JACK PINE. 5 
and gravels), and collected in pockets. There are immense areas 
‘barren or valuable only for timber growing. 
Jack pine is distinctly a tree of cold climates. Great variations of - 
temperature take place within its range, and it occurs, for instance, 
where the winter temperature is often 60° F. below zero and the 
summer heat sometimes over 105° F. above. The growing season 
within its range varies from two to four months. 
The heaviest rainfall of the jack-pine belt is in parts of Nova Scotia 
and New Brunswick, where it usually amounts to from 20 to 40 inches 
annually. The precipitation in the western portions of its range 
varies from 14 to 29 inches a year. Although essentially a dry-land 
tree, jack pine demands a climate with a moderate rainfall and 
produces the best stands where the annual precipitation is about 25 
inches. Snowfall is generally abundant throughout its region of 
distribution, and protection is thereby afforded to the ground and 
the young growth. 
FOREST TYPES. 
Jack pine occurs chiefly in the following forest types: (1) In pure 
stands, on what is known as jack-pine land; (2) in mixture with 
Norway pine, on Norway pine land; (3) in mixture with white pine 
and other species, on white pine land; (4) in mixture with poplar 
(aspen); (5) in coniferous swamps and muskegs. The first and the 
last of these forest types occur throughout the range of the species, 
while the second and third are limited to the United States and the 
southern part of Canada. In general, the types in which jack pine 
occurs are relatively transient ones, as this species perpetuates itself in 
nature largely through the accidental agency of fire. (See Pls. ITI, 
IV, and V.) 
JACK PINE LAND. 
Land composed of poor, medium-to-coarse sands or land which is 
impoverished by fire and on which Norway or white pine does not 
readily spring up and thrive is the kind on which pure or nearly pure 
stands of jack pine constitute one of the principal forest types of the 
North. Even on this land, if for a number of years fires are excluded, 
soil and humus conditions improve and jack pine gradually gives way 
to the longer-lived and more persistent Norway pine, or in some cases 
to spruce. In the Lake States this land is usually known as “jack 
pine plain” because of its comparatively flat topography. In 
Canada it is usually known as “‘jack-pine ridge,” although often it is 
only a few feet in elevation above the level of the coniferous swamp or 
muskeg. In the Lake States the “jack pine plain” in many cases 
formerly supported a good growth of Norway or white pine and the 
process of reversion to these species is now going on. On the border 
of the prairie region in Minnesota and Manitoba, ‘‘jack-pine prairies” 
occur which have only a scattering growth of small jack pine trees. 
