228 CLIMAX FORMATIONS OF NORTH AMERICA. 



"4. Many complex conditions of growth are introduced after fire. The 

 species that have seed-bearing trees near the burn will generally be represented 

 in the new forest. 



"5. Repeated burnings at intervals of 10 to 30 years will establish a lodge- 

 pole pine forest where formerly there ejdsted a normal mesophytic forest. 



"6. Repeated burnings at intervals of 5 years or less will destroy all forest 

 growth. 



"7. After the lodgepole forest is once established and the fires are checked, 

 it will slowly be replaced by the species that exist in the normal forests. 



"8. The lodgepole pine is not successful in the bull pine belt." 



Clements (1910) has studied the detailed successional relations of the domi- 

 nants in the coniferous forests of northern Colorado, especially after fire: 



The high mountains exhibit two climaxes, a lower or montane one of Pinua 

 ponderosa and Psevdotsuga, and a higher subalpine one of Picea engelmannii and 

 Abies lasiocarpa. The major portion of these two belts is occupied by lodge- 

 pole pine, Pimis murrayana, which has become a highly typical subclimax in 

 consequence of repeated fires. As a result, the lodgepole subclimax consti- 

 tutes by far the larger portion of the forests of Estes Park. With the increasing 

 control of fiires, however, it is gradually giving way to Pseudotsuga and Piniis 

 in the montane climax, and to Picea and Abies in the subalpine one. 



Humphrey and Weaver (1915:31) have described the subsere produced by 

 fire in the mountains of northern Idaho: 



The pioneers are Funaria and Marchantia, followed by Chamaenerium and 

 Carduus breweri as dominants, together with Erigeron acris, Arnica cordifolia, 

 Antennaria, and Salix. Salix, Physocarpus, Rosa, and Rvbus are the first 

 shrubs. Many seedlings of Thuja, Larix, and Psevdotsuga and a few of Abies 

 had sprung into existence during the second year after the fixe. These repre- 

 sent the subclimax of Pseudotsuga and Larix and the climax of Thuja, while on 

 the drier southern slopes, Pinus ponderosa and Psevdotsuga form the new forest. 



Hofmann (1916) has recently foimd that secondary succession in the burned 

 areas of Washington depends primarily upon the preservation of viable seeds 

 of tree dominants in the soil (of., p. 70). 



Sampson (1908, 1909) has made a detailed experimental study of the effect 

 of overgrazing on mountain communities in Oregon and of the natural process 

 of revegetation. Since this is the first thoroughgoing series of experiments 

 upon the relation between grazing and succession, the author's conclusions 

 (1914 : 146) are given in fuU: 



" (1) Normally the spring growth of forage plants begins in the Hudsonian 

 zone about June 25. For each 1,000 feet decrease in elevation this period 

 comes approximately 7 days earUer. 



"(2) In the Wallowa Mountains the flower stalks are produced approxi- 

 mately between July 15 and August 10, while the seed matures between 

 August 15 and September 1. 



" (3) Even under the most favorable conditions the viability of the seed on 

 summer ranges is relatively low. 



" (4) Removal of the herbage year after year during the early part of the 

 growing season weakens the plants, delays the resumption of growth, advances 

 the time of maturity, and decreases the seed production and the fertiUty of 

 the seed. 



