A paleoecological fire and vegetation history in southeastern Wyoming

The Medicine Bow Range of southeastern Wyoming acts as a conduit for vegetation migration from Colorado into southeastern Wyoming. Macroscopic charcoal and pollen from Long Lake, Wyoming were used to reconstruct past fire and vegetation changes in conjunction with local, regional and broad-scale climatic changes. Distinct changes in pollen influx, along with high peak magnitudes (calculated using from CharAnalysis), were used to identify high fire severity fire episodes. The late Glacial period experienced cold and dry conditions, with low fire occurrence because there was low connectivity among the vegetation. As the climate shifted to warmer conditions in the early Holocene, conifers began to migrate into the region, creating a greater fuel source. Greater fuel sources corresponded to increased fire episodes during the middle Holocene. Fire episodes during the middle Holocene were likely high severity, stand replacing events as a result of the wetter than previous conditions. The middle Holocene experienced four climatic shifts from effectively wetter conditions to drier conditions and back. Large fires occurred around 9,000 and 5,900 cal yr B.P., which were identified based on peak magnitude and changes in the pollen influx. These fires occurred during the transition from wetter conditions to drier conditions. Tradeoffs between Pinus and Artemisia pollen were seen throughout the records with wetter conditions resulting in higher percentages of Pinus, and periods of drier conditions resulting higher percentages of Artemisia. Three evenly spaced fires occurred between 3,900-3,200 and allowed Populus to dominate the watershed. These high severity fires were detected in the pollen influx and peak magnitude data. These fires also occurred during a time of regional drying. The late Holocene saw a shift to even drier conditions than previous conditions and fire episodes increased in frequency. European settlement in the area began in the 1800s CE. Lodgepole pine timber from the Medicine Bow National Forest was one of the main sources for the building of the Transcontinental Railroad. Heavy logging began around 1860 CE and continues today. The logging disturbance is recorded in the pollen data.