Date: 22nd of October 2025, 10:30 AM
Anna Mariager Behrend will defend her doctoral thesis in Restoration Ecology at the Faculty of Environmental and Forest Sciences at the Agricultural University of Iceland.
Anna Mariager Behrends dissertation is entitled "Patterns and processes of birch establishment in space and time: Implications for large-scale woodland restoration."
Anna Mariager Behrends supervisors are Professor Ása L. Aradóttir, Agricultural University of Iceland; Dr Kristín Svavarsdóttir, Land and Forest Iceland, and Professor Þóra Ellen Þórhallsdóttir, University of Iceland.
Her opponents are Professor Alison J. Hester, The James Hutton Institute, and Professor Susana Bautista, University of Alicante.
Abstract
The continuous global ecosystem loss and degradation calls for extensive ecological restoration. Iceland has lost more than 95% of its original native mountain birch (Betula pubescens ssp. tortuosa) woodlands since the country’s settlement in the 9th century CE. This has prompted an ambitious pledge for their restoration by the Icelandic government with the acceptance of the Bonn Challenge, aiming to increase native birch woodland cover from 1.5 to 5%. This is only going to be possible through passive and low-intensity restoration strategies, and such strategies must be grounded in an in-depth knowledge of colonization processes of the targeted species.
The overall aim of this thesis was to improve knowledge on the patterns, processes and drivers of mountain birch woodland expansion through natural processes in order to guide their restoration. It encompasses studies at different scales, including field surveys, seeding experiments and remote sensing, based on ten study areas in most lowland areas of Iceland.
Analysis of aerial photos from different years showed that the studied birch woodlands expanded on average by 2% annually over a period of 38-65 years. Areas that had been protected from grazing had higher expansion rates than those open for grazing, and the area with the highest expansion rate had also undergone revegetation. This expansion has mainly happened through natural colonization as revealed by surveys of colonization patterns: a process mainly limited by local environmental factors at the early establishment phase. This includes microsite availability, wind and soil type, and disturbance in the form of presence of domestic grazers. Seedling densities were greatest within 20 m of the woodland edge, indicating dispersal limitation, but colonization patters varied among areas. However, most areas had densities of more than 100 seedlings m-2 out to at least 100 m. The results also show a positive effect of greater woodland heights on the effective colonization range of birch, and on the morphology of saplings growing at the woodland edge. Seeding experiments confirmed the importance of favourable microsites (safe sites) for recruitment. Recruitment of mountain birch was furthermore highly variable among different land classification types (habitat types), dependent on safe site availability and partly on origin of the seed source used. These are factors that can be controlled in restoration to improve conditions for birch establishment and survival.
The results show the feasibility of upscaling mountain birch woodland restoration by applying knowledge on natural processes to promote natural colonization and regeneration. The increased knowledge on birch colonization processes supports more targeted guidance on how natural recovery processes can be enhanced by limited interventions.
