Estimates of the acreages of the 11 strata occurring within a particular land 

 management unit--whether it be a Ranger District, a compartment, or any geographic 

 area of special interest- -will be computed from the proportions of the photo points 

 falling in the respective strata. 



GROUND SAMPLING PROCEDURE 



A referenced base line is laid out through each selected s ub compart men t . The 

 base line provides starting points for line-plot sampling of the entire s ub compart men t . 

 Starting points along the base line are established for permanency and referenced for 

 re measurement. Transects are run perpendicularly to the base line at intervals of 

 10 chains horizontal distance. Plots along the transects are spaced at 5-chain 

 intervals. This frequency provides a sample point for each 5 acres of area. All 

 plots are referenced to the stand in which they occur as delineated on the photos. 

 Figure 1 is a schematic diagram of the grid layout. 



The inventory field procedure at each point is similar to individual points in the 

 1-acre 10-point cluster system. Some features of this procedure are: 



a. A fixed plot 1/300 acre in size for recording trees less than 5 inches d.b.h. 



b. A variable plot for recording trees 5.0 inches and larger. 



c. Azimuth recorded to each tree over 5.0 inches d.b.h. 



d. Each tree over 3.0 inches d.b.h. tagged. 



e. On nonstocked areas, satellite plots (1/300 acre) are taken 1/2 chain ahead, 

 1/2 chain back, and 1/2 chain perpendicularly to each side of the principal point of 

 the transect. Variable plots are only taken at the principal plot location. 



In addition to the typical tree data normally recorded on the plot that provide 

 volume and condition information, inventory crews record the ecological situation as 

 represented by vegetative indicators. We are using the Daubenmires ' (1968) habitat 

 type classification for north Idaho and eastern Washington. The inventory classifica- 

 tion of habitat type will permit us to develop criteria for mapping the entire forest 

 by habitat types. 



NET VOLUME SUBSAMPLING PROCEDURE 



Since 1964, net volume has been estimated in the Northern Region using a destruc- 

 tive subsampling procedure. This procedure of dissecting felled trees provides 

 adjustment factors for three sources of error in estimates of net volume: (1) volume 

 tables; (2) cull and defect allowances; and (3) inaccurate height estimation. 



The subsample has been comprised of randomly selected locations. Under the new 

 approach, the same procedure will be followed by drawing the subsample from the 215 

 locations established in the preceding inventory of 1961-62. Although the remeasurement 

 of these sample plots will provide useful data on growth and mortality in addition to 

 volume-table and cull and defect allowances, it will not provide control of 

 measurement error in the current inventory. Accordingly, the destructive sampling 

 will extend to a subsample of the points being established in the subcompartments 

 of the current inventory. 



The field procedures for the destructive sample and subsequent net tree volume 

 calculations are described by Stage and others (1968) . 



8 



