678 RYDBERG: PHYTOGEOGRAPHICAL NOTES 
Different authors have fixed the timber line differently, as for 
instance: 
1. At the forest line; i. e., where the continuous forest stops. 
2. At the grove line; i. e., where the trees cease to form com- 
munities of larger or smaller size. 
3. At the tree line; i. e., where the arboreal species cease to 
form trees. 
4. The absolute timber line: i. e., where these species disappear 
altogether, even as krumholz. 
To me it seems superfluous to consider more than two of these 
“lines,” viz. the ‘forest line” and the ‘‘absolute timber line,” 
which may be called the Lower and the Upper Timber Lines. 
But to fix the limit between the alpine region and the subalpine 
region at either of the two would be erroneous in certain respects. 
The region between these two timber lines is a transition zone 
between the two, or it may be still better called a zone of strife. A 
continuous warfare goes on between the forest and the alpine grass- 
land. A seed from the forest succeeds in germinating between the 
low alpine plants. A tree grows up. The alpine plants are 
smothered in the shade. More tree seeds have a chance to germi- 
nate and a grove is formed and the forest region is carried upwards. 
On the other hand, snow and wind kill the trees on the edge 
of the forest or the grove, the shade is gone and the alpine plants 
soon take possession. But more on this subject below. 
The width of this transition zone or zone of strife depends on 
many factors. In one place the forest meets a steep cliff and stops 
abruptly. In such places there is no transition zone. In other 
places the lower timber line has been pushed down by a ledge of 
snow thick enough to last the larger part of the summer and having 
the power of smothering the trees, but not the herbaceous alpine 
vegetation. Still above the lower timber line at these places, 
there might be found isolated trees or groves of trees a thousand 
feet higher up, especially on higher ground, where the snow has 
not been so deep. In other places the lower timber line might have 
been pushed down by wind, not so much by its mechanical force as 
by its desiccating effects. 
In treating the alpine region, I would be inclined to place the 
boundary at the lower timber line, i. e., the forest line, so as to 
