Agenda - Environmental Policy Board - 07/19/2021

Home

Title 190 — National Foresty Handbook Zig-Zag Transect Method The zig-zag transect is best suited for even -aged, single -layer, and single -species forest stands of a uniform nature. These conditions would likely be encountered in a plantation type of stand. However, experienced users are also able to apply this method in measuring multilayered stands with a diversity of tree species. The zig-zag method can be used to determine— • Average tree diameter. • Range of tree diameters. • Stocking rates (TPA). • Stand composition. • Stand condition (health). Information from the zig-zag transect can be used to derive an estimate of the BA of the sampled stand. The zig-zag transect is performed by selecting a point in the stand where the transit will begin, along with determining a direction of travel (a general route which will best capture the stand attributes) (fig. 12). A compass and bearing are used to guide the route. The transect will normally be conducted along the contour when stands are on sloping topography. A "starter tree" anchors the transect and is not measured. An imaginary 90° quadrant, bisected by the direction of travel, is used to determine the area where the first sample tree will be selected. • From the starter tree, select the next closest sample tree from within the 90° quadrant. This provides a degree of randomness. Measure the distance from the starter tree to the first tree. Species, DBH, height, tree condition and other attributes of this first sample tree are recorded. • The first tree that was sampled serves as the reference point in selecting the second tree. The same process that was used with the starter tree is repeated in order to select the next sample tree. Continue in this manner until 20 or more trees have been sampled. • Be careful to exclude uncharacteristic openings. The true tree -to -tree distances will reveal the general stand density only if openings are excluded. The same logic applies to clumps of trees or other configurations that obviously do not represent the general stand structure. Figure 13 illustrates this concept. • Collectively, these "atypical" conditions should occur infrequently within the stand. If they don't, and if these areas become significant in cumulative size, then the overall stand description must be revised to account for the openings or clumps. • See Montana's Technical Note MT-22 for additional detail on the zig-zag transect method (Logar and Wiersum 2003). (Technical Note No. 190-FOR-01, Jul 2018) 23