Holocene vegetation and fire reconstructions from the Aquarius Plateau, Utah, USA

Micropaleontological assemblages from two lakes located on the Aquarius Plateau in southern Utah were investigated to evaluate changes in vegetation, fire disturbance, and paleoclimate over the last 8600 years. This paper presents reconstructions of Holocene landscape conditions and wildfire dynamics in the subalpine zone of the Colorado Plateau. During the early Holocene, forests on the Aquarius Plateau were dominated by spruce and pine at upper elevations and mixed conifer forests at mid-elevation sites. Fire return intervals were the most frequent of the record, averaging 250 years between burning episodes. Proxy-based reconstructions of the middle Holocene suggest warmer climate conditions relative-to-present with variable moisture availability. During the middle Holocene, the forest zone on the Aquarius Plateau contracted where both lower and upper timberline retreated upslope and downslope, respectively. Fire frequency was similar to early Holocene though overall charcoal accumulations were reduced. In the late Holocene, forests in the subalpine zone became dominated by spruce, fir, and aspen while at mid-elevation forests dominated by Douglas fir, spruce, and pine established. The most striking result indicates that evidence of fire was essentially absent from the Aquarius Plateau during the late Holocene until the arrival of European settlers to the region c. 1850.