Davidsonia

Waters, I., et al. 2008. Impact of a severe flood on canopy composition, tree regeneration, and ground flora of the lower floodplain of gallery forests along the Red River, Canada. Davidsonia 19(2):54-76

The 1997 Red River flood afforded a valuable opportunity for studying the impact of an infrequent severe disturbance on gallery forests. In 1997 and 2002 we sampled two sites protected and two sites unprotected by a flood control structure near Winnipeg, Manitoba, Canada using three 150 m transects in the lower floodplain (n = 45 quadrats per site). The mature canopy of unprotected sites consisted of Fraxinus pennsylvanica Marsh. and Ulmus americana L. at low cover whereas protected sites contained five tree species. Regeneration data suggest F. pennsylvanica will continue to dominate in unprotected sites, with treefall providing opportunities for pioneer flood specialists like Salix amygdaloides Anderss. Fewer gap openings occurred in protected sites, in which Acer negundo L. and F. pennsylvanica will likely become co-dominants.

Understorey taxa normally able to survive the moderate disturbance associated with seasonal inundation of the lower floodplain of protected sites succumbed to the harsh conditions in the unprotected sites. Many were knocked back or eliminated by 2002, with greater reductions in richness and diversity in unprotected sites. Ruderals were promoted in unprotected sites but most were less prominent by 2002. Although several taxa, e.g., Vitis riparia Michx. and Bidens frondosa L. had significantly higher cover in protected sites by 2002, Xanthium strumarium L. and Polygonum amphibium L. were the only understorey species with significantly higher cover in the unprotected sites. Correspondence analysis indicated flood protection generated differing trajectories, with site differences contributing to variable successional outcomes.