ASPEN REPRODUCTION AND MANAGEMENT 395 



The 70-year-old stand was located on a flat in the middle of the 

 aspen zone where development is most rapid and the stands are at 

 their best. The 90-year-old stand was on a southwest exposure, at 

 nearly the lower altitudinal limits of the species, while the iio-year-old 

 stand was on a southwest exposure above the optimum range of aspen. 

 Moreover, two of the stands were not strictly even-aged, the 90-year 

 and iio-year-old stands having understories of younger trees which 

 reduced the average diameters on these stands very markedly. The 

 only thing of importance brought out in the above table is that the 

 sprout reproduction of aspen is very heavy at all ages at which it is 

 merchantable and on all sites. If the sprouts are cut or are grazed off 

 annually, however, there is no opportunity for the further accumula- 

 tion of food materials in the roots, and the stores laid up by the parent 

 stand become diminished and finally exhausted, so that sprouting 

 ceases. If the sprouts are destroyed each year for three years, as 

 shown on sprout areas at the Experiment Station which were grazed 

 by sheep, the roots are no longer able to respond and sprouting en- 

 tirely ceases. 



Sprouting in Virgin Stands 



When it is considered that any injury to the shallow aspen roots 

 stimulates them into immediate activity, it is rather surprising that 

 there are not more aspen sprouts under the parent stands, especially 

 where grazing is heavy and trampling has injured many roots. Care- 

 ful examinations beneath representative aspen stands show that there 

 is a continuous and fairly dense reproduction by sprouts every year; 

 but these sprouts are very weak and seldom reach a greater height 

 than a few inches, after which they die of suppression, as they are 

 very intolerant. A few beneath openings in the canopy manage to sur- 

 vive and grow into small, crooked trees. The relation of sprouts to 

 light is shown approximately by the following data gathered from t6 

 permanent sample plots and thinned areas, in uniform stands aver- 

 aging from 3 to 7 inches in diameter : 



Since the intensity of cutting, age of stand, and site, as well as light, 

 have also affected the sprouting on these plots, the table is only indie- 



