FACTORS INFLUENCING TREE GROWTH. 19 
nant, intermediate, oppressed, and suppressed) for each pound of 
small twigs was as given in Table 4. 
TABLE 4.—Amount of wood produced annually by different classes of trees for 
each pound of small twigs. 
Classes. Good soils. | Poor soils. 
Cu. in Cu. in 
ATO) TNT TATA Ge a ee alee neg rH Day a Ey aaah CN ae i Te Me ep eyed Oo 7 15.8 
(Qroyskosaatih avs wal atte ee veh Bes er yet le oN 5 IE gu Oe I, a Se WOE ee 73.2 20. 4 
AMAT AiG SRT CTE Ga aera ayia Goa ato a Eee dh HUANG ita PU MRR GN gh MLE MolTare AUP ML TS 49.6 16.5 
TOTES SE CL Reese sie et aes rte reece NI SS aS WNC Vara NAL CLES ct 32.8 17.3 
SUL DRESSC Chie ie Ase lea ecec CL Eh pat ee A So OI Uaioe acai ek I Sc PS Spies seen e 
These figures clearly show the influence of soil conditions upon 
the assimilative activity of the leaves, and consequently upon the 
variation in tolerance of trees according to soil fertility. 
AGE, VIGOR, AND ORIGIN OF TREE. 
Trees are more tolerant in early youth than later in life. In fact, 
it may be said that during the first year or two all trees are tolerant. 
As they grow their demands for light increase and the distinctive 
hght requirements of different species become more and more empha- 
sized. This increase in light requirements becomes especially ap- 
parent at the time of the most rapid height growth, after which the 
light requirement remains stationary for a long time and increases 
again only late in life. White pine is a very good example of a tree 
which in early youth is tolerant, but in later life is distinctly intol- 
erant. White pine seedlings will start in dense shade; but can not 
often live under such conditions for more than 10 to 15 years; and 
may perish from lack of hght in the first 2 to 5 years, even if abun- 
dant moisture and nourishment are present. 
The amount of light needed for flowering and fruiting is greater 
than for mere growth, so that demands for light vary not only with 
age, but with season. Thus, early in spring at the time of bursting 
of buds, the minimum light intensity for larch is 1/2 of the total 
daylight, later it falls to 1/5; for beech the minimum light intensity 
at the time of unfolding of buds is 1/4; and later it sinks to 1/60 of 
the total daylight. These differences in light demands are well 
known from common experience. Thus, in a coppice forest it is 
often necessary, in order to awaken the dormant buds of the stumps, 
to clear away the brush around them and expose them to higher 
light intensities. It is a well-known fact that trees in the open 
begin to bear seed earlier than trees in a close stand. Foresters esti- 
mate the average retardation due to close stand at 20 years. The 
preparatory cuttings for natural reproduction under the shelter-wood 
