Sea Oats: Builder of Dunes & Guardian of the Coast

August 20, 2019

Coastal habitats can be really unforgiving to life. Anything that makes a living along the coast has to be tough and they don’t come much tougher than sea oats (Uniola paniculata). This stately grass can be found growing along much of the Atlantic coast of North America as well as along the Gulf of Mexico. What’s more, its range is expanding. Not only is this grass extremely good at living on the coast, it is a major reason coastal habitats like sand dunes exist in the first place. Its presence also serves to protect coastlines from the damaging effects of storm surges. What follows is a celebration of this amazing ecosystem engineer.

Sea oats is a dominant player in coastal plant communities. Few other species can hold a candle to its ability to survive and thrive in conditions that are lethal to most other plants. The ever-present winds that blow off the ocean bring with them plenty of sand and salt spray. Sea oats takes this in strides. Not only are its tissues extremely tough, they also help prevent too much water loss in a system defined by desiccation.

Photo © Don Henise licensed by CC BY 2.0

The life cycle of sea oats begins with seeds. Its all about numbers for this species and seat oats certainly produces a lot of seed. Surprisingly, many of the seeds produced are not viable. What’s more, most will never make it past the seedling stage. You see, sea oat seeds require just the right amount of burial in sand to germinate and establish successfully. Too shallow and they are either picked off by seed predators or the resulting seedlings quickly dry up. Too deep and the limited reserves within mean the seedling exhausts itself before it can ever reach the surface.

Still, enough seeds germinate from year to year that new colonies of sea oats are frequently established. Given the right amount of burial, seedlings focus much of their first few months on developing a complex, albeit shallow root system. Within two months of germination, a single sea oat can grow a root system that is as much as 10 times the size of the rest of the plant. This is because sand is not a forgiving growing medium. Sand is constantly shifting, it does not hold on to water very long, and it is usually extremely low in nutrients. By growing a large, shallow root system, sea oats are able to not only anchor themselves in place, they are also able to take advantage of what limited water and nutrients are available.

It is also this intense root growth that makes sea oats such an important ecosystem engineer in coastal habitats. All of those roots hold on to sand extremely well. Add to that some vast mychorrhizal fungi partnerships and you have yourself a recipe for serious erosion control. The interesting thing is that as sea oats grow larger, they trap more sand. As more sand builds up around the plants, they grow even larger to avoid burial. This process snowballs until an entire dune complex develops. As the dunes stabilize, more plants are able to establish, which in turn attracts more organisms into the community. A literal ecosystem is built from sand thanks to the establishment of a single species of grass.

As sea oats mature, they will begin to produce flowers, and the process repeats itself over and over again. As mentioned above, the sea oats seeds are subject to a lot of seed predation. This means that as sea oat populations grow, more and more animals can find food in and among the dunes. So, not only do sea oats build the habitat, they also supply it with plenty of resources for organisms to utilize.

The power of sea oats does not end there. Because they are so good at controlling erosion, they help stabilize the shoreline from the punishing blow of storm surges. Dune systems, especially those of barrier islands, help reduce the amount of erosion and the momentum of wave action reaching coastal communities. Many states here in North America are starting to realize this and are now protecting sea oat populations as a result.

Sea oats, though tough, are not indestructible. We humans can do a lot of damage to these plants and the communities they create simply by walking or driving on them. Pathways from foot and vehicle traffic kill off the dune vegetation and create a path of least resistance for wind, which quickly erodes the dunes. Apart from that, development and resulting runoff also destroy sensitive dune communities, making our coastlines that much more vulnerable to the inevitable storms that threaten their very existence.

As our climate continues to change at an unprecedented rate and storms grow ever stronger, it is very important that we recognize the role important species like sea oats play in not only providing habitat, but also protecting our coastlines. Dune stabilization and restoration projects are growing in popularity as a cost effective solution to some of the threats facing coastal communities. Among the many techniques for restoring dunes is the planting of native dune building species like sea oats. If you live near or simply like to enjoy the coast, please stay off the dunes. Foot and vehicle traffic make quick work of these habitats and we simply cannot afford less of them.

