14 BULLETIN 1059, U. S. DEPARTMENT OE AGRICULTURE. 



to germination and development of the small and very sensitive 

 seedlings. The forester is often concerned only with the problem 

 of " securing reproduction." realizing that, once the seedlings of a 

 given species are established, the future of the stand is quite 

 definitely assured and practically beyond his ability to influence. 

 In forestry particularly, because perennial plants are the subjects of 

 study, the seedling stage presents the most acute practical problems 

 and those most deserving of scientific study. What bearing this 

 has on the methods to be followed in ecological investigations may be 

 readily illustrated. If. for example, it should be noted that seedlings 

 of a given species die in great numbers during their first or second 

 winter and it is desired to determine why such losses occur and 

 whether they are preventable, it might be deemed necessary to study 

 the rate of evaporation and the amount of drying to which such 

 seedlings are subjected during periods when the soil is frozen. Obvi- 

 ously, it would be necessary to determine this period precisely and 

 to know (1) when the soil was frozen throughout the root zone of 

 the seedlings, and (2) when it was frozen at the surface so that 

 moisture obtained below might not reach the aerial portion. On 

 the other hand, the atmospheric stresses and the tendency toward 

 evaporation losses generally might be measured, that is to say. for 

 the locality and at a convenient spot : but it would be apparent that 

 if the seedlings under observation were covered b} T snow the rate 

 of evaporation above that snow layer would have no significance 

 whatever. 



The point, therefore, needs the greatest possible stress that, in the 

 investigation of many of the particular problems of reproduction and 

 distribution of the species, the investigator must be concerned with the 

 immediate conditions of the surface soil and the atmospheric and solar 

 conditions at an elevation barely above the surface soil, in connection 

 with germination, with survival before the seedling becomes well 

 rooted, and with possible injury through heat or drought at the soil's 

 surface before the young stem is protected by an effective corticle. 

 Measurements at depths of even 1 foot in the soil, or at elevations of a 

 foot above it. will usually only be made to give general, comparative 

 indications of the conditions which it is really necessary to under- 

 stand ; and because the rapidly fluctuating conditions of the soil's sur- 

 face are in many ways extremely difficult to cope with. 



In considering the conditions which affect reproduction, an eleva- 

 tion of 6 inches above the surface may possibly be accepted as the 

 lowest level at which aerial measurements are practicable, but by the 

 exercise of ingenuity it should be possible to improve on this. In soil 

 study, greatest attention must be paid to the near-surface conditions. 

 The actual moisture of the covering of litter and humus, as well as 

 that of the first mineral soil, is obviously important, but extremely 



