McKayla Susen (University of Georgia)
Each year, GTC awards 1-2 grants of up to $3,000 each to undergraduate and/or graduate students researching gopher tortoise biology and ecology, or other relevant aspects of upland habitat conservation and management within the range of the gopher tortoise. McKayla Susen was a Landers Grant recipient in 2021. Keep reading to learn more about her research on gopher tortoise habitat structure in southwest Georgia.
I am a first-year master’s student in Warnell School of Forestry at the University of Georgia. I am co-advised by Dr. Lora Smith from the Jones Center at Ichauway and Dr. Steven Castleberry from the University of Georgia. My research examines the relationship between gopher tortoises (Gopherus polyphemus) and habitat structure in southwest Georgia. I have two objectives to help explore this dynamic relationship, 1) to assess the effect of gopher tortoise population density on movement behavior and vegetation structure and composition, and 2) evaluate the effect of soil texture on gopher tortoise burrow abundance, structure (i.e., length and depth), and environment (i.e., temperature). I am currently conducting research at two locations. The first site is located in Baker County at Jones Center at Ichauway. The habitat at Ichauway is comprised of mature second-growth longleaf pine (Pinus palustris) forests, mixed pine-hardwood forests, isolated wetlands, and wildlife food plots. The second site, the Greenwood Tract, is located in Thomas County. Greenwood is dominated by old growth and second growth longleaf pine forests.
In June of this year, I trapped adult gopher tortoises at Ichauway to assess the effect of population density on behavior. This was achieved by attaching GPS loggers to gopher tortoises in low- and high-density populations, distinguished as two different plots within the Ichauway site. GPS loggers collected a location every 30 minutes to capture movement across the landscape, and were modified to extend battery life up to 6 months. I tagged and released 18 tortoises from each plot for a total of 36 tortoises. Movement data from tracked individuals will be used to evaluate behavioral differences related to population density (i.e., average daily movements, home range size, and home range overlap) at the two plots. To assess the effect of population density on the surrounding habitat I am collecting vegetation structure and composition measurements. I am recording height and density estimates of understory, midstory, and canopy cover to examine structural differences in habitat. To explore compositional differences, I categorize plants inside a quadrat into seven groups: grasses, forbs, legumes, ferns, sub-shrub tree, bare ground, and debris.
In addition to tracking gopher tortoise movements, I’m also examining soil characteristics at both Ichauway and Greenwood to examine how soil texture (i.e., percent sand and clay) affects gopher tortoise burrow abundance, structure, and environment. Ichauway has karst topography with sandy permeable soils while Greenwood has rolling hills sculpted by surface drainage causing well-drained loamy soils with iron-rich clay layers within three feet of the soil surface. Although gopher tortoises are generally more abundant in deep, sandy soils, they can create burrows in soil types varying in percent sand, silt, and clay. However, not much is known about how these textural differences affect burrow structure and temperature. For instance, clay particles cohere more than sand particles which could make burrows in clayey soils more difficult to excavate but more resistant to collapse than burrows in sandy soils. In addition, clay is more insulating than sand. Therefore, burrows in clayey soil may reach stable temperatures at shallower depths than burrows in sandy soils.
Overall, this diverse array of field work allows me to explore the dynamic relationship between gopher tortoises and habitat structure. I am on track to finish the study by February of 2023, and I look forward to presenting my final results at the GTC annual meeting in 2023.