398 AMERICAN FORESTRY 



mother trees, in spite of the grass. (This probably happens chiefly during 

 unusually favorable seasons.) Such trees in turn become the centers of 

 additional groups. The seedlings themselves in each group grow into trees, 

 bear seed, and continue the work of conquering the grass. Each group also 

 continues to spread and so shade out more grass, which favors the starting 

 of still more seedlings. All of this takes an immense amount of time, on 

 account of the slow growth of the existing trees and the difficulty with which 

 new ones get started. 



But, slow as it is, there comes a time when the number of groups has 

 increased sufficiently and each one has so spread out that all of them are 

 in contact with one or more other groups. This is the last stage before the 

 complete return of the forest. Small openings, a few yards in diameter, 

 still occur, but most of the land is now covered with trees. Figure 6 shows 

 a portion of such a stand. Practically all of the trees in the picture have 

 come from the large mother tree, marked ''x." The opening here is only ten 

 paces wide. It is interesting to note the wide variation in size, and so in 

 age, of the different trees. This stage also shows tliat the very small parks 

 are only a result of the breaking up of the large ones. 



Ultimately, of course, all of the small openings are filled up, and the 

 forest cover is reestablished after an interval of hundreds of years. Extensive 

 stands occur at present which have obviously originated in this way. They 

 are extremely uneven, aged, and, though the cover is complete, can still be 

 easily resolved into the original groups with the big mother tree distin- 

 guishable in the center of each one. The very conical form of these mother 

 trees and the numerous, persistent branches that extend clear to the ground 

 prove that they lived a great part of their existence in the open, rather than 

 in such a closed stand as the present one. 



The filling-in process, described above, is further hastened by a seeding 

 in from the side along the edges of the timber that remained uninjured by the 

 fire. 



Fig. 7 shows a narrow arm of a park that is being rapidly filled up from 

 the end and sides. 



III. REPRODUCTION OF SPRUCE UNDER ASPEN. 



Since the seed of the aspen is very much lighter than that of the spruce, 

 it is carried by the wind for longer distances and in large numbers. When 

 such seed falls into a fresh "burn," where grass has not appeared, it produces 

 a dense stand of this inferior wood. If there were such a thing as a portable 

 pulp-mill, however, there ought to be some money even in aspen. 



These stands often cover extensive areas, growing to an average diameter 

 of twelve to sixteen inches and an average height of sixty to seventy feet. 

 Apparently they own the land. But 



Usually the aspen is surrounded by spruce forests. Now spruce can 

 start and grow well under the shade of aspen, but aspen cannot live under 

 spruce. Every year some spruce seed blows into the edges of the aspen stand 

 and starts to grow. In time, the trees thus started also bear seed, which they 

 scatter farther into the ranks of the aspen. (See Fig, 8-) Finally, the spruces 

 and balsams overtop the aspen and kill it with fheir heavy shade. The aspen 

 is also at a disadvantage in being a short-lived species, while the spruce is 

 long-lived. Thus it is that aspen is called a ''temporary" type. The spruce 

 has triumphed again, but in this case does not show the group arrangement 

 that is so characteristic when the park was the first step in the process. 



It was also found that spruce sometimes reproduces without interference 

 from grass and without the aspen stage upon areas near timberline that have 

 been denuded by fire or by snowslides. 



