Shrub mound formation and stability on semi-arid slopes in the Northern Negev Desert of Israel: A field and simulation study

In semi-arid areas vegetation is scarce and often dominated by individual shrubs on raised mounds. The processes of formation of these mounds are diverse and still debated. Often, shrub mound formation is directly related to the formation of vegetation patterns, thereby assuming that shrub mound formation is driven by biological interactions. We hypothesize that water-related erosion and sedimentation are also important drivers of shrub mound formation in the Northern Negev Desert of Israel. We test this hypothesis by combining field observations with model simulations. We studied shrub mounds in the semi-arid catchment of Sayeret Shaked in the Northern Negev Desert (200 mm annual precipitation). Height and diameter of shrub-canopy and shrub mounds were measured and micro-morphological techniques were used to reconstruct the formation of the shrub mounds. We used landscape evolution model LAPSUS to simulate shrub mound formation at short (single precipitation event) and longer (100 years) timescales at different slope angles. Both field and model results indicate that shrub mounds in Sayeret Shaked are at least partly formed by redeposition of eroded material below the shrubs, and by erosion and lowering of the surrounding crust. Additional model simulations suggest that mounds are formed most under low shrub density and large shrub-canopy diameter. Shrub mound formation increases with slope. In dryer and wetter climates than the studied 200 mm rainfall semi-arid climate zone, shrub mound formation is less likely.