Sample Unit Selection for Studies of Herbaceous Oldfield Vegetation

Abstract

The size and number of sampling units needed to sample herbaceous oldfield vegetation must be determined for each situation. Prior to obtaining data for a long-term study of early oldfield plant succession at the Waterloo Mills Field Research Station, Pa. statistical tests and theoretical considerations were evaluated. Of the five sizes of circular quadrats tested, the 0.03125 m2 size was determined to be suitable to obtain detailed data efficiently and yet sample within the estimated smallest scale of heterogeneity. A sample of 100 quadrats, the minimum number needed to compare frequencies, was determined to be adequate (within 10%) from calculations of the standard error of the mean, running means, and species-area curves. Subsequently, annual samples were obtained at 100 points from a stratified grid of 570 quadratcenter points in each 6.40 x 9.12 m subplot studied.