FOEEST PLANTING IN THE EASTERN UNITED STATES. 15 



T lie presence of dead or dying trees in the stand, a very dense 

 crown cover, or an apparent stagnation in the growth of the living 

 trees indicates that a thinning is needed. The usual practice is to 

 thin when the product is of sufficient size to pay for the operation 

 and to repeat the process thereafter as often as the material has 

 accumulated in sufficient quantity to again pay for the cost. Many 

 plantations, however, need their first thinnhig before they reach this 

 state. Silver maple, black locust, and other species have a decided 

 tendency to grow toward openings in the crown canopy, and in 

 then efforts to reach these the trunks become crooked. Under such 

 conditions a thinning should be made whether the operation will pay 

 for itself or not. The first thinning may be needed by the time the 

 stand is 10 years old. 



As a rule, trees of the least potential value should be the ones 

 removed in a thinning. In the early life of a stand the trees range 

 themselves into several crown classes — dominant, codominant, in- 

 termediate, suppressed, and dead. The dominant trees are the 

 tallest ones, whose crowns receive almost complete sunlight; co- 

 dominant trees are those of slightly less height, with relatively narrow 

 crowns which are not fully exposed to sunlight; intermediate trees 

 are considerably smaller than those of the first two classes, but 

 still healthy, because their crowns continue to occupy open spaces 

 in the canopy; suppressed trees are those hopelessly behind in height 

 growth, and which will eventually be killed by the shade of the other 

 trees. The trees which remain after a thinning should, as a rule, 

 be those which are most vigorous, of the best form, and presumably 

 of the highest final market value. THis does not mean that no 

 codominant or dominant trees should ever be cut, or that no interme- 

 diate and suppressed trees be allowed to remain. High-grade trees 

 must sometimes be cut to obtain the proper opening of the crown 

 canopy, and inferior trees may serve the useful purpose of shading 

 the soil, thus tending to retard evaporation and prevent the growth 

 of harmful vegetation on the forest floor. Except where needed for 

 soil shading, however, suppressed and intermediate trees should 

 generally be thinned in preference to the larger trees of the first two 

 classes. When it can be done cheaply dead trees should be removed 

 in order to rid the stand of material likely to increase the danger 

 from fire. 



The extent to which the crown of a stand may be opened depends 

 largely upon the rate of growth of the species and their demand for 

 light. In general, openings should not be so large that they will not 

 close again within from three to five years by the growth of the remain- 

 ing crowns. Rapid-growing trees, such as Cottonwood or silver maple, 

 should have their crowns opened to a much greater extent than 



