Potential Bias in Pan Trapping as a Function of Floral Abundance

Abstract

Our study sites were located at the Marvin Klemme Research Range (MKRR) and the Stillwater Research Range (SRR). The MKRR is located approximately 15 km South of Clinton in west-central Oklahoma and is predominantly a mixed-grass prairie. We used the MKRR to evaluate pan trap effectiveness at sites with and without floral resource removal via herbicide applications. An aerial application combining 2,4D (2,4-Dichlorophenoxyacetic acid), picloram, and AllyH XP herbicide (0.7 kg acid equivalent/ha) was applied 15 May 2009. Herbicide applications reduced forb species richness by 63.6%, 100%, 88.9%, and 83.3% during June, July, August, and September, respectively, within the study plots. Forb abundance also was reduced by .95% each month in the herbicide treated plots. Four separate pastures (two treated with herbicide and two untreated controls) ranging in size from 40 to 50 ha were sampled at the MKRR, with two sampling areas located a minimum of 200 m apart in each pasture. The SRR is located approximately 21 km southwest of Stillwater in north-central Oklahoma and is predominantly a tallgrass prairie. We used the SRR to evaluate the effect of low and high floral resource availability generated by annual variations in precipitation on pan trap effectiveness. 2006 was a drought year with 30.5% less rainfall than normal based on the 30 year average from 1971–2000, whereas 2007 was a wet year with almost twice as much rainfall as normal (data obtained from a Mesonet station located on the SRR; http://www.mesonet.org/). Although no formal estimates of floral resource availability were recorded, flower resources were very limited in 2006 and abundant in 2007 (KAB, pers. obs.). Three separate pastures