54 
The Colorado Experiment Station 
Pig. 2 0.—Above Pagosa Springs. Yellow pines dominate the sur¬ 
rounding hills; scattered yellow pines in a field of timothy. Alfalfa, small 
grain and potatoes grown in vicinity. 
cal distribution varies considerably; sometimes it goes as low as 
7,500, and as high as 11,000 feet. 
The chief tree-associates of lodgepole pine are the aspen 
(. Populus tremuloides) , Douglas fir at its lower limit, and Engel- 
mann spruce at its upper limit. The narrow-leaf cottonwood does 
not penetrate the zone; it is climatically restricted to the yellow 
pine belt. The chief shrubs of the lodgepole pine zone are blue¬ 
berries (Vactinium erythrococcum, and V. oreophilnm) , bear berry 
( Arctostaphylos uva-ursi), American twin flower ( Linnaea ameri- 
cana ), shrubby cinquefoil ( Dasiphora fruticosa) , elder (Sambucus 
microbotrys) , honeysuckle ( Lonicera involucrata) and Canadian 
buffalo-berry (Eepargyrea canadensis) . Some of the most com¬ 
mon herbs are anemone or pasque flower {Pulsatilla- hirsutissima ), 
candy tuft ( Thlaspi coloradense) , buckbean ( Thermopsis diva\ri- 
carpa), wall flower {Erysimum wheeleri) , fireweed ( Chamaenerion 
angustifolium) , Indian paint brush {Castilleja spp. ),Arnica {Ar¬ 
nica cor difolia) , beard tongue {Pentstemon alpinus, P. procerus), 
and erigeron {Erigeron eximius, E. macranthus ). 
Climate, and Relation to Agriculture. —The mean annual tem¬ 
perature in the lodgepole pine belt ranges from about 28° to 40°. 
The average of 11 stations is 34.9° (see Table XX). In many parts 
of the state, the 40° isotherm follows quite closely the lower limit 
