34 BULLETIN 1437, U. S. DEPARTMENT OF AGRICULTURE 
On the lower slopes of the coast mountains of Washington and Ore- 
gon it usually grows in pure stands of relatively small area, and 
takes possession of burned-over lands which have been slow to re- 
forest with conifers. Here it tends to give way after maturity to 
conifers such as Douglas fir, western hemlock, Sitka spruce, and 
western red cedar, which come up beneath its cover. 
SOIL AND CLIMATIC REQUIREMENTS 
For its best development as a tree or forest type, red alder de- 
mands a deep, fertile, loamy soil, although it will grow in gravel, 
sand, or clay. Abundant soil moisture is a prime requirement of 
this species, and it will prosper in very wet ground but not in bot- 
toms subject to overflow. 
The climate within the range of its best growth is temperate and 
humid, with an annual precipitation that averages more than 40 
inches, and sometimes reaches 100 inches or more. The growing 
season is long, and is free from frosts for four or five months. The 
fact that alder is confined to low elevations indicates that it will not 
endure severe cold and requires mild temperatures. 
LIGHT REQUIREMENTS 
Red alder is below the average in its ability to endure shade when 
compared with its associated broad-leaf trees, with the possible ex- 
ception of black cottonwood. It never grows in deep shade, nor 
casts an extremely dense shadow, and usually requires some side 
light as well as light from above. In mixtures with other species, 
the tree appears to demand a dominant or codominant position in 
the crown canopy. The fact that considerable light is needed sug- 
gests that the largest yields will be obtained in even- aged stands, 
where all the trees are about the same height and all receive direct 
top light (fig. 10). 
SUSCEPTIBILITY TO INJURY 
Up to the time of its maturity, or at about 50 years of age, red 
alder is exceptionally free from all sorts of diseases and injuries. 
Damage to red alder from forest fires is unusual ; in fact, red alder 
serves to protect adjacent conifer stands from fire damage. The 
debris which accumulates under alder stands is not ordinarily in- 
flammable. This, together with the dampness of the ground, consti- 
tutes a fire guard. Only during seasons of exceptional dryness will 
fires run in alder stands. The bark, although thin, is sufficiently 
fire-resistant to protect the tree from light surface fires. 
Until mature red alder is relatively free from serious fungous 
diseases, particularly within its commercial range. A few fungi at- 
tack the leaves ; and one species deforms the scales of the fertile cat- 
kins, but without affecting the fruit itself. A canker disease, which 
kills young trees and the twigs and branches of older trees, is found 
occasionally. The most important disease is white heart rot, caused 
by the false-tinder fungus (Fomes igmarius (L.) Gill.). This 
fungus attacks the wood of both living and dead trees, finally re- 
ducing it to a yellowish-white spongy mass. In the aggregate these 
diseases cause trifling economic loss, if the stands are cut at about 50 
years of age or earlier. 
