Sand Dunes have a “beach succession” model that follows a predictable pattern. Way back in 8th grade earth science, I was a little fascinated with the idea of forest succession. You probably remember the graphic that showed the way certain plants colonized an empty field first based their sunlight and nutritional needs, and then other plants could grow in the shade, and eventually a mature forest stood where once was nothing. So I couldn’t stop thinking about this when the Dewees Island Conservancy had a “Dune Planting” work party a few weeks ago. As each group got started, Island Ecologist Lori Sheridan Wilson helped us understand how beach succession works and how plants colonize the dunes.
Sand itself is made up of mostly inorganic materials: tiny grains of rock and some shell material. Plants need both nutrients and moisture to survive. So when sand is first blown and trapped by something on the beach to stop it, unless there are some plants to provide structure, it might just keep blowing again. But the salty, sandy environment seems pretty inhospitable.
Wrack is the line of broken seaweed and organic matter that washes up on the beaches. It can catch some sand as it blows, and then the organic matter decays. Often there are seeds mixed in. It provides structure to build little mounds and also shelter and food for shorebirds.
Beach succession: the order plants get established
The first plant to colonize the dunes is the salt-resistant Sea Rocket. (Stay tuned– each of these plants has their own superpower and will be the topic of later posts.) But you can see the way Sea Rocket starts out in a line on the beach.
Eventually, Seaside Panicum will take hold, and it will set the stage for all sorts of other dune plants. Since dune plants offer stabilization, they are an important resource in a changing climate and rising sea levels.
The reason you see those signs to stay off the dunes is that dune plants have fragile roots and the more people that walk on them, the more fragile they are. They are also nesting and resting places for shorebirds, seabirds, sea turtles, and land mammals like beach mice, raccoons, and more. When the Dewees Island Conservancy wanted to help a dune berm stabilize with plants, the sea rocket was already growing on its own. The next plant to go in was Seaside Panicum. They approached this project with a clear understanding of natural dune succession. We can’t wait to see how it grows over time.