In the Sangre de Cristo Mountains, cooler temperatures with increasing elevation cause moisture in the air to condense and precipitation to increase, creating different life zones. The alpine life zone supports only low shrubs and a few hardy plants in a cold, windy climate. The subalpine life zone contains dense, moist forests of spruce and subalpine fir trees. The montane life zone has aspen trees in moist locations and ponderosa pines in drier sites. The foothills life zone is a dry shrub ecosystem dominated by pinons and junipers.