Relict woolly mammoth (Mammuthus primigenius) populations survived on several small Beringian islands for thousands of years after mainland populations went extinct. Here we present multiproxy paleoenvironmental records to investigate the timing, causes, and consequences of mammoth disappearance from St. Paul Island, Alaska. Five independent indicators of extinction show that mammoths survived on St. Paul until 5,600 ± 100 y ago. Vegetation composition remained stable during the extinction window, and there is no evidence of human presence on the island before 1787 CE, suggesting that these factors were not extinction drivers. Instead, the extinction coincided with declining freshwater resources and drier climates between 7,850 and 5,600 y ago, as inferred from sedimentary magnetic susceptibility, oxygen isotopes, and diatom and cladoceran assemblages in a sediment core from a freshwater lake on the island, and stable nitrogen isotopes from mammoth remains. Contrary to other extinction models for the St. Paul mammoth population, this evidence indicates that this mammoth population died out because of the synergistic effects of shrinking island area and freshwater scarcity caused by rising sea levels and regional climate change. Degradation of water quality by intensified mammoth activity around the lake likely exacerbated the situation. The St. Paul mammoth demise is now one of the best-dated prehistoric extinctions, highlighting freshwater limitation as an overlooked extinction driver and underscoring the vulnerability of small island populations to environmental change, even in the absence of human influence. mammoth | extinction | Holocene | St. Paul Island | ancient DNA

Aim The Bering Land Bridge (BLB) connected Asia and North America during glacial periods, supported a diverse ecosystem of now‐vanished megafauna, and is a proposed glacial refugium. This study tests whether southern coastal Beringia was a refugium for woody taxa during the Last Glacial Maximum (LGM) and hypotheses about habitats available on the BLB before and after megafaunal extinction. Location St. Paul Island, Alaska. Methods We analysed sediment cores from the Lake Hill, with a new age model anchored by 18 radiocarbon dates and multiple palaeoecological indicators (sedimentary ancient DNA [sedaDNA], macrobotanical fossils, and pollen) for the presence/absence of four woody genera: Picea, Betula, Alnus and Salix. We reconstructed vegetation history and compare St. Paul tundra composition to mainland counterparts. Results St. Paul has been continuously occupied by graminoid‐forb tundra with prostrate shrubs (Salix, Ericaceae) since 18,000 years before present (yr bp). Fossil pollen of Picea, Pinus, Betula and Alnus is present in the Lake Hill sediments at low relative abundances and accumulation rates, consistent with long‐distance transport. Macrobotanical fossils and sedaDNA analyses do not support Picea, Betula and Alnus presence. The St. Paul modern and fossil pollen assemblages are compositionally unlike mainland counterparts, but most closely resemble Arctic herbaceous tundra. Stratigraphically constrained cluster analysis indicates no major change in the vegetation after woolly mammoth extinction at 5600 yr bp, although Poaceae, Cyperaceae, Equisetum and forb abundances increase. Main conclusions This study strongly indicates that St. Paul and, by implication, southern coastal Beringia were not refugia for woody taxa during the LGM. The persistence of prostrate shrub‐graminoid tundra supports interpretations that herbaceous tundra prevailed on southern Beringia during the LGM, whilst not ruling out the possibility of mesic shrub tundra in the interior. This herbaceous tundra supported an island refugium for woolly mammoth for 8000 years, showing no major vegetation composition changes after extinction.

Mesic tree species such as Fagus grandifolia and Tsuga canadensis experienced multiple abundance declines in eastern North America during the last 8000 years, but the causes remain unclear. This paper presents a new sub-centennial record of Holocene vegetation, fire and sedimentological changes at Spicer Lake, IN, to test hypotheses about the role of fire and hydrological variations on shifts in vegetation composition. Four pollen zones are reported: Abies–Picea forests (15–11.8 ka BP), Pinus-dominated mixed forest (11.8–10.6 ka BP), transitional mixed forest (10.6–6.8 ka BP), and deciduous forest characterized by the expansion and high variability of F. grandifolia (after 6.8 ka BP). Macroscopic charcoal indicates five to seven fires between 6.1 and 4.4 ka BP and no fires between 4.4 and 2 ka BP, despite several large declines in F. grandifolia, and more fires after 1.8 ka BP likely linked to declining F. grandifolia abundances after 1.1 ka BP. Six peaks in mineralogenic sediments are suggestive of hydroclimate variability, but do not consistently correspond to shifts in F. grandifolia abundances. A Bayesian change-point analysis of 15 regional F. grandifolia pollen records identifies peak probabilities of events at 4.8 and 1.1 ka BP, similar in timing to variations in T. canadensis at other sites. Hence, fire can be ruled out as a driver of the mid-Holocene declines of F. grandifolia, but more work is needed to confidently establish the regional timing of F. grandifolia declines and to link them to past droughts and T. canadensis declines in eastern North America.

Plants will experience considerable changes in climate within their geographic ranges over the next several decades. They may respond by exhibiting niche flexibility and adapting to changing climates. Alternatively, plant taxa may exhibit climate fidelity, shifting their geographic distributions to track their preferred climates. Here, we examine the responses of plant taxa to changing climates over the past 18,000 y to evaluate the extent to which the 16 dominant plant taxa of North America have exhibited climate fidelity. We find that 75% of plant taxa consistently exhibit climate fidelity over the past 18,000 y, even during the times of most extreme climate change. Of the four taxa that do not consistently exhibit climate fidelity, three—elm ( Ulmus ), beech ( Fagus ), and ash ( Fraxinus )—experience a long-term shift in their realized climatic niche between the early Holocene and present day. Plant taxa that migrate longer distances better maintain consistent climatic niches across transition periods during times of the most extreme climate change. Today, plant communities with the highest climate fidelity are found in regions with high topographic and microclimate heterogeneity that are expected to exhibit high climate resilience, allowing plants to shift distributions locally and adjust to some amount of climate change. However, once the climate change buffering of the region is exceeded, these plant communities will need to track climates across broader landscapes but be challenged to do so because of the low habitat connectivity of the regions.