FOREST TYPES IN CENTRAL ROCKY MOCNTAINS. 



11 



apart, which possibly gives the soil moisture a trifle more than the 

 average value for the slope as a whole. (See PL III, fig. 1.) 



The site represents a somewhat common condition in the yellow 

 pine forests of the region, which, when not too strongly insolated, 

 give way to Douglas fir as a climax, in agreement with, Clements' 

 description (10). Here it appears that the succession may have been 

 arrested by the fire which burned over the whole territory about GO 

 years ago, but on this area merely scarred the mature yellow pine 

 trees. These are now in a decadent condition and somewhat in- 

 fected by mistletoe, which, through its attacks on the yellow pine 

 saplings, seems to be an important factor in hastening succession. 

 In the tally of the trees within a radius of 50 feet of the station center, 

 it will be noted, the Douglas fir does not hold so prominent a place 

 in the younger reproduction as in the class from 2 to 5 inches in dia- 

 meter at breast height. 



Class. 



Yellow 



Douglas 



pine. 



fir. 



20 



6 



15 



7 



4 



9 



17 



3 



Limber 

 pine. 



Reproduction under 4. .5 feet 



Saplings, to 2 inches 



Saplings, 2.1 to 5 inches 



Trees over 5 inches 



The site then is evidently such that the slightest disturbance might 

 cause a swing toward either Douglas fir or yellow pine predominance. 

 The occurrence of considerable aspen (Populus tremuloides) and limber 

 pine is not considered significant. 



All observations have been taken at or in the ground. The equip- 

 ment has been as follows: 



1 and 4 foot soil thermometers, in iron pipes, July 9, 1914, to December 12, 

 1914; March 3, 1915, to March 1, 1916; and May 11, 1917, to September, 1920. 

 1-foot iron pipe replaced by wooden tube, April 26/1918. 



Ground and soil-surface temperatures, May to September, 1920. 



Soil well after Julv, 1914, with soil-moisture samples taken during the open 

 seasons of 1914, 1915, and 1917. 



Evaporimeter, inner-cell, Type 4, February to September, 191S, May, 1919, to 

 September, 1920. 



F.-o: Fremont Canyon spruce. — Elevation, 9,044 feet; aspect, S. 

 20° E.; slope, 10 per cent. Conditions here are very similar to those 

 of Station F-3, except that Station F-5 is in the creek bottom, about 

 10 feet north of the east- west channel. There is no surface stream 

 here, but the underground seepage must be considerable. The soil 

 is alluvial and contains considerable granitic gravel. 



The spruce stand forms only a narrow band along the stream chan- 

 nel and the base of the north slope. Aspen reaches better develop- 

 ment here, perhaps, than anywhere else in the vicinity. The station 

 is practically at the base of a spruce 18 inches in diameter by 70 feet 

 high. (See PL III, fig. 2.) It is strongly shaded except on the 

 southwest, where an artificial opening permits some light to enter. 

 A. natural opening also permits sunlight to reach the ground for an 

 hour or more before noon. 



The equipment and observations have been the same as for the 

 preceding station. 



