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The Auburn University Shade Tree Evaluation: Its Roots and Fruit

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The Auburn University Shade Tree Evaluation: Its Roots and Fruit The Auburn University Shade Tree Evaluation: Its Roots and Fruit J. David Williams,1 Charles H. Gilliam,2 Gary J. Keever,2 and John T. Owen3 ADDITIONAL INDEX WORDS. variety trial, landscape SUMMARY. The Auburn University Shade Tree Evaluation is an ongoing trial of a moderately diverse range of species, and varieties of larger-growing trees. The study was initiated in 1980 with the planting of 250 selections in three replications of three trees each, located at the Alabama Agricultural Experiment Station, Piedmont Substation in east–central Alabama. Among the fruit of the investigation have been an evaluation of 10 red maple (Acer rubrum) selections with respect to growth and fall color characteristics; a comparison of growth rate and aesthetic characteristics of 14 oak (Quercus) selections; a comparison of the growth and fireblight (Erwinia amylovora) susceptibility of 10 callery pear (Pyrus calleryana) selections; and a 12-year evaluation of the overall best performing trees. The Shade Tree Evaluation has served as a precedent for six additional landscape tree evaluations in Alabama. It has provided a living laboratory for a wide range of educational audiences including landscape and nursery professionals, county extension agents, urban foresters, Master Gardeners, garden club members, and horticulture students. Knowledge gained from the Shade Tree Evaluation has been shared through presentations at meetings and conferences. he Auburn University Shade Tree Evaluation is a replicated, ongoing evaluation of a moderately diverse range of species Tand varieties of larger growing trees that, at the time the study was implemented, ranged from commonly used to rarely used landscape trees in the South. The study is located at the Alabama Agricultural Experiment Station (AAES), Piedmont Substation adjacent to Camp Hill, about 25 miles (40 km) northwest of Auburn. The substation is situated about 90 miles (145 km) southeast of Birmingham, and about 60 miles (97 km) northeast of Montgomery, two of the largest metropolitan areas in Alabama. The evaluation site occupies about 20 acres (8 ha) and is characterized by gently rolling terrain typical of the piedmont plateau region of the state. The soil type is a Cecil gravelly sandy loam. A total of 572 trees, consist- ing of 95 different selections are currently maintained in the evaluation (Table 1). Roots The Auburn University Shade Tree Evaluation was born out of concern that many of the tree selection recommendations made for consumers, landscape professionals and municipalities were not based on scientific evaluation, but rather on testimony, nursery advertisements, or popular literature. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1Associate professor, Department of Horticulture, 101 Funchess Hall, Auburn University, AL 36849. 2Professor, Department of Horticulture, 101 Funchess Hall, Auburn University, AL 36849. 3Superintendent, Piedmont Substation, Camp Hill, AL 36850. 358 ● July–September 2001 11(3) Limited tree evaluations had been Continued management fireblight. Fireblight was found to be performed by arboreta, cities, and uni- a severe problem in ‘Aristocrat’ and versities, especially related to the re- Initially, soil tests were made on ‘Autumn Blaze’ (Fare et al., 1991). gional adaptability of these trees. Trees an annual basis and in 1986, 2 tons/ Fourteen oak selections were evalu- were often selected for use in land- acre (4400 kg·ha–1) of agricultural lime ated for landscape potential based on scapes before adequate information was applied; none has been applied growth rate. Sawtooth oak (Quercus was available. For example, many trees since then. The current nutritional acutissima) was noted as the fastest were selected for use because of their program consists of one maintenance growing selection (Fare et al., 1992). excellent fall foliar color in other re- fertilizer application of N at 1 lb/inch In a comparison of 10 red maple selec- gions of the country. However, many caliper, made annually in late winter. tions, ‘Autumn Flame’, ‘Tilford’, of these tree selections did not provide Until 1987, weed control consisted of ‘Gerling’, and ‘Bowhall’ were identi- good fall color under climatic condi- two applications per year of glyphosate fied as having the most consistent fall tions common in the southeastern or paraquat for post-emergence weed color characteristics (Fare et al., 1990). United States. High temperatures, high control, and a spring application of Top-performing trees were character- humidity and different daylengths from oryzalin at (a.i.) 4 lb/acre (4.5 kg·ha– ized based on vigor, appearance, and where they were selected may suppress 1) for preemergence weed control. landscape use potential in the region fall color development in trees that Herbicides were applied with a di- (Williams et al., 1995). have outstanding fall color elsewhere. rected spray at the base of each tree. Results of the research to