Abstract
Summary A study has been made of the features associated with repeating bands of vegetation in the Butana region of the Sudan. Aerial observations show that they have similar features to those described by MacFadyen in British Somaliland except that the curved bands lie on the interfluves and are convex downslope. The patterns consist entirely of grasses and herbs, and lie on very gentle slopes of about I in zoo; there is no measurable difference in elevation between the grasses and bare areas. Slopes of less than I in 500 have no patterns. The width of the bands is variable, but commonly between 8 and 12 m., and the bare ground about twice the width of the grass. The profile consists of a grey‐brown clay loam, with an A horizon slightly lighter in colour and texture. No difference in profile, composition, or properties between the soil under grass and under bare ground has been detected, except in pH, nitrate, and moisture. There are differences in soil surface, the bare areas being smooth and the grassed areas broken by cracks and potholes which form at the beginning of the rains and concentrate just upslope of the previous season's grass. Experiments to simulate on the bare ground the moisture and growth conditions obtaining under the grass bands were partially successful. The current season's grass concentrates at, and in advance of, the previous season's front, and there is an annual migration of the grass bands upslope. The vegetation consists dominantly of the grasses Aristida spp., Schoenfeldtia gracilis, Cymbopogon nervatus , and Sehima ischaemoides. Species of grass may have a restricted position in the grass band, the most striking being Schoenfeldtia. Herbs are more ephemeral, but are prominent during the rains in the old grass areas. The origin of the patterns appears to be related to water supply, topography, and soil, but not to wind. Comparison with gilgai is made, but reasons are given for considering that the patterns have a different mode of origin, and an initiation due to a type of soil slip or to a rhythmic deposition of vegetation is considered possible.
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Claims 7
Claim · model-written summary
The vegetation bands were convex downslope on interfluves.
Verbatim
e0“the curved bands lie on the interfluves and are convex downslope”
t0“GRASS”
Claim · model-written summary
The patterns occurred on gentle slopes, but were absent below the stated slope.
Verbatim
e0“Slopes of less than I in 500 have no patterns”
t0“GRASS”
Claim · model-written summary
Grass bands commonly measured 8 to 12 m wide.
Verbatim
e0“The width of the bands is variable, but commonly between 8 and 12 m.”
t0“GRASS”
Claim · model-written summary
Grass and bare areas differed in pH, nitrate, and moisture.
Verbatim
e0“No difference in profile, composition, or properties between the soil under grass and under bare ground has been detected, except in pH, nitrate, and moisture”
Claim · model-written summary
Grass bands migrated upslope each year.
Verbatim
e0“there is an annual migration of the grass bands upslope”
Claim · model-written summary
The vegetation was dominated by four named grass taxa.
Verbatim
e0“The vegetation consists dominantly of the grasses Aristida spp., Schoenfeldtia gracilis, Cymbopogon nervatus , and Sehima ischaemoides”
Claim · model-written summary
Pattern origins appeared related to water supply, topography, and soil.
Not reportedDirection
Verbatim
e0“The origin of the patterns appears to be related to water supply, topography, and soil, but not to wind”
t0“GRASS”