Often it is the only tree found in such places. It reproduces itself freely from root suckers as well as from stump sprouts.
The earliest extensive plantings for checking erosion are to be found in the brown or loessial silt loam soils over western Tennessee. Since 1914, in cooperation with landowners, the State forest service has assisted in the reforesting of several thousand acres. These landowners became demonstrators in stopping soil washing and gullying.
The approval in 1933 of an extensive Federal flood-control project in the central Mississippi River Basin by means of revegetating eroding lands started the planting of black locust on a vast scale (fig. 4). Later the expanding soil conservation program greatly increased the use of trees for checking soil erosion.
GROWTH
The rate of growth of black locust varies widely in different soils and climates in the United States, ranging all the way from extremely fast to very slow. Much depends also upon the spacing or tree density on the ground. Open-spaced trees grow more rapidly in diameter than closely grown trees. Where the soil and climate are favorable the growth should average from 2 to 4 feet in height a year and from one-quarter to one-half inch a year in diameter after the first few years.
Under such conditions it grows rapidly and yields fence posts in 10 to 20 years. In poor, very acid, or dense soils, including subsoils in borrow pits and on badly eroding slopes where locust often spreads naturally, growth is usually slow. Slightly acid soils seem favorable. In good soils, especially deep loamy soils, early growth is sometimes phenomenally rapid, up to 10 feet a year (fig. 5).
In well-spaced stands on average-quality soil within the region of fair to good growth, the trees may be expected at 15 years of age to reach average heights of 20 to 30 feet and diameters (outside the bark at breast height) of 3 to 5 inches; and at 20 years, diameters of 4 to 7 inches. In overcrowded stands or in poor locations the trees may be expected to be smaller, while in favorable situations they will usually be even larger.
In any situation black locust is a tree that reaches commercial maturity comparatively early; it should be cut usually before it is 25 to 30 years old. Under unfavorable conditions trees and stands after reaching an age of 15 to 20 years are often injured badly by insects and by heart rot diseases or fungi. Trees live for 40 or more years, in good soil and favorable regions, before showing signs of old age.
One of the essentials of good soil for growing locust is the presence of nitrifying bacteria, as indicated by the abundance of nodules on the roots. These bacteria seem to have a direct bearing on the growth and therefore the extent of attack by the locust borer. In places where the roots show relatively few nodules, the insect infectation is more serious than in places where the root nodules are abundant. Additional information about growth and insect attack is needed for different regions.
