Floodplain rehabilitation in North Cameroon: Impact on vegetation dynamics

Abstract

Abstract. Since the construction in 1979 of a dam in the Logone floodplain in the Sahelo‐Sudanian zone of Cameroon, annual inundations have decreased, reducing perennial vegetation as important grazing source for nomadic herds and wildlife during the dry season. Presently, possibilities exist to release excess water for floodplain rehabilitation. In 1994 a pilot release was executed, reflooding 200 km2, to verify predicted advantages. Vegetation has been studied from 1984 onwards along a transect covering flooded, recently reflooded and desiccated parts of the floodplain. Since 1993, the floristic composition has also been monitored in a grid in the centre of the impact zone. Cover of perennial grasses, most notably Echinochloa pyr amidalis and Oryza longistaminata increased from 41 to 61% in the reflooded zone. Vetiveria nigritana, a tussock grass that used to be dominant, disappeared slowly after the dam construction and has not shown a comeback. The cover of annual species, most notably Sorghum arundinaceum, a dominant annual grass only since the mid‐1980s, decreased in the reflooded zone from 58% to 34%. If the present conversion rate of annual into perennial grassland is extrapolated, recovery towards a 100% perennial state may be reached after the 2003 flooding season. Apart from favourable climatic conditions, recovery might be dependent on the restoration of soil fertility, limiting an approach focusing on flooding depth only.

Misreading a pastoral property regime in the Logone floodplain, Cameroon

“…In other words, pastoralists effectively distribute themselves over the available resources within the floodplain as in an ideal free distribution (Moritz et al 2014a). Similarly, we found that when the grasslands in the floodplain recovered after the reflooding project in the 1990s, the increase in grazing pressure closely tracked the increase in biomass (Scholte et al 2000(Scholte et al , 2006. This also suggests that pastoralists distribute themselves over seasonal grazing areas in an ideal free distribution (Moritz et al 2014b).…”

“…It is only if studies of the social system are combined with studies of the ecological system that we are able to evaluate that argument. For example, if Haller et al (2013) had conducted a longitudinal study of the changes in vegetation in the floodplain or reviewed the literature (Scholte et al 2000, Scholte 2005, they would have found that grassland dynamics are driven by flooding, not by grazing, and that after the reflooding project in the 1990s, pasture quality increased in response to the increase in flooding and that there was no decrease because of overgrazing. They would then have to conclude that flooding, and not institutional change, is the main driver in the floodplain.…”

Open Access, Open Systems: Pastoral Management of Common-Pool Resources in the Chad Basin

“…This led to changes in vegetation and transhumance patterns of mobile pastoralists, which we documented in five different years between 1993 and 1999 (Scholte et al 2006). Vegetation has shown a steady increase in cover of perennial grass species (from 41 to 75 %) whereas no increase in invading plant species has been observed between 1993 and 2003 (Scholte 2005;Scholte et al 2000). Grass productivity increased with the increasing above-ground biomass due to increased flooding as measured in (Scholte 2007.…”

“…In addition, forage quality and below-ground biomass has been assessed in respectively 1996 and 1994, 1995. The results of these studies, on which we build our argument regarding the lack of overgrazing, have been published elsewhere (Scholte 2007;Scholte et al 2000).…”

Pastoralist Responses to Floodplain Rehabilitation in North Cameroon

“…In combination with lower than average rainfall during the last two decades (Beauvilain, 1995), the dams reduced flooding in an area of about 1500 km 2 , which included Waza National Park, an important refuge for wildlife such as elephant, lion, antelopes, and waterfowl (Scholte et al, 1996a). Annual grasses invaded previously productive perennial grasslands, limiting regrowth in the dry season and reducing the floodplain's carrying capacity for wildlife and livestock (Scholte et al, 1996a). Studies that documented the detrimental effects of the dam on ecology and local economies (Drijver and Marchand, 1986) were the impetus for a reflooding program, which took shape in the Waza-Logone Project.…”