FOREST PLANTING IX THE LAKE STATES 33 
although on old lines a single light harrowing is sometimes sufficient. 
Where double lines are maintained, clearing the strips of brush annu- 
ally and burning the grass are usually necessary. The annual cost of 
harrowing with a team is $4 to $5 a mile on single lines, and on 
double lines, including harrowing, cutting brush, and burning grass, 
usually $16 to $18 a mile. Eecently on the Huron National Forest 
the use of a tractor, with a heavy disk plow for fire-line construction 
and a heavy T-foot double disk for maintenance, has been found to 
reduce costs below those for the same work with horses, and for 
annual maintenance to the low figure of $5 a mile for double lines. 
Fire publicity work, particularly appeals to campers, automobile 
travelers, fishermen, and hunters, reduces the number of man-caused 
fires. Even though the people in a region are in sympathy with 
the forest fire-protection program and cooperate to the fullest extent 
in fire prevention, a workable local fire plan which will provide for 
prompt decisive action when fires start is always needed. The 
owner of a plantation who has an investment at stake can do much to 
increase the safety of his investment by promoting local sentiment 
and action for better fire protection. 
CLIMATIC CONDITIONS 
Critical weather conditions such as prolonged periods of drought 
and extreme temperatures are so important in certain years that 
they may be responsible for the difference between success and 
failure in a plantation. 
DROUGHT 
A drought period of more than 10 days at the time of planting 
or during the first season following will usually cause heavy losses 
among the planted trees. The sooner the drought period follows 
planting, especially in the spring, the more severe is the loss. From 
a classification of the weather "conditions of the seasons in which 
the different plantations examined were established, it appears that 
the mortality in the most unfavorable years, such as 1916 in southern 
Michigan and 1917 in northern Minnesota, is almost certain to be 
more than 25 per cent and is likely to be more than 50 per cent. 
Apparently the loss is actually as serious when the 'drought follows 
fall planting as it is in the spring, although theoretically spring 
droughts should cause the heavier losses. (Fig. 4.) 
In moist seasons, plantations of jack pine mixed with northern 
white pine resulted in a survival of 31 to 57 per cent of the jack pine 
and 44 to 55 per cent of the white pine. An area planted under sim- 
ilar conditions, except that the trees were put in in the midst of a 
13-day drought in a dry fall, had only 29 per cent of the jack pine 
and 28 per cent of the northern white pine living. Another jack 
pine-northern white pine plantation planted in a dry fall in the 
middle of an 11-day drought had only 30 per cent of the jack pine 
and 34 per cent of the white pine living, as compared with 54 per 
cent and 50 per cent, respectively, in a plantation on the same soil 
where competition and rabbit damage were more severe, but no 
40146°— 29 3 
