Figure 23. — Dousing a peal fire wil/i water. In recent ^rars, because prevention and protection hare been stepped up, Jorest fires are no longer the 

 leading cause of timber mortality in Minnesota. Windstorms and disease now destroy more merchantable timber than fire does in a typical year 

 (Photo courtesy Minnesota Conservation Department) . 



Currenl Croivlh Alainly On Small Trees 



Although sawdmber growth increased considerably 

 between 1936 and 1953, it is significant that the bulk 

 of this growth is on trees of very small diameter. 

 Approximately two-thirds of the total consists of 

 "ingrowth,"' i. c., board-foot volume credited to trees 

 that pass from poletimber-size to minimum sawtimber- 

 size (9 inches d. b. h. for softwoods, 11 inches d. b. h. 

 for hardwoods). The other one-third of growth is 

 spread over larger trees. Probably less than 3 percent 

 accumulates on trees 20 inches or larger d. b. h. 



In poletimber stands likewise, the greater part of 

 the growth is "ingrowth" into the 6-inch diameter 

 class. 



Before the forests can \ield in reasonably large 

 quantities the sizes and grades of logs and bolts pre- 



ferred by industries, it will be nccesSciiA lo Iniilcl up 

 the growing stock. 



(jruuili Cdiilaitis Toa Lillle Softwood 



Eight million acres of Minnesota forest lands are 

 well adapted to the |)roduction of softwood limber, 

 but only AVo million acres are occupied by softwood 

 types at present. \Vith reasonable protection and 

 care, the existing stands and areas that will restock 

 naturally may produce 30 percent more softwood 

 growth by 1975 and, with a modest planting program, 

 can yield at least twice as much eventualK . 



Quality of Hardwood Growth jXeeds Ittijnovcnicnl 



\\'\\h such a large share of the growth accumulating 

 on trees of .small size and on trees of iiilcrior quality. 



22 



Forest Resource Report No. 13, U. S. Department of Agriculture 



