Sporobolus airoides (alkali sacaton) in White Sands National Monument, New Mexico

Sporobolus airoides specimen next to dune

I visited the White Sands National Monument in New Mexico in September 2019 in order to see some of the tenacious grasses that have managed to gain a foothold in this rugged environment, and I wasn't disappointed.

The dunes themselves were eerily beautiful, an otherworldly world of towering white sand dunes that stretched away for kilometers in all directions. The origin of this natural wonder lies several hundred million years in the past, when the continents still formed the massive landmass called Pangaea. During this time, the area that would become southern New Mexico was covered by a shallow sea called the Permian Sea. The rise and fall of the sea level at this time created layers of gypsum and other minerals on the sea floor. Over the next several million years the bottling up of the Tularosa Basin where the monument lies, the deposition of more minerals from the surrounding mountains, and the final drying of the lake (Lake Otero) that covered the basin slowly resulted in t he creation of the White Sands Monument that people see today.

You can learn more about the origins of the monument here.

The environment in the dunes is a harsh one for any organism trying to live on it. Not only does the sand shift and threaten to bury plants that take root in it, but water is usually at a premium and the very high salt concentrations in the gympsum sand make it toxic to most plants.

Nevertheless, I found many plants living in the relatively flat areas between dunes. Chief among them was Sporobolus airoides, which is commonly called Alkali Sacaton in the local language. This grass is a halophyte, an organism that tolerates and in fact flourishes in areas of high salt concentrations, and I found that most of the grasses I encountered were of this species.

In some of the more established specimens, mounds of sand had accumulated at the bases, and this reminded me of how beach dune grasses also trapped grains of sand on their bases, and thus helped in the stabilization of the beach dunes.

Sporobolus airoides during sunset

I spent some time taking in situ macro photographs of the inflorescence, which had tiny spikelets with unequal glumes and one floret nestling in each of them.

In addition to the widespread S. airoides, I also stumbled on other grasses. One was Oryzopsis hymenoides, or Indian Rice Grass, which looks superficially like S. airoides, and whose seeds are a major food source for various desert animals.

The Native Americans also used the seeds to make bread when their maize crops did not do well.

Spikelets of Indian Rice Grass

The other grass I found while on a hike was Schizachyrium scoparium, commonly known as Little Bluestem. This species is commonly a denizen of the prairies, and in fact was one of the major components of the tallgrass prairies of yore. Its presence in the dunes was at first a mystery, but I found out it was explained by the fact the water table in the lower parts of the dunefield is quite high, which provides enough water for this species even in the absence of enough precipitation.

All in all, the trip to the White Sands National Monument was fantastic, and I would wholeheartedly recommend this for anyone interested in how organisms can survive in extreme environments.