2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/69604The Faber-Krahn theorem states that among all bounded domains with the same volume in ${\mathbb R}^n$ (with the standard Euclidean metric), a ball that has lowest first Dirichlet eigenvalue. Recently it has been shown that a similar result holds for (semi-)regular trees. In this article we show that such a theorem also hold for other classes of (not necessarily non-regular) trees. However, for these new results no couterparts in the world of the Laplace-Beltrami-operator on manifolds are known.19 pages, 5 figuresCombinatoricsSpectral Theory05C35; 05C75; 05C05; 05C50text