LIFE HISTOEY OF SHOETLEAF PINE. 39 
stands of pine. Near Womble, on the Arkansas National Forest, 
is such a fully stocked, even-aged stand on a strip averaging approxi- 
mately one-half mile in width by 14 miles in length. The tornado 
occurred on May 8, 1882, and a large amount of the young stand 
dates from the same spring, showing the coincidence of a heavy seed 
crop the previous fall and favorable conditions for germination. 
Damage from ice storms is increased by the effect of wind upon the 
heavily laden trees. Ice or sleet storms cause serious injury at 
varying intervals of 6 to 12 years. An ice storm in December, 1898, 
in southwestern Arkansas uprooted and broke down so many trees 
that it completely blocked road traffic over all of the timbered roads 
for nearly one week. The damage from snow press is relatively 
small. 
Lightning kills trees occasionally and injures very many. The 
secondary injury from winds and lightning is possibly even greater 
than the direct effect, since injurious insects and fungi find their 
chief avenue of attack in freshly opened wounds in the bark and 
cambium, or living layer, of the tree. 
YIELD. 
FACTORS INFLUENCING YIELD. 
The growth of a stand as a whole determines its productiveness or 
yield. First, regions favorable to the greatest volume production 
in the individual tree likewise produce the largest crops or highest 
yields per acre of timber. The yield of well-stocked stands of 
65-year-old shortleaf in central North Carolina is much greater than 
that of stands of similar age and density in New Jersey, and in the 
Arkansas-Louisiana region not less than 20 per cent greater than in 
North Carolina. 1 Second, the number of trees per acre affects directly 
the size and volume production of the individual tree and of the stand, 
and therefore the quality of the yield. Overstocked as well as 
understocked stands decline rapidly in saw-timber production as the 
number of trees departs in either direction from the normal or best 
condition of stocking. The decline in total cubic volume is not so 
great, especially in fully stocked stands. What the conditions are 
in any region can be accurately determined by measuring stands 
similar in all points except the degree of stocking. One nearly always 
finds wide differences occurring in respect to the number of trees per 
acre and the corresponding yields, both within adjacent stands and 
in portions of the same stand. Third, the yield varies with the age of 
the stand. The yield of a stand rises with age to a point of maximum 
production, after which there is a decline due to the progress of 
natural thinning by the loss of trees through declining vigor and 
1 This difference is undoubtedly due to regional differences in the supply of atmospheric and soil moisture, 
temperature, and the physical texture and composition of the soil. 
