Post-fire vegetation dynamics and the invasion of Paulownia tomentosa in the southern Appalachians

Kuppinger, Dane

The last two decades have seen an increased awareness of fire’s importance in xeric southern Appalachian forest communities and an increase in its use as a management tool. In the last ten years, managers have also witnessed the invasion of Paulownia tomentosa (hereafter Paulownia) following some of these fires, and apparently as a consequence of the fires. If the pattern of Paulownia invasion is to be understood and the species targeted for control, it is essential to determine the variables that favor the spread of this exotic species into natural areas following fire and determine if it is impacting native communities or species. This work found that fire increases similarity between locations as measured by species composition and that the strength of this effect increases with fire severity. This is counter to Ryan’s Fire Severity Matrix which predicts that similarity will be negatively correlated with fire intensity. Although similarity between study sites increased after burning, each remained distinctive in ordination space and those differences increased over time as species reestablished themselves and environmental gradients shifted towards their pre-fire distributions in response to site-specific differences. This thesis also documents Paulownia seed dispersal up to 3.5 kilometers from mature individuals; distances which are orders of magnitude greater than those over which dispersal is generally measured. It also demonstrates that although Paulownia seeds may enter the seed-bank under appropriate conditions, they are killed by all but the least severe fires unless protected by burial. These buried seeds, even when only under 2cm of soil in the absence of litter, exhibit very limited germination. Together this demonstrates that invasion is controlled by the yearly seed rain rather than an accumulation of seeds within the seedbank. Habitat models document Paulownia’s range restriction over time as the initially prevalent high light and low competition conditions disappear with increasing native vegetation cover. Paulownia habitat is however maintained along cliff margins and narrow, shallow soiled benches suggesting that Paulownia will persist where these land forms are present. Although no significant correlation was found between Paulownia’s presence or cover and native species cover or diversity, this may not continue as Paulownia’s cover increases with stem maturity.