Pa ea 
m SIOLOGICAL FOUCRNAL. 
Vot. II. APRIL, 1892. No: 1." 
“FORMS OF TREES AS DETERMINED BY CLIMATIC 
| INFLUENCES. 7 
BY GUSTAV EISEN. 
A traveler from the Arctics or from the high wooded mountains, 
in any district of the world, cannot but be impressed by the differ- _ 
ent forms which trees and shrubs assume in the respective regions. — 
Nowhere is this difference in form more striking than between | 
the trees inhabiting the pine region of Sierra Nevada and those 
which grow on the lower plains in the interior valleys. 2 
_ We have so constantly been accustomed to take things as they | 
are, without inquiring into the causes why they are so, that it seems _ 
to us quite natural that the forms of trees of the high mountain 
should be different from those of the lowlands and valleys. Sti 
this difference is so great and so very apparent that the causes which 
perate in making up these different forms must be very great 
very important ones. 
In the high Sierras, for instance, in that region Helow te sno’ 
e, where the pines and spruces dominate, we find that almo 
every shrub and every tree resembles the other in a general wa 
The trees are tall and erect, with a central undivided trunk from 
which the branches slope down towards the ground. The shrubs 
again, are low and depressed, spreading out horizontally, form 
ing dishlike masses, hugging the ground instead of seeking the 
sky. A few thousand feet further down in the region where th 
evergreen pines and spruces have ceased, the trees as well as th 
shrubs begin to assume a different aspect. The trees in this region 
are not so erect, their branches are less sloping, their crowns extend 
urther, the trunks are often branching; there is, in fact, a decided 
difference in their general form. The shrubs, again, are more erect 
and bushy, forming often dense Pee, which show little or 
pency. to flatten out. © 
