REPRODUCTION OF WESTERN YELLOW PINE. 51 



nately no figures on the original density of seedlings on stump 

 patches are available. It is a significant fact, however, that on the 

 plots examined in August, 1920, following the dry period of June 

 and first half of July, 78 seedlings were recorded as dead against 

 only 17 living, indicating a loss of 82 per cent, whereas nearby plots 

 in typical bunch grass showed only 44 per cent dead. 



PLANT SUCCESSION IN RELATION TO REPRODUCTION OF WESTERN YELLOW PINE. 



Another phase of the subject, which has been studied only inci- 

 dentally, is plant succession. The most casual observations show 

 that appreciable changes in herbaceous vegetation take place after 

 cutting. The question is. Can any definite laws be established re- 

 garding the association of pine reproduction with stages of plant 

 succession ? 



First, it should be understood that the disturbances brought about 

 by a properly regulated cutting in western yellow pine are much 

 less violent than in the case of a clear cutting, or a moderate cutting 

 in denser stands. Unless natural conditions have been seriously dis- 

 turbed by fire or overgrazing, the herbaceous vegetation in the open- 

 ings, even in a virgin forest, is already in its highest stage of develop- 

 ment; that is, the subclimax stage, regarding the trees as climax stage 

 of the series. Cutting, as practiced by the Forest Service, removes 

 about three-fourths of the volume and somewhat less of the crown 

 canopy. Removal is confined almost entirely to mature and over- 

 mature trees which normally occur in even-aged groups. The great- 

 est changes are in these felled groups, which, after cutting, leave 

 open spaces relatively bare of vegetation, or in some cases occupied 

 by shade-enduring plants belonging to the lower stages of succes- 

 sion. Logging operations also bring about partial or complete de- 

 nudation on small localized areas such as roads and landings. Con- 

 siderable patches are covered by debris, which is sometimes left 

 practically as it falls, sometimes scattered, and sometimes piled and 

 burned. In the first two instances the herbaceous vegetation may 

 suffer a temporary reduction in density, but the composition is not 

 greatly changed. It is only where there has been appreciable dis- 

 turbance of the subclimax association, as on stump patches, burned 

 brush areas, and overgrazed areas, that succession comes into active 

 play. 



Sample plots 3a and 3b have afforded a good opportunity to 

 observe the changes in herbaceous vegetation after cutting, with 

 grazing eliminated. Beginning in 1914, five years after the original 

 establishment of the plots, 20 natural and the same number of de- 

 nuded quadrats were established. Two of each were charted, and 

 complete lists were made of the species on all other plots. Figures 

 7 and 8 show the charts of a natural and a denuded quadrat in 



