Resilience of wetland vegetation to recurrent drought in the Inland Niger Delta of Mali from 1982 to 2014

The response of vegetation to variable flood regimes is an important research question for floodplains in semi-arid sub-Saharan Africa experiencing climate change. The Inland Niger Delta (IND), located within the Sahelian zone of Central Mali, is a large floodplain that has experienced a historically-significant period of recurrent drought from 1970 to 1994 followed by a recovery of floods since. Vegetation associations, as determined through 2014 fieldwork at 538 IND sites, were compared to the sites’ vegetation associations as mapped in 1982. Site-specific flood histories were constructed through the analysis of Landsat imagery across the 1982–2014 period. In more deeply flooded portions of the floodplain, observations of vegetation associations in 2014 show remarkable consistency with those existing in 1982. In areas flooded infrequently and for the shortest duration, vegetation trajectories are more complicated with evidence for bush encroachment noted at 4.5% of all sites. Flood history explains only a portion of the few site-specific changes observed over the study period. Significant changes were more likely to be associated with more recent flood history (post 1999) rather than the flood history during the preceding abnormally dry period (1982–1991). These findings point to remarkable resiliency of IND vegetation to widely fluctuating levels of flooding that are driven not only by rainfall and run-off across the watershed but also by land use, water withdrawals and damming upstream. Given the low species diversity of IND vegetation, its resiliency derives from the combination of the seasonal plasticity of perennial grass growth in relation to rainfall and flood regimes and the efficiency of their vegetative and reproductive propagation in the context of highly seasonal grazing. The co-occurrence of interannual resiliency of the IND vegetation with annual vegetation production varying significantly with annual rainfall-flood conditions is consistent with non-equilibrium ecosystem dynamics.