PhD defence Solveig Höfer
Solveig Höfer (ConsEco)
Promotores: Prof. T. van der Heide, Prof. M.J. Wassen (UU); Copromotor: Dr V. Reijers (UU)
From shifting sands to stable dunes
Disturbance responses at the individual-plant and community levels across coastal dune landscapes
Coastal dunes protect the hinterland from flooding, store drinking water and support biodiversity. Yet climate change, rising sea-levels, construction and recreation threaten these landscapes. This thesis examines how dune plants and communities respond to disturbance. The first part focuses on marram grass, a dune-building plant. Marram grass traps wind-blown sand and helps dunes grow. Conditions benefiting young plants are not always best for mature ones. The dynamic beach made it difficult for young plants to establish, but mature plants recovered best there after disturbance. In more stable backdunes, young plants established more easily, while mature plants recovered less well. As young plants developed, some changes in form were linked to growth, while others reflected adjustments to sand burial. Conditions that initially supported survival became less beneficial over time, resulting in lower survival and less vigorous growth. The second part examines grey dunes, the biodiversity hotspot behind the first dune ridge. Communities with more plant species recovered better from widespread disturbances such as trampling and above-ground biomass removal. However, greater species richness did not improve recovery from dune-specific disturbances involving sand sprinkling and burial. No single stage of dune development recovered best from every type of disturbance. Together, the findings show that functional dunes require a balance between dynamic and stable conditions. These conditions support different life stages of marram grass, while a mosaic of successional stages and communities with different numbers of species supports grey-dune recovery from different disturbances. Protecting this natural variation will help dunes support people and nature.