68 FORESTRY 



rapid methods. It is not uncommon in pine timber for a 

 single man to estimate a half section or 320 acres of land, 

 in a day. 



The method most used by foresters has been to meas- 

 ure the diameters of all trees on a strip four rods wide 

 run on compass courses straight through the forests. This 

 is known as a valuation survey and gives the forester a 

 good opportunity to make a map of the topography and 

 types of timber during the running of the strips. 



Determining the Growth of Stands — Yield Tables. 



While the volume of standing timber may be quite ac- 

 curately measured if time enough is devoted to it, the pre- 

 diction of the growth of a stand is more difficult. The past 

 growth of a single tree is easily studied, but this will not 

 show what a forest or a single stand will produce. The 

 laws of the growth of stands differ from those of single 

 trees, for the number of trees in a stand is constantly dim- 

 inishing with age. The average tree of a 50 year old stand 

 will not be the average at 100 years, but may be crowded 

 into the suppressed class or may even be dead. So the 

 yield of a stand at 100 years of age is best found by meas- 

 uring stands of that age, to find how many trees survive, 

 and their total contents. If stands of all ages can be 

 found, a series of plots is obtained which will show di- 

 rectly in terms of stand per acre, the results that can be ob- 

 tained by growing trees. European yield tables are so con- 

 structed. In America the chief difficulty in obtaining such 

 data is the irregular and poorly stocked condition of our 

 forests. The stands actually present may not be more 

 than half as heavy as the forest is capable of producing 

 owing to damage from fire, and unregulated competition 

 of poor species. Tables of this kind can only be made for 

 even-aged stands composed largely of a single species and 

 are used to predict the yield of plantations and of densely 

 stocked stands. 



