Perry and Thill compared five types of visual mast surveyed with seed trap data from 105 white oaks (Quercus alba L.) during 1996-1997 in the Ouachita Mountains of Arkansas. They also evaluated these visual survey methods for their usefulness in detecting differences in acorn density among areas. Indices derived from all five methods were highly correlated with acorn densities derived from traps, and the Koenig method had the highest r-values. Categorical surveys using fewer than six categories yielded significantly different acorn densities among all categories, whereas surveys using nine or ten categories did not. All survey methods detected moderate to large acorn density differences among four study areas. The authors found no difference in the effectiveness of visual survey in dense versus open-forested conditions. Visual surveys are an effective method for evaluating acorn production and may be superior to seed traps for comparisons of acorn production in tree canopies since they are not affected as greatly by wildlife removal. However, visual surveys can be biased by observer differences, whereas trap data are not.
Perry, Roger W.; Thill, Ronald E. 1999. Estimating mast production: an evaluation of visual surveys and comparison with seed traps using white oaks. Southern Journal of Applied Forestry. 16(3): 164-169.