Map 3                       Map 4                        Map 5                                                              
Map 6
Flora According   to   the   survey   carried   out   by   P.   Hiernaux   and   L.   Diarra,   the   flora   of   the   inland   Delta   contains   52   woody   species   and 137   herbaceous   species.   The   taxonomy   of   species   is   taken   from   the   flora   by   Hutchinson   &   J.M.   Dalziel:   Flora   of   West   Tropical Africa    (2nd   edition),   Keay,   R.W.J.   &   Hepper,   F.N.   (eds), Vol.   1-3. The   flora   of   the   inland   Delta   is   poor   (189   species),   even   compared to   that   of   the   surrounding   Sahelian   lands,   which   is   characteristic   of   flooded   lands.   By   way   of   comparison,   the   Gourma   region   in   the Niger   loop   has   about   350   species.   The   characterization   of   the   floristic   composition   of   each   plant   association   combines   two   notions: that   of   indicator   value   and   that   of   abundance-dominance   of   species.   The   indicator   value   of   the   species   is   indicated   by   probability thresholds   of   the   presence   of   the   species   within   a   100   m²   plot   selected   in   the   plant   association.   The   relevant   thresholds   and corresponding   codes   are   the   same   as   for   the   ecological   profiles   and   correspond   to   those   indicated   in   the   section   dealing   with   the   data processing.   The   abundance-dominance   is   indicated   independently   by   the   distinction   of   three   categories   of   species:   the   dominant, accompanying   and   occasional   species.   It   is   proposed   to   ascribe   to   these   categories   a   contribution   of   respectively   80%,   15%   and   5% to   the   production   of   the   herbaceous   mass.   These   arbitrary   rates   are   to   be   shared   between   the   species   listed   in   each   category.   In   other words   (Table   2),   the   floristic   form   of   a   plant   association   comprises   a   list   of   species,   each   species   being   characterized   by   its   indicator sign   (0,    ,+,   ++,   +++)   and   an   indication   of   abundance-dominance   status   in   the   association   as   coded   according   to   Table   1,   translated into a quantitative contribution of the species to herbage mass and production. T able 1 : Abundance-dominance status of the species                               Table 2 : profile card for B bourgoutière with Echinochloa stagnina
CODE   Abundance - dominance status   HD   Dominant Herbace o us   HA   Herbac eous companions    HO   O c casional Herbaceous   LD   Dominant Woody   LA   Woody companions   LO   Occasional Woody
The   plant   association   coded   B   only   comprises   herbaceous   plants.   The   dominant   herbaceous   species   of   a   plant   association   tally 80%   of   the   herbaceous   mass,   the   rule   of   equitable   distribution   prevailing   between   species   of   the   same   status,   two   in   this   case,   40% for   Echinochloa   stagnina    and   40%   for   Vossia   cuspidata .   Herbaceous   companions   account   for   15%   of   the   herbaceous   mass,   and occasional   herbaceous   plants   account   for   the   remaining   5%.   Again,   the   rule   of   equal   distribution   prevails   between   species   of   the same   category.   When   a   plant   association   comprises   herbaceous   and   woody   plants,   the   same   distribution   rules   apply   separately   to the 100% herbaceous mass and the 100% leaf mass of the woody plants.
The   layer   FLORE1   keeps   the   Delta   vegetation   units   (VEG4   layer)   but   associates   them   to   a   data   table   listing   the   189   plant   species (137   herbaceous   and   52   ligneous)   present   in   the   Delta.   The   structure   of   the   data   table   is   therefore   imposed   and   has   190   columns   -   or fields   -   (1   "acronym"   field   and   189   "species"   fields)   by   120   lines   (1   line   for   each   vegetation   type   listed   in   the   layer   VEG4).   For   each plant   species,   its   contribution   to   the   herbaceous   mass   or   the   woody   plant   foliage   mass   is   indicated   for   each   vegetation   type.The   absence of a particular species is coded "0". In   order   to   facilitate   the   creation   of   the   table,   the   fields   of   the   137   herbaceous   species   listed   in   alphabetical   order   have   been referred   to   as   "her_1"   to   "her_137",   the   woody   species   being   referred   to   as   "lig_1"   to   "lig_52".   A   table   in   the   annex   indicates   the correspondence between the name of the field and the name of the plant species. Working   from   FLORE1,   it   is   therefore   possible   to   map   the   spatial   distribution   of   each   plant   species   present   in   the   Delta,   either   in terms of "presence/absence" or by means of queries related to rates of participation to the plant mass in each association.
