A formula method recognizing areas in various 

 stand-size classes, total volumes, growth, condition of 

 the present stand, and rotation age was used in com- 

 puting allowable cut for even-aged types such as 

 aspen and jack pine. The basic formula was as 

 follows: 



HC-- 



V^% 



Where: 



/fC= annual harvest cut 

 F=volumc of timber in the mature size class 

 G=;annual growth of the mature size class 

 « = liquidation period of the mature size class 



In application this formula was modified depending 

 upon the length of the liquidation period and the 

 number of size classes involved for the particular 

 forest type. A detailed explanation of the formula 

 method is included in the Lake States Forest Survey 

 Handbook. 



In addition to the harvest cut, inlcrmediate cuts 

 from immature stands are included to arrive at the 

 total allowable cut for the even-aged types. 



For types usually handled under an uneven-aged 

 system of management, the cutting recommendations 

 of field crews, including silvicuJtural as well as 

 operability factors, were used to compute allowable 

 cut. In order to recognize operability limitations, in 

 the northeastern division a stand was not judged 

 operable unless the timber available for cutting 

 exceeded 1,500 board-feet per acre for sawtimber, or 

 3 cords per acre for pulpwood cuts. In the southern 

 districts where stands are more accessible, the mini- 

 mum cuts considered operable were 500 board-feet 

 per acre for sawtimber and 1 cord per acre for cord- 

 wood material. 



For both even and uneven-aged forest tvpes, the 

 basic concept was that the cut should be as high as 

 possible while building up or maintaining sufficient 

 growing stock to meet specified growth goals. Peri- 

 odically, during the progress of the survey the esti- 

 mates of allowable cut, as well as other forest survey 

 statistics, were reviewed by the Minnesota Forest 

 Survey Committee in order to maintain agreement 

 on methodology and concepts. 



Timber Cut 



All sawmills, pulp and veneer mills, and other 

 wood-using industries were canvassed by mail or 



interview to get an estimate of the amount of wood 

 produced as primary forest products. Other survevs 

 were made to estimate the amount of fuelwood and 

 fence-post production. Studies were also made of 

 timber residues to adjust the production by com- 

 modities to timber cut from inventory volumes. In 

 addition, all public agencies were canvassed for ilie 

 amount of wood sold during the cutting year, and 

 this information was used to break down the total 

 cut by ownership. 



Accuracy of Survey 

 Areas 



There were two sources of error in estimating ihr 

 forest land area: (1) Errors in classifying the type, 

 size, and stocking classes and in compiling the data, 

 and (2) sampling errors. Frequent checks were made 

 during the collection and compilation of the data, 

 both in the field and in the oflfice, to minimize the 

 operational errors. The sampling intensity was 

 sufficient to provide an estimate of the forest area of 

 the State with a standard error of about 0.5 percent. 



Volumes 



The sources of error in estimating timber volume 

 include: (1) Errors in measurement of plot radius, 

 tree diameter, height, and cull; (2) improper con- 

 struction or use of tree volume tables; (3) errors in 

 collecting or compiling the plot data; and (4) sampling 

 errors. As in the area determinations, every effort 

 was made to obtain accurate measurements and final 

 statistics through frequent checks and training. The 

 number of plots taken in the State was adequate to 

 provide a sampling error for total cubic-foot volumi- 

 of not more than 1 percent, and a sampling error for 

 total sawtimber volume of less than 1.5 percent. In 

 all tables shown, the totals are more accurate than the 

 subtotals, and the subtotals are more accurate than 

 the individual items in the tables. Any item that is 

 small in relation to the totals — for example, an\- 

 volume estimate less than 10 million cubic feet — is 

 subject to large sampling errors. 



Definition of Terms 



Land-Use Classes 



Forest l.and .\ke.\. — Includes (1) lands that are at | 

 least 10 percent stocked by trees of any size and 

 capable either of producing timber or other wood 



48 



Forest Resource Report No. 13, U. S. Defartment of Agrioilturc 



