Holocene fire, vegetation, and climate history of western Yellowstone National Park

Abstract

The Greater Yellowstone Ecosystem is the largest intact temperate ecosystem on Earth, spanning 22 million acres. Diverse geo-ecosystem dynamics support an array of vegetation types, large intact predator-prey systems, and the highest concentration of continental thermal features in the world. This area's unique setting and land designation, which permits natural processes to occur with little active management, create unparalleled opportunities to understand how climate, environment, and disturbance interact. Harlequin Lake, located in lodgepole pine forest on the western edge of Yellowstone National Park, preserves a >9,000-year sedimentary record of vegetation, climate, and fire history. Pollen data indicate that Pinus subgen. Pinus, attributed to lodgepole pine, has been dominant since the early Holocene, reflecting persistent subalpine forest cover. Charcoal accumulation reveals that high-severity fires occurred regularly (<150 years between fire-episodes) during the early Holocene. Fire frequency declined in the mid-Holocene under cooler, wetter climates and returned to early Holocene patterns during the late Holocene, though some large-magnitude fire episodes occurred during the Medieval Climate Anomaly. Comparisons with paleoenvironmental records from sites within the region suggest that Harlequin Lake has experienced more late-Holocene fire episodes than other rhyolite lodgepole sites on the Yellowstone Plateau, likely due to its position along the western GYE margin, where the effects of interannual climate variability on fire occurrence may be more pronounced. Together, these findings provide a long-term context for evaluating modern and future fire regimes in western Yellowstone, demonstrating the resilience of lodgepole pine forests to past climate variability.