74 Forestry Quarterly. 



BOTANY AND ZOOLOGY. 



Boulder County, Colorado, extends from 

 Forest Types the continental divide eastward to a dis- 

 in tance of about 12 miles from the base of 



Colorado. the Rocky Mountains. The topography of 



the region from its eastern boundary con- 

 sists of plains ; foot hills, broken by deep canyons, and attaining 

 a height of 7,300 feet; a plateau region rising from the latter 

 elevation to 9,750 feet and the mountain crests and ridges extend- 

 ing at their highest elevations to 13,000 feet. The climate of the 

 region is semi-arid, the average rainfall for 9 years at the base 

 of the mountains being 17 inches. The precipitation was 10 

 inches greater than this on the summit of the range during one 

 of the years (1904) in which the study was made. 



The author, Mr. Robert Young, divides the forests of the 

 region into seven formations and he gives for each the tempera- 

 ture, relative humidity, soil water content measurements, taken 

 during the two summers (1904-1905) of study in the field. Pass- 

 ing by two poplar-willow formations which occur along the 

 banks of streams, one finds that the dry mountain slopes are oc- 

 cupied by three formations, namely, the Finns scopulorum forma- 

 tion extending from the base of the slopes, at an altitude of 5,300 

 feet, to about 7,800 feet ; the Firms murrayana formation, extend- 

 ing from the latter elevation to 12,750 feet; the Finns Hexilis 

 formation extending from 7,300 feet up to timberline. 



The moister slopes and bottoms of the canyons support two 

 formations, the Pseudotsnga mucronata-Picea engelmanni and 

 the Picea en gelmanni- Abies lasiocarpa formations. In the former, 

 Pseudotsuga is far more extensive, P. engelmanni being con- 

 fined to the cool, moist bottoms of the canyons where it forms 

 only a straggling society. Pseudotsuga on the other hand ex- 

 tends up the drier slopes until it meets the pines. The area 

 which this type dominates lies between 5,800 feet and 8,700 feet. 

 The Picea engelmanni- Abies lasiocarpa formation occupies 

 chiefly the canyons, although it may be found on ridges between 

 9,200 feet and the timber line. 



The author does not state his reasons for making P. engel- 

 manni one of the type trees of two formations. It would seem 

 to one reading the text that the presence of the trees in the 



