100 A Study of the Vegetation of 
In case of a limited but severe burn in the midst of a mixed 
forest, provided a few lodgepole seed-trees are present, the fol- 
lowing generation is usually predominated by the lodgepole pine. 
Provided the various tree seedlings have an equal start, the lodge- 
pole, because of its more rapid height-growth, gains an ascend- 
ency over its neighbors. Likewise, by its habit of early repro- 
duction (I have frequently found trees only seven years old bear- 
ing cones) it furnishes seeds for any unoccupied areas or for the 
entire area if seeds of other trees for any reason fail to be present. 
I have seen a few such areas dominated by lodgepole pine but 
comparatively they are not abundant. 
But because of its early maturity and its inability to reproduce 
in its own shade, in spite of the advantage gained in the middle- 
aged forest, the lodgepole is the first tree to drop out of the 
mature forest. Unless aided by another fire before its competitors 
reproduce, it assumes a less and less important role. Indeed, in 
most of the forests it occurs only as scattered individuals, al- 
though, as previously stated, in areas cut and burned-over thirty 
to fifty years ago the lodgepole pine is not infrequently an im- 
portant tree. 
THE HYDROSERE 
We shall now take up the development of the hydrosere. An 
outline of the vegetational units of this sere together with their 
relation to the xerosere may be found on page 19. Because of 
the peculiar topography of the region, combined with the arid 
climate, hydrophytic and meso-hydrophytic communities are not 
widely represented. However, along the streams and in small 
ponds and lakes, the latter occurring especially in the north- 
western part of the region, the following communities are found. 
The three well marked associes of the water sere showing strik- 
ing changes of habitat and life form as well as definite floristic 
differences, are those dominated by submerged, floating, and 
swamp plants respectively, in their successional sequence. The 
last stage is succeeded by a wet meadow community which is 
usually followed by a consociation of the Agropyron-Festuca 
association but may be replaced by the flood-plain forest associes. 
100 
