  We construct symmetric monoidal categories $\LRF, \FD$ of rooted forests and
Feynman graphs. These categories closely resemble finitary abelian categories,
and in particular, the notion of Ringel-Hall algebra applies. The Ringel-Hall
Hopf algebras of $\LRF, \FD$, $\HH_{\LRF}, \HH_{\FD}$ are dual to the
corresponding Connes-Kreimer Hopf algebras on rooted trees and Feynman graphs.
We thus obtain an interpretation of the Connes-Kreimer Lie algebras on rooted
trees and Feynman graphs as Ringel-Hall Lie algebras.
