54 
The Colorado Experiment Station 
Pig. 20.—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 
( Populns 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. oreophilum) , bear berry 
( Arctostaphylos uva-ursi) , American twin flower ( Einnaea ameri- 
cana), shrubby cinquefoil ( Dasiphora fruticosa), elder (Sambucus 
microbotrys) , honeysuckle (Lome era invo liter ata) and Canadian 
buffalo-berry ( Lepargyrea canadensis) . Some of the most com¬ 
mon herbs are anemone or pasque flower ( Pulsatilla hirsutissimai ), 
candy tuft (Thlaspi color ad ense) , buckbean (Thermo p sis divari- 
carpd) , 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. m acrant hits ). 
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 
