\makeatletter
\@ifundefined{HCode}
{\documentclass[screen,CRGEOS,Unicode,biblatex,Thematic,published]{cedram}
\addbibresource{crgeos20240602.bib}
\let\Lbreak\newline
\newenvironment{noXML}{}{}
\let\citep\parencite
\let\citet\textcite
\def\xcitealp#1#2{\citeauthor{#1}, \citelink{#1}{#2}}
\def\citealt#1#2{\citeauthor{#1}, \citelink{#1}{#2}}
\newcommand*{\citelink}[2]{\hyperlink{cite.\therefsection @#1}{#2}}
\def\defcitealias#1#2{}
\let\citetalias\textcite
\let\citepalias\parencite
\def\thead{\noalign{\relax}\hline}
\def\endthead{\noalign{\relax}\hline}
\def\tbody{\noalign{\relax}}
\def\tabnote#1{\vskip4pt\parbox{.92\linewidth}{#1}}
\def\xxtabnote#1{\vskip4pt\parbox{.82\linewidth}{#1}}
\def\tsup#1{$^{{#1}}$}
\def\tsub#1{$_{{#1}}$}
\def\ndash{\text{--}}
\def\hyphen{\text{-}}
\def\og{\guillemotleft}
\def\fg{\guillemotright}
\def\0{\phantom{0}}
\makeatletter
\g@addto@macro{\UrlBreaks}{\UrlOrds}
\gappto{\UrlBreaks}{\UrlOrds}
\RequirePackage{etoolbox}
\usepackage[most]{tcolorbox}
\usepackage{upgreek}
\def\inlinefig#1{\includegraphics{#1}}
\def\jobid{crgeos20240602}
%\graphicspath{{/tmp/\jobid_figs/web/}}
\graphicspath{{./figures/}}
\def\xmorerows#1#2{#2}
\newcounter{runlevel}
\usepackage{multirow}
\def\nrow#1{\@tempcnta #1\relax%
\advance\@tempcnta by 1\relax%
\xdef\lenrow{\the\@tempcnta}}
\def\morerows#1#2{\nrow{#1}\multirow{\lenrow}{*}{#2}}
\let\MakeYrStrItalic\relax
\def\refinput#1{}
\let\ubreak\break
\csdef{Seqnsplit}{\\}
\def\botline{\\\hline}
\def\back#1{}
\newcommand*{\hyperlinkcite}[1]{\hyper@link{cite}{cite.#1}}
\DOI{10.5802/crgeos.321}
\datereceived{2024-07-18}
\daterevised{2025-05-30}
\datererevised{2025-10-05}
\dateaccepted{2025-11-25}
\ItHasTeXPublished
}
{
\PassOptionsToPackage{authoryear}{natbib}
\documentclass[crgeos]{article}
\usepackage[T1]{fontenc}
\def\CDRdoi{10.5802/crgeos.321}
\def\citelink#1#2{\citeyear{#1}}
\def\xcitealp#1#2{\citealp{#1}}
\let\ubreak\relax
\def\xxtabnote#1{\tabnote{#1}}
\makeatletter
\def\hyperlinkcite#1#2{\citeyear{#1}}
}
\makeatother

\usepackage{upgreek}

\dateposted{2026-01-30}
\begin{document}

\begin{noXML}

%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{Human Environment Observatory}
%\def\cdr@specialtitle@french{Observatoire Homme Milieu (OHM)}
%\makeatother

\CDRsetmeta{articletype}{review}

\TopicFR{D\'eveloppement durable, am\'enagement}
\TopicEN{Sustainable development, landscaping}

\editornote{Article submitted by invitation}
\alteditornote{Article soumis sur invitation}

\title{Ten years of research on the biodiversity of the Great 
Green Wall by the International Human-Environment observatory
T\'{e}ss\'{e}k\'{e}r\'{e} in Senegal}

\alttitle{Dix ans de recherches sur la biodiversit\'{e} de la Grande
Muraille Verte par l'Observatoire Hommes \textendash{} Milieux
International T\'{e}ss\'{e}k\'{e}r\'{e} au S\'{e}n\'{e}gal}

