ASPEN AS A TEMPORARY FOREST TYPE 301 



jured aspens, thus giving rise to even-aged or two-aged stands. 

 Moderate barriers that would interrupt the continuity of the dense 

 grass, however, would stop them. Thus we find open groups of old 

 conifers on rocky knolls and frequent stands of white fir and Douglas 

 fir on north slopes all through the "permanent" aspen belt. However, 

 it is not intended to convey the idea that the latter are not subject to 

 fires. They have probably not been subject to the recurrent grass 

 fires, but have been burned severely at more infrequent intervals, since 

 on north slopes coniferous reproduction is most vigorous and has much 

 the best chance of eliminating the only moderately tolerant grasses. 



Grazing and protection are the two great factors of the present time 

 which have eliminated the fires and thus broken up the apparent 

 stability of aspen. Everywhere in the presence of seed trees reproduc- 

 tion is rapidly coming in. It is useless to expect the impossible, how- 

 ever, and to find a vigorous invasion of conifers far from seed trees, 

 particularly against the prevailing winds. Thus it is that many 

 areas such as those cited by Fetherolf as typical of the permanent 

 aspen must remain without conifers for a long time yet, for in such 

 places as Joe's Valley on the Manti Forest and Gooseberry Valley on 

 the Fishlake National Forest repeated fires must have run without ob- 

 struction through miles of uninterrupted grass, till not a single conifer 

 has been left. The slowness of the reseeding is evinced by figure 3, 

 which shows the distribution of seedlings under aspen about isolated 

 white fir seed trees (i) in the case of a tree exposed to moderate winds 

 from all directions, and (2) in the case of a tree exposed to strong west 

 winds only. Everywhere within the seeding limits of the trees the re- 

 production is vigorous and ample. On a permanent sample plot located 

 in aspen near a body of white fir and Douglas fir, well below the limits 

 of alpine fir, and therefore in the general "permanent" aspen belt, there 

 are 4,182 seedlings and saplings per acre. On the end farthest from 

 seed trees, about 150 feet distant, they run 2,178 per acre, and on the 

 other and 60 feet distant there are 67.518 ])er acre. As the ability of 

 these conifers to crowd out aspen as a type is undoubted, although in- 

 dividual trees are bound to persist in almost coniferous stand, it is 

 very evident that this aspen is far from j^ermanent. Similar data have 

 been secured in many other places in the aspen stand and all lead to one 

 conclusion : The aspen is essentially temporary, although the seeding 

 in of large areas by conifers is a very slow process. 



As Fetherolf' remarks, a proper knowledge of the permanence of 

 aspen is necessary to the proper management of the type. If from an 



