. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 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
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 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
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