ASPKX AS A TEMPORARY FORKST TVPK 290 



only attacks trees that were seriously weakened or already dead. Many 

 failures of plantations thus ascribed to "snow fungi" associated with 

 aspen leaves may not be due primarily to this at all. Their ability to 

 attack natural reproduction is negligible in any case. 



In regard to rabbits, conditions are much the same. Damage is un- 

 deniably great, particularly where the conifers are very scattering. 

 Nevertheless, death rarely ensues from this cause. The trees are 

 usually from two to four feet tall and well established during the time 

 of greatest damage, and although the leader is removed year after 

 year, the tree does not die, but spreads laterally and finally escapes and 

 makes rapid development. On a permanent sample plot recently es- 

 tablished, practically every white fir seedling about two feet in height 

 showed rabbit injury, yet not a dead tree was found on the area. Rab- 

 bit injury to plantations is very frequent and heavy. Nevertheless, a 

 study of the rabbit damage on the yellow pine planting of 191 5 showed 

 59 per cent of the uninjured trees living, against 55 per cent of the trees 

 •damaged by rabbits — an insignificant difference of 4 per cent. It ap- 

 pears, therefore, that as a cause of mortality, rabbits are not very 

 powerful. At most they could only be recognized as slowing down 

 the succession and thus making the subclimax stage somewhat more 

 persistent. 



Accordingly, therefore, there is no evidence that aspen, either of 

 itself or by means of associated fungi and biotic factors ,is able in any 

 case to withstand an invasion by white fir or Douglas fir in the so- 

 called "permanent" aspen belt. 



If aspen is to be regarded as temporary its present prominence in 

 such pure stands over large areas must be accounted for by repeated 

 fires in the past, which have eliminated the conifers, but have favored 

 the aspen, which reproduces by sprouts. The point which has been 

 raised in defense of permanence, that aspen is negligible as a type in 

 the forests of Idaho, where fires are as frequent as they are in the 

 Great Basin forests, and therefore that its permanent aspects in the 

 Great Basin are independent of fire agencies, does not take into ac- 

 count the fact that the Idaho forests are within the range of lodgepole 

 ])ine, which replaces aspen there, since it holds a similar ecological ]iosi- 

 tion in relation to fires. 



The fact that the fires have been very numerous in Great Basin aspen 

 stands in the past may be definitely proven. Charcoal is abundant in 

 every soil under a.spen cover; sometimes it is from conifers, but usually 

 from aspen. Kven-aged stands arc frequent. Striking two-aged stands 



