On the formation of dense understory layers in forests worldwide: consequences and implications for forest dynamics, biodiversity, and succession

摘要: The mechanistic basis underpinning forest succession is the gap-phase paradigm in which overstory distur- bance interacts with seedling and sapling shade tolerance to determine successional trajectories. theory, ensu- ing simulation models, typically assume that understory plants have little impact on advance regeneration layer's composition. We challenge assumption by reviewing over 125 papers 38 species worldwide form dense persistent canopies. Once established, this layer strongly diminishes tree regeneration, thus altering rate direction of succession. term these strata recalcitrant layers. Over half cases re- viewed were linked increases canopy disturbance either altered herbivory or fire regimes. Nearly 75% studies declared competition allelopathy likely interference mechanisms decreasing yet only 25% used manipulative field experiments test putative mechanisms. present a con- ceptual model links factors predisposing formation layers their subsequent impacts propose presence constricts floristic diversity ar- gue for explicit inclusion dynamics theory models. Finally, we offer management suggestions limit establishment mitigate impacts.