Abstract
Estimates of number of wetlands derived from quadrat sampling are inherently biased when wetlands on quadrat boundaries are counted. Bias complicates comparisons of wetland density or abundance between years or studies, or between regions with different wetland sizes. Simulated quadrat sampling was conducted to evaluate the magnitude of bias in estimates of the number of temporary, seasonal, semipermanent, and total wetlands from samples of square quadrats of different sizes. All estimates were biased except for number of temporary wetlands derived from samples of the largest quadrats. Bias ranged from +101% (SE=0.39%) for estimates of the number of semipermanent wetlands sampled with 0.64 km2 quadrats to +0.19% (SE=0.19%) for the number of temporary wetlands sampled with 25.60 km2 quadrats. Bias was greatest when large wetlands were sampled using small quadrats and was related to quadrat perimeter: area ratio (km/km2) and to quadrat size. Managers and researchers should correct for bias in estimates of number of wetlands by deriving correction factors with the equations presented or by deriving correction factors using aerial photographs to determine the geometric centers of wetlands in and around a subset of sample quadrats.
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Johnson, R.R., Higgins, K.F. Bias in quadrat-derived estimates of number of prairie wetlands. Wetlands 18, 329–334 (1998). https://doi.org/10.1007/BF03161528
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DOI: https://doi.org/10.1007/BF03161528