70 MEASUREMENT OF WHOLE WOODS. 



2. Estimating by Trees. 



Under this method each tree is estimated separately, the 

 volume of the wood being obtained bj^ adding together the 

 volumes of the several trees. "With great care, an experienced 

 estimator can obtain fairly accurate results, but, if done care- 

 fully, the operation takes almost as much time, as if the 

 diameters of all trees and the height of some of them are 

 measured ; in the latter case, the volume can be calculated by 

 means of form factors or volume tables, a procedure which 

 yields far more reliable results. 



The method is only justified in open woods, consisting chiefly 

 of old trees, such as standards in high forest or in coppice with 

 standards, or where a low degree of accuracy meets the require- 

 ments of the case. In such cases, the estimate may extend 

 over the whole area, or over a sample plot only. 



3. Estimating aceording to the Results of Past Fellings. 



Where fellings have been made and the fall accurately 

 measured, the results can be used to estimate the standing 

 crop in similar woods. In such cases, it is necessary to 

 take into consideration any differences in the age, density of 

 stocking, height, etc. 



Frequently fellings, made in strips clearing for roads or 

 rides, give useful data for estimating the crop of the adjoining 

 woods. In all such cases the estimate is based on the volume 

 per unit of area. 



4. Estimating the Volume by means of Yield Tables. 



In the same way as volume tables of single trees are con- 

 structed, which give the average volume of trees arranged 

 according to diameter, height, form factor and age, so tables 

 can be compiled, on the basis of extensive measurements, 

 which show the volume of whole woods according to species, 

 age, quality of locality, etc. (see Appendix III.). 