\author{\firstname{Papa Ibnou} \lastname{Ndiaye}\CDRorcid{0000-0002-9978-564X}\IsCorresp}
\address{D\'{e}partement de Biologie animale, Facult\'{e} des Sciences
et Techniques, Universit\'{e} Cheikh Anta Diop de Dakar, S\'{e}n\'{e}gal}
\address{OHMi T\'{e}ss\'{e}k\'{e}r\'{e}, IRL 3189 Environnement-Sant\'e-Soci\'et\'es 
(CNRS/UCAD/UGB/USTTB/CNRST), Dakar, S\'{e}n\'{e}gal}
\curraddr[P. I. Ndiaye]{D\'epartement de Biologie animale, Facult\'e des Sciences
et Techniques, Universit\'e Cheikh Anta Diop de Dakar, BP5005 Dakar-Fann,
S\'en\'egal}
\email{ibnou.ndiaye@ucad.edu.sn}
\email[P. I. Ndiaye]{papaibnoundiaye@gmail.com}

\author{\firstname{Priscilla} \lastname{Duboz}\CDRorcid{0000-0002-5869-379X}}
\addressSameAs{2}{OHMi T\'{e}ss\'{e}k\'{e}r\'{e}, IRL 3189 Environnement-Sant\'e-Soci\'et\'es 
(CNRS/UCAD/UGB/USTTB/CNRST), Dakar, S\'{e}n\'{e}gal}
\address{UMR 7268 ADES (CNRS/AMU/EFS), Marseille, France}
\email[P. Duboz]{priscilla.duboz@cnrs.fr}

\author{\firstname{Christophe} \lastname{Diagne}\CDRorcid{0000-0002-6406-1270}}
\address{CBGP (INRAE/CIRAD/IRD/Institut Agro Montpellier), Montpellier, France}
\email[C. Diagne]{christophe.diagne@ird.fr}

\author{\firstname{Laurent}\nobreakauthor\lastname{Granjon}\CDRorcid{0000-0003-1182-3793}}
\addressSameAs{4}{CBGP (INRAE/CIRAD/IRD/Institut Agro Montpellier), Montpellier, France}
\email[L. Granjon]{laurent.granjon@ird.fr}

\author{\firstname{Fulvio} \lastname{Licata}\CDRorcid{0000-0001-8234-9676}}
\address{Centro de Investiga\c{c}\~{a}o em Biodiversidade e Recursos
Gen\'{e}ticos (CIBIO), InBIO Laborat\'{o}rio Associado, Universidade do
Porto, Campus de Vair\~{a}o, 4485-661 Vair\~{a}o, Portugal}
\address{BIOPOLIS Program in Genomics, Biodiversity and Land Planning,
CIBIO, Campus de Vair\~{a}o, 4485-661 Vair\~{a}o, Portugal}
\email[F. Licata]{fulvio.licata@cibio.up.pt}

\author{\firstname{Aly} \lastname{Diallo}\CDRorcid{0000-0001-7567-3187}}
\addressSameAs{2}{OHMi T\'{e}ss\'{e}k\'{e}r\'{e}, IRL 3189 Environnement-Sant\'e-Soci\'et\'es 
(CNRS/UCAD/UGB/USTTB/CNRST), Dakar, S\'{e}n\'{e}gal}
\address{Universit\'{e} Assane Seck de Ziguinchor, Casamance, S\'{e}n\'{e}gal}
\address{D\'{e}partement de Biologie v\'{e}g\'{e}tale, Facult\'{e} des Sciences et Techniques, 
Universit\'{e} Cheikh Anta Diop de Dakar, S\'{e}n\'{e}gal}
\email[A. Diallo]{aly.diallo@univ-zig.sn}

\author{\firstname{Natalia} \lastname{Medina-Serrano}\CDRorcid{0009-0009-6455-5543}}
\address{UMR 5175 CEFE, University of Montpellier/CNRS/EPHE/IRD, Montpellier, France}
\email[N. Medina-Serrano]{natalia.medina-serrano@cefe.cnrs.fr}

\author{\firstname{Moustapha\nobreakauthor Bassimb\'{e}}\nobreakauthor\lastname{Sagna}\CDRorcid{0009-0001-6871-9375}}
\addressSameAs{2}{OHMi T\'{e}ss\'{e}k\'{e}r\'{e}, IRL 3189 Environnement-Sant\'e-Soci\'et\'es 
(CNRS/UCAD/UGB/USTTB/CNRST), Dakar, S\'{e}n\'{e}gal}
\addressSameAs{8}{D\'{e}partement de Biologie v\'{e}g\'{e}tale, Facult\'{e} des Sciences et Techniques, 
Universit\'{e} Cheikh Anta Diop de Dakar, S\'{e}n\'{e}gal}
\email[M. B. Sagna]{moustaphabassimbe.sagna@ucad.edu.sn}

