Inventory Procedures 



The timber resource inventory was designed to provide inventory data 

 for the individual working circles in Montana and the state as a whole. 

 Because reliable county data was desired in Working Circle 3, a large number 

 of field plots were sampled. This allowed the data to be stratified further to 

 provide better information at the county level. 



Forest inventory data was collected on all private, state, county, munici- 

 pal, and some miscellaneous federal lands in the working circle. These 

 miscellaneous federal lands included USDI Fish and Wildlife Service lands, 

 lands within national monuments, and lands controlled by the U.S. Army 

 Corps of Engineers and the USDI Bureau of Reclamation. The sampled area, 

 which totalled 6.6 million acres, included forested and nonforested lands. 

 (NOTE: Timber Resources on USDA Forest Service, USDI Bureau of Land 

 Management, and National Park Service Lands were not inventoried). 



Sample points were selected, measurements taken, and data analyzed 

 through the following methods: 



1. Initial area estimates were based on the classification of 52,463 

 sample points systematically placed on the latest aerial photographs available. 

 The dates of these photos ranged from 1955 to 1976; most were 1972 photos. 

 The sample points were summarized and grouped into strata for subsequent 

 field sampling. The photo points, adjusted to meet known land areas, were 

 used to compute area expansion factors for the field stratum means. 



2. Land classification and estimates of timber characteristics and volume 

 were based on observations and measurements recorded at 460 ground sample 

 locations. Sample trees were selected using a 10-point cluster that included 

 fixed plots (1/300 acre) for trees less than 5.0 inches d.b.h. and variable 

 plots (40 BAF) for trees 5.0 inches d.b.h. or larger. 



3. All photo and field data was sent to the Intermountain Experiment 

 Station in Ogden, Utah, to be punched onto computer cards and stored for 

 machine computing, sorting, and tabulation. Computerized edits were sent to 

 the inventory crew for corrections. Final estimates were based on statistical 

 summaries of the data. 



Data reliability is listed in Appendix 1. 



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