Compensatory plant growth may be a significant ecological process that minimizes the reduction of primary production in direct proportion to the severity of defoliation in some species and systems given the appropriate combination of environmental variables. However, the potential benefits of compensatory growth should not obscure the well—established ecological processes governing the sustainability of grazed systems in the face of large scale environmental degradation and a rapidly expanding human population. The sustainability of grazed systems is a more fundamental issue than grazing optimization.