Shared and divergent rates and trajectories of Arctic vegetation community reorganization after fire and fertilization

Climate warming and increasing fire frequency are reshaping Arctic vegetation communities through changes in disturbance and nutrient availability, yet whether fire and nutrient enrichment drive similar or distinct pathways of vegetation reorganization remains unclear. We assessed rates and trajectories of vegetation change using a 10-year, two-factor nitrogen and phosphorus fertilization experiment (N ⁺ , P ⁺ , NP ⁺ ) in burned and unburned Alaskan treeless moist acidic tussock tundra. Fertilization at the burned site began after canopy closure, allowing assessment of how fire legacy effects from approximately a decade earlier influenced tundra responses. Nitrogen and phosphorus co-limitation strongly regulated vegetation responses, with NP ⁺ producing the largest increases in canopy leaf area, surface greenness, and compositional change. Fire and NP ⁺  drove similar directional shifts in vegetation composition, characterized by declines in mosses and lichens and increases in forbs and deciduous shrubs. These changes were associated with reduced community resistance, increased divergence from unfertilized controls, and higher leaf area index and surface greenness. Fire accelerated community reorganization, while NP ⁺ promoted persistent movement toward novel community states in both burned and unburned tundra. Limited fire × fertilization interactions suggest largely additive effects, with implications for shrubification, ecosystem function, and fire–climate feedbacks under continued warming.