Above-Cliff Tundra Reveals Hidden Seabird Footprint: Evidence from Bjørnøya (Svalbard)

Abstract Bjørnøya (Bear Island) hosts one of the largest seabird colonies in the Barents Sea, with high breeding densities on steep cliffs. While most guano-derived nutrients return to the ocean, a fraction is transported inland by wind, fertilizing tundra above the colonies. We investigated how these seabird nutrient subsidies influence tundra by analysing soil properties, δ 15 N in soil and plant tissues, vegetation composition, and plant cover along six transects spanning SEABIRD (above-colony) and REFERENCE tundra. PERMANOVA confirmed strong effects of seabird presence on soil chemistry, vegetation composition, and δ 15 N. SEABIRD soils were more acidic and had elevated NH 4 + , NO 3 − , PO 4 3− , K + , total nitrogen (TN), phosphorus (P), organic carbon (TOC), Na, and moisture. Soil δ 15 N was markedly elevated in SEABIRD plots and closely tracked vegetation change. LINKTREE identified a NO 3 − threshold of 354 mg kg −1 , showing that higher NO 3 − in SEABIRD plots sharply separated them from REFERENCE plots and defined the main differences in plant composition between the two groups. A distance-based linear model identified TN, P, and Na as strongest predictors of vegetation composition. SEABIRD plots had significantly higher median plant cover (87.5%) than REFERENCE plots (15%), characterized by vegetation dominated by mosses, lichens, and nutrient-responsive vascular species. A structural equation model revealed an indirect nutrient cascade: seabird-derived nitrogen, indicated by δ 15 N, increased soil fertility (TN and P), which in turn enhanced vegetation composition and cover. These findings show that seabird nutrients shape inland tundra above the colonies, revealing a redistribution mechanism with limited attention in Arctic research.