Errors resulting from thickness of point quadrats

Abstract

When the needles used for point quadrat analyses have appreciable thickness, this causes overestimation of leaf area. A theoretical study, supported by practical trials, shows that the resultant error in estimates of "relative frequency" doubles with a doubling of quadrat diameter or a halving of leaf breadth. With the point quadrat techniques that have been in normal use the errors often exceed 50% and the estimates obtained are usually less accurate than visual estimates. However, results of sufficient accuracy for rough work can be obtained by using a narrow quadrat needle and applying correction factors; and errors can be altogether avoided by recording contacts with the sharpened point, but not the sides, of a needle gradually lowered through the vegetation.