;^6 PSYCHE [April 



EFFECTS OF DEFOLIATION BY CATERPILLARS ON 

 TREE GROWTH. 



BY F. H. FOSTER, CLARKMONT, N. H. 



In the year 1897 Clisiocatnpa disstria appeared in parts of Central and 

 Western New Hampshire in great numbers and caused serious damage to forest 

 and shade trees, especially to sugar maples. The insects appeared in still greater 

 numbers in 1898 and 1899, when many trees in the infested districts were com- 

 pletely defoliated. Many old trees were killed outright and others fell into a state 

 of hopeless decrepitude. 



At the request of Mr. W. Y. Fiske of the Entomology Division of the 

 U. S. Department of Agriculture, who at the time of the Clisiocampa outbreak 

 was assistant Entomologist at the New Hampshire Experiment Station, and who 

 spent some time in studying the parasites of this insect, the writer recently pro- 

 cured a section of the trunk of a live sugar maple about eight inches in diameter 

 which disclosed some interesting history. 



The sugar orchard from which this specimen was taken had suffered very 

 severely. Many trees in it have died and been cut up for fuel. 



The last four annular rings in this tree corresponding to the seasons of 

 1900, 1901, 1902 and 1903 were the thickest rings in the tree, averaging one eighth 

 inch making a total increase in diameter for the four years since the abatement 

 of the Clisiocampa pest, of one inch. The rings next preceding, however, corre- 

 sponding to the years of more or less complete defoliation, were thinner than 

 any others in the tree and were somewhat indistinct and confused, suggesting 

 a doubling more or less perfect of the rings in those years. 



This doubling might be the result of a checking of the growth during 

 early summer followed by another period of formation of wood tissue in late 

 summer when the tree had put forth another partial crop of leaves. Allowing 

 two of these rings for a year, the section plainly shows that the amount of wood 

 formed annually during the years of the pest (1897, '98 and '99) was less than 

 half the amount formed in the succeeding years or with two or three exceptions 

 in any of the preceding fifty or more years of the trees' existence. Many trees 

 in this orchard showed damage by borers, but the one examined was selected 

 for its apparent freedom from injury from this cause in order not to have the 

 case complicated by damage from other causes than Clisiocampa disstria. 



