16 BULLETIN 275, U. S. DEPARTMENT OF AGRICULTURE. 



extensive future period." If " condition ' ' is defined as state of health, 

 not only as far as thrift iness of growth is concerned, but also with 

 special regard to degree of merchantability as influenced by decay, 

 the condition factor becomes a subject of pathological study. 



Condition of the timber we hope to raise for the future, in the 

 definition as given above, has a strong bearing on the possible 

 regulation of yield. There can be no sense in figuring cutting 

 cycles or rotation for future generations to follow unless we assume 

 X that our successors will find the area we have cut over covered 

 with a stand not only apparently but really merchantable; in other 

 words, with timber that is not rendered valueless by decay. The 

 most ingenious speculation as to future yield is without any value 

 whatever unless we have some way of figuring how long the steadily 

 increasing but admittedly perishable timber stock can be left in the 

 forest before it is liable to destruction by fungi. 



The most important problem before us, therefore, is the determi- 

 nation in definite values of the condition of timber stock, present and 

 future. 



CONDITION OF TIMBER STOCK. 



The condition of the timber as a factor in regulation may be 

 expressed as the relation of the volume of timber destroyed or rendered 

 unmerchantable by injurious agencies to the ideal volume of merchant- 

 able timber; or, in so far as forest regulation is interested not merely 

 in the present but in the future, as the relation of the mean annual 

 total loss to the mean annual increment. 



It has already been pointed out that the concept of the relation of 

 the mean annual total loss to the mean annual increment is without 

 any value whatsoever as long as both factors are unknown. We are 

 beginning to know in a small way something about the mean annual 

 increment of certain species in certain types of some of the national 

 forests. We are still completely ignorant as to the influence that the 

 only silvicultural act of any importance open to the Forest Service, 

 that is, cutting on timber-sales areas, will have on the increment of 

 the remaining trees. This knowledge will come in due time. The 

 value of the total-loss factor is altogether unknown. In order to 

 attack this problem it is necessary to analyze it, to reduce it to its 

 several components, and to study each in its turn. By synthesis the 

 total loss can then be computed and the true relation to increment 

 determined. 



TOTAL LOSS. 



The analysis of total loss already given shows that its components 

 are known, but not their values. Of all these components the most 

 important, the one that has the strongest bearing on the value of the 

 stock of timber at hand, is loss from decay or heart rot caused by a 

 group of heartwood-destroying fungi. Very young trees are not 