date Inadequate information has led to the Since that time, weed control has in- have been shared at International So- use of trees that are poorly suited to volved only the postemergence con- ciety of Arboriculture Conferences in landscapes in the southern U.S., re- trols. No preventive insecticide or fun- Chicago in 1991, Vancouver, B.C., in sulting in poor performance, high gicide applications have been made. 1988, and Halifax, N.S., in 1994. Pre- maintenance, and high removal costs. Limited selective pruning occurred pre- sentations were made at the Southern A lack of regional evaluation at the dominately during the dormant sea- Nurserymen’s Association research time led to research being initiated to son, except for removal of suckers at conference in Atlanta in 1987 and provide information about growth, the base of the trees (discontinued in 1988. aesthetic characteristics, and adaptabil- 1994). Besides the direct benefits of the ity of selected shade and ornamental Attrition of poorly adapted trees Shade Tree Project, this study has set trees for the southeastern United States. has resulted in the current number of a precedent for establishing five addi- The objective of the Auburn Uni- 95 tree selections remaining in the tional long term tree evaluations: An versity Shade Tree Evaluation is to trial. Many of the trees have encroached evaluation of 16 red maple selections provide information about character- on one another so plots are being initiated in 1990 and an evaluation of istics and adaptability of selected shade thinned by removal of the center tree 17 sugar maple (Acer saccharum) se- trees for the southeastern United States. in each replication. lections initiated in 1992, both at the Because of its size and scope, this Piedmont Substation; an evaluation project remains unique in the region. Fruit of 60 flowering crabapple (Malus) va- Audiences served by this project rieties in 1992 at the AAES Brewton Project initiation have been diverse and far reaching, Experimental Field; a trial of 38 dog- Initial plantings were made in Dec. including consumers, landscape archi- wood (Cornus) varieties and species 1980 and continued through winter tects and designers, arborists, land- and a study of 45 crapemyrtle of 1981. Bareroot whips, 3 to 4 ft (1.0 scape contractors, utility company per- (Lagerstroemia) selections, both initi- to 1.2 m) tall, were planted in a Cecil sonnel, urban foresters, commercial ated in 1993 at Auburn University; gravelly sandy loam soil. Subsequent plant producers, county extension and a study of 60 crapemyrtle selec- tree plantings were made from 1982 agents and other educators, and mas- tions initiated in 1998 at the AAES until 1985 resulting in a total of 250 ter gardeners. The benefits of the study Gulf Coast Substation in Fairhope. All selections. Trees were planted 25 ft are presented within the framework of of these studies are ongoing. within rows and 30 ft between rows (7.6 the traditional landgrant mission of × 9.1 m). Three trees each were planted Auburn University—research, exten- Future research in three replications, for a total of nine sion, and instruction. Data have been collected for a trees of each selection in a randomized comparison of incidence and extent of complete block design. Supplemental Research products surface rooting and suckering among irrigation was not applied. A complete We have identified 24 selections various selections. An evaluation of fertilizer (13N–5P–10.5K) was applied that were subject to a high rate of southern magnolia (Magnolia gran- in early spring at 1 lb N/1 inch caliper attrition; that is, the majority of the diflora) growth rate and foliar charac- (178 g·cm–1 caliper). trees of that selection have not sur- teristics has been submitted for publi- Evaluation criteria were annual vived. Many of these could be consid- cation. A comparison of the various growth rate, natural attrition, and aes- ered to be poorly adapted to the re- ash (Fraxinus) selections and an up- thetic characteristics (flowering and gion due to their being introduced date of a report originally describing fall color). Growth rate was deter- from other geographic areas (Will- performance of oak selections in the mined annually by recording tree iams et al., 1993). Callery pear and study are some of the immediate is- height, canopy spread, and caliper nine varieties were compared with re- sues under consideration for further [measured 12 inches (30 cm) above spect to growth rate, flowering char- investigation. the soil line]. acteristics, and susceptibility to ● July–September 2001 11(3) 359 Extension products Table 1. Tree selections currently maintained in the Auburn University Shade Tree Evaluation at the Alabama Agricultural Experiment Station, Piedmont Knowledge gained through this Substation, in east–central Alabama. project has been shared with a diverse range of audiences in many settings Common Scientific Varietal and through various media. name name name FIELD DAYS. Two AAES Pied- Florida maple Acer barbatum --- mont Substation Shade Tree Field Days Trident maple Acer buergeranum --- were held in 1993.
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