660 



TIMBER RESOURCES FOR AMERICA'S FUTURE 



ings were made according to site quality or other 

 factors that influence them. 



Two examples will indicate the kind of insect 

 and disease data available: Mortality caused by 

 the littleleaf disease in the Southeast came from 

 31 permanent plots in 5 States supplemented by 

 records from 3,552 Forest Survey plots. Reduc- 

 tion in growth rate caused by the littleleaf disease 

 was based on 5-year remeasurements of 565 in- 

 dividually tagged trees in all stages of decline on 

 35 permanent sample plots. Losses from western 

 pine beetle attacks on ponderosa pine in California 

 were obtained from complete inventories on more 

 than 70 sample plots having an aggregate area of 

 over 10,000 acres. Many other examples also 

 might be cited where there was a large volume of 

 data available for growth impact determinations 

 by cause of damage. 



In general, the estimates of mortality by cause, 

 having been accumulated in most parts of the 

 country by the Forest Survey on a large number 

 of field sample plots, are more reliable than the 

 estimates of growth loss by cause. The growth 

 loss statistics represent no more than a first ap- 

 proximation. Neither the methodology nor the 

 field force required for the accumulation of precise 

 data on all types and causes of growth loss were 

 available. Nevertheless, through a State by State 

 appraisal by specialists of each element of gi'owth 

 loss, by causal agency, and by the major tree 

 species involved, there is no doubt that the growth 

 impact data in this report do represent an adequate 

 basis for appraising timber losses over the Nation 

 as a whole. 



PRODUCTIVITY 



The estimates of productivity of recently cut 

 lands are relative rather than absolute. They can 

 be understood and evaluated only in relation to 

 the concepts on which they are based, as explained 

 in the section Productivity of Recently Cut Lands. 

 The productivity criteria, as such, are not subject 

 to sampling or other eiTors. They are the result 

 of the best professional judgment, research, and 

 experience tliat could be brouglit to bear. On the 

 other hand, the productivity data are subject to 

 the possibility of both sampling and nonsampling 

 eiTors. These errors are likely to be minor and the 

 data are believed to be entirely adequate for des- 

 cribing the condition of recently cut lands b}' 

 regions and ownership classes.* 



A Special Study of Productivity Was 

 Made 



The condition of recently cut lands was deter- 

 mined by field examination. Data on small pri- 

 vate ownerships were obtained by examining 



* The adequacy of the ownership data, as distinct from 

 productivity data, is described under Forest Land and 

 Timber Ownership, p. 664. 



sample properties. For medium private owner- 

 ships, sampling procedures were also used in most 

 States having 15 or more such ownerships; in all 

 other States, every medium private ownership 

 was covered by the stud}^ Except for six prop- 

 erties to which access was denied, all large private 

 ownerships were examined in every State but 

 Florida, where they were sampled. Federal, 

 State, and other public ownerships generally were 

 covered 100 percent. 



On both public and large private ownerships 

 organized by working circles, each working circle 

 was treated as an individual ownership and re- 

 ported on separately. Where working circle or- 

 ganization was not used, each block or unit of land 

 in the ownership recognized for administrative 

 purposes was examined separately. 



Field examinations were made b^^ foresters 

 familiar ^\^th the silvicultural requirements and 

 growth characteristics of the local forest types. 

 Group training for field men was provided to in- 

 sure uniform interpretation of criteria used in the 

 ratings. 



The productivity ratings were made with con- 

 sideration of the stand both before and after cut- 

 ting, using the detailed criteria described in Cri- 

 teria for Rating Productivity, page 671. Although 

 the field examinations were made after cutting, the 

 age, composition, stocking, and general thrift of 

 the cut stand were estimated by observing and 

 measuring stumps, tops, and other evidence left on 

 the ground. The rating criteria used were chosen 

 primarily to express directly either existing or 

 prospective stand conditions, rather than inten- 

 tions or actions of owners or economic or other 

 indirect factors which influence stand conditions 

 in varying degrees. 



Four key factors affecting growth were recog- 

 nized: (1) The density of crop trees in the residual 

 growing stock left on the ground after cutting, 

 together with such trees established since cutting, 

 (2) pi'ospective stocking as indicated by numbers 

 and species composition of seed trees or other 

 sources of regeneration and the relative abund- 

 ance of inhibiting or beneficial factors affecting 

 regeneration, (3) the species composition of exist- 

 ing stands, and (4) the effect of the actual felling 

 age on the rate of gi'owth. 



When the ratings for a property having cuttings 

 in several types were summarized, the rating for 

 the recently cut area in a given type was weighted 

 by the acreage of that type in the ownership. The 

 same principle was followed in summarizing the 

 ratings for all properties in a given class of owner- 

 ship or in a region. 



Sampling Procedure Affects 

 Reliability 



In the nationwide field survey made to appraise 

 productivity on recenth' cut lands, the require- 



