Rothrock.] ±Ji± [March 2, 



There is no species of tree whose rate of growth is independent of 

 environment. In Germany fifty cubic feet of wood is reckoned a large 

 annual production for an acre. In this country there are abundant facts 

 to prove that from one hundred to one hundred and twenty -five cubic 

 feet is not unusual for the same time and on a like area. 



To bring tlie question to a more practical presentation, it is fair to say 

 that the average annual growth of a white oak on our mountain sides is 

 between one-sixteenth of an inch and one-eighth. A tree of the same 

 species growing on the alluvial flats of the lower Delaware or Susque- 

 hanna would show an average year's growth of from one-eiglitli to one- 

 fourth of an inch. The rock chestnut oak on the" rocky side of a moun- 

 tain will probably require from eighty to one hundred years in Pennsyl- 

 vania to attain a diameter of one foot. The same species of tree I have 

 known to reach the same size in forty-five years on better soil. Our 

 common black oak illustrates the same principle in the lifetime of one and 

 the same tree. Thus there are specimens in Centre countj'^ which grew 

 with the average rapidity of the species for, say, forty years and then 

 suddenly ceased to grow and began to die at the top because their roots 

 had reached a bed of limestone just beneath the surface of the soil. So, 

 too, I have in mind specimens of white and scarlet oak, which, under 

 favorable conditions, kept pace in growth with sugar and silver maples 

 near which they were planted. 



A second growth, sprouting from vigorous stumps, develops much more 

 rapidly than the original growth Avhere the roots were smaller in propor- 

 tion to the trunk. This explains the peculiar strength and value for cer- 

 tain mechanical purposes of the second-growth wliite oak in the rich lands 

 of Indiana and Illinois. It is simply an illustration of the statement al- 

 ready made that the larger year's growth made a better lumber than the 

 smaller (in the same species). 



As a rule, we may say that a century will be required to mature wliite 

 pine, hemlock and the hickories. The oaks will require half as much 

 longer time. Chestnut may be regarded as making a fair body of mature 

 wood in seventy-five years. 



V. Obstacles to the Growth of Timber. 



(a) Natural Obstacles. 



These have been in part anticipated by the statements already made. 

 Among these poverty of soil may be regarded as first in importance. 

 This, however, is connected with an induced poverty due to removal of 

 an earlier forest growth whereby on the steeper slopes the soil is washed 

 away more rapidly than it is renewed. Indeed, one philosophical ob- 

 server has stated that if the forests were removed from our Pennsylvania 

 mountains and they allowed, for any considerable time, to remain with- 

 out trees, that reforestation would be practically impossible. Whether 

 this statement is, or is not, true as a scientific principle, it may at least be 



