PRODUCTIVITY OF RECENTLY CUT LANDS 



231 



The general relationship shown in figure 78 has 

 been found true for all species, but the rate at 

 which average annual gi'owth increases, the age at 

 which the peak occurs, the period over which this 

 peak is maintained and the rate of declme follow- 

 ing the peak varies with species, growth potential 

 of the soil, and other environmental factors. Like- 

 wise, the general relation holds whether the average 

 annual growth is measured in board -feet, cubic 

 feet, or cords. The main effect of different product 

 measures is that peak growth is reached at younger 

 ages when the product admits small trees. Hence 

 the maximum growth is attained at younger ages 

 for cordwood than for saw logs. 



Because of this growth cycle, clear cutting prior 

 to the age at which peak growth is attained reduces 

 the mean annual growth realized as well as the 

 total yield recovered. Conversely, if clear cut 

 after the peak, the yield recovered is somewhat 

 less, but for most species the value recovered is 

 higher because of the greater proportion of high- 

 quality wood in older trees than in yoimger ones. 

 However, the relation of age to the volume and 

 volume growth of different quality levels or grades 

 of wood has been insufficiently studied in the 

 United States. Therefore, specific information is 

 unavailable for development of standards including 

 consideration of the growth of quality wood. 



Appraisal of felling age effects upon financial re- 

 turns is another concept not yet implemented with 

 basic information to the extent necessary for wide- 

 spread application. Therefore, felling age was used 

 in this survey to appraise its effects upon growth 

 of wood volume only. 



The discussion of figure 22 has shown how the 

 clear cutting of timber at ages younger than those 

 of peak growth reduces the yield and the growth 

 attained. Such cutting has been termed "pre- 

 mature cutting." If such cutting becomes preva- 

 lent in a county, a State, or an ownership class, the 

 average annual yields of timber harvested there- 

 from are materially lower than if young stands 

 were thinned or partially cut and clear cut only at 

 age of peak growth. The growth attainable by any 

 degree of stocking and composition is likewise re- 

 duced bj'' premature cutting. 



Through use of the specific growth cycle rela- 

 tionships illustrated by example in figure 78 and 

 established for many of our species, factors were 

 derived showing the portion of attainable growth 

 realized by clear cutting at given ages. These 

 factors expressed as decimals of attainable growth 

 were applied to the stocking rating as modified by 

 composition to arrive at a final productivity 

 rating. 



This concept of applying a felling age factor 

 assumes that the prevalence and degree of prema- 

 ture cutting wUl remain the same in the future as 

 at present. Any interpretation of results should 

 recognize that the results of the survey will change 

 to the extent that effects of premature cutting 

 may be more severe or less so in future years. 



In devising standards for evaluating effects of 

 premature cutting, all available information on 

 growth cycles was used. Fortunately, some infor- 

 mation has been accumulated for most of the 

 major species or types. Where not available, the 

 judgment of experienced foresters was called upon 

 to devise standards. In a few cases, this resulted 

 in the substitution of tree diameter for age as a 

 standard for judging felling-age effects. 



Standards were set up for each species or for 

 species groups by site or geographic area within a 

 forest type showing the percentage of the peak 

 growth attained at various ages. These percent- 

 ages express the effects of felling age. In the 

 example presented by figure 78, the felling-age 

 factor for a stand cut at 75 years would be 0.80. 

 Thus these factors estimate the proportion of the 

 attainable growth realized by cutting at given 

 ages. In field application, the ages of stands clear 

 cut were determined by annual ring counts on 

 stumps and the appropriate felling-age factor 

 found by reference to the Criteria. 



Modifications of this general concept were neces- 

 sary in application, and these are summarized 

 below: 



1. Felling-age factors were applied only to re- 

 cently cut lands which were clear cut or to 

 the clear-cut portions of such lands. For 

 purposes of this survey, a clear cutting was 

 defined as one which removed 80 percent or 

 more of the trees that were merchantable 

 for the products harvested and which re- 

 sulted in removal of substantially all of the 

 overstory present before cutting. 



2. A number of situations were recognized 

 where determination of felling-age effects was 

 not appropriate. These occur where stand 

 conditions indicate that the future volume 

 growth will be low compared to that result- 

 ing from, clear cutting and starting a new 

 stand. Examples of this are young stands 

 badly damaged by fire or forest pests; over- 

 mature timber beyond the age of peak growth 

 and where growth will continue to decline; 

 young stands where initial low stocking 

 resulted in limby trees of such poor quality 

 as to create doubt regarding the usefulness 

 of any additional growth. 



There are also a few wood products based 

 on such strict or specialized standards that 

 volume of wood involved is a minor con- 

 sideration. Examples are Christmas trees, 

 poles, piling. Here the greatest usefulness 

 of such trees is reached at a stage in develop- 

 ment when they comply with product 

 standards. Effect of felling age was not de- 

 termined for the relatively limited amount 

 of clear cutting for these products. 



3. The effect of felling age was appraised for the 

 general size class of product removed. Thus 