\author{\firstname{Martine} \lastname{Hossaert-McKey}\CDRorcid{0000-0001-9274-0994}}
\addressSameAs{2}{OHMi T\'{e}ss\'{e}k\'{e}r\'{e}, IRL 3189 Environnement-Sant\'e-Soci\'et\'es 
(CNRS/UCAD/UGB/USTTB/CNRST), Dakar, S\'{e}n\'{e}gal}
\addressSameAs{9}{UMR 5175 CEFE, University of Montpellier/CNRS/EPHE/IRD, Montpellier, France}
\email[M. Hossaert-McKey]{martine.hossaert@cnrs-dir.fr}

\author{\firstname{Aliou} \lastname{Guisse}}
\addressSameAs{2}{OHMi T\'{e}ss\'{e}k\'{e}r\'{e}, IRL 3189 Environnement-Sant\'e-Soci\'et\'es 
(CNRS/UCAD/UGB/USTTB/CNRST), Dakar, S\'{e}n\'{e}gal}
\addressSameAs{8}{D\'{e}partement de Biologie v\'{e}g\'{e}tale, Facult\'{e} des Sciences et Techniques, 
Universit\'{e} Cheikh Anta Diop de Dakar, S\'{e}n\'{e}gal}

\author{\firstname{Gilles}\nobreakauthor\lastname{Bo\"{e}tsch}}
\addressSameAs{2}{OHMi T\'{e}ss\'{e}k\'{e}r\'{e}, IRL 3189 Environnement-Sant\'e-Soci\'et\'es 
(CNRS/UCAD/UGB/USTTB/CNRST), Dakar, S\'{e}n\'{e}gal}

\author{\firstname{Doyle} \lastname{McKey}\CDRorcid{0000-0002-7271-901X}}
\addressSameAs{2}{OHMi T\'{e}ss\'{e}k\'{e}r\'{e}, IRL 3189 Environnement-Sant\'e-Soci\'et\'es 
(CNRS/UCAD/UGB/USTTB/CNRST), Dakar, S\'{e}n\'{e}gal}
\addressSameAs{9}{UMR 5175 CEFE, University of Montpellier/CNRS/EPHE/IRD, Montpellier, France}
\email[D. McKey]{doyle.mckey@cefe.cnrs.fr}

\shortrunauthors

\keywords{\kwd{Biodiversity}
\kwd{Great green wall project}
\kwd{International observatory of Human-Environment T\'{e}ss\'{e}k\'{e}r\'{e} interactions}
\kwd{Sahel}
\kwd{Sahelian ecosystems}
\kwd{Socio-ecosystem}}

\altkeywords{\kwd{Biodiversit\'{e}}
\kwd{Projet grande muraille verte}
\kwd{Observatoire international hommes -- milieux T\'{e}ss\'{e}k\'{e}r\'{e}}
\kwd{Sahel}
\kwd{\'{E}cosyst\`{e}mes Sah\'{e}liens}
\kwd{Socio-ecosyst\`{e}me}}

\thanks{Labex DRIIHM, French programme ``Investissements d'Avenir''
(ANR-11-LABX-0010), which is managed by the ANR (French National
Research Agency)}

