LIFE HISTORY OF SHORTLEAF PINE. 



15 



mately the same as the height of the marginal trees. Incidentally 

 this close response in growth to varying degrees of light makes short- 

 leaf a good recorder of unusual climatic or other events which strik- 

 ingly alter existing light relations. Typical examples of this are 

 given on page 32, under the discussion of recovery after suppression. 

 Because of its inherently narrow crown and medium light require- 

 ments, the density of shortleaf stands remains high to a relatively 

 advanced age. So many factors enter into the problem that it is 

 impossible to determine the absolute position of shortleaf in the scale 

 of light requirements without a much greater number of exact meas- 

 urements. To compare it, however, with other southern pines, under 

 similar conditions of soil, heat, moisture, and age, shortleaf through- 

 out life requires less light for development than longleaf , does not in 

 early life tolerate shade so well as loblolly, but retains longer the 



Fig. 5. — Effect of light supply upon height growth, shown by a vertical section through a 2-year-old short- 

 leaf stand. Fully stocked, even-aged shortleaf stand, 11 years old and 22 feet high. (Drawn from actual 

 stand.) 



power of growth under limited light supply, showing this retention of 

 power by a relatively later and slower decrease in tree density. 



NATURAL THINNING AND STAND DENSITY. 



The dependence of shortleaf on a full supply of light in early life is 

 seen in the rapid reduction of very high tree density in natural 

 unthinned stands. A square rod of 8-year-old saplings, encroaching 

 upon a cotton field in Nevada County, Ark., contained a stand of 

 about 58,000 per acre. At 10 years, as many as 25,000 to 40,000 trees 

 per acre over limited areas are not uncommon. At 20 years the 

 normal stand contains from 900 to 1,200 trees. 



In fully stocked stands natural thinning progresses very rapidly 

 during the first decade and at an increasingly slower rate during the 

 following 20 to 30 years. After this period the loss of trees is very 

 noticeably gradual for the remainder of life. Natural thinning is 

 most rapid and culminates earliest hi the best quality of situations 

 both from a regional and local standpoint. In the central Mississippi 



