Geomorphic processes and spatial patterns of primary forest succession on the Bogue Chitto River, USA

1 The Bogue Chitto River, Louisiana, USA, is a meandering river with 16 early successional tree species having > 1% relative dominance. We hypothesized that geomorphic processes associated with river planform promote predictable spatial patterns of tree species within each river bend by influencing the physical conditions under which the forest is initially established. We predicted that (i) species of trees differ in their location of recruitment along the point bar, and trees on older land reflect the spatial patterns of recent recruits; (ii) the location of recruitment differs among tree species in elevation, soil texture, herbaceous cover and light; and (iii) a specific pattern of elevation, soil texture and tree species in the earliest stage of forest succession characterizes multiple river bends in a reach. 2 On the floodplain interior to one bend, we mapped all trees and sampled seedlings and saplings, elevation, soil texture, herbaceous cover and light. In newly established forest adjacent to the point bars of eight bends, we surveyed spatial patterns of tree species, elevation and soil texture. 3 Trees of most species had characteristically become established along either the upstream or downstream segment of each point bar. Variation in tree species composition was gradual both along the point bar and along an axis of increasing age of land. The locations of recruitment and mature trees were the same for eight of 11 common species on the focal river bend. 4 The locations of tree recruitment and of mature trees of specific species on the focal bend were related to spatial patterns of elevation (corresponding to flood regime), soil texture, light, herbaceous cover and the inferred pattern of shear stress by flood water on the point bar. The same patterns of elevation and soil texture and locations of tree species characterized multiple river bends. 5 Geomorphic processes related to the river planform of the Bogue Chitto River promote spatially complex but predictable patterns of primary forest succession.