REPKODUCTION OF ENGELMANN SPRUCE AFTER FIRE 397 



As time goes on, one dead tree after another blows over and begins to 

 decay, until the timber is practically all down, as in Figure 2. This is the 

 next step in the process that was begun by the fire. The grass has become 

 still more firmly established, and part of the timber that went earlier has 

 decayed and disappeared. The exposure of the area to the action of sun and 

 wind has made conditions very unfavorable for the moisture loving spruce, 

 so that only a few have gained a foothold near the edges of the "burn." 



After the timber is once down and in contact with the ground, the pro- 

 cesses of decay go on much more rapidly, and in a relatively short time, the 

 area assumes the appearance of that in Figure 3. Most of the timber has 

 gone back to the soil and air from which it came, and what was once a heavy 

 spruce forest has already become a summer home of the cattle, tempted thither 

 by the abundant grass. 



The final decay of the small remaining amount of dead wood leaves a 

 clear, grassy expanse, either dotted with scattered spruces or absolutely 

 treeless, and the park has arrived at completion. (See Fig. 4.) 



Now someone may ask whether some parks at least may not owe their 

 existence to windfall. It is true that large areas of spruce are sometimes 

 blown down, thus forming openings in the woods. But there are several 

 reasons why these areas do not become parks. For the sake of completeness, 

 it may be well to briefly state those reasons here. 



An unusually heavy wind may overthrow all of the timber on a given 

 area, but the destruction is not complete, as in the case of fire, since many 

 of the small trees, most of the seedlings, and the forest floor, or duff, are left 

 unharmed by the wind. The presence of the duff and the shade afforded by 

 the down timber tend to prevent for a time the unfavorable drying out of 

 the soil, so that the seedlings that are left have a chance to readjust them- 

 selves and continue to grow, and seed that blows in from the nearby timber 

 has a better chance to germinate. On account of these conditions, the area is 

 again more or less covered with a young forest before the down timber has 

 had time to disappear. 



Again, most of the parks occur on south slopes, and practically all of 

 them occur on south, east, or west slopes. These exposures are the ones 

 that are most subject to drying-out, so that fire starts most easily on them 

 and also runs more readily after it is once started. Practically all areas that 

 still show evidences of burning-over are also on the same slopes. This 

 strengthens the appearance of a relation between the two. 



A little digging in any park soon reveals charcoal not far below the 

 surface, showing conclusively that fire once passed over the area and found 

 timber to feed upon where there is none at present. 



The circumstances, therefore, seem to point to the conclusion that fire, 

 and fire only, has been the primary cause of parks. 



II. THE FATE OF THE PARK. 



Next comes the question. Does the park, once formed, always remain a 

 park? 



Take the case of such a park as is shown in Fig. 4, where a few spruces 

 have succeeded in starting before the grass came in. On account of their 

 open position, such trees have branches clear to the ground. These branches 

 shade out the grass around the base of the tree and keep the soil relatively 

 moist and loose. Such conditions are favorable to the germination of the 

 seed, some of which the tree is bearing nearly every year. The result is 

 shown in Figure 5. A large number of seedlings of all sizes have grown up 

 around the "mother tree" in the area protected by its branches. 



As these trees continue to bear seed that is carried here and there by the 

 wind, other trees occasionally succeed in starting at some distance from the 



