White Sands National Monument is located at the northern limits of the Chihuahuan Desert, and as expected, the majority of plants are drought tolerant species . In addition, many of these plants must be adapted to alkaline, nutrient poor soils with a high gypsum content. The highly mineralized water table under these soils ranges from about 3 feet below the surface at Lake Lucero and the interdune flats to more than 20 feet outside the dune field.
Plants surviving here must also endure being buried by moving dunes and be able to tolerate extreme fluctuations in temperature, with common sub-freezing winter lows to occasional 100+ summer days.
The majority of plants in WSNM are found in 6 distinct ecological units, primarily on the basis of soil type and mineral concentration, dune activity, and water availability. A description of each unit, along with examples of plant species found in each, follows:
Lake Lucero (Unit A) and Alkali Flat (Unit B) - Alkali Flat is the exposed lake bed of ancient Pleistocene Lake Otero, which has dried into its present condition. Occasionally water stands in the southern end of the flat, forming seasonal Lake Lucero. Extreme alkaline conditions and occasional flooding prevent the growth of plant life in these two areas except for a few scattered grasses and pickleweed. Salt cedar, an invasive nusiance shrub, has managed to survive in places along the fringes of these two areas.
Unit C is primarily dome, transverse, and barchan dunes and presents some of the most extreme environmental conditions for plant life on the monument. These dunes creep forward as much as 30 feet per year and even fast-growing plants such as yucca and rosemarymint cannot outgrow them. Occasional pedestals topped with sumac, rosemarymint, or saltcedar are left in the trail of a moving dune. The interdune areas may contain sand verbena, evening primrose, woolly paperflower, Indian ricegrass, yucca, ephedra, and alkali sacaton.
Unit D is composed mostly of parabolic dunes, which extend two to three miles into the dunefield from its southern and eastern boundaries. These are slower moving, vegetated dunes and are separated by large grassy, interdune areas. Grasses found here include several members of the dropseed tribe, gyp grama, little bluestem, sandhill muhly, and alkali sacaton. Soaptree yucca, rosemarymint, skunkbush sumac, Rio Grande cottonwood, and scattered stands of the exotic saltcedar are the primary woody plants found in this area. This area has the most complex and varied plant community on the monument.
Unit E can best be described as a saltbush/alkali sacaton association, dotted with an occasional sumac bush, hedgehog cactus and cane cholla. This extremely flat area of grey-green vegetation over gypsum/alkali soils extends from the eastern and southern monument boundaries to the edges of the dunefield.
Unit F is composed of mesquite hummocks near the edges of Alkali Flat and Lake Lucero and creosote bush on alluvial fans that extend to the monument boundary from the base of the San Andres Mountains. Alkali sacaton and a few other grasses are found above the lake floodplain into the margins of the mesquite dunes (composed of quartz sand rather than gypsum).