8HORTLEAF PINE IN VIRGINIA 13 



Protection of stands from fire, from insects, and from fungus 

 diseases is necessary to insure fully stocked stands and sound 

 timber. 



The figures relating to the growth and yield of shortleaf pine 

 are based on stands which are growing on soil formerly covered 

 with forests of shortleaf pine mixed with white oak, southern red 

 oak (Quercus digitata), black oak, and white hickory. The rate 

 of growth on such sites is regarded as the average or usual rate. 

 Where the pine now grows on soils which were formerly covered with 

 forests of shortleaf pine mixed with post oak, with black-jack oak, 

 or with Spanish oak (Quercus coccinea), or with a large propor- 

 tion of these oaks together with other oaks, the rate of growth and 

 the yield of the stands will be considerably lower than that given. 



FULLY STOCKED AND CROWDED STANDS 



A stand is fully stocked when it contains all the well-grown, 

 vigorous trees which the soil can support. This number decreases 

 with the age of the stand and the consequent increase in the size 

 of the trees. In a natural twenty-year-old stand of shortleaf pine 

 the number to the acre should exceed 1,500; at forty years it has 

 decreased to about 750 ; at sixty years it has fallen to less than 450. 

 This reduction of the number of trees in a stand progresses nat- 

 urally. As the trees become older and larger, their crowns spread 

 and their roots extend in search of food and moisture. Competi- 

 tion for light, food and moisture ensues, and this in turn results in 

 the dying of the smaller and weaker trees, which are overtopped 

 and crowded out by the more vigorous ones. 



A fully-stocked stand, in which natural thinning is taking place 

 rapidly, is crowded (plates I, II and IV). At any age the fact 

 that a stand is crowded is indicated by a close crown cover and the 

 presence of many dead trees and slender live trees with narrow 

 crowns. In a young stand of this character less than thirty-five 

 years old the crowding is so great that the crown of each tree al- 

 most touches the crowns of its neighbors and direct sunlight hardly 

 reaches the soil. The shade is sufficient to prevent the start of 

 young trees and most shrubs beneath the pines and the carpet of 

 pine needles is so thick as to exclude grass, while small dead trees 

 are numerous. In stands more than thirty-five or forty years old 

 there is a wider distance between adjacent crowns, due to the rapid 

 dying of the larger of the slender narrow-crowned trees. This 

 opening of the stand admits more sunlight, and young oaks, hick- 



