Precipitation Effects on Tree Ring Width for Ulmus americana L. in Oklahoma City

1. Precipitation Effects on Tree Ring Width for Ulmus americana L. in Oklahoma City Carmen L. Cowo, Christopher Butler, Chad King, and Jim Bidlack; University of Central Oklahoma, Edmond, OK 73034 Abstract Cores from twenty UlmusamericanaL. (American elm) trees were obtained from a forested region in Oklahoma City. Tree ring widths for 2008- 2013 were compared to annual precipitation rates of northern Oklahoma City for the corresponding years. Results using a one- way ANOVA revealed a significant difference in tree ring widths by year (F5, 114= 2.950, p= 0.015). Tukey’s HSD post hoc tests showed a significant difference for years 2011 (2.120± 1.059 mm min, p= 0.010) and 2013 (3.940± 2.428 mm min, p= 0.010). Calculation of a Spearman rank- order correlation coefficient indicated a significant positive relationship between annual rainfall in northern Oklahoma City and American elm tree ring width (rs= 0.189, p= 0.030). Knowing the effects of drought can help predict future responses of trees to changes in precipitation. Results A significant difference between tree ring width and corresponding years was observed (F5, 114= 2.950, p= 0.015; Fig. 3). Tukey’s HSD post hoc tests revealed a significant difference for 2011 (2.120± 1.059 mm min, p= 0.010) and 2013 (3.940± 2.428 mm min, p= 0.010). There is also a significant correlation between annual rainfall in northern Oklahoma City for year’s 2008- 2013 and tree ring diameter (rs= 0.189, p= 0.039). Discussion This study demonstrates that American elm trees serve as a biological species indicator for changes in precipitation. However, variation in ring diameters may also correlate with additional external factors. Further research should include an analysis of annual temperature and soil composition. Drought is the most limiting factor for tree growth in the southwestern USA. (Adams and Kolb, 2004). Although U. americanaL. isknown to be drought resistant, this study found that effects of drought are still observable in growth rings for American elm (USDA, 2013). The effects of drought on tree species are important because trees are essential components of viable ecosystems. Being able to predict responses can aid in the formulation of conservation efforts for ecological communities by revealing what land and species require protection. This study suggests that future increases in drought frequency may impede U. americanaL. growth, but due to its adaptability, adverse effects on its population are not anticipated. Figure 1: Study site in Oklahoma City where cores were collected. Introduction Dendroclimatology involves an examination of annual growth rings to determine climate history (Bidlack and Jansky, 2011). Rainfall affects the size of annual rings due to the amount of nutrients and water made available to the tree for growth, resulting in wider rings with increased rainfall and narrower rings with decreased rainfall (Bidlack and Jansky, 2011). There is little literature published on the effects of low precipitation on tree ring diameter for UlmusamericanaL. in Oklahoma. Knowing how changes in climatic variables compromise tree growth can help researchers generate predictions of resulting environmental effects, for example, population decreases or changes in species distribution. Goals of this project include comparing tree ring widths of UlmusamericanaL. for years 2008- 2013. Using these measurements, in conjunction with rainfall data for northern Oklahoma City, a correlation between tree ring width and annual precipitation during 2008-2013 may be determined. Literature Cited Adams, H. and T. Kolb. 2004. Drought responses of conifers in ecotone forests of northern Arizona: tree ring growth and leaf δ13C. Oecologia. 140: 217-225. Bidlack, J. and S. Janskey. 2011. Stern’s Introductory Plant Biology. 12 Ed. New York: McGraw- Hill. Mesonet. Weather: Rainfall. Mesonet Rainfall by Monthly Table: Oklahoma City North. <http://www.mesonet.org/ index.php/weather/monthly_rainfall_table/OKCN>. U.S.D.A. Natural Resources Conservation Service. Plants Database. Ulmusamericana L., American elm <http:// plants.usda.gov/core/profile?symbol=ULAM>. Figure 2: Twenty core samples used for analysis. Methods The study site was a forested region of northwestern Oklahoma City near the Bluff Creek suburb (Fig. 1). Twenty randomly selected American elm trees provided one core for data analysis (Fig. 2). DBH (diameter at breast height measured at 1.37 meters) for living trees exceeded 10 cm to ensure sufficient age for study years under analysis. Cores were removed using a 14” JIM-GEM increment borer and required sanding with sandpaper of increasing grit. Annual precipitation levels (cm) for northern Oklahoma City were accessed through the Oklahoma Mesonet website: 2008= 93.24, 2009= 103.41, 2010= 88.29, 2011= 69.70, 2012= 83.21, and, 2013= 120.22 (mesonet.org). One- way ANOVA and Tukey’s HSD post hoc tests were used to determine a significant relationship between ring width and years. Results are reported as mean ± standard deviation. To determine if there is a correlation with ring diameter and annual rainfall, a Spearmans rank- order correlation coefficient was calculated. Acknowledgements I would like to offer my thanks to the UCO Department of Biology for providing research materials. I appreciate the Parks and Recreation Department of the City of Oklahoma City for giving permission to use their land. I would like to thank Francisco Esqueda for aid in field sampling. Figure 3: Box plot results of ring widths (mm).