BASIC PROBLEMS IN FOREST PATHOLOGY 221 



insects, lightning, storms or frost. In other words, the ratio of risk 

 grows with time. The older the tree the greater the cumulative risk. 



It seems quite feasible thus to devise a system of rating for the 

 relative importance of all factors conducive to loss, which will eliminate 

 the vagueness now so prevalent in the literature and will reduce to 

 a minimum the temptation to gauge the seriousness of a disease accord- 

 ing to the interest it presents to the botanist or mycologist. 



The value of such a standardization of data gained from a point 

 of view of forestry and given in definite symbols rather than in 

 descriptive words is evident. Tables of cumulative risk will supple- 

 ment yield tables. Areas of equal rating will naturally be drawn 

 together in broad belts or zones showing at a glance all the competent 

 factors of cumulative risk in the forest. 



In a former paper- the author has proposed to establish broad 

 zones of equal pathological conditions in which the cull per cent per 

 species is given in definite figures. These zones record the past path- 

 ological history of the forest and its present condition. They will be 

 of immediate use for the utilization of privately as well as Government 

 owned timber. At the present time the estimate of cull is mere guess- 

 work. It is impossible to predict with certainty the amount of sound 

 timber a given tract will yield in cutting. The private timber owner 

 and the timber buyer often experience very unpleasant surprises owing 

 to the lack of reliable indications of the cull per cent. The Govern- 

 ment is eually handicapped both in determining in advance the 

 possible yield on a given area and in computing stumpage rates, on 

 account of the uncertainty of this important factor. 



Tables of cumulative risk and zones of equal relative importance 

 of cull factors, on the other hand, are expected to be of assistance to 

 silviculture in any endeavor to influence the future forests by rational 

 management. They will give reliable information regarding all factors 

 of loss to which growing forests are exposed. 



The sanitation of the virgin forest as a first step toward regulation 

 must be based upon standardized ratings. At the present time the 

 attempt is made on Government timber sales to rid a given area at 

 least of the more serious heartwood-destroying fungi, in other words, 

 of those elements which affect the capital of timber in sight. The 

 disease affecting the increment, the future crop, cannot yet be given 

 the attention they will undoubtedly command in the future. Once an 



2 Loc. cit., p. 57. 



