METHODS OF DETERMINING TOLERANCE. PA 
in a young stand touch each other there begins a struggle for exist- 
ence among the individual trees, which finally results in the differen- 
tiation of the stand into dominant and suppressed trees with all the 
intermediate stages. The trees which lag behind their neighbors 
receive less light, their growth is retarded, and they become more and 
more suppressed, until finally they die and thus gradually reduce the 
number of individuals in the stand. The rate at which this process 
takes place depends largely upon the degree of tolerance of the species 
composing the stand. Natural thinning, however, is a very complex 
phenomenon which is conditioned by a number of factors. Although 
light plays an essential part in the process, it has thus far proved im- 
possible to separate fully its influence from that of the other factors 
concerned. 
CONDITION OF REPRODUCTION. 
The condition of the young growth under an older stand as an indi- 
cation of tolerance has the same objections, since the extent to which 
a species can stand suppression is far from being determined exclu- 
sively by its tolerance. This method, however, although entirely 
empirical in character, has accomplished a great deal of good, and is 
one of the most prevalent ways of determining the tolerance of trees 
in this country. 
RELATIVE HEIGHT. 
The relation between the height and the diameter of a tree varies 
with the amount of hght which it receives. Thus a tree in the open 
grows more in thickness, while a tree in a dense stand grows more in 
height. The ratio between the height of a tree and its diameter, ob- 
tained by dividing the total height by the diameter at breastheight 
(expressed in the same unit of length), has been called its relative 
height, and it has been clearly demonstrated by actual measurements 
that 1t depends upon the amount of light received. 
On the basis of such measurements, Medevev (1884), a Russian 
forester, obtained the following maximum and minimum figures of 
relative heights for isolated and suppressed trees: 
Tsolated Suppressed 
trees. trees. 
NEAT steers sea cee SUR SR RMR a Sen ARR EN ULE Ry AC ANEMIA ROU bat AOA ASL 4.9 126.0 
PSION ELG LS ee as a eID CAE COL CM LT Ne ei RR Oo EO EA ce 39.8 130. 0 
1BXS1eYO) Oey AARNet ete aie BON ME RS ON UU AU Aba a ae SUN NSN Rr Uea eds 8 157.5 
Between these extreme figures are included the relative heights of 
trees in all the intermediate degrees of illumination. The more 
shade-enduring a species the lower is the light intensity at which it 
can grow, and consequently the greater the relative height at. which 
it becomes completely suppressed and dies. It is possible, therefore, 
by determining the relative height of a given species to determine 
