The research is published in the journal Biogeosciences.

How seabird guano shapes dunes

Seabirds bring a lot of nutrients with their droppings (guano). These are not produced locally, but are brought in by birds from elsewhere. On small, uninhabited islands—where there are few other sources of nutrition—guano can therefore have a major impact on plant growth.

"In places where there is a lot of breeding, and where a lot of guano ends up in the soil, you see vegetation growing much faster than in other places," Van Rees observed from satellite images. "And so-called dune-building grasses such as marram grass and sand couch can retain sand well, so they are extremely important for dune formation." The plants in breeding areas also grow faster early in the season, thanks to the nutrients from the guano. "And that also allows them to retain more sand."

Wider ecological effects on vegetation

In addition to the grass species mentioned above, annual herbaceous plants also benefit from guano fertilization on sandy soils. "In more organically rich soils, it is species such as sea couch and Atriplex that thrive in bird breeding sites," said Van Rees.

Van Rees' research once again demonstrates the dynamics of the Wadden Sea region. "We are, of course, talking about low-lying islands that are vulnerable to high waves. Sometimes, after a storm, there is a temporary setback in the form of erosion, but nature is resilient: for example, you see faster greening in the spring at the breeding sites, which means that the landscape recovers more quickly. If the number of breeding pairs changes, this can have consequences not only for the birds themselves, but also for the landscape in which they breed and rest."