Supervisors:

PI: Michael Kleyer, Co-PIs: Gerhard Zotz, Vanessa Minden (AG Kleyer), Thorsten Balke (AG Kleyer)

Projects and Research:

Coastal dunes and salt marshes are valuable ecosystems, both in terms of nature conservation and coastal protection. Understanding the responses of plant traits to environmental constraints and their effects on ecosystem functioning is key to reach conservation targets and ensure a resilient natural coastal defense.

On a typical Wadden Sea island, coastal dunes are found on the wind and wave exposed side dominated by wave action and eolian sediment transport. Salt marshes occur mainly at the sheltered lee of the island, where the geomorphic development is dominated by tidal inundation. In both ecosystems plants with distinct functional traits are able to establish and subsequently influence the landscape development through so called biogeomorphic feedbacks. Dunes and salt marshes display non-linear behavior in response to changes in environmental conditions which is depending on establishment thresholds and physical properties of the plants.

Established coastal dunes and salt marshes are situated along disturbance (sediment disturbance) and stress (salinity, flooding and water stress) gradients from the dynamic fringe towards the higher and more stabilized areas away from the main source of disturbance. This gradient determines species distribution as a function of their trait expressions. However, plant traits also determine the type and strength of the positive feedbacks arising from biophysical interactions (e.g. plant stiffness and root architecture to trap sediments and reduce erosion or litter production to support soil development). Hence ecosystem functioning, mainly determined by establishment dynamics and ecosystem engineering capacity of the plants are strongly trait dependent in complex biogeomorphic ecosystems.

This project will focus on the interaction of environmental processes with plant traits for understanding and predicting ecosystem functioning and biogeomorphic development of coastal dunes and salt marshes. We seek to develop a conceptual framework of plant traits and biogeomorphology via meta-analysis and literature review of coastal dune and salt marsh studies. In-depth studies on the importance of plant traits for germination, resistance and resilience of biogeomorphic ecosystems will focus on dune pioneer vegetation.

Main research questions:

1. Can we formulate a conceptual framework to unify biogeomorphic concepts (such as biogeomorphic succession and ecosystem engineering) and recent developments in plant trait ecology and BEF studies (Biodiversity effects on Ecosystem Functioning) using dune and salt marshes as model systems.

2. Does species composition of the seed source in dunes increase the chance of vegetation establishment and therefore the chances for initiating a biogeomorphic succession towards a resilient and resistant dune system.

3. To what extend do trait expressions of dune plants affect ecosystem resistance and resilience of coastal dunes? We hypothesize that stability traits (e.g. stiffness, dry matter content, C/N ratio, root architecture) can be identified and are positively correlated to pioneer dune stability and resilience.