Biases in volume increment estimates derived from successive angle count sampling

Several large-scale forest inventories are now being conducted using angle count sampling, and the method is commonly used for timber cruising and corporate forest assessment. The calculation of basal area or volume increment from angle count sample data is not trivial, and three alternative methods are currently in common use: the difference method, the starting value method, and the end value method. This article develops the hypothesis that in various circumstances these methods are susceptible to bias as a result of measurement error and mis-sampling of trees. After reviewing prior work in angle count mathematics and developing the theoretical basis of our hypothesis, we present a supporting example based on a large permanent sampling plot at Hirschlacke in northern Austria. Our results suggest that the errors resulting from using calculation methodologies susceptible to bias from measurement error may in practical circumstances be more than 10% of volume increment, which could have ramifications for sustainable forest management or carbon sequestration budgeting