LIFE HISTORY OF SHORTLEAF 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. 



