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Harnessing Ecological Theory and Species Interactions to Accelerate The Revegetation of Coastal Dunes

Joseph P. Morton

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Atlantic ghost crabs (Ocypode quadrata) facilitate dune grass growth

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Successional facilitation

TIME

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Leveraging successional facilitation to improve restoration of foundational dune grasses

Successional facilitation is the priming of a habitat by pioneer species that enables establishment by climax species

Download a pdf of the paper here: Fischman et al. 2024

Restoration Ecology

Transplanted sea oats grew better when planted adjacent to bitter panicum

This is some work by my colleague Hallie Fischman on how we might leverage successional facilitation to enhance dune restoration. Successional facilitation happens when pioneer species prime a habit, preparing conditions amendable for the establishment of climax species. Hallie had done some surveys that suggested that bitter panicum is a pioneer and sea oats a climax species. When she planted transplanted sea oats adjacent to stands of bitter panicum, she found that they grew considerably better. In contrast, bitter panicum planted next to established sea oats was outcompeted. So, in a restoration context, we might be able to leverage successiona facilitation, planting panicum first so that the growth of sea oats planted later is enhanced.

Hallie’s got a great decision mtrix in that paper that will tell you which revegetation methods to use based on geomorphic context.

What Hallie found was that when transplants of sea oats were planted 50cm away from mature bitter panicum they grew 35% more stems and were 12cm taller than standard plantings, but bitter panicum was outcompeted when planted near sea oats

Transplanted sea oats grew better when planted adjacent to mature bitter panicum

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Interspecific facilitation

Intraspecific facilitation

Nutrient addition

Strategic planting and nutrient amendments accelerate dune revegetation

In this last, I’ll tell you about a project that I did that I am very existed about. So, thus far I think I’ve impressed on you that ccelerating the growth, expansion, and community benefits of dune vegetation may be achieved by reducing abiotic stress or by manipulating biotic interactions. Nutrient addition in the form of chemical fertilizers is a pretty common approach in a lot of dune restoration projects. However, many current dune restoration practices don’t explicitly include the effects of positive ecological interactions. Conventional dune restoration approaches frequently focus on reducing negative species interactions by deploying transplants in dispersed configurations that reduce competition, yet there is a growing body of research in this and other similarly stressful habitats that suggests that positive plant=plant interactions might be leveraged to enhance the growth of transplanted vegetation.

Reducing the spacing of transplants may jumpstart neighborhood stress amelioration benefits, and improve transplant performance. Likewise, diversifying the composition of transplanted species may take advantage of interspecific facilitation that increases revegetation rate. We also might expect some ecological surprises: given the ubiquity of nonlinear dynamics in mediating ecosystem structure and functioning, biological facilitation may interact with abiotic stress reduction strategies to yield outsized effects on growth rates of foundation species.

So, we wanted to test what combinations of planting density, outplant species composition, and nutrient addition maximized the rate of dune plant growth and the recovery of key ecosystem function (sand accretion). We deployed a fully factorial experiment on a half-kilometer of a restored dune in North Florida in July 2022. We planted some plots at a standard restoration density and others at four times that density. We used two grass species, the most commonly planted dune macrophyte (sea oats) and a less-frequently planted early successional species (bitter panicum). Some plots were planted with monoculture sea oats, others a monoculture of panic grass, and others a mixure of the two grasses. And finally, half of these plots received nutrients in the form of slow-release fertilizer.

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Nutrient addition interacts with increased planting density to boost growth!

Control + Nutrients

High density Low density

Bitter panicum

Sea oats

Sea oats + Bitter panicum

(Click x 2) After three months, plants in low density treatments with no nutrients added had not really grown at all regardless of which species were there. Nutrient addition in low density plots yielded a modest increase in aboveground growth. (Click) Things get really interested in the high density plots. As with the low density plots, aboveground production in high density plots without fertilizer was either negligible or slightly negative. BUT, we found that increased planting densities interacted strongly with nutrient addition, elevating aboveground plant biomass by 868-2,961%. Notably, monocultures of bitter panicum - the less commonly deployed early successional grass - performed best out of all the treatments in terms of aboveground growth.

(Click) We found similar effects with Belowground biomass: fertilizer interacted with increasing planting density to enhance root and rhizome growth, especially in plots planted with bitter panicum.

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Restoring ecosystem functioning:� Sand Accretion

Hurricane Ian

Sept. 28^th 2022

Vilano Beach, FL

St. Augustine, FL