoming are intermediate. The tallest sources in this study, particularly those from north-central Nebraska, also generally performed better than average at other sites throughout the midwest (11). He suggested that sources that performed well at most midwestern locations have intermediate genetic constitutions which enables the high degree of adapatability necessary to survive in non-native environments such as the eastern Great Plains.

Relative height ranking among sources in this plantation has stabilized, so reliable seed source recommendations are now possible. Wakeley (13) and Read (9) suggested that selection of southern pines and ponderosa pine, respectively, for height growth should not be made until age 15 because height growth performance of young trees is imperfectly related to that at maturity. Age-age correlations in this study suggest the fastest growing seed sources probably could have been identified when the plantation was 10 years old, but not before. Van Haverbeke (11) and Lambeth (6) suggested selection between ages 5 and 10 is practical for ponderosa pine.

Western pine tip moths have frequently limited screening efficiency and ornamental value of ponderosa pine plantings, and they severely damaged some seed sources in this study. However Dix and Jennings (3) reported that trees from seed sources 720 and 757 were able to outgrow tip moth infestation or were less desirable hosts in a central Nebraska plantation; other fast growing individuals may interact similarly with tip moths. Van Haverbeke et al. (12) indicated application of systemic insecticides can effectively protect young ponderosa pine from tip moth damage, but insecticides may not be necessary if proper seed sources are used.

This study and others have shown that selection for foliar characteristics among ponderosa pines is possible. Taller sources generally have foliar characteristics that are more desirable than shorter ones for ornamental and screening purposes because they retain a high percentage of green needles for up to three years. Peterson (7) found differences among seed sources with respect to resistance to Dothistroma needlecast; trees from taller sources generally were above average in resistance. Read and Sprackling (10) suggested that differences among seed sources with respect to susceptibility to hail damage were attributable to differences in needle characteristics. Collectively, these results suggest selection for foliar characteristics could lead to improved aesthetics and windbreak efficiency of future ponderosa pine plantings.

Conclusions

Hardiness and site adaptability are among the most important criteria that horticulturists and arborists use in making tree selections. Sources of ponderosa pine from north-central Nebraska and south-central South Dakota demonstrate a high level of hardiness as evidenced by their superior survival, height growth, and foliage characteristics. Individuals from some areas in Montana and Wyoming also perform well in the eastern Great Plains. Foliage characteristics vary among seed sources; trees from taller seed sources generally have foliar characteristics that are more favorable for ornamental and screening purposes than short ones. Age-age correlations indicate selection for height may begin as early as age ten.