GrIGGS: EDGE OF FOREST IN ALASKA 383 
that conditions were unfavorable for growth, and that the trees 
were barely able to maintain themselves. When growing alone 
their shape contrasted strikingly with the familiar slender spires 
seen further east. They were squatty and broad with thick stocky 
trunks (r1G. r) and evidently grew very slowly. They did better 
when growing in clumps but the dependence of the individuals on 
the protection of the clump as a whole was very striking. Regard- 
less of the age of the trees there was a very definite clump-contour 
beyond which no single branch projected. The growth of the 
individual members was evidently conditioned on that of the 
clump. Each tree was kept in exact proportion to its neighbors. 
The trees in the center were the tallest while those near the edges 
were progressively shorter and shorter until those on the edges 
were nearly as much dwarfed as those standing alone. 
Apparently here was what I had looked for in vain in studying 
species on the edges of their ranges in the Sugar Grove area of Ohio,* 
namely a species which had reached the limits imposed by climatic 
conditions so that it could go no further. The climatic extreme in 
this case would appear to be Merriam’s “Effective Temperature 
Factor” which has been positively assigned as the cause by Piper,t 
who says “Undoubtedly this effective temperature factor is the 
principal cause of the sharp demarkation between the timbered 
and timberless regions on the Alaska coast.” 
As far as observation could determine, then, here was a clear- 
cut case of a species which had reached the limits imposed on its 
extension by its adaptability to climatic conditions. But as a 
matter of fact this is not at all the case for the edge of the range of 
the spruce is not held stationary but is advancing rapidly. 
The advance is so rapid that it is evident to persons who have 
lived in Kodiak only a few years. According to Mr. M. D. Snod- 
grass of the Experiment Station all of the old men of Kodiak 
remember when there were but a few trees on Woody Island which 
is now heav ‘ily forested. On Near Island there are large numbers 
of eee trees ee coming in on land that was never eisai before. 
* Griggs, R. F. Observations on the behavior of some species on the edges 
of their —- Bull. Torrey Club 41: 25-49. f. 1-6. 1914. 
t » C. V. The grasslands of aa South Sa ay coast. U.S. Dept. Agr. 
Bur. Pl. gen Bull. 82: 27. 1905 
