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Establishment of different riparian plant communities from the same soil seed bank

PhD ceremony:Mr G.N.J. (Gerard) ter Heerdt
When:February 19, 2016
Start:12:45
Supervisors:prof. dr. J.P. (Jan P.) Bakker, W.H. van der Putten
Where:Academy building RUG
Faculty:Science and Engineering
Establishment of different riparian plant communities from the same
soil seed bank

The thesis of Gerard ter Heerdt shows that weather conditions during the first year of establishment, strongly affect the composition of riparian plant communities. This is one of the factors determining if some goals of the Water Framework Directive and Natura 2000, reed beds and accompanying bird species, can be met. Increased summer drought due to climate change will make it more difficult to reach these goals.

The composition of riparian plant communities establishing during a drawdown can vary largely. For example, in the Oostvaardersplassen nature reserve, Typha latifolia establishes in large numbers in one month, while a month earlier or later Senecio congestus or Chenopodium rubrum become abundant. This variation is not caused by variation the soil seed bank, which contains the same species everywhere.

During a series of experiments, the effect of several simulated weather conditions on seedling emergence, establishment, growth and competition of various riparian plant species was tested. The various species have strongly different preferences for temperature and moisture conditions. For example, Phragmites australis and Typha latifolia prefer very wet growth conditions Senecio congestus prefers wet conditions and Chenopodium rubrum dry conditions.

Using species preferences and observed weather conditions, it was possible to simulate the plant communities that established during a drawdown in the Oostvaardersplassen. Experimental results were coupled with climate scenarios, obtained from the Royal Netherlands Meteorological Institute. Increasing summer drought will make that Phragmites australis and Typha latifolia will not be able to establish often. A modified water level management will be needed to avoid a drawdown during periods that are too dry for these species.