COMPARISON OF 1949 AND EARLIER ESTIMATES 



At least six different estimates have been published of Montana's 

 timber resource in the past. (Table l) Differences between the 

 1949 and earlier estimates are accounted for by (1) the sampling 

 errors of the portion of the statistics derived by sampling 2/, 

 (2) technique errors , (3) variations in definitions , inclusiveness , 

 and standards of measurement, and (4) actual change . Of these, only 

 the sampling errors are definitive Analysis of sample variations 

 indicate that, on the basis of odds of 2 out of 3 S the sampling 

 errors of the portion of the 1949 estimates derived by sampling lie 

 between limits as follows Total forest land t 146 thousand acres, 

 commercial forest land ± 152 thousand acres, other forest land t, 63 

 thousand acres, and commercial saw-timber volume - 1,397 million 

 board feet. Noncompensating technique errors such as misclassif ica- 

 tion and imperfect tree-volume tables affect both the sampling and 

 complete survey statistics. 



The apparent increase in total forest and commercial forest land 

 can be at least partially accounted for by changes in definition and 

 inclusiveness o Prior to the completion of the systematic survey in 

 1949 only extensive estimates were available for the area eas t of 

 the Continental Divide. Hardwood areas and volumes were disregarded 

 entirely prior to 1938. Until recently, too, with little prospect 

 for development and use, a considerably larger portion of the total 

 forest land area in eastern Montana was considered noncommercial. 

 Volume estimates of 1918 and 1923 include all forest land as in- 

 dicated in table lj whereas later estimates are for commercial for- 

 ests only. Part, and perhaps all, of the apparent difference be- 

 tween the 1945 and 1949 estimates may be accounted for by variations 

 in minimum standards. The 1949 board-foot estimates include the 

 saw-timber volume of trees of all species 11.0 inches d.b.h. and 

 larger. The 1945 estimates included only pines and hardwoods to 

 this diameter, the minimum diameter of other species being 13 o0 

 inches d.b.h. The minimum standards for saw-timber trees were not 

 defined for estimates prior to 1945 . 



For the foregoing reasons a comparison of the 1949 and previous 

 estimates provides no definite indication of quantitive changes or 

 trends in either direction. However, there have been changes in 

 the character and distribution of the timber volume. The propor- 

 tion of the volume in prized species such as ponderosa and white 

 pines is diminishing and the volume of these and other species is 

 becoming less concentrated in large blocks. 



2/ Approximately one third of the forest area was derived by sampl- 

 ing, the remaining two thirds from complete surveys . 