Watch our short film DUNES to learn more about these incredible ecosystems.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3] [4] [5]

The Hidden Anatomy of Grass Flowers

October 8, 2017

Grass flowers have their own unique beauty. Examine them with a hand lens and a whole new world of angiosperm diversity suddenly opens up. Unlike other flowering plants, their charm lies not in showy sepals or petals, but in an intricacy centered around the utilization of wind for pollination. However, such floral organs are not lacking. Grass flowers do in fact produce a perianth, the function of which has been highly modified.

To see what I am referring to, you need to do some dissection under a scope. Pull off a flower and peel away the sheaths (the palea and lemma) that cover it. Inside you will see an ovary complete with feathery stigmas as well as the anthers. At the base of the ovary sits a pair of scales called lodicules. These lodicules are thought to be the rudimentary remains of the perianth. They certainly don't resemble sepals or petals but that is because the function of these structures is not to attract pollinators. They assist in pollination in another way.

When grass flowers are ready for reproduction, the lodicules begin to swell. This swelling serves to push apart the rigid palea and lemma that protected the flowering parts as they developed. Once apart, the anthers and stigma are free to emerge and let wind do the dirty work for them. Lodicules differ quite a bit from species to species in their size, shape, and overall appearance. Much of this is likely tied to the overall structure in grass flowers.

Photo Credits: [1] [2]

Buffalo Grass, A Big Plant In A Small Package

September 5, 2017

Grass identification is a bit challenging for me. However, there is one species I can always pick out of a crowd and for that, it holds a special place in my heart. My predilections aside, it is a fascinating species with an ecology worth getting to know a bit better. Today I would like to introduce you to the indomitable buffalo grass.

Known scientifically as Bouteloua dactyloides, this is one of the few dioecious grass species you can readily encounter here in North America. It is a denizen of the great planes and once thrived in the wake of disturbance left by massive herds of bison. Today you are more likely to encounter it growing alongside trails and other areas where taller vegetation is kept at bay. It is a hardy species and does exceptionally well in drought-prone soils. Like all warm season grasses, its photosynthetic machinery employs the C4 pathway, allowing buffalo grass to conserve moisture while ramping up photosynthesis during the hottest months of summer.

Colonies of buffalo grass are stoloniferous, sending out creeping horizontal stems that will grow into new plants over time. Its small stature makes it easy to overlook. Flowering changes that. As mentioned above, buffalo grass is dioecious, which is kind of an odd trait for a grass. For the most part, male and female flowers exist on separate plants. Because pollen is wind dispersed, male flowers reach far above the leaves, ready to take advantage of the slightest breeze. Female plants present their flowers much closer to the ground, perhaps as a way of avoiding herbivory. Research has shown that, in any given population, monoecious plants are produced from time to time. It is thought that this might give buffalo grass a leg up when it comes to colonizing new habitats. If buffalo grass was strictly dioecious, both male and female seeds would have to find their way into a new habitat at the same time in order for a new population to establish. However, by producing monoecious seeds on occasion, the chances of being able to successfully reproduce in a new habitat increases.

Why this species has evolved to be dioecious is a bit of a mystery. Research on other dioecious plants suggest that it is a way of dealing with various environmental stresses such as competition and herbivory. Work on buffalo grass shows no significant bias towards males or females in any region. Most populations studied exhibit a 1:1 male to female ratio. Some plants seem to be able to switch over their lifetime, especially as it relates to new plants produced on stolons. Regardless of the selective pressures, buffalo grass seems to be doing quite well. Due to its small size and hardy disposition, many are looking towards buffalo grass as a great native lawn alternative. It doesn't require mowing and hot summer days don't seem to bug it. Couple that with its turf-like growth habit and you have yourself an excellent alternative to grasses like Kentucky bluegrass (Poa pratensis), which requires endless amount of water, fertilizer, and mowing to keep it up to our (dare I say) absurd standards.

Further Reading: [1] [2] [3]