Involved in the gamma-resorcylate (2,6-dihydroxybenzoate) catabolism. Catalyzes the reversible decarboxylation of gamma-resorcylate to resorcinol. The reaction is reversible, but equilibrium greatly favors the decarboxylation reaction. Also catalyzes the decarboxylation of 2,3-dihydroxybenzoate to catechol, but does not act on 2,4-dihydroxybenzoate, 2,5-dihydroxybenzoate, 3,4-dihydroxybenzoate, 3,5-dihydroxybenzoate, 2-hydroxybenzoate, or 3-hydroxybenzoate. Only resorcinol is carboxylated by the reverse reaction