The Perseverance of Pocket Gophers during Dune Reactivation in the Nebraska Sand Hills: A Study of Late Holocene Gopher Burrows

The dunes within the Nebraska Sand Hills are currently vegetated and stabilized, but have been active periodically during the Holocene. The last reactivation of the dunes occurred during the Medieval Warm Period, from 950 to 650 years ago. In some places, eolian sand deposited during this time period directly overlies paleosols, providing a stark contrast in sand coloration. Burrows are easily recognized in these locations and are common both in the paleosol and the eolian sand. Burrows within the eolian sand are typically composed of dark material matching the paleosol below. Measurements of the burrows reveal widths that are consistent with the known size range for modern pocket gophers (Geomys sp.) that currently occupy vast areas of the Sand Hills, suggesting these animals as the likely burrowers. Horizontal and lateral networks of tunnels are recognized and are similar to tunnel networks of modern pocket gophers. Burrows are most common in areas of nearly horizontal bedding, near interdunes and on the plinths of the dunes. The interdunes and plinths of the dunes are some of the last regions to lose vegetative cover during dune reactivation and therefore would have been ideal places for the gophers to inhabit during the initial stages. As eolian sedimentation began to dominate the landscape and eliminate vegetation, the underlying paleosol may have provided a source of food for the pocket gophers. Burrows with dark fill are recognized up to 120 cm above the top of the paleosol, which is a much greater depth of tunneling than recognized for modern pocket gophers, indicating the environmental stress on the animals and their ability to adapt to the conditions. At higher intervals, the absence of gopher burrows suggests that the gophers were unable to survive under the continuing sedimentation and burial of their food source.