276 CLARENCE F. KORSTIAN 



solepis, Q. undulata, and Cercocarpus breviflorus, while western yel- 

 low pine predominates on the more gradual slopes which are more 

 retentive of soil moisture. In the more protected and more 

 moist situations, such as canon bottoms and north slopes at the 

 higher elevations, Pseudotsuga taxifolia, Abies concolor, Pinus 

 fiexilis, Picea engelmanni, P. parryana, and Populus tremuloides 

 are found. Western yellow pine occupies the more gradual slopes 

 and situations at the intermediate elevations. A rather erratic 

 altitudinal distribution of the species is evident in the San Mateo 

 Mountains. At the elevation of the plots, which is approximately 

 8000 feet above sea level the cafion bottoms, north slopes and 

 lower south slopes are occupied by an almost pure stand of 

 western yellow pine which is typical of the San Mateo Moun- 

 tains, while a belt of the more xerophytic species is frequently 

 found on the more exposed upper south slopes above the western 

 yellow pine. 



The plots were established in 1910 with the principal object 

 of determining the rate of growth and decadence of western 

 yellow pine in this locality. They are located in the cafion bot- 

 toms and on the slopes, the gradients of which vary from 3 to 

 50%. Prior to the establishment of the plots the area had been 

 cut-over, removing many of the mature and over-mature trees 

 and a large proportion of the merchantable material. A modi- 

 fied selection system of cutting to a variable diameter limit was 

 followed when the timber was marked. Occasionally large 

 merchantable trees were reserved as seed or fire insurance trees 

 or to maintain the general continuity of the forest cover. When 

 the plots were established in 1910, the diameters and total 

 heights of all trees 3.6 inches or more in diameter at 4.5 feet 

 above the ground were measured. Each tree was described, 

 especially with reference to its vigor, health or decadence, its 

 crown class and all diseases, defects or abnormalities were noted. 

 The plots were remeasured and examined in 1915, thus giving 

 their history for the intervening five-year period. 



Two well-recognized forms of Pinus ponderosa are distin- 

 guished, "black jack" and "yellow pine," based on age, rate 

 of growth, and the resulting color of the bark. The term "black 