\begin{abstract} 
The Sahel has long been plagued by drought, which along with human
pressure has caused ecosystem degradation, biodiversity loss, and
increased poverty of local populations. Thus, in 2005 African heads of
state set up a project, named the ``Great Green Wall'' (GGW), to
restore Sahelian ecosystems. Establishment of the GGW led to the
founding in 2009 of the ``International Human-Environment observatory
T\'{e}ss\'{e}k\'{e}r\'{e} (OHMi T\'{e}ss\'{e}k\'{e}r\'{e})'', between
France's National Center for Scientific Research and Cheikh Anta Diop
University (Dakar, Senegal), to assist decision-making by providing
scientific information. The OHMi's research is conducted in the Ferlo,
northern Senegal. This paper summarizes knowledge of the region's
biodiversity and how the GGW may affect it. Semi-natural grazed
parklands dominated by grasses with scattered trees occupy over 90\% of
the surface. Eighty-two woody plant species, representing 55 genera and
26 families, have been recorded. Forbs (non-graminoid herbs) are more
diverse but account for a small proportion of vegetation cover. The
study of arthropod biodiversity is just beginning. A first study showed
that 427 insect morpho-species visit the flowers of a single common
tree species, \textit{Balanites aegyptiaca}. Vertebrate biodiversity
includes seven species of amphibians, eleven species of reptiles and
217 bird species, among them palearctic migratory species (including 60
waterbirds) some of which are classified at high protection levels on
the IUCN's Red List. Four species of micromammals (in order of
decreasing abundance, \textit{Gerbillus nigeriae},
\textit{Arvicanthis niloticus}, \textit{Taterillus pygargus} and
\textit{Mastomys erythroleucus}) occur in the area. Nine species of
large wild mammals occur, of which eight are nocturnal.
\vspace*{-2.5pt}
\end{abstract}

\begin{altabstract} 
Le Sahel Africain est victime de longues ann\'{e}es de s\'{e}cheresse
qui, conjugu\'{e}e \`{a} la pression humaine, a entra\^{i}n\'{e} une
d\'{e}gradation des \'{e}cosyst\`{e}mes, une perte de biodiversit\'{e}
et une augmentation de la pauvret\'{e} des populations locales. C'est
pourquoi, en 2005, des chefs d'\'{E}tat Africains ont mis en place un
projet b\^{a}ptis\'{e} \guillemotleft{} Grande Muraille Verte \guillemotright{} (GMV) afin de
restaurer les \'{e}cosyst\`{e}mes sah\'{e}liens d\'{e}grad\'{e}s. La
cr\'{e}ation de la GMV a conduit \`{a} la fondation en 2009 
de l'\guillemotleft Observatoire Hommes-Milieux International T\'{e}ss\'{e}k\'{e}r\'{e}
(OHMi T\'{e}ss\'{e}k\'{e}r\'{e}) \guillemotright, entre le Centre National de la
Recherche Scientifique de France et l'Universit\'{e} Cheikh Anta Diop
de Dakar (S\'{e}n\'{e}gal), afin d'aider \`{a} la prise de d\'{e}cision
en fournissant des informations scientifiques aux d\'{e}cideurs. Au
S\'{e}n\'{e}gal, les recherches de l'OHMi sont men\'{e}es dans le
Ferlo, au Nord du pays. Ce manuscrit r\'{e}sume les connaissances sur
la biodiversit\'{e} de la r\'{e}gion et l'impact potentiel du GMV sur
celle-ci. Les espaces naturels p\^{a}tur\'{e}s, domin\'{e}s par des
gramin\'{e}es et parsem\'{e}s d'arbres, occupent plus de 90 \% de la
surface. Quatre-vingt-deux esp\`{e}ces de plantes ligneuses,
repr\'{e}sentant 55 genres et 26 familles, ont \'{e}t\'{e}
r\'{e}pertori\'{e}es. Les plantes herbac\'{e}es non gramino\"{i}des
sont plus diversifi\'{e}es, mais ne repr\'{e}sentent qu'une petite
partie de la couverture v\'{e}g\'{e}tale. L'\'{e}tude de la
biodiversit\'{e} des arthropodes n'est qu'\`{a} ses d\'{e}buts.

Une premi\`{e}re \'{e}tude a montr\'{e} que 427 esp\`{e}ces d'insectes
visitent les fleurs d'une seule esp\`{e}ce d'arbre, \textit{Balanites
aegyptiaca}. La biodiversit\'{e} vert\'{e}br\'{e}e comprend sept
esp\`{e}ces d'amphibiens, onze esp\`{e}ces de reptiles et 217
esp\`{e}ces d'oiseaux, parmi lesquelles des esp\`{e}ces migratrices
pal\'{e}arctiques (dont 60 oiseaux aquatiques). Certaines esp\`{e}ces
d'oiseaux sont class\'{e}es \`{a} des niveaux de protection
\'{e}lev\'{e}s sur la Liste rouge des esp\`{e}ces prot\'{e}g\'{e}es de
l'Union Internationale pour la Conservation de la Nature (UICN). Quatre
esp\`{e}ces de micromammif\`{e}res (par ordre d\'{e}croissant
d'abondance, \textit{Gerbillus nigeriae}, \textit{Arvicanthis
niloticus}, \textit{Taterillus pygargus} et \textit{Mastomys
erythroleucus}) sont pr\'{e}sentes dans la r\'{e}gion. On y trouve neuf
esp\`{e}ces de grands mammif\`{e}res sauvages, dont huit sont
nocturnes.
\end{altabstract} 

