Tree squirrel seed predation patterns may influence American chestnut restoration success

Abstract

Restoration of the functionally extirpated American chestnut (Castanea dentata) to landscapes of the eastern United States is planned with the successful propagation of a blight-resistant hybrid tree. Predicting the response of rodent seed consumers to this novel source of mast will be critical to restoration success, as rodents are important seed predators and dispersers in forests that once included chestnut. In particular, frequency-dependent foraging responses by rodents could affect the rate of spread of rare chestnuts following reintroductions. We conducted field trials to test for seed preferences and frequency-dependent selection by fox squirrels (Sciurus niger) when combinations of American chestnut and two common associates [northern red oak (Quercus rubra) and white oak (Q. alba)] were available in varying frequencies. Fox squirrels tended toward positive frequency-dependent seed predation when combinations of white oak and chestnuts were available, consuming more common mast items at a higher rate than expected based on availability. No preferences were observed between American chestnut and either red or white oak independent of frequency, but red oak was preferred over white oak. Frequency-dependent consumption of more common white oak acorns could benefit rarer chestnut during restoration, as squirrels would feed disproportionately on established white oak; however, this management strategy should only be considered following larger-scale and longer-term studies that consider impacts on white oak regeneration. Lack of preference or frequency dependence for chestnut when paired with red oak suggests that negative impacts of fox squirrel consumption on restoration will vary with the relative availability of the two seed types.