Mississippian lycopsid forests in growth position are extremely rare, and their community-scale ecology remains enigmatic. This is a significant gap in our knowledge, not least because they represent the precursors of Pennsylvanian ‘Coal Forests’. In this paper, nearly 700 in situ fossil trees are described from 13 entisol or inceptisol horizons in the mid-Tournaisian Albert Formation (Horton Group) at Norton, near Sussex, New Brunswick, Canada. These trees, almost all of which are lycopsids of the Protostigmaria–Lepidodendropsis-type, are rooted mostly in the flood-disturbed interdistributary wetland deposits of prograding wave-dominated deltas. Tree mapping on extensive palaeosol surfaces indicates the existence of extremely dense forest vegetation. Scaled up to standard forestry units, densities of 10 000–30 000 trees per hectare are inferred. A significant inverse linear relationship between tree diameter and density for the five most extensive palaeosols indicates that inter-tree competition led to natural self-thinning as the forests matured. Forest maturation also led to a reduction in tree-spacing heterogeneity. Flood events regularly killed whole stands at Norton, burying trees in sandstone sheets, and preventing establishment of climax vegetation. Charcoal remains demonstrate that wildfire was another important disturbance process.