FOREST BIOLOGY 



By p. S. Lovejoy 



Assistant Professor of Forestry, University of Michigan 



About fifty years ago there were some billions of feet of good 

 tamarack standing on some millions of acres through the Lake States 

 and the Northeast. The tamarack saw-fly has practically eliminated 

 the species as a forest tree. The insect is a native and there is no 

 reason to suppose but that it was present and did more or less damage 

 to the tamarack for untold years. But it increased tremendously 

 within a decade or so and the tamarack seems to have been eliminated 

 from commercial consideration throughout its eastern range. It is 

 known to attack Larix of several species and no Larix is known to 

 be at all immune. Perhaps it will appear before long in the Montana- 

 Idaho country and repeat its performance on the western larch. 

 Perhaps it is at present in the Rockies. Is there any species of Larix 

 that can be considered at all safe in America? It is a very valuable 

 species. Its loss is a serious matter. 



Through all the western yellow pine region, the great majority 

 of "over-mature" trees are actually killed by the work of Den- 

 droctonus, even though they might be expected to succumb from other 

 causes within a few years if the insect did not make its attack. About 

 twenty years ago, in the Black Hills, the Dendroctonus became 

 unusually active. It attacked not only the very old and injured indi- 

 viduals, but spread generally through the stand, killing practically 

 everything from the small pole stage up, even though it seemed to 

 "show a preference" for the older trees. Of late years this heavy 

 infestion has appeared to be stationary or to be on the decrease. 

 Hundreds of millions of feet of good pine has been killed and large 

 areas have been practically denuded. In many other regions the beetle 

 is very active and is sufificiently damaging to have warranted large 

 expenditures in its attempted control. In still other places, where 

 stumpage values or the character of the stands do not warrant it, the 

 beetle is at work unchecked. New areas of infestion are reported 

 annually. The future of the exclusively yellow-pine Black Hills 

 forest is certainly in doubt. If the Black Hills experience is to be 

 duplicated in other pure western yellow pine stands, or if the con- 

 ditions now reported are to be accepted as "normal," is a forest of 

 this species of pine a safe forest? 



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