The influences of ecological factors on tiger bush and dotted bush patterns along a gradient from Mali to northern Burkina Faso

Seven catenas across contracted vegetation patterns, including tiger bush a nd dotted bush, were studied in the Gourma region in Mali and in northern B urkina Faso (mean annual rainfall 200-550 mm). The tiger bush encompasses a n alternate succession of bands oriented nearly perpendicularly to the wind direction NE-SW: sandy grassy microdune, sloped band of bare crusted groun d and woody depressive band. A similar succession, without wind orientation , is found for the dotted bush. In this region, tiger bush develops under s pecific conditions: (1) same orientation but opposite direction of wind and slope, (2) sedimentary and metamorphic rocks (sandstone and schist ironcru st), (3) shallow (<1 m) and impervious soils. Under such circumstances, the dynamics of banded patterns result from alternate and successive action of water and wind erosion. Field evidences showed that vegetation bands migra te upwards with a velocity of 0.2-0.7 m yr(-1). (C) 1999 Elsevier Science B .V. All rights reserved.