US Forest Service (FS) research in the Ouachita Mountains of Arkansas suggests that decades of fire suppression have reduced the area's food supply for migrating monarch butterfliesand that restoration efforts that include prescribed burning can reverse this trend. Craig Rudolph and Ron Thill, research ecologists with the FS Southern Research Station (SRS), along with SRS ecologists Charles Ely, Richard Schaefer and J. Howard Williamson, report their findings in the latest issue of the Journal of the Lepidopterists' Society.
Every fall, masses of monarch butterflies migrate across eastern North America to remote sites in central Mexicoa long flight fuelled only by nectar from flowers still blooming on the way. In recent years, there have been concerns about the continued health of monarch populations, and of the migration itself, as land use change has altered both breeding habitat and migratory pathways.
Studies have focused on food availability for larvae, pesticides, and loss of overwintering sites in Mexico as possible threats. Less attention has been paid to how landscape-level changes affect the availability of the butterfly's preferred nectar sources along their migratory routes. In September and October, large numbers of monarchs pass through the Ouachita Mountains, a largely forested area in Arkansas and Oklahoma where fire suppression, logging, and pine production practices have altered forest structure, leading to a drastic reduction in the quality and abundance of the flowering plants the butterflies rely on for nectar.
"The area was dominated by fire-maintained shortleaf pine forests until the early 20th century," says Rudolph. "The forest was open, with a high mostly pine canopy, sparse midstory, and a diversity of herbaceous plants in an understory dominated by bluestem grassthe kind of habitat enjoyed by the endangered red-cockaded woodpecker."