Long-distance transport of terrestrial plant material by convection resulting from forest fires

Paleoecologists widely accept macroscopic plant remains preserved in lake sediment as good indicators of the vegetation communities growing within and adjacent to the margin of a lake or mire. However, the study of ash fallout from a small to moderate size forest fire in a low elevation Pseudotsuga menziesii/Pinus contorta/Abies lasiocarpa stand near Bozeman, Montana suggests that certain macroscopic plant remains can be transported long distances through the atmosphere. Conifer needles, pollen cones, cone scales, bracts and wood fragments were transported via the atmosphere and subsequently deposited at least 20 km from the forest fire. The majority of the plant remains that were identified were A. lasiocarpa needles. Pseudotsuga menziesii and P. contorta needles were also identified, but both were less abundant than A. lasiocarpa. The plant material that was recovered exhibited varying degrees of charring suggesting that it may be difficult to distinguish plant material that has been transported long-distances by forest fires from that which has been derived locally. Severe convection and vortices associated with intense forest fires are believed to be the primary mechanisms responsible for transporting plant material via the atmosphere.