Potential lasting impacts of industrial herbicides on ungulate nutrition

Abstract

Glyphosate-based herbicides (GBH) are an effective, yet controversial, tool for reducing the survival and growth of deciduous vegetation in commercial tree plantations. While glyphosate residues can be stored in plants for over 10 years, the nutritional impacts of GBH for ungulate forage are unknown. Here we compare the energy and protein content of moose ( Alces alces) food plants in central British Columbia, Canada. Willow ( Salix bebbiana), dogwood ( Cornus sericea), and fireweed ( Chamaenerion angustifolium) samples were obtained from regenerating cut blocks 1, 3, 6, and 12 years after GBH treatment and from untreated controls with identical initiation dates. We predicted that surviving plants would exhibit reduced palatability, digestibility, and nutritional value compared to controls, and that these effects would last at least 1 year before dissipating. Contrary to predictions, concentrations of digestible protein were higher in treated blocks 1 year after herbicide application, but in subsequent years there were few significant differences in protein from treated versus untreated forage. Digestible energy concentrations were identical to controls 1 year after exposure, but significant reductions were observed after 12 years. Results indicate potential nonlinear, complex, and long-lasting effects of GBH on the constituents of understory plants with implications for ungulate forage quality.