SEED CHARACTERISTICS IN CONIFEROUS FORESTS 11 



that, wherever a ravine or spring keeps a south slope moist, seedlings from 

 the species of the north slope are found. 



Different slopes often get about the same amount of precipitation, but 

 there is such a marked difference in the evaporation that the exposed 

 slopes dry out while the north and protected slopes remain moist. 



The effect of site exposure is clearly shown by the following summary 

 table of meteorological data gathered near the Wind River Experiment 

 Station at a station on a south slope, at an elevation of 2,150 feet, one on 

 a north slope at an elevation of 1,750 feet, and one on an intermediate 

 flat at an elevation of 1,150 feet. All stations were in the same watershed 

 and less than one-half mile apart. 



The important features of these results are the marked differences in 

 evaporation during the critical drought period. During August the 

 evaporation from water surface on the south slope was 15.1 inches, while 

 on the north slope it was only 1 . 8 inches, with a corresponding moisture 

 content of the surface soil on the south slope of only 1.0 per cent, while 

 the north slope contained 6.5 per cent. With this extreme dry surface 

 soil on the south slope, there still remained 11.2 per cent of moisture at 

 6 inches deep and 10.4 per cent at 12 inches. This would support plant 

 growth providing a large enough proportion of the absorbing root systems 

 were contained in this layer of soil. 



In the spring of 1913, 100 seed-spots of Douglas fir were sown on each 

 of the sites, south slope, north slope, and flat, and 25 per cent of the spots 

 on each site were protected by cone-shaped wire screens to prevent damage 

 by rodents. 



Three examinations were made. At the end of the season the seed-spots 

 on the south slope had no seedlings, either in protected or unprotected 

 spots, since all that germinated during the season died in the dry part of 

 the summer. On the north slope the protected spots had an average of 

 .69 seedlings per spot, and 44 per cent of the spots contained seedlings, 

 while the unprotected spots averaged .25 seedlings per spot and 22 per 

 cent of the spots had seedlings. On the north slope there was no loss of 

 the total number germinated. On the flat the protected seed-spots averaged 

 2 . 85 seedlings per spot and 88 per cent of the spots had seedlings, while 

 the unprotected spots averaged .31 seedlings per spot and 34 per cent of 

 the spots contained seedlings. The loss of the total germination on the 

 flat was 6 per cent. 



In the spring of 1913, the following species were sown under wire screens 

 on each site: Douglas fir, noble fir, western white pine, and western yellow 

 pine. An area of about 16 square feet was sown to each species, one half 

 of the area being put in as a regular seed-spot and the other half broadcasted 

 without preparing the soil. 



