Effects of Bush Encroachment and Bush Removal on Soil Microbial Communities in a Savanna Ecosystem.

Bush encroachment reduces the value of savanna habitats to wild and domestic grazing animals, resulting in smaller prey populations for predators. In Namibia the Cheetah Conservation Fund has attempted to restore savannas by removing encroaching woody plants. We studied the soil microbial communities under bush and grass at three sites where encroaching bush was harvested in 2003-4, 2007, and 2009. Samples were also taken from adjacent control sites where bush was not harvested. Samples were taken in May and August of 2012 and November of 2013. PLFA and TRFLP were used to analyze soil microbial biomass and community structure. Soil C and N were increased under bush compared to grass, while pH was increased under bush relative to grass and  control sites compared to harvested sites. Microbial biomass, and the biomass of major taxonomic groups, was increased under bush compared to grass. Microbial community structure of Eubacteria, Archaea, and fungi were all affected by bush vs. grass, harvest vs. control sites, pH, N, C, and years since harvest. We conclude that (1) bush encroachment increases soil microbial biomass and alters microbial community structure in part through increased soil C, N, and pH; and (2) bush removal leads to substantial recovery of the microbial community over a time period of several years.