Life Zones

Great Sand Dunes National Park and Preserve encompasses a stunning diversity of life zones—journey from sand to alpine areas, all within a day’s hike! Climb from the arid sabkha and sand sheet of the valley floor, past the dunes and into piñon-juniper woodland, through shaded montane forest and finally onto the cool tundra of 13,000 foot mountain peaks. The borders between life zones are indistinct, perhaps unapparent as you hike. But each time you pause to catch your breath, you’ll find yourself surrounded by a different community of plants and animals—a different life zone.

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Sabkha

The low-lying sabkha is a landscape of sand cemented into a fragile crust by the alkaline minerals of a high water table. Due to the high water table, moisture is plentiful (despite only seven inches of rainfall per year). But most plants won’t tolerate the harsh chemical environment. Four wing saltbush and saltgrass are among the few plants adaptable enough to thrive in this life zone. From the thin shade of the vegetation comes the slight call of the sage sparrow. Circus beetles wander over the alkalai flats, stilt-like legs elevating their bodies above the hot surface. Golden eagles soar overhead, travelling miles on broad wings in search of prey.
 

Sand Sheet

The vast sand sheet is slightly higher than the sabkha, and far less alkaline. This life zone includes mobile sand dunes. But most of the sand is anchored by rabbitbrush, prickly pear and yucca, their deep tap roots reaching down to the water table. Sand verbena and prairie sunflower provide swathes of color in an otherwise dusky panorama. Pronghorn race across the sand sheet at speeds of 60 mph. When still, pronghorn blend into the background of knee-high vegetation. Hiding right on the sand, camouflaged sandhoppers evade American kestrels and northern grasshopper mice. Thirteen-lined ground squirrels and endemic silky pocket mice burrow into the sand sheet, seeking refuge from red-tail hawks hunting from the sky.
 

Dunefield

From a distance, the dunes appear barren. But there is life on the dunes, some of it so uniquely adapted that it is found no where else in the world. Fragile looking Indian rice grass and blowout grass withstand forceful winds and blasting sands. Scurfpea roots are horizontal, ready to send up a new shoot when blowing sand covers the original plant. Among the patches of sparse vegetation, endemic noctuid moths take cover from intense sunshine and Great Sand Dunes tiger beetles search for prey on sand surfaces that can reach 140 degrees F. The kangaroo rat, with its array of water conservation adaptations, is the only mammal that can survive on the dunes. Other mammals, like the coyote, may wander onto the margin of the sand, but they don’t linger long in this demanding life zone.
 

Piñon-Juniper Woodland

At the base of the mountains, short shrubs give way to deep green woodlands. Annual precipitation in this life zone is twelve inches, a scant amount for a piñon pine or a juniper tree. In response to little moisture, the trees space themselves widely, filling the open air with their resinous scent. This life zone provides rich food for rock squirrels, chipmunks, and birds. Screeching flocks of gregarious piñon jays collect and cache thousands of calorie-packed pine nuts. Most are eaten over the winter. But some pine nuts are forgotten, remaining in their earthy hiding places to germinate and grow into new piñon pine trees. Mule deer graze on blue grama grass and bed down under the trees, alert to mountain lions roaming through this life zone and others. Bobcats sneak up on plump cottontail rabbits, and great horned owls silently search the night for piñon mice.
 

Montane Forest

With rising elevation, piñon-juniper woodlands give way to taller, more dense montane forests (montane means mountain). Douglas fir trees mix with white fir, ponderosa pine and aspen. In the cool, moist shade, thick club moss cushions the ground. Breaks in the tree canopy create puddles of sun where one-sided penstemons and columbines flower. The moisture of the montane forest supports diverse plants, which in turn attract a variety of animals. Hungry black bears gorge on wax currants. Twittering pine siskins feed on conifer seeds and juncos forage on the forest floor. Northern goshawks navigate the forest with short wings and long, rudder-like tails in pursuit of these small birds. By night, little brown bats flit through the dark forest in search of insects. By day, they roost under the loose bark of snags. Also at home in these dead trees are cavity nesting birds like the chickadee and downy woodpecker.
 

Subalpine

The subalpine life zone is the upper limit for trees—and only the hardiest trees survive the cooler temperatures and heavier snows of this elevation. Engelmann spruce, blue spruce, and subalpine fir, dark boughs sweeping the ground, grow in stands separated by fingers of rocky talus. Yellow-bellied marmots are the sentries of the talus slopes, quick to whistle a warning at any intruder. Fat from tender summer greens, marmots spend more than half the year hibernating. Ptarmigan brave the winters in the subalpine and alpine life zones, subsisting on spruce and willow buds protruding from the snow; dense feathers between its toes serve as snowshoes to support this stout bird.
 

Alpine

The peaks of the Sangre de Cristo mountain range top 13,000 feet. Locked in snow and ice for nine months of the year, the highest peaks are bare rock. In places, lichens have found a foothold, beginning the process of breaking down rock into soil. Where thin top soil has accumulated, moss campion and purplefringe form miniature gardens. The plants are mere inches tall, hugging the ground to avoid dessicating winds. Deceptively delicate in appearance, they withstand the crush of many inches of snow. The snow pack is welcome insulation against frigid winter temperatures, and a vital source of moisture. Summer in this life zone is a frenzied time of replenishment. Alpine plants bloom against a background of lingering spring snowdrifts, rushing to produce seeds before the short summer ends. The pika hurries to collect grass and dry it in the sun, stockpiling hay against a winter of activity under the snow. Birds like the horned lark migrate back to the mountain tops to nest after wintering in lower, warmer life zones.
 

Water

Water and low temperatures define a life zone. The amount of water available and the lowest winter temperatures determine which plants can grow, and the plants determine which animals frequent a life zone. The snow pack of the Sangre de Cristo Mountains supplies the water for every life zone at Great Sand Dunes. Melting snow fills high cirques to form clear, cold alpine lakes full of Rio Grande cutthroat trout. The lakes spill into mountain streams whose lushly vegetated banks are marked by the work of gnawing beavers. Springtime streams carry water through the piñon-juniper woodlands and down to the dunefield, recycling sand blown into the mountains, defining the borders of the dunefield, and making possible the shady stands of aromatic cottonwoods alongside the dunes. In a good year, the water flows as far as the sand sheet before it sinks away to replenish the huge aquifer underlying the east side of the valley. This water resurfaces to form wetlands, havens for herons and tiger salamanders.
 

Each life zone is a unique community of plants and animals with fascinating habits and adaptations for survival. The life zones of Great Sand Dunes are made even more special by their proximity to each other. Just think...how many other places in the world can you experience such diversity in just one day’s hike?