JOURNAL OF AaaCOLHIBAL RESEARCH 
Vol. XXX Washington, D. C., June 1 , 1925 No. 11 
FACTORS AFFECTING REPRODUCTION OF ENGELMANN 
SPRUCE 1 
Bjr \V. C. Lowdermilk 
Northern Rocky Mountain Forest Experiment Station, Forest Service, United States 
Department of Agriculture 
INTRODUCTION 
With the purpose of obtaining much- 
needed information regarding the laws 
governing reproduction of Engelmann 
spruce ( Picea engelmanni ) in the north¬ 
ern Rocky Mountain region, studies 
were undertaken during the summers 
of 1920 and 1921 covering representa¬ 
tive tracts of cut-over and burned-over 
land in the spruce type, as well as 
additional reproducing areas in the 
natural forest. The areas studied were 
located in western Montana, in the 
Blackfeet National Forest. While the 
data obtained must be regarded as 
incomplete in many respects, they are 
of considerable value in view of the 
great lack up to the present time of 
sufficient controlled examinations of 
spruce reproduction, and the far too 
theoretical conceptions of the require¬ 
ments for the establishment of the 
species that have prevailed. Current 
timber sales on the national forests, 
as well as the increase in cutting in 
spruce stands that is now in sight, 
make imperative a more definite under¬ 
standing of these requirements, and 
bring about an urgent demand for 
data that may be made the basis of 
timber marking, slash disposal, and 
selection of logging equipment. As at 
least a partial response to this demand, 
the following data and conclusions are 
submitted. 
SEED PRODUCTION 
Engelmann spruce is a heavy seed 
producer. Good crops of cones are 
produced at intervals of three to four 
years, while in intermediate years in¬ 
dividual trees yield heavy crops of seed. 
The cones are produced in quantities 
at the tops of the tree crowns and in 
the northern Rockies the seed ripens 
about September 15. Southerly or 
northerly exposure will hasten or retard 
ripening about a week. After October 
1, seed begin to shed. 
The number of seeds average 125,000 
per pound for Colorado, 122,400 for 
Utah, and 190,000 for Montana (3-year 
average). In past tests, from 0.8 to 
1.2 pounds of Montana seed have been 
extracted from 1 bushel of cones, or 
at an average rate of 190,000 seeds to 
the bushel. No data are available on 
the number of bushels of cones to the 
acre that a stand of mature trees will 
produce. It is probable, however, that 
not less than 3 or 4 bushels per acre 
are borne by the trees in a good seed 
year. The quantity of seed thus show¬ 
ered upon the forest floor is very great. 
Germination varies widely. Tests 
at the Savenac Nursery, Lolo National 
Forest, Montana, indicate that a ger¬ 
mination of 50 to 60 per cent is possible. 
Nevertheless, spruce seedlings are few 
in number under most natural condi¬ 
tions. Why this should be generally 
true is a question that can be answered 
here in part at least. The answer will 
also serve to indicate the means of ob¬ 
taining reproduction in logged-off areas. 
REPRODUCTION STUDIES 
Many of the factors which influence 
the survival of spruce seedlings are to 
be seen in the life histories of spruce 
stands under natural conditions. Al¬ 
though the course of renewal of such 
stands varies with the zonal position 
in the spruce type, a general uniformity 
of reaction to physical conditions is 
evident. Within the type local varia¬ 
tions occur, due to soil, abrupt slopes, 
or exposure, but these will not affect 
the conclusions for the type generally. 
BURN ED-OVER AREAS-UPPER AETI- 
TUDINAI, ZONE 
A field study of reproduction in the 
upper altitudinal spruce zone was made 
i Received tor publication July 17,1924; issued August, 1925. 
Journal of Agricultural Research, Vol. XXX, No. 11 
Washington, D. C. June 1, 1925 
Key No. F-30 
52243—25t-1 
(995) 
