72 Fair et al.: Maple (Acer spp.) Response to Soil Compaction and Pre-plant Nitrogen research that has explored growth rate, autumn color presenta- tion, resistance to potato leafhopper, and wound response (Gal- lagher and Sydnor 1983), which all vary at the cultivar level for both red and Freeman maples (Townsend and Douglas 1998). ‘Magnificent Magenta,’ for example, may be an appropriate se- lection for small urban spaces where a slow growth rate may be appropriate. Anecdotally, the study authors found it an aes- thetically pleasing tree with vibrant burgundy autumn color, de- spite compaction. ‘Bowhall’ trees also had a slow growth rate (lowest annual caliper growth on average), produced a notice- ably ganglier crown (smallest leaf biomass measures) with a lighter green color (anecdotal observations), despite soil treat- ment compared with cultivars such as ‘Magnificent Magenta’ and ‘Fairview Flame.’ Although ‘Bowhall’ may be desirable for its slow growth, it is unlikely to be aesthetically acceptable to urban residents and may be less stress tolerant. The research- ers have no explanation for ‘Bowhall’ trees’ lack of response to compaction. All trees were treated similarly. If still a mar- ket favorite, this anomaly warrants further investigation; oth- erwise, the research suggests selecting other red maple culti- vars for urban sites. ‘Celzam’ Freeman maple grew the fastest and though affected by compaction, it produced more biomass than other cultivars despite compaction, thereby increasing its chances of surviving establishment and growing normally if compaction alleviates over time. Both ‘Celzam’ and ‘Fair- view Flame’ maples would be appropriate cultivars for clay- based, compacted urban soils in the Midwest United States. This research indicates leaf dry weight and leaf area in- crease when applying nitrogen at a rate of 100 mg·L-1 compared to a lower rate of 25 mg·L-1. The increase in leaf growth with the higher fertilization rate may be of benefit to trees whether growing in compacted or uncompacted clay-type soils; howev- er, no significant increases were observed with the 100 mg·L-1 rate for tree height and caliper growth or stem dry weight. Figure 3. (a) Root system of ‘Celzam’ tree grown in C1 compacted plot clearly illustrating the location of the original root system within the 13 L pot. Much of the root system seems to be growing within the top 15 cm of the soil, just beneath the mulch, support- ing findings from Gilman et al. (1987). (b) Root system of ‘Celzam’ tree growing in non-compacted soil plot illustrating a spreading root system, and no anecdotal evidence of root growth only be- neath the mulch. The majority of cultivars that received the standard rate of production nitrogen (100 mg·L-1 larger SDW than trees treated with the low rate (25 mg·L-1 N) had larger LA, LDW, and N) each year of the study, under all compaction treatments. Ex- ceptions were ‘Bowhall,’ ‘Morgan,’ and ‘October Glory,’ which were unaffected by production nitrogen rate in any year. There was no interaction between N rate and soil treatment, there- fore it is unlikely that the standard rate of pre-plant production N rate affects tree establishment in similarly compacted soils. CONCLUSIONS The most significant factor affecting growth response to com- pacted soil is plant species. Cultivar-to-cultivar differences dominated any overall differences between the Freeman and red maple groups in response to soil compaction (P < 0.0001, Table 2), despite the close genetic relationship between Freeman and red maple. This variation among cultivars is consistent with other ©2012 International Society of Arboriculture Acknowledgments: This research was supported by funds from the Kip- linger Endowment for Floriculture, a gift from the Ohio Nursery and Landscape Association and financial support from Dr. Daniel Struve. Sal- ary and additional research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. This paper is based on a portion of a disserta- tion submitted by B. Fair in partial fulfillment of the requirements for the Ph.D. degree in horticulture. We would like to thank A. McGill & Son Wholesale Nursery, John Holmlund Nursery, LLC. and J. Frank Schmidt & Son Co. for donating the trees. We would also like to thank Dr. William Swallow (NCSU) for his invaluable statistical expertise, without which this manuscript would still be far from completion. LITERATURE CITED Abercrombie, R.A. 1990. Root distribution of avocado trees in a sandy loam soil as affected by soil compaction. Acta Horticulturae 275, Tropical and Subtropical Fruits. pp. 505–512. Alberty, C.A., H.M. Pellett, and D.H. Taylor.1984. Characterization of soil compaction at construction sites and woody plant response. Jour- nal of Environmental Horticulture 2:48–53. Andrade, A., D.W. Wolfe, and E. Fereres. 1993. Leaf expansion, pho- tosynthesis, and water relations of sunflower plants grown on com- pacted soil. Plant and Soil 149:175–184. Ares, A., T.A. Terry, R.E. Miller, H.W. Anderson, and B.L. Flaming. 2005. Ground-based forest harvesting effects on soil physical proper-
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