Channel migration and streamside forests

Posted on December 15, 2009

River channels continually alter their positions in the floodplain as they maintain a balance between valley gradients and water and sediment transport.   They move sideways by eroding on their outer meander banks (cutbacks) and depositing sediment on their inner banks (point bars).  The effects of these dynamics on riparian forests aren’t well understood, but research on theCongareeRiver(South Carolina) has clarified some general principles.  Channel migration was slower on upstream than on downstream meander reaches.  Cutbacks opened up edge habitat, with higher levels of light, plant density and species richness.  This effect was strongest when the rate of lateral channel migration was low because this increased the time available for plant colonisation.  Unlike cutback forests, point bar forests showed species succession between the edge and the interior, but diversity and density stayed fairly constant along this gradient.  In other words, cutbacks mainly affected forest structure while point bars affected forest composition.

Reference:  Meitzen, K.M.  2009.  Lateral channel migration effects on riparian forest structure and composition, Congaree River, South Carolina, USA.  Wetlands 29, 465-475.