Teixeira, L. H., Weisser, W., & Ganade, G. (2016). Facilitation and sand burial affect plant survival during restoration of a tropical coastal sand dune degraded by tourist cars. Restoration Ecology. doi:10.1111/rec.12327
The setting: The sun is shining as you’re obviously headed to the beach for an afternoon of fun now that it’s spring break. Someone suggests taking a drive in a dune buggy and you readily agree—sounds like it could be a blast. You wouldn’t be alone in taking a spin in one of these cars, but have you ever stopped to consider what kind of an impact those tires have on the fragile ecosystem supported by sand dunes?
Coastal dunes are incredibly important features along beaches, providing vital ecosystem services that range from buffering against storms to being economic drivers in the tourism industry. Unfortunately, dunes are also delicate microclimates that often prove very difficult to restore once damaged. Dune ecosystems in temperate zones have received more attention from conservationists, but comparatively little work has been done on dunes in tropical areas; this is often attributed to the harsher conditions and the constant reshaping of dunes by winds. Therefore, Leonardo Teixeira and colleagues set out to study and improve restoration techniques in northeastern Brazil, where dune buggy tourism is a critical part of the local economy.
In particular, Teixeira’s team wanted to answer four specific questions:
- Can existing patches of vegetation be used to increase seedling survival in restoration efforts?
- Will seedlings survive equally well in an artificial substitute for existing vegetation?
- Are seeds a better, more economical approach to restoration?
- Does early watering of seedlings enhance survival?
The method: To answer these main questions, Teixeira and his team conducted two separate experiments along plots of land in the Environmental Protected Area, Jenipabu. The model species selected for dune restoration was Canavalia maritima, a jack-bean plant.
For the first experiment, the team used a split-plot design (see Fig. 1), planting seedlings in areas within patches of vegetation or outside existing patches and with or without an artificial mesh (here, a coconut fiber mesh). Survival of seedlings was monitored over the course of three months during which measurements of abiotic factors were also recorded. Specifically, the scientists were measuring air humidity, soil surface temperature, soil temperature at a depth of 10 cm, and the amount of sand burial occurring around seedlings.
For the second experiment, a similar design was used, except this time seeds and seedling survival were measured, planting both in areas far from existing vegetation. This was to assess the potential to increase vegetation cover in previously barren areas. The same coconut mesh was used in half of the plots, and half of the plots also received additional water to properly irrigate the seeds and seedlings.
The end result: Teixeira and his team determined there were many factors that contributed to the long-term loss of vegetation caused by disrupting dune crests. Existing vegetation provided shade and extra humidity—things necessary for seeds to successfully germinate and grow. Indeed, the best survival rates were seen in seedlings growing in patches of existing vegetation. And while the coconut mesh did increase survival of seedlings, it wasn’t nearly as effective as live plants. When comparing seeds to seedling survival, the team found that field conditions could favor seeds if they were scarified (partially cut open) before planting, which allowed for faster germination.
The critical problem, in all scenarios though, was sand burial. Seeds buried too deeply would not germinate, and seedlings could also suffer a similar fate if the moving sand rapidly engulfed them. Repeated disturbing of soil by dune buggies can loosen sand further, and without vegetation to hold it in place, the abundant sand grains become increasingly mobile.
The moral of this beach read: Overall, the team concluded that protecting existing vegetation should be the first step in minimizing both the problem and long-term restoration efforts. Ironically, although the study was conducted in an environmentally protected area, the shifting of the dunes caused fence markers to be buried, and dune buggies would often come barreling through while the field team was collecting data. While this would suggest that stronger enforcement policies are needed, the authors also stressed the need for increasing environmental education and awareness.
And that is where you, our audience, come in. By all means, go out and have fun on your trips to the beach. Just remember that there are small biomes out there vital to the continued survival of coastlines everywhere. While you’re thinking about it, do you have any other suggestions for how to increase awareness about vulnerable or fragile environments people often take for granted?