The Significance of Percentage Area Determinations Yielded by the Percentage Area or Density List Method of Pasture Analysis

Abstract

The percentage area method is discussed. The difficulty of using estimated percentage area results for the detection of change in pasture or grassland is pointed out. Although a strong correlation exists between the estimations made by different observers on the same quadrat, each observer estimates differently and the results of several observers cannot be compared until reduced to the same scale. It is proposed that the measurements of area covered made by means of a pantograph be used as a constant scale, that all observers correlate their estimations with pantograph measurements at regular intervals and that they reduce all estimated percentage area results to the pantograph scale. In deciding on the significance of change shown in results obtained by different observers at different times, it is necessary to reduce all observations to the same scale, to compute the standard deviation of the difference of the means, and to compare the difference with its standard deviation, or with the derived value, the probable error.