CLASSIFYING FOREST SITES 381 



forecasts which, as explained at the beginning of this paper, form the 

 prime object of site classification, yield tables or some kind of forecast 

 tables must, however, be provided. By conforming all yield tables 

 which are made to the various standards and sites provided in a gen- 

 eral height-growth classification system, it will quite likely be possible 

 to reduce the number of yield tables otherwise necessary, since means 

 of evaluation from one species in terms of another may be found 

 practicable. This might, for example, be accomplished through com- 

 parisons of the total basal area per acre. Forecasts are always subject 

 to the uncertainties of the future and so are none too reliable even 

 when based upon yield tables definitely representing the type and site 

 concerned. Such evaluations may therefore come well within a reason- 

 able limit of error. 



' CONCLUSION 



Height growth, like any other criterion of site value based on the 

 actual crop, cannot be used for classifying bare lands. In young 

 stands it must be used cautiously, although in these it may often be the 

 onlv criterion of any use whatever. To balance these shortcomings 

 is the undeniable advantage that it can be used in vmderstocked as 

 well as fully stocked forest, in wild woods as well as in plantations. 

 Being thus widely applicable, it furnishes a medium by which the 

 grow^th potentialities of large areas now covered with irregular forest 

 may be estimated and classified. 



Under the proposed plan, existing and future site classifications for 

 individual species would be co-ordinated into one general scheme. Re- 

 semblances and contrasts would be given a practical bearing. A given 

 forest soil would be judged in terms of the different species dominant: 

 oak as compared with maple, spruce with larch, etc. White pine sites 

 in New England would be placed on a common basis of comparison 

 with white pine sites in Tennessee and Minnesota. Yield tables for 

 different species, based upon the common age-height classification, 

 could be much more readily compared than at present and the pro- 

 ductive capacity of the site thus gauged in terms of each species. All 

 this could be accomplished without an intensive study of the causative 

 factors, -although such studies would by no means be excluded and the 

 site classification could later be enforced or verified by determinations 

 of the physical factors. 



