by Elizabeth Bach and Devin Edmonds

Prescribed fire is an essential management tool in grassland systems. It can help suppress invasive species, particularly woody species, and maintain native plant diversity. Some plants and animals thrive in recently burned habitat, others prefer some thatch cover or have larval stages that overwinter in surface litter. When managing for the entire ecosystem, it is helpful to maintain a rotation of burned and unburned areas, providing opportunities for a strong diversity of species with differing fire tolerance to thrive at the landscape level. This is certainly a challenge in highly fragmented landscapes like tallgrass prairie within the midwestern United States.

Habitat fragmentation is a leading cause of declining biodiversity throughout the Midwest region. This is particularly true for reptiles like ornate box turtles. As a result of fragmentation, the ornate box turtle is a state-threatened species in Illinois, where they persist in small, isolated areas. Prescribed fire is needed to maintain the open grassland habitat the turtles prefer as well as support overall biodiversity.

Ornate box turtles spend winters belowground. As temperatures cool in the fall, turtles begin digging holes and spending nights underground. Once temperatures reach a certain level, they will stay belowground essentially sleeping through the winter. As temperatures warm in the spring, turtle metabolism ramps up and they dig out of their holes. The days and weeks when the turtles enter and emerge from their burrows are a sensitive time. Their metabolisms are running more slowly, they physiologically move and respond to their surroundings slowly. If a fast-moving grass fire moves through their habitat, they may not be able to burrow down or hide quickly enough to avoid injury, or worse, death.

To help land managers identify these sensitive turtle times, Devin Edmonds and colleagues from the Illinois Natural History Survey and University of Illinois Urbana-Champaign conducted a study to determine exactly when turtles burrow in the fall and emerge in the spring. Devin attached radio-trackers to turtles in three different populations in Illinois. Observed turtle presence aboveground was correlated with air temperature, soil temperature, shell temperature, and soil inversion date to generate a predictive model land managers can use to determine conditions when turtles are most likely present aboveground.

Air temperature was the most predictive of all the environmental variables considered. In the fall, turtles can remain aboveground in cooler temperatures than in spring. Warmer air temperatures are needed in spring for turtle emergence.  The best model includes both air temperature and day of year to accurately predict ornate box turtle presence aboveground in Illinois:

Author recommended thresholds in bolded bottom row.

Lower air temperatures further reduce the probability that turtles are aboveground. We encourage land managers to be aware of areas where ornate box turtle populations exist and prioritize prescribed fire activity in those areas during the dormant season, before temperatures trigger emergence in the spring and after turtles go under in the fall. Prescribed fire in areas without known turtle populations can be prioritized outside these recommended conditions. This paper provides the most robust recommendations to date on predicting emergence and submergence dates, giving land managers more power to achieve prescribed fire objectives for the whole ecosystem and avoid turtle injury or mortality.

This study was recently published in the peer-reviewed Journal of Wildlife Management: https://wildlife.onlinelibrary.wiley.com/doi/10.1002/jwmg.22510

The paper is open access and available to download for free.