The long-term development of reedbed coverage in Lake Tåkern showed a decline in recent years, primarily driven by reductions in the western, south-western, and south-eastern reed areas. In contrast, long-term monitoring of greylag geese numbers at Lake Tåkern indicated a consistent increase from 1998 to 2023. This rise reflects an international trend of growing greylag goose populations in Europe and North America due to favorable environmental conditions and easily accessible food sources in abundant agricultural fields. The comparison of the geese numbers with the long-term development of reedbeds in Lake Tåkern now indicates potential ecological interconnections.
The field exclosure experiment supported the long-term analysis result with significant effects of geese grazing on reed growth parameters. Grazing significantly reduced the height of ungrazed reed stems located in grazed areas. Higher expansion into open water demonstrated that the absence of geese provides young shoots more chance to grow further into open water and establish, increasing the reedbed area. Higher expansion and increased heights were also supported by the significantly increased biomass of young reed in the open water parts of the cages. These three results together lead to the conclusion that geese grazing weakens the whole reedbed system.
Other parameters did not show significant results; however, their long-term importance should not be overlooked, as the effects over an extended period can be significant.
Reeds play a critical role in maintaining wetland biodiversity and providing essential ecosystem services and functions such as habitat provision and biodiversity support, carbon sequestration, nutrient cycling, water filtration, soil formation and stabilisation, climate regulation, disturbance prevention, as well as provisioning, cultural, and recreational services. Given the global decline of wetlands, addressing both natural and anthropogenic factors affecting wetland habitats is essential for combating it. Future research should focus on understanding the long-term effects of geese grazing on reedbed ecosystems and identifying effective management strategies to ensure their conservation and sustainable use.
To access the complete thesis with additional results and explanations, please click here [link coming later].
Acknowledgements
I am deeply grateful to my supervisors, Mr. Karl-Olof Bergman and Mr. Anders Hargeby, for their unlimited patience, guidance, and support throughout this project. A special acknowledgement to Mr. Anders, who devoted countless hours to assisting me in the field and laboratory, sharing his motivation and expertise on Tåkern, limnology, aquatic invertebrates, and more. I deeply appreciate the valuable feedback and discussions from my examiner, Mrs. Anna Eklöf. Many thanks to Mr. Lars Gezelius and the Tåkern Field Station for logistical support and historical data, and Mr. Adam Bergner for guidance through the vast reedbelts in the south-western part of the lake. Special thanks to Mr. Gunnar Gunnarson and Ms. Elsie Kjeller for their valuable suggestions and feedback. Thanks to Ms. Helen Pružina for her dedicated assistance in the field in August. Thanks to Mr. Veaceslav Purcic for encouragement and Mr. Sergey Pidgaiko for creating the 3D cage model and trap figure included in the thesis.