Map   1   represents   Echinochloa   stagnina    -   the   “burgu”   -   according   to   its   presence   /   absence.   Map   2   depicts   Echinochloa   stagnina   based   on   its   participation   to   the   herbaceous   mass   of   each   unit,   giving   a   very   different   picture:   the   Delta   bourgoutieres”    correspond only to the areas where Echinochloa stagnina  is the dominant species. The   abundance   of   one   species   marks   the   vegetation   units   characterized   by   a   single   plant   association   in   which   that   species dominates   –“ bourgoutière” ,   wild   rice,   Vetiver   and   Eragrostis   savannas   -   but   those   plants   are   also   present   in   multiple   mosaics.   Thus, Echinochloa   stagnina    is   dominant   in   the   bourgoutière    B   and   in   the   deep   bourgoutière    BP,   but   it   also   contributes   with   various   mass shares to nearly thirty vegetation types, as shown by the comparison of maps 1 and 2. Maps   3   to   5   present   the   spatial   distribution   of   very   common   species   in   flooded   or   dry   vegetation   types.   On   the   contrary,   map   6 presents the distribution of a species that is an environment marker.
Map 2
The layer «FLORE1»
Map 1
The   three   maps   3   to   5   show   the   spatial   distribution   of   the   presence   of   three   very   common   herbaceous   species   in   the   flooded and   dry   environment.   Vetivera   nigritana   (her_134)   is   ubiquitous   as   soon   as   there   is   flooding.   Referring   to   a   level   dominated   by Vetivera   nigritana,   as   found   in   part   of   the   literature   devoted   to   the   Delta   vegetation,   is   therefore   a   contradiction:   not   only   do   the various   Vetiver   savannas   occupy   flood   levels   ranging   from   level   3   to   level   6,   but   Vetivera   nigritana    is   also   found   in   the   deepest flood   level   -   level   7   -   in   the   PAK   association   and   in   the   shallowest   flood   level   -   level   2   -   in   the   ZB   association,   as   an   accompanying herbaceous   in   both   cases.   Oryza   longistaminata    (her_93)   is   very   abundant   in   the   flooded   plains   of   the   Delta   and   marks   well   the areas with regular average flooding. In   contrast   to   Oryza   longistaminata ,   the   association   of   Piliostigna   reticulatum    (lig_39),   Acacia   seyal    (lig_10)   and   Acacia raddiana   (lig_8)   characterizes   the   dry   "wooded"   Delta,   mainly   located   on   the   margins   and   on   the   hillocks,   the   Togge    and   the
Peroudji ,   where   the   villages   are   preferentially   located   as   well as   the   Bille ,   the   pastoral   camps   where   the   herds   rest   when they   are   not   grazing   in   the   flooded   plains   of   the   "grassy" Delta,    which    is    exploited    by    fishermen,    rice    farmers    and pastoralists.   There   are,   however,   a   few   exceptions   of   woody plants   growing   in   flooded   plains   such   as   Mimosa   pigra    and Acacia kirkii . Map    6    illustrates    an    environment    marker.    Hyphaene thebaica    (lig_32),   the   dum ”   palm   tree,   has   the   particularity of   being   born   "feet   in   the   water",   so   in   more   or   less   flooded lands.   It   is   in   particular   common   in   the   riverine   forest   of Sahelian   wadis .   As   an   adult   plant,   however,   Hyphaene    can pump   water   from   very   deep   water   tables.   It   is   a   tree   that   lives long   -   more   than   300   years   -   and   may   be   located   in   places still   flooded   to   day   or   on   the   contrary,   in   places   that   are never   reached   by   the   flood   but   might   have   been   flooded   one, two     or     three     centuries     ago.     The     comparison     of     the distribution    of    the    dum     palm    tree    with    the    limits    of    the current   flood   (by   spatial   data)   would   allow   us   to   spot   "fossil flood" locations.
Flora annexes
Dominant or   codominant species   Accompanying species     Occasional species     Echinochloa   stagnina   +++   Ipomea aquatica   +   Melochia corchorifolia   +   Vossia cuspidata   ++   Nymphaea lotus   ++   Utricularia inflexa   +       Nymphaea maculata   +   Vetiveria nigritana   +       Polygonum spp.   +