The assembly of a salt-marsh ecosystem. The interplay of green and brown food webs

PhD ceremony: Mr. M.J.J. Schrama, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: The assembly of a salt-marsh ecosystem. The interplay of green and brown food webs

Promotor(s): prof. H. Olff

Faculty: Mathematics and Natural Sciences

In his research along the 100-year old successional sequence of the salt marsh of Schiermonnikoog, Maarten Schrama shows that the early stages of the ecosystem are externally fuelled. That means that the nutrients and organic material are derived from other ecosystems, thus stressing the relevance of links between different ecosystems.

Along succession, he found that biodiversity increases in early succession, but decreases towards late succession.

Ecological succession encompasses a fascinating process during which all building blocks of ecosystems are put together. Places with a sequence of developmental stages can therefore yield a great deal of information on the functioning and regulation of ecosystems. The salt march of Schiermonnikoog is one of those special areas.

We know that large herbivores such as cows play a major role in ecosystems, but why they enhance biodiversity in some areas, while depressing it in others is not well understood. Also on Schiermonnikoog, cows enhance biodiversity in the late stages of succession. Schrama shows that on the salt marsh clay soil, cows change the soil physical conditions by trampling it, thus creating a set of conditions that facilitate for a species-rich (early successional) vegetation. However, this effect was not found on a sandy soil, which indicates that the positive effect of large herbivores is likely to occur only on soils with a fine texture. This may be an important explanation for the fact that nature management with large grazers often does not result in the desired plant community.