Estimating Mast Production: An Evaluation of Visual Surveys and Comparison with Seed Traps using White Oaks

We compared five types of visual mast surveys with seed trap data from 105 white oaks (Quercus alba L.) during 1996-1997 in the Ouachita Mountains of Arkansas. We also evaluated these visual survey methods for their usefulness indetecting 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. We found no difference in the effectiveness of visual surveys 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 ince they are not affected as greatly by wildlife removal. However, visual surveys can be biased by observer differences, whereas trap data are not. South. J. Appl. For. 16(3):164-169. Acorns are used xtensively by wildlife and are ssential for oak regeneration. Because of their importance, land managers and researchers have attempted to estimate acorn crops for decades. However, direct measures of acorn production are difficult given the height, canopy size, and density of leafy vegetation of oaks, especially in the southeastern United States. Accurately counting all acorns in a tree, or in a fixed portion of the canopy, cannot be done from the ground, and doing it in the canopy is impractical. Acorn traps, plots located on the ground, and visual surveys are three commonly used methods for estimating acorn crops. Acorn traps, which catch acorns as they fall from the tree, have been used in the majority of studies on acorn production (e.g., Downs and McQuilkin 1944, Christisen and Korschgen 1955, Goodrum et al. 1971) and in most studies relating acorn production with wildlife parameters (e.g., Nixon et al. 1975, McShea and Schwede 1993). Many types of acorn traps have been developed (Thompson and McGinnes 1963). However, traps are labor intensive and costly because they must be built, placed on site, maintained, and checked periodically. Moreover, acorn traps and ground plots only estimate the density of acorns that reach the ground, although arboreal acorn consumption by wildlife can sometimes be Nox•: R.W. Perry is the corresponding author--Phone: (501) 321-9825; Fax: (501) 623-0186; E-mail: rperry/[email protected]. Manuscript received May 15. 1998. accepted November 13. 1998. estimated when acorn fragments fall into traps. Nevertheless, a reliable estimate of complete arboreal removal of acorns by wildlife cannot be assessed using acorn traps or ground plots. Visual surveys are commonly used to estimate acorn crops. These surveys are much less labor intensive because they can be completed rapidly, require only a single visit to each tree, and require little equipment. Although visual surveys do not yield quantitative estimates of acorn biomass, they provide indices that can be compared among trees, sites,