The Aleutian Archipelago lies on the southern margin of Beringia, with islands arcing like stepping stones across the North Pacific, linking Asia and North America (Fig. 1). The associated peninsulas and islands of the North Pacific Stepping Stones (NPSS), including Kamchatka, the Commander (Komandorsky) – Aleutian Islands, and the Alaska Peninsula, host a subarctic maritime tundra flora that overlaps with, but differs from that in the more continental Bering Land Bridge region due to a long history of a warmer oceanic climate. The NPSS has been described as a “two-way filter bridge”, regulating the flow of species from both continents, with a progressive decline in Asiatic species from the western to eastern Aleutians. The NPSS is thus suspected of providing an important dispersal corridor especially for less cold-adapted taxa. The present flora, however, is inadequately documented and thus the past and potential future of plant distributions across the bioregion remain uncertain. This uncertainty has significant conservation implications, as 25% of the globally rare to imperiled plant species in the Alaska are restricted to the Aleutian and Bering Sea islands despite the small area.
Figure 1. North Pacific land masses, including the Aleutian Archipelago.
A. Current sea-level (blue) with degree of shading indicating bathymetry. Sampling locations are numbered: 1) Kamchatka, 2) Commander Islands, 3) Central Aleutians, 4) Pribilof Islands, 5) Alaska Peninsula, and 6) Kodiak Island. B. Glacial extent (white) during the Last Glacial Maximum when sea- level was ~120 m below current (green & blue boundary).
Our aim is to document the diversity and distribution of the flora along the NPSS. Such baseline information on the flora is critical for estimating the history of the region, identifying areas and taxa of special interest, and monitoring and preparing for potential changes in the future. Accomplishing this objective will yield thousands of permanently archived specimens from across the region in national herbaria with precise population and geographic location data and publicly accessible digital records. Secondly, we will test biogeographic hypotheses concerning the factors that have given rise to the current state of the flora. This will enable us to root the flora in history, adding to our understanding of the NPSS region and Beringia in general, identify potential refugia, source and sink locations, migration routes, and the impact of barriers on species with differing dispersal capabilities. Our third and final objective is to estimate current and future distributions of plant species potential habitats along the NPSS. This will provide an understanding of how different plants (e.g., endemics, cosmopolitan taxa, those of ethnobotanical importance) have been impacted by and may vary in their response to future environmental changes. In sum, addressing these three objectives will yield a deeper understanding of the history, evolution, and potential future of the flora along the NPSS.
Our examination of the past, present, and potential future of the flora of the NPSS is possible due to funding from the National Park Service Shared Beringian Heritage Program.