Line Intersect Sampling

Abstract

WARREN and OLSEN (1964) published a “line intersect technique” which they propagated as a method to obtain quickly volume estimates of logging residue on clearfelled areas. These authors were faced with the problem of annually assessing, with limited manpower, the quantity of merchantable material not extracted by pulpwood contractors, from clearfellings in Pinus radiata stands in New Zealand. Though the contractors were liable for payment of royalties regarding this roundwood residue, the low price per unit was prohibitive of intensive sampling designs. Previous work by MITCHELL in New Zealand (WARREN and OLSEN, l.c.) had shown that sampling with quarter-acre circular plots not only was too time-consuming and expensive, but also had to be very intensive in order to yield results of acceptable precision. As most time went to searching of plot areas for qualifying pieces, attention subsequently was directed to long and narrow rectangular plots in which the logs were encountered automatically, thus reducing searching time. Though these narrow plots seemed to sample the population more representatively, the gain in precision and time was not sufficient to make the inventory economically feasible under prevailing restrictions. The authors then conceived the idea of reducing plot width to a line, and paying attention only to the volume of the logs that intersected with that line, as this volume, they reasoned, should bear some relationship to total volume present in a given area. On a semi-empirical basis they developed an estimator for residue volume per acre in which, apart from the number (n) of intersecting logs and line length (L), two empirical values appear of which the first depends on dimensional characteristics, and the second on the directional orientation of the logs relative to the sampling line.