8 BULLETIN 11, U. S. DEPARTMENT OF AGRICULTURE. 
usually takes place in spite of any impeding forest floor. On dry 
sites the seedling requires a good deal more light for its develop- 
ment or existence even than on moist to wet situations,, which is 
one of the main reasons for the lack of loblolly reproduction under 
the shade of large trees, where the soil is not moist. For this reason 
lumbering as a rule improves the seed-bed conditions for loblolly pine 
and increases its reproduction, provided seed trees of the species are 
left. The abundance of direct sunhght let in by cutting of the forest 
also causes the impeding forest floor to decompose rapidly, so that the 
roots of the seedlings can more readily reach the soil. Another 
great hindrance to germination and growth of loblolly-pine seed 
which falls after lumbering, in addition to that of a thick undecom- 
posed forest floor, is a luxuriant growth of ground cover and under- 
brush, including hardwood sprouts and seedlings, which in places 
may be so dense as to preclude pine reproduction entirely. 
Seedling Development. 
The growth in height of loblolly seedlings for the first two years is 
slow, but during this period there is vigorous root development. 
Under average conditions seedlings in the open reach a height of from 
2 to 6 inches the first and from 6 to 12 inches the second season. 
After this there sets in a rapid height growth of from 1 to 3 feet a 
year, which continues for from 30 to 50 years before beginning to 
fall off. 
SUSCEPTIBILITY TO INJURY. 
WlXD. 
Loblolly pine is usually windfirni, since -it grows mainly on soils 
conducive to the development of a deep taproot with strong laterals. 
It is only where there is an impenetrable subsoil that it develops a 
shallow, flat root system and is easily wind-thrown. It seldom suffers 
much damage from windbreak, and where broken off will usually 
show that it has first been killed or weakened by fire, insects, or 
fungi. 
Fire. 
The thick bark of loblolly pine gives it unusually good protection 
from damage by surface fires. Table 3 shows the average thickness of 
bark for trees of different diameters and heights 20 to 50 years old, 
which indicates then 1 relative susceptibility to damage. 
