676 



TIMBER RESOURCES FOR AMERICA'S FUTURE 



'■'Felling factor." The products of the stocking 

 percentages and the corresponding felling-age fac- 

 tors were computed, and these products totaled. 

 (The felling-age factor for the nongrowing stock 

 trees is always 1.00.) The total of these products 

 was 27.34. The total stocking percentage for the 

 stumps tallied was 29. Therefore, the weighted 

 felling-age factor is 27.34 _ 

 ""29""" 



Final Productivity Rating 



The estimated total adjusted stocking percent- 

 age is multiplied by the felling-age factor to obtain 

 the estimated productivity rating for the plot. 

 The final rating for the plot is the product (61 X 

 .94 = 57 percent). 



The sample calculation of productivity given 

 here was chosen to include all possible factors. 

 Quite often in the 1953 survey, calculation of a 

 composition factor was unnecessary because 50 

 percent or more of the existing stocking was com- 

 posed of "desirable" species. Also, no felling- 

 age factor was calculated when stands were par- 

 tially cut, i. e., when less than 80 percent of the 

 volume of merchantable sizes was removed. 

 Often the calculations required to obtain a 

 weighted felling factor for uneven-aged stands 

 were not needed because of the even-aged character 

 of the stand cut. 



PROCEDURES FOR WESTERN 

 UNITED STATES 



In the West, including South Dakota, Nebraska, 

 and Kansas, stocking, composition, and the effect 

 of felling age were measured by the point sampling 

 method. Applied to stocking, this method is 

 based on the concept that when a number of 

 sample points are classified according to presence 

 or absence of stocking at each point, the percent of 

 total points classed as stocked is an estimate of 

 the percentage of the area stocked. In using the 

 system, methods were prescribed to provide for 

 location of sample points without bias and dis- 

 tribution of them over the entire area being 

 sampled. 



Existing Stocking 



The examiner first determined for each observa- 

 tion point whether or not the growing space 

 represented by that point was stocked with a 

 crop tree. Decision was based on stocking tables 

 showing the maximum radii within which trees of 

 various sizes must occur to classify the point as 

 stocked. Where two or more trees occurred 

 within prescribed radii, the closest tree to the 

 point having an equal or better chance of survival 

 than its competitors was used to determine the 



stocking. As shown in the regional stocking 

 tables, for example table 104, the area stocked is 

 directly related to tree size, i. e., the larger the tree 

 the greater the area stocked by it. 



The species of crop tree stocking the point 

 was recorded on the field worksheet as either "D" 

 or "A" (for desirable or acceptable, respectively) 

 in accordance with species listings for each type or 

 type group. Certain species were considered 

 as noncount in the type criteria. Where onl}' 

 noncount species occurred within prescribed radii, 

 the point was classed as nonstocked. 



Prospective Stocking 



When a sample point was not stocked with an 

 existing crop tree, the examiner determined 

 whether or not the chances for future stocking were 

 favorable. The decision was based on guides for 

 each forest type or type group. Such guides 

 recognized distance to acceptable seed source, 

 competing undesirable vegetation, and other 

 measurable factors affecting reproduction. The 

 point was classified as prospectively stocked if it 

 met the standards given in the guides; otherwise 

 it was classed as nonstocked. 



After all of the points in a timber type within a 

 cutting area had been classed as stocked or non- 

 stocked, the total number stocked (including both 

 existing and prospective) was expressed as a per- 

 cent of the total number of points examined. 



Points falling on old roads and skidways that 

 were to be used again before a new tree crop 

 reached usable size were reported as nonstocked. 



Effect of Composition 



14 



In order to measure the effect of species com- 

 position, species that stocked or showed potentials 

 for stocking the points were classified as desirable 

 or acceptable according to individual type criteria. 

 For each type, a standard of at least 50 percent 

 of the points stocked with desirable species was 

 established. The ratio of points stocked with 

 desirable species to all stocked points was calcu- 

 lated. This ratio was then compared with the 

 50-percent standard. If the ratio obtained was 

 equal to or greater than the standard, no adjust- 

 ment was made. Otherwise the ratio was divided 

 by the standard and the quotient obtained was 

 used as the adjustment factor. If the adjustment 

 factor obtained was less than 50 percent, the factor 

 50 was used. 



" The calculations referred to here were completed in 

 che field by each examiner, except for a part of the data 

 collected in California, Oregon, and Washington. Calcu- 

 lations from basic data collected in those States were 

 completed in the Washington Office of the Forest Service. 

 The results of additional supplementary data taken in the 

 three States are presented in the section Productivity of 

 Recently Cut Lands, p. 263. 



