  We show that the second term in the asymptotic expansion as t approaches 0 of
the trace of the Dirichlet heat kernel on Lipschitz domains for unimodal L\'evy
processes, satisfying some weak scaling conditions, is given by the surface
area of the boundary of the domain. This brings the asymptotics for the trace
of unimodal L\'evy processes in domains of Euclidean space on par with those of
symmetric stable processes as far as boundary smoothness is concerned.
