Ornithogenic vegetation: How significant has the seabird influence been on the Aleutian Island vegetation during the Holocene?

Abstract

Abstract In the Aleutian Islands during the Holocene, terrestrial predators were actually absent; as a result, large seabird colonies thrived along the coasts or across entire islands. Bird guano enriches the soil with nitrogen, which can lead to the formation of highly modified ornithogenic (bird‐formed) ecosystems. For a more detailed investigation of avian influence, we reconstructed more than 10,000‐year‐old vegetation dynamics of the coast of Shemya Island (Near Islands) by pollen analysis. At the initial stages of vegetation development (10,000–4,600 cal year BP), sedge–heather tundra grew in the studied area. A seabird colony existed on Shemya from 4,600 to 2,400 cal year BP according to stable isotope analysis. During a period of at least 2,200 years, nitrogen enrichment led to the development of ornithogenic herb meadows with a high presence of Apiaceae. A long‐term increase in δ15N above 9–10‰ led to radical shifts in vegetation. Noticeable reduction of seabird colonies due to human hunting led to grass‐meadows spreading. After a prolonged decrease δ15N below 9–10‰ (2,400 cal year BP to present), there was a shift toward less productive sedge‐tundra communities. However, the significant enrichment of guano affected only the coastal vegetation and did not alter the inland Shemya Island.

Keywords

• Aleutian Islands
• islands ecosystems
• pollen analysis
• seabird guano
• vegetation dynamics