Recalcitrant understory layers revisited: arrested succession and the long life-spans of clonal mid-successional species

In their recent review of arrested succession, Royo and Carson (A. A. Royo and W. P. Carson. 2006. Can. J. For. Res. 36: 1345-1362) demonstrate that recalcitrant understory layers'' are widespread and pervasive modifiers of ecosystems and disruptors of forest regeneration. They rightly point out that many plant species associated with arrested succession are characterized by rapid vegetative spread. Extending their review, we point out that most of such species are clonal or thicket-forming and suggest that an additional reason why these plants so effectively suppress succession for extended periods is their long life-spans.