NATURAL REGENERATION OF DOUGLAS FIR. 39 
fire. Large regions south of Tacoma, Wash., known as the Steila- 
coom Plains, have not been covered with forests for a long time, 
perhaps even centuries. The only apparent reason forests do not 
now cover this region is that young growth has been regularly 
destroyed by fire. The plains were probably frequently burned 
over by the Indians, or possibly the fires were caused by other 
agencies. That the forest was held back by some foreign agency is 
evident from the progress it 1s now making in taking possession of 
these plains. Where the forest is pushing its frontiers out into 
hitherto unoccupied regions an opportunity is afforded to study 
migration. (PI. XIT.) 
These plains are, on the whole, somewhat unfavorable for forest 
growth, but some seedlings become established here and there within 
seeding distance of the forest. The belts of successively younger 
trees as the distance from seed- -producing trees Increases are con- 
clusive evidence that the forest is moving out into the prairie by 
steps. Each belt, representing a forward movement of 3 to 5 and in 
some instances 10 chains, contains age classes from 1 to probably 
20 or 25 years old. The advance seedlings beyond this strip are 
so rare that they can hardly be considered in the migration of the 
forest. It is evident that when these advance strips reach seeding 
age the forest 1s ready to advance another strip of about the same 
width. After trees become established the forest floor soon resem- 
bles that of a typical Douglas fir forest, and forest conditions are 
developed. Where forests of this type have reached maturity and 
have been cut or burned, the succeeding growth is the same as that 
elsewhere in the Douglas fir region. 
This migrating type of forest is in such strong contrast with the 
stands of young growth generally found in the Douglas fir region 
of the Pacific Northwest that it is evident the seed from which the 
stand originated had a different source. The first forest that in- 
vaded this prairie region consists of a very uneven-aged stand con- 
taining trees from 1 to 40 years of age. The second forest following 
in the same region after the mature forest was destroyed is the typical 
even-aged young Douglas fir. 
On areas that have been burned two or three times in other parts 
of the Douglas fir region, this same type of migration has been 
noted, but the variation in ages 1s not so distinct. Scattered seed- 
lings of Douglas fir are frequently found at long distances from 
green timber. Sometimes clumps of young trees appear, and occa- 
sionally slopes are covered with good stands, although no other 
young growth is found in the vicinity. Such young stands or seed- 
lings have been found to come from seed that had its source within 
the area. Sometimes, however, it is not possible to obtain a definite 
record of the conditions through the different fires. The definite 
migration in the prairie region also makes it seem unlikely that the 
young growth appearing here and there in large burned areas origi- 
nated from seed that came from the green timber remaining around 
the edges of the burn. 
Migration in the Steilacoom Plains is a clear demonstration of 
the progress of a Douglas fir forest when it is dependent upon seed- 
ing from adjacent timber. The aridity of these plains reduces the 
number of seedlings; but the proportion of age classes at different 
distances from the timber shows the rate of seeding, as conditions 
