Planning on re-planting with dune grass? You might want to read this first.

By Linda Alice Dewey
Sun contributor

“The most common practice within dune restoration is to plant only beach grass, because beach grass introduces succession over time,” observes biologist and ecologist Lukas Bell-Dereske, a University of New Mexico doctoral candidate. “Succession” refers to the natural introduction of other native plant species into an area over time.

For his doctoral dissertation, Bell-Dereske has been studying dune grass in the Sleeping Bear Dunes National Lakeshore. He created an experiment in which he mimicked one of the effects of climate change — increased precipitation in larger pulses — to see how dune plants would respond.

He was also interested in looking at the effects of “fungal mutualisms,” or how plants with fungi might agree with other plants — in this case, beach grass. Bell-Dereske describes “Marram grass” or “American beachgrass” (Ammophila breviligulata) — the one with the reedy top that everyone plants — as native. Therefore, because it is not alien, it is not “invasive,” counter to what some might believe. “It’s the primary dune builder,” he points out. “It’s the first to colonize as the lake levels drop. They are really good competitors.”

A few years ago, his advisor, Dr. Jennifer Rudgers, who is also at the University of New Mexico, discovered a fungus which grows between the cells of 20 percent of Marram beach grass naturally. The fungus only lives within beach grass and does not spread to other plants, he reassures us.

“With beach grass,” he explains, “this mutualistic fungus is at a low rate naturally; but whenever we do this restoration of dunes on private land such as with a septic system, where you bring in a different genotype of grass, we think that there’s an induction of this fungus at a higher rate than naturally. So we’re also interested in seeing how this affects other plants species. So that’s what got me started.”

Bell-Dereske incorporated this species into his current experiment. “We grew Marram grass with either 100 percent of the individuals with the fungus or with 0 percent of the individuals with the fungus,” hoping to observe the way the fungus affects the growth of the beach grass.

Then, he wanted to look at how climate affects both. “And then I became interested in climate change, which is what led to this experiment, which is testing both the effects of this fungus and also testing the effects of altered precipitation on plant communities. The National Park Service is really interested in that.”

A final goal was to test whether plants grown in mixed communities respond to additional precipitation differently than plants grown in a monoculture (a single species). He says that more heavy rain events are predicted, spaced between longer droughty periods. (See companion article.) “I’m interested in how these changes in the timing and the magnitude of these precipitation events will affect the growth of beach grass and other dune plants within the Great Lakes dunes.”

His findings may change the way we restore sandy areas along Lake Michigan when we build a home or install a septic system.

The experiment

Bell-Dereske planted his experimental plots in 2012 and began implementing precipitation treatments from 2013 through 2015. He planted some plots in mixed plant communities with other plants that grow naturally in the area. Other plots only contained plants of the same species. “These are all native plant species,” he explains. “I collected all the seeds in this area here and Sleeping Bear Dunes. We propagated them at Greystone Gardens (near Empire).”

Using a solar-powered irrigation system that pulled water from Lake Michigan, Bell-Dereske designed three types of treatment which he applied from mid-May to mid-September. Because additional precipitation followed by drought is expected with climate change in this area, all three treatments involved adding water.

He wasn’t allowed to simulate drought conditions. “This is a designated wilderness area, so I was limited in some of the things I could do. I was only able to manipulate the amount of precipitation by adding water. I couldn’t create a rainout shelter that limited the amount of water the plants got.”

“During that time, we had a huge swing from a drought into heavy rain. I added more precipitation to these periods of slightly colder summers with more rain, even during the drought period.”

The first of the three treatments — the “control” — involved adding no water beyond natural rainfall. To the second, he added 30 percent precipitation in weekly events of seven gallons per 9 sq. meter plot. To the third, he added one large monthly rain event (27 gallons in 27 minutes) on a plot.

Findings

Even with climate change, Bell-Dereske observed, “Marram grass grows better with the fungus irregardless of the presence of other plants. Marram grass also grows better in monoculture irregardless of the presence of the fungus, so Marram grass grows best with the fungus and in monoculture.”

In addition, plants in mixed communities seem to do better with added precipitation than those planted in monocultures, except in the case of beach grass with the additional fungus. Sand bar willow responded very well to additional weekly waterings, but the other plants didn’t change much with the additional precipitation. Finally, plants in mixed communities did not do as well with Marram grass present if it had the fungus. He did not measure whether they would do better without Marram grass present at all, but believes that regular Marram grass would help any plot.

Ramifications

So what does this mean for you and me, the average Joe?

“When you are just restoring just beach grass, you want to add genotypes with the fungus, because beach grass grows larger. It’s a better competitor.”

However, we might contend that beach grass can become very thick and seems to crowd out other plants. “It depends on what you’re interested in,” he clarifies. “Beach grass is the best at controlling erosion in the dunes. If your goal for your restoration is to reduce the erosion of the shoreline, then you would probably want to plant just beach grass with this fungus present.” He notes the cliffs along the Lake Michigan shoreline, where wave action erodes the beach. Beach grass holds the sand in place better than other plants.

“But,” he counters, “if your goal is to restore a plant community with many species and [to] have these species seem to be more hardy to changes due to climate change, you would want to plant beach grass without the fungus with other plant species.”

Therefore, when planting mixed communities, use the regular Marram grass, without the added fungus. Use the genotype containing the additional fungus when planting Marram grass alone if your goal is to have it grow thick.

Bell-Dereske says it is interesting that he did not find a big change in plant growth with the added precipitation, “because this community is predicted to be fragile” because of the high winds we get off the lake. However, “it seems to be rather hardy to these changes in precipitation.”

There are several other studies being conducted in the area. According to Bell-Dereske, one at the Leelanau State Park found that “grass species other than beach grass are colonizing at a higher rate when there’s more precipitation than when there’s a reduction in precipitation.” This was not true in Bell-Dereske’s study. The difference may be that his plants were mature, where the Leelanau State Park plants were colonizing in, and were therefore younger. “A lot of science is all about trying to control all of the variables outside of what you’re manipulating,” he admits.

Although he stopped watering his plots at the end of the 2015 growing season, Bell-Dereske continues to monitor his plots for long-lasting “legacy effects” of the additional precipitation he once added on them. He hopes to publish his study in a scientific journal this fall and graduate with a doctorate in November.