384 GRrIGGS: EDGE OF FOREST IN ALASKA 
Mr. Snodgrass himself has observed the advance of the spruce on 
the station lands at the head of Kalsin Bay, which is within a few 
miles of the extreme edge of the range. Land which was prairie 
pasture six years ago when he came to Kodiak is now growing up in 
spruce. 
This unstable condition of the edge of the forest has already 
been reported by Fernow* who says: 
“There is some evidence that this western limit is not, or may 
not remain, stable—that the spruce has wandered in recent times 
and may still wander. There is also evidence that the treeless 
country beyond, made up of the Alaska peninsula and the Aleutian 
Islands, is not incapable of growing trees. 
‘An interesting evidence of the progress of the spruce may be 
seen on Long Island, a few miles east of Kadiak, where an extensive 
spruce grove has established itself within the last century. Many 
trees had been freshly cut and a count of the rings showed none 
older than ninety or a hundred years. While on Kadiak and Wood 
Islands the oldest growth was found to be between 125 and 150 
years with some few rotten stumps possibly older. This difference 
in age of entire groves so near together allows the inference that the 
older has furnished seed for the younger and that the spruce has 
wandered from Kadiak to Long Island.”’ 
It might seem a simple matter of arithmetic to determine from 
the data at hand the rate of advance of the spruce forest. This 
however is not the case. The probability is that the advance goes 
by long jumps at considerable intervals of time. Fernow (I. c-) 
pointed out that it is conditioned on the conjunction of a good seed- 
year and a favorable wind, the prevailing winds being adverse. 
The limits of the spruce which he reports are exactly the same as, 
those we observed after an interval of fourteen years. It must 
be clear also that after one step forward, further advance is 
delayed until the trees along the newly established boundary begin 
to fruit and in their turn supply seed for further invasion. Thus 
while it may be that there was no actual advance during this 
fourteen-year period, it is clear from Mr. Snodgrass’s experience 
that the vanguard has been spreading over the newly acquired 
territory and strengthening itself, so to speak, for another move 
forward. 
eta aaah 
anne 
* Fernow, B. E., Ll. ¢. 244. 
