900-1 



^ 600- 



H 

 U 

 3 

 Q 



g 300- 



TOTAL 



1 — \ — \ — I \ I r 



8 12 



1 1 



16 



YEARS SINCE CLEARCUTTING 



Figure 1. — Trends in understory production on lodgepole pine aleccrcuts as 



affected by time. 



The concurrent increase in shrub production and decrease in herbaceous plants is 

 attributed to grouse whortleberry (Vaccinium scoparium) which constituted about one-half 

 of the shrub cover on these sites. The roots of grouse whortleberry lie mostly within 

 2 or 3 inches of the soil surface. This soil zone is freer of roots of the other vege- 

 tation than are the deeper zones; also, it is often the sole recipient of moisture from 

 light summer rains. The competitive advantage thus accorded grouse whortleberry enables 

 it to prosper at the expense of the other understory plants. 



Except for scattered individuals of other shrub species, grouse whortleberry 

 is often the sole shrub in older stands of lodgepole, where it often dominates the 

 understory . 



TREE FACTORS 



Tree regeneration variables are highly unstable quantities for a few years after 

 clearcutting ; thus, they are of limited usefulness for predicting yields of understory 

 vegetation. They are of interest, however, because they do affect these yields. 



The general trend of production with time conforms to expectation. As tree cano- 

 pies thicken and root systems expand, understory vegetation succumbs to the increasing 

 competition for light and moisture, as evidenced by the usual paucity of understory 

 plants in overstocked stands of lodgepole pine that are at the sapling-or-older stage 

 of development. 



4 



