Thursday, October 21, 2021

Exploring the Layered Series of Grasses in an Island

Image 1. Ammophila breviligulata in center

Assateague Island straddles both Maryland and Virginia. It is a narrow barrier island that I visited and hiked this month, and it contains several ecological areas that made it quite diverse when it came to species diversity. Click here to look at a map of the island.

While I was there it came to me that the distribution of the grass species could be described as a series of layers. The major species were different as one went inward from the beaches to the marshes, and then to the drier meadows, and it was quite interesting to see how the species changed  as one hiked inward from the beach dunes.

Image 2. Panicum amarum

In the first and outer layer (the beaches), the two main grasses were Ammophila breviligulata and Panicum amarum. Both are dune building species, and A. breviligulata especially is crucial in creating the huge dunes that protect beaches. It is the dominant dune grass along the northeast coast, and I was familiar with it from my trips to the beaches in New Jersey. 

The two species are also easy to tell apart, with A. ammophila having very thin leaves, while P. amarum has much wider and bluish green leaves. You can clearly see this in Image 3 below.

Image 3. Ammophila breviligulata (left) and Panicum amarum (right)

Their inflorescences are very different as well, as you can see in Image 4 below. A. breviligulata has a whitish spike like inflorescence, while P. amarum has the typical Panicum type spikelets,

Image 4. Ammophila breviligulata (left) and Panicum amarum (right)

As I continued hiking inland into the marshes I came upon the second layer, which is actually composed of several sublayers (see Image 5 below). The area of the marsh closest to the sea (the low marsh) is inundated daily and has higher salt concentrations, and this area was dominated by Sporobolus alterniflorus (Spartina alterniflora). The so-called "high marsh" is farther away, is not inundated all the time, and is less salty. Here I found Sporobolus pumilus (Spartina patens) and the graminoid Juncus roemerianus, which is in the rush plant family and is NOT a grass. 

Image 5. Marsh

It was fairly easy to tell the two grass species apart. S. pumilus has wavy looking blades that look quite beautiful and distinctive. In the image below (Image 6) the species looks almost like a nice soft fluffy lawn.

Image 6. Sporobolus pumilus (Spartina patens) in foreground (NJ pic)

Sporobolus alterniflorus is more erect in form, and it forms the vast bulk of the vegetation that people associate with marshes as they drive towards the beach. The geometric shapes of their vast stands was quite pleasing to the eye, and I spent some time taking various artistic pics of the scenery.  

Image 7. Geometric stands of S. alterniflorus (S. alterniflora) in the background

I even found flowerheads on some of the nearby specimens. The inflorescences were spike-like, with white anthers dangling out from the flattened spikelets and looking quite grub-like.

Image 8. Inflorescence of S. alterniflorus (S. alterniflora)

Beyond the marsh layer was a forested area, but also pockets of large meadows. This most inner layer is surrounded by the beaches and marshes, and I was astonished to find some species that I would never associate with islands. 

Next to the trail were rows of what I believe were Schizachyrium scoparium (little bluestem), and behind them the beautiful panicles of Panicum virgatum (switchgrass) waved in the breeze. Farther back were dense stands of the invasive Phragmites australis (common reed), which also was present in the high marsh.

Image 9. Meadow layer with a series of grass species

It was an amazing thing to be surrounded by such grasses, when just a few minutes away was marshy waters. But unfortunately, the drier landscape, combined with the disturbance regime due to human activity, has also introduced invasive species to the area. I found dense pockets of Microstegium vimineum (Japanese Stiltgrass) in some of the trails, the silvery lines on the upper surfaces of their leaves the most distinctive sign of their presence.

Image 10. Microstegium vimineum

Nevertheless, I really enjoyed visiting and hiking the short trails in the island, and I loved the structured layering of these major grass species throughout the area.

If you ever visit one of these barrier islands, do keep an eye out for the plants around you. The narrowness of such areas make it possible to go from one ecological region to another with just a short walk.

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