16 REFORESTATION ON THE NATIONAL FORESTS. 



also an " off " one for Engelmann spruce, western white pine, and 

 white pine, and comparatively small quantities of these seeds could 

 be obtained. The accompanying maps (figs. 1 and 2) show for west- 

 ern yellow pine and Douglas fir the seed-crop areas in 1909 and 1910. 



The influences which cause a " seed year " for the various species 

 are very widespread in their effect. Climatic conditions during the 

 growing season appear to exert an influence upon the crop of seed 

 produced the next year. A severe drought one year means appar- 

 ently a good seed crop the next. 



In studying the question of seed crops it is impossible not to be 

 impressed with the relationship which exists between the production 

 of tree seed and rodent life in the forest. If western yellow pine, 

 for instance, bore a uniform crop of seed each year, the animals 

 which feed upon this seed might soon become so numerous as to 

 seriously endanger the existence of the tree as a part of the forest. 

 It is only by the production of occasional or periodic crops of seed 

 that conditions are made favorable for the natural reproduction of 

 the tree species. There is reason to believe that the persistent trap- 

 ping of the pine marten, which feeds upon squirrels, has, by permit 

 ting an abnormal increase in the squirrel population, had an appre- 

 ciable effect upon tree reproduction in certain places. 



GATHERING THE SEED. 



The Forest Service itself collects most of the seed of native species 

 needed for the National Forests. This can be done usually for con- 

 siderably less than the seed would cost if purchased from regular 

 collectors or seed dealers. 



Before beginning the actual work of collecting the seed of any 

 species, information regarding the seed crop in various portions of 

 the tree's range is obtained. Knowledge of the relative abundance 

 of cones and the possibility of economically collecting seed in the 

 different localities make it possible to concentrate the work where 

 the best results can be had at the least expense. Small, scattered 

 operations, of course, add greatly to the cost. 



Cones of most of the pines take two years to mature, and a few 

 require three years, so that a crop can often be predicted in ad- 

 vance. The spruces and firs, including Douglas fir, ripen their cones 

 in one season, as do western larch and western red cedar. 



Cones ripen at different times not only in different parts of the 

 tree's range, but even at different altitudes and in different localities 

 in the same region. A careful examination of the cones is necessary 

 in order to determine when collecting should begin. The external 

 appearance of the cone is not a sufficient indication of the condition 

 of the seed, but a number of cones should be cut open and the seeds 

 themselves examined. This can readily be done by cutting off the 



