THE PACIFIC NORTHWEST 39 



whether one or several, which can grow beneath its own shade. 

 The understories of varying ages are as dense as their light re- 

 quirements and the density of the overwood permit. 



The common hardwood forests of the East illustrate one 

 type of the natural selection forest. On the Pacific slope an 

 example is afforded by hemlock, either practically pure or 

 mixed with white fir, but probably the most typical is the 

 ordinary Western yellow pine under certain conditions. At 

 its best this tree composes a forest so dense that all young 

 growth is shaded out, but everyone is familiar with the fre- 

 quent opener stand containing all ages. The younger trees 

 are often called blackjack. 



EVEN-AGED FORESTS 



On the other hand, trees extremely intolerant of shade 

 occur only in what the forester calls even-aged forests. Being 

 unable to start in the darkness of an existing stand of any 

 considerable density, they must seize opportunities to recover 

 openings. The Douglas fir of the Northwest, more commonly 

 called red or yellow fir, is an excellent illustration. In the 

 interior states this species reproduces under cover to some 

 extent, because there is a stronger light average throughout 

 the year and because the stand is not so dense. In the typical 

 Douglas fir forests of Oregon and "Washington, discussed in 

 this booklet, it never does so. While hemlock, cedar and 

 white fir undergrowth may be abundant, Douglas fir seedlings 

 are seldom seen except in burns, slashings, roads, or open 

 spots in the woods. And the fir trees composing the domi- 

 nant stand are of nearly the same age. 



How, then, did this even-aged fir forest begin? Close 

 scrutiny will practically always find the answer in fragments 

 of charred wood. Long ago another similar forest occupied 

 the ground until lightning or an Indian's fire started a new 

 cycle. Possibly recurring burns swept the area many times 

 before wind-blown seeds began to start advance groups of fir, 

 which, Avhen fifteen or twenty years old, themselves fruited 