\maketitle

\vspace*{-2pt}

\twocolumngrid

\end{noXML}

\defcitealias{Faye2020}{ibid.}
\defcitealias{Billen2015}{ibid.}

\section{Introduction}\label{sec1}

\vspace*{-2pt}

The Sahel, the semi-arid region just south of the Sahara, is frequently
subjected to long years of drought. This bioclimatic zone is defined by
rainfall levels between isohyets of 250~mm and 500~mm, an 8--10-month
dry season and steppe vegetation \citep{CasenaveValentin1989}. Rainfall
is highly variable across years. Climatic fluctuation and climate
change, combined with anthropogenic pressures on the environment such
as overgrazing and the abusive use of chemical fertilizers for
agriculture, among others, have led to the degradation of ecosystems,
accompanied by biodiversity loss and increased poverty of local
populations \citep{Zwarts2009,Zwarts2012,Zwarts2018}. This is why African heads of
state, in a 2005 meeting of the African Union (AU), took the decision
to set up a restoration project, which they named Great Green Wall
(GGW). The aim of this project is to restore Sahelian ecosystems
weakened by the dual impact of climate (drought) and human activity
(extensive livestock farming). Eleven African countries are involved in
the GGW project, which in its original conception covers a strip 7800
km long and 15~km wide, between the Atlantic Ocean and the Red Sea (the
Senegal segment is 550~km long). 

{\advance\baselineskip by .14pt

The establishment of the GGW inspired the creation in 2009 of the
International Human-Environment observatory (OHMi)
T\'{e}ss\'{e}k\'{e}r\'{e}, a partnership {between} France's CNRS and the Cheikh Anta Diop University in Dakar (Senegal). The OHMi is one of
13 Human-Environment Observatories established by the CNRS. All are
based on a founding ternary (\url{https://www.inee.cnrs.fr/fr/ohm}): a
socio-ecological framework, a disrupting event and a focal object. For the OHMi
T\'{e}ss\'{e}k\'{e}r\'{e}, the first element is the socio-ecological
context of the northern Sahel, where the primary mode of subsistence is
extensive pastoralism, with ecological challenges posed by scant and
irregular rainfall and heavy anthropogenic pressure. The focal object
is the Sahelian savannahs of the Ferlo region of northern Senegal. The
disrupting event is the establishment of the GGW. The aim of the OHMi
is to study, through an interdisciplinary and multi-scale approach, the
medium-term impacts of the GGW on Sahelian socio-ecosystems, including
both human populations and the environments with which they interact 
\citep{Guisse2013}. \looseness=-1

}

Before the creation of the OHMi, ecological, health and demographic
data were either completely unavailable or too fragmented to be very
useful. The initial work of the OHMi has thus consisted in \mbox{building} up
baseline data that will enable monitoring the {impact} of the
implementation of the GGW. Alongside research activities, OHMi
T\'{e}ss\'{e}k\'{e}r\'{e} has contributed to restoration activities of
the GGW, planting trees and favoring natural regeneration in protected
plots. The OHMi also includes a component aimed directly at poverty
alleviation and local development (e.g., diffusion of multi-purpose
village gardens), a sine qua non for the project's acceptance and
success. 

Work carried out by the OHMi is thus multi-sectoral, and increasingly
interdisciplinary, exploring the manifold links between biodiversity,
ecosystem services, the local economy, and human health
\citep{Sandifer2015,APGMV2018}. The first aim of this article is to present, on
the basis of work carried out by OHMi T\'{e}ss\'{e}k\'{e}r\'{e}
researchers, baseline data on the environment and its plant and animal
biodiversity. The second aim is to begin to analyze the impacts of the
GGW on biodiversity and its implications for the development and
improved well-being of human populations in Senegal's Ferlo region.
Restoration of ecosystems takes time, typically decades, and the GGW,
facing numerous challenges in this semi-arid environment, is no
exception. Although the full impact of the GGW cannot yet be judged, we
point to promising directions for the future.


\section{The International Human-Environment observatory
T\'{e}ss\'{e}k\'{e}r\'{e} : an integrative model of international
cooperation based on scientific research}

More than 100 researchers, post-docs, PhD students and Master's
students at several universities and research institutions in Africa
and Europe work under the auspices of the OHMi
T\'{e}ss\'{e}k\'{e}r\'{e}. Work within the OHMi
T\'{e}ss\'{e}k\'{e}r\'{e} currently focuses on four major themes:
biodiversity, health, water and soil, and social systems. Most of the
work has been carried out at Koyli Alpha, Widou,
T\'{e}ss\'{e}k\'{e}r\'{e} and Labgar (Figure~\ref{fig1}).

\begin{figure*}
\vspace*{-4pt}
\includegraphics{fig01}
\vspace*{-6pt}
\caption{\label{fig1}Localization of the study area.}
\vspace*{-6pt}
\end{figure*}

Biodiversity is the basis of essential environmental services on which
life on the planet depends. Consequently, its conservation and
sustainable use are of paramount importance. Habitat degradation and
resource overexploitation are particularly crucial as drivers of
biodiversity loss across Africa. Information on biodiversity is
incomplete for many organisms. Preserving an area's natural
biodiversity and the genetic diversity of harvested species can boost
resistance to insect invasions and disease outbreaks, thereby reducing
agricultural losses. For all these reasons, identifying locations of
high biodiversity for several major groups, allowing the protection of
a large proportion of biodiversity in a comparatively small area, is an
important research objective \mbox{\citep{Scholes2006}}. To this end,
researchers from a variety of backgrounds and specialities have been
involved in the activities of OHMi T\'{e}ss\'{e}k\'{e}r\'{e} to
generate knowledge about biodiversity and ecosystem services in the GGW
route area. This knowledge currently covers:
\begin{itemize}
\item Plant biodiversity, species recommended for reforestation, and
local people's uses and perceptions of vegetation;
\item Animal biodiversity, with identification of current and extinct
fauna, and local people's uses and perceptions of wildlife;
\item Interactions between fauna, flora, domestic animals and human
populations. 
\end{itemize}

\subsection{Plant biodiversity}\label{sec11}

The phytoecological characterization of ecosystems plays an important
role in the study of Sahelian ecosystems in Senegal. The mapping of
land use along the GGW route by \citet{Sylla2019} provided an initial
opportunity to determine the current state of plant communities and
their spatio-temporal dynamics. The results obtained in the
municipality of T\'{e}ss\'{e}k\'{e}r\'{e} showed 13 land-use units and
their current state. These are wooded savannah, shrub to wooded
savannah, shrub savannah, wooded steppe, shrub to wooded steppe, shrub
steppe, market gardening, rainfed cultivation and fallow land,
residential areas, ponds, bare areas and areas occupied by tree
plantations. There is great diversity and dominance of the ``natural
vegetation formation'' category (in reality, ``semi-natural''), with
eight classes occupying over 90\% of the surface. All 13 land-use units
were present in 1984, i.e., after the great drought of the 1970s, with
the exception of the plantation class, which today occupies 2.04\% of
the surface. The conversion of land to plantations is due to
tree-planting campaigns of the GGW, whose first
interventions in the area began in 2008. Overall, analysis of changes
in land use showed that 27.5\% of the municipality's surface area
remained in its initial state, 65.5\% underwent modifications and 7\%
conversions.

Several studies have characterized woody vegetation in different areas
within the Ferlo \citep{Ndiaye2013,Ndong2015a,Kebe2020}, recording 35,
38, and 23~species, respectively.  Combining the results of the three
studies, the total is 82 woody species, representing 55 genera and 26
families. While there is substantial overlap in species composition
between the western part of the study area (Sahelian climate), and the
eastern part (Sahelo-Soudanian climate), the latter is more diverse
(73~species,  47~genera and 22 families) than the former (44~species,
36~genera and  17~families). The most represented families are Fabaceae
(21~species), Combretaceae (12 species), Capparaceae (7~species),
Malvaceae  (6~species), Apocynaceae (5~species), Moraceae and Rubiaceae
(3~species of each family). In this flora, the genera \textit{Acacia}
(now divided into three genera) and \textit{Combretum} are best
represented, with 11 and 8~species respectively. The former genus
\textit{Acacia} has been revised; African species are now placed in the
genera \textit{Senegalia} (including the former \textit{A. Senegal})
and \textit{Vachellia}. In its present circumscription, the genus
\textit{Acacia} is restricted to Australia. \textit{Balanites
aegyptiaca} (Zygophyllaceae) is the most abundant species along the
route. In the Sahelo--Sudanian sector, \textit{Combretum glutinosum}
(Combretaceae), \textit{Balanites aegyptiaca} and \textit{Guiera
senegalensis} (Combretaceae) are the most frequent. In the Sahelian
zone, on the other hand, the most frequent species are
\textit{Balanites aegyptiaca}, \textit{Vachellia tortilis} subsp.
\textit{raddiana}, \textit{Boscia senegalensis} (Capparaceae) and
\textit{Leptadenia hastata} (Apocynaceae). 

Herbaceous cover in the region is dominated by grasses, among the most
abundant species being \textit{Aristida mutabilis, Schoenefeldia
gracilis} and \textit{Cenchrus biflorus} \citep{Ndong2015a}. Forbs
(non-graminoid herbaceous plants) are more diverse but occupy a smaller
proportion of cover. \citet{Miehe2010} recorded 131 species of
herbaceous plants in the Ferlo, including 40 species of Poaceae and 91
species of forbs. Work on the herbaceous stratum by OHMi researchers
has focused on the impact of protection from grazing on biodiversity
and vegetation structure \citep{Badji2020} and on the importance of
topographic depressions and ponds in conserving this biodiversity
\citep{Faye2020}. \citetalias{Faye2020} compared herbaceous vegetation in
two grazed depressions and one ungrazed (fenced) depression near Widou
Thiengoly. They found a total of 55 herbaceous species, distributed
across 41 genera and \mbox{22~botanical} families. Protection from grazing had
a marked effect on species composition and richness, vegetation cover,
and plant growth, all being higher in the fenced depression. That plot
was also the only one that harboured certain species that are rare in
the region. These results underline the importance of opographic
depressions and ponds in biodiversity conservation in this semi-arid
region \citep{Dendoncker2023}.

Results of \citet{Badji2020} and \citet{Faye2020} show that protection
from grazing can make a significant contribution to restoring
ecological functions in the GGW area. While the results presented
concerned herbaceous plants, which, with their short life cycles,
respond quickly to restoration efforts, our results indicate that
protection from browsing can also benefit trees. The potential for
natural regeneration in protected plots is very high for the following
tree species: \textit{Acacia tortilis}, \textit{A.~raddiana},
\textit{Balanites aegyptiaca} and \textit{Boscia senegalensis}. For
other woody species, such as \textit{Terminalia leiocarpa} (formerly
named \textit{Anogeissus leiocarpus}; Combretaceae), \textit{Grewia
bicolor} (Malvaceae), \textit{Sclerocarya birrea} (Anacardiaceae) and
\textit{Sterculia setigera} (Malvaceae), among others, the potential
for natural regeneration is extremely low or non-existent, both inside
and outside the protected plots. Most of these species originate from
old, non-spiny (and generally less drought-resistant) stands that are
currently dying back in Senegal's Sahelian ecosystems as a result of
climate change.\looseness=-1

\subsection{Animal biodiversity}\label{sec12}

The GGW project was initially announced as a reforestation
project. Perhaps some people thought it was going to be limited to this
objective. This was not the case, as the implementation of activities
and the involvement of researchers through the OHMi
T\'{e}ss\'{e}k\'{e}r\'{e} demonstrated the need to involve several
disciplines with mixed teams of researchers. Thus, following the
identification of the tree species most suitable for reforestation,
other researchers turned their attention to herbaceous plants and to
wildlife, in particular insects, amphibians, reptiles, birds, and
mammals, and to ecosystem services provided by biodiversity.

\subsubsection{Insects}\label{sec121}

Restoration initiatives in the Ferlo region have mainly focused on
trees, and few studies have taken an ecosystem-wide approach to
examining the interactions between organisms. Biotic interactions play
a central role in ecosystem function and resilience
\citep{Carlucci2020,Dicks2021}. Our research on insect-flower
interactions provides an entry point to explore the diversity of biotic
interactions and their contributions to ecosystem function
\citