A field test of regeneration in an isolated population of violet collinsia (Collinsia violacea)

Violet collinsia (Collinsia violacea) is a winter annual ranging primarily from Missouri to Kansas. An isolated population occurs in central Illinois, 200 km from the nearest Missouri population, in a series of colonies on adjoining river bluffs. Its oak woodland habitat was undergoing vegetation changes consistent with mesophication including establishment of a subcanopy of sugar maple (Acer saccharum). We conducted a field study on one Illinois colony to determine violet collinsia response to early dormant-season fire and to test whether this species might be limited by leaf litter accumulation or absence of fire stimulus. We collected baseline data on plant density and frequency using a stratified-random grid of 72 plots (0.5 m2) overlaying the colony. We applied two experimental treatments, fire and leaf litter removal, and a no-treatment control, each with 24 replicates. We used a sheet-metal burn box in the replicate burn plots and a garden rake in leaf-litter removal plots. Only the burn plots had significant changes immediately following treatments, increasing tenfold (12 to 123 plants) between the baseline and post-treatment growing season, and increasing in frequency from 17% to 67%. Post-treatment monitoring indicated there were no carry-over treatment effects. Violet collinsia appears to be a fire-annual with the capacity for persistence in soil seed banks. Following the experiment, a prescribed burn implemented throughout the study unit during the early dormant season also yielded a tenfold increase in the colony.