NATURAL HISTORY OF THE FOREST. 159 



having become mere undergrowth. Hence, while 

 on the whole the volume accretion has been in- 

 creasing, there has been also a constant loss by 

 the death of the inferior trees, a loss in volume 

 which is equal to at least 30 to 40 per cent of 

 the final harvest, and which, in part at least, can 

 be saved by timely interference and utilization. 



It is evident that, with the great variety of con- 

 ditions possible, the rate of production of useful 

 wood, i.e. wood of log and bolt size fit for the arts, 

 varies greatly. Yet through painstaking analysis 

 and classification of the collected measurements, it 

 has been possible to construct for each species and 

 site so-called yield tables, which under the premise 

 of a fully stocked stand, i.e. full crown cover, and 

 of proper practice in thinning out the dying trees, 

 record the progress of volume accretion. These 

 tables, then, are standards of measurement, with 

 which the forester can compare his actual forest, to 

 see how far he is away from the possible or normal 

 conditions, and what he may expect to produce 

 in the future. These state, for a given species and 

 given site, usually in periods of ten years, the total 

 amount of wood per acre which will have been 

 produced every ten years, and possibly the differ- 

 ent classes or sizes of wood, stated at least percent- 

 ically, the number of trees to be present, their 

 average height and diameter, and other similar in- 

 formation. For illustration such a table will be 

 found in the Appendix. 



