Determining Girard Form Class in Central Hardwoods

Publisher： Society of American Foresters

ISSN： 0742-6348

Source： Northern Journal of Applied Forestry, Vol.14, Iss.4, 1997-12, pp. : 202-206

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

Abstract

Girard form class is widely used to describe tree form. Tree volume estimates change about 3% per unit change of Girard form class (Mesavage and Girard 1946). Hardwoods growing in close proximity have been observed to have a wide range in Girard form class. Accurate determination of Girard form class can therefore be important in getting accurate estimates of hardwood timber volume. However, the cost of estimating Girard form class for every tree being measured in the stand would be prohibitively expensive. Thus, estimation of average Girard form class for a stand is considered here. Three instruments used to estimate Girard form class--a Wheeler pentaprism optical caliper, a wedge prism, and a Spiegel relaskop--were compared to direct measurement. Number of sample trees to achieve desired half-widths of the confidence interval of ±1 and ±1 1/2 units of Girard form class was calculated for each method. Direct measurement requires the fewest trees to achieve the desired results. However, it requires considerably more time per tree than any of the instruments tested. The Wheeler pentaprism requires only a few more trees than direct measurement, and considerably fewer trees than either the wedge prism or the Spiegel relaskop. Use of all three instruments is hindered when understory vegetation obscures the top of the first log. North. J. Appl. For. 14(4):202-206.