| Summary: | Currently warming at more than twice the rate of the global average, the Arctic is rapidly changing with global consequences. Climate change enables arctic shrub expansion, which alters ecosystem structure and contributes to permafrost degradation. This research demonstrates that landscape disturbances (such as fire and thermokarst) enhance shrub expansion by facilitating shrub seedling establishment. Through a manipulative seed-addition experiment, this research shows that disturbances result in over a four-fold increase in the number of seedlings surviving the 2nd growing season, a critical bottleneck for seedling establishment. Mortality is higher in undisturbed areas, where 4% of seedlings survived their first year of growth (compared to approximately 20% in disturbed areas). Seedling survival is controlled by seedbed quality and microsite suitability, which are altered by landscape disturbance. As disturbance regimes are increasing in frequency and severity, shrub expansion is expected to increase at a greater rate than is predicted from warming alone.
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