LOBLOLLY OR NORTH CAROLINA PINE. 57 



amount of hygroscopic water held by heavy clays which is not available 

 for plant growth. 



Old Field Stands. The old field stands on very sandy uplands and on 

 clay uplands, particularly those on the Piedmont red clays (Cecil soil 

 series) when young fall for the most part into Quality I or Quality II, 

 but their rate of growth declines rapidly after a few decades, some- 

 times before the end of the second decade, and they eventually fall 

 into Quality III. The chief cause for this is that the demands 

 of the stand upon soil moisture soon reach the limits of available 

 supply. Moreover, on the upland clays the top soil in the old cul- 

 tivated fields is at first loose, permitting the roots freely to pene- 

 trate it, and has a high moisture carrying capacity. In a 'few years this 

 soil becomes more compact and its water carrying capacity declines. 

 This checks the growth of the lateral roots and as the taproot descends 

 deeper into the unbroken layer which has never been disturbed by the 

 plow, the rate of growth of the tree declines. 



DETERMINATION OF QUALITY SITES. 



The rate of height growth or the height of dominant trees at a given 

 age in fully stocked groups is the most ready method of ascertaining 

 the quality site when there is growing timber (Table 13). It is de- 

 sirable in the case of middle-aged or old stands to correlate height with 

 volume and basal area per acre (Table 35), relative height, relation of 

 diameter to total height (Table 15). In the case of young stands espe- 

 cially on dry upland sites all of these are unreliable factors for predict- 

 ing the capacity of the soil to sustain old stands and they should be sup- 

 plemented by ascertaining the texture of the soil and depth of water 

 table. The original forest type where indications of it remain should 

 be examined to determine the undershrubs and to compare with Table 1. 

 Abundance of particular undershrubs is a general guide to this extent; 

 a rank growth of gallberry (Ilex glabra] indicates a site highly favor- 

 able for the rapid growth of the pine ; wire grass (Aristida stricta) and 

 low bush black huckleberry (Vaccinium tenellum) indicates sites which 

 are becoming too dry; sphagnam mosses and evergreen fetter bush 

 (Andromeda or Pieris nitida} sites which are becoming too wet. The 

 approximate relation of the height of the water table in different kinds 

 of soil to the quality site for loblolly pine is shown in Figure 3 which 

 gives the results of a preliminary study of these important problems. 

 The impossibility of depending solely upon height at younger ages for 

 interpreting quality site is illustrated in the stand which is presented in 

 Tables 14, 18 and 20, column 4. The rapid diameter and height growth 

 of this stand during the early decades is followed during the fifth 

 decade by an abrupt decline which is reflected by an equally abrupt cul- 

 mination in the volume of the stand. On the other hand, the growth of 

 the trees in column 1 in the same tables shows a slower but sustained 

 rate of height growth, while the. decline does not begin until a much later 

 period. 



