A Comparison of Yields. 507 



water in the soil, the shorter growing season and the low temper- 

 attire hinder the processes of decay and favor the accumulation 

 of humus in the soil. This has a favorable effect upon the chem- 

 ical and physical composition of soils. 



It may be urged in opposition to the facts so far presented 

 that the data are inadequate. It is true that there are few ade- 

 quate yield figures for hardwoods in the different regions. How- 

 ever, comparison of such figures as are available corroborates 

 the evidence furnished by the softwood and poplar yield tables. 

 The dense stands of spruce on the high mountains of the South- 

 ern Appalachians may be cited as instances of heavy volume pro- 

 duction in the Southern Appalachians. These stands, however, 

 are growing under conditions which are very similar to condi- 

 tions in the northeast. The growing season is short, the precipi- 

 tation is heavy and evaporation and transpiration are reduced 

 to a minimum, but even then the stands are not as dense as in the 

 northeast. 



Further investigation will, of course, be needed to determine 

 the real causes of the apparently greater volume production in 

 the northeast than in the southeast. Yield tables for the same 

 species in both sections would be the best data. Furthermore, 

 dense tree stands wherever they may occur should be mvestigated. 

 This would include the luxuriant growths of some types of trop- 

 ical forests and the hea\7' stands found in Washington, Oregon 

 and British Columbia. 



COMPARISON OF CLIMATES. 

 (U. S. Weather Bureau Records.) 



