REPRODUCTION OF WESTERN YELLOW PINE. 39 



PROTECTION VS. COMPETITION. 



That herbaceous vegetation must exercise an important influence 

 upon forest reproduction is self-evident. On the one hand, there is 

 competition for moisture and light, in which young seedings may be 

 assumed to be handicapped in the struggle with their older neigh- 

 bors, particularly the grasses. On the other hand, this vegetation 

 affords protection against excessive insolation, wind, frost, and other 

 adverse physical conditions. What the net results of these opposing 

 influences might be has* for several years been a matter of conjec- 

 ture. Studies during the past two years have furnished consider- 

 able new data on this subject. 



Sample plots 3a and 3b, fenced against all grazing animals for 

 over 10 years, show that competition with grasses is less disastrous 

 to yellow-pine seedlings than might be expected. Although the grass 

 has no doubt retarded the rate of progress, reproduction is proceed- 

 ing steadily, as shown by Table 2. On portions of these plots, the 

 bunch grasses, Festuca arizonica, Muhlenbergia montana, and Ble- 

 pharoneuron tricholepsis, grow 2 or 3 feet high and probably have 

 attained the maximum densit} 7 which the soil and climatic conditions 

 will permit. In the densest grass areas reproduction appears to be 

 strongly handicapped, but even here a few seedlings have succeeded 

 in establishing themselves. In moderately dense grass, where about 

 half the ground surface is covered, progress has been very encour- 

 aging. Although some seedlings are unquestionably shaded out, the 

 consequences of shade are not on the whole really serious. Root 

 competition is the vital factor. The critical time during the first 

 season is in September, after the summer rains have ceased and the 

 grasses still make heavy demands upon moisture. If the summer 

 rains are light and of short duration, the seedling loss is likely to 

 be heavy. If, as in 1919, the soil is well supplied with moisture 

 through the growing season and well into the fall, competition for 

 moisture is not severe. Early frosts that stop the activity of her- 

 baceous plants also retard the depletion of soil moisture. In the 

 summer of 1919 great numbers of seedlings sprang up in the densest 

 herbaceous cover. Some were killed or injured by shade, particu- 

 larly under leafy plants such as lupine and vetch, but there was no 

 evidence of injury by drought, and on the whole the survival was 

 good. 



GERMINATION AND EARLY SURVIVAL FAVORED BY HERBACEOUS COVER. 



Denudation by cultivation. — In 1914, thirty-four 5 by 10 foot plots 

 on sample plots 1b, 3a, and 3b were cultivated to a depth of 6 to 8 

 inches with a mattock, and cleared of all vegetation, including roots, 

 as far as possible. Parallel to each of these plots and separated by 



