GPR CHARACTERIZATION OF NORTHERN PINE SNAKE BURROWS WITHIN THE PINELANDS NATIONAL RESERVE, NEW JERSEY

Biogenic sedimentary structures (burrows, tramplegrounds) and plant roots affect many critical zone processes such as soil formation, sediment mixing and compaction, as well as water exchange. Burrow distribution, extent, and morphology also provide insight into the habitat and lifestyle of the tracemaker. For certain species, such as the threatened northern pine snake (Pituophis melanoleucus), traditional methods of neoichnology such as casting and excavation are too invasive, so a non-destructive method of burrow analysis is crucial for the protection of the species. In the Pinelands National Reserve of New Jersey, adult and neonate pine snake burrow systems were imaged using a digital ground-penetrating radar (GPR) system. A pseudo-3D 800 MHz survey grid (0.3 m line spacing) was established within a 4.5 x 4.5 m protective enclosure. The bioturbated substrate is composed of an entisol (psamment) overlying a well-developed spodosol (orthod) that formed in a sand-dominated aeolian sequence. The images captured a naturally constructed burrow network composed of sub-horizontal backfilled tunnels, excavation-waste mounds, brooding chamber, and hollow neonate escape structures. In addition, a 2.3 GHz antenna was used to image several small escape structures identified through digital time lapse photography of the newly hatched snakes emerging from the subsurface. High-amplitude anomalies in the radargrams are attributed to snake burrows with diameters ranging from 2-6 cm. Extension of GPR transects and shallow trenching outside the enclosure confirmed that aligned point-source diffraction hyperbolas were generated by shallow 2-cm-thick pine roots. Our results indicate that tunnels, shafts, and chambers are discernible from the surrounding matrix at mesoscale resolution. Furthermore, geophysical information can be used to constrain the depth, size, and position of the subsurface features with minimal disturbance to the tracemakers. Therefore, high-frequency GPR imaging has immediate implications for documenting the subsurface expression of the lifestyle and nesting habits of the protected species in an attempt to improve the ongoing conservation efforts. In addition, this study aids in recognition and interpretation of ancient snake burrows in paleosols.