PhD defence Jon Dickson
Jon Dickson (ConsEco/MarBio)
Promotores: Prof. T. van der Heide, Prof. B.D.H.K. Eriksson, Prof. L.L. Govers; copromotor: Dr O. Franken
Sunken driftwood
A lost ecosystem
Vast amounts of large wood was exported to sea from rivers and forested coastlines for hundreds of millions of years. Since landscape domestication, conversion of forests to agriculture and urban development along with river engineering such as dams, dykes, and debris traps has greatly lessened or eliminated this regular flow of large wood to sea. This large driftwood used to provide regularly-renewed large, stable hard-substrate habitat for large amounts of aquatic species, as well as creating a land-sea nutrient linkage. We mimic these large, complex historical woody structures such as root wads by building ‘tree-reefs’ out of waste orchard trees in the subtidal Dutch Wadden Sea. These tree-reef blocks provide a large amount of elevated, colonizable hard substrate which resulted in numerous sessile organisms growing on the trees; species richness increased with height off the sea floor. Mobile species were found to be 6x as numerous, 10% larger, and 7x as biodiverse as nearby sandy control areas. Tree-reefs may be able to partially mimic historic ecosystem services provided by sunken wood, and as a result, may be a cost-effective method to scale up estuarine and marine restoration at a meaningful scale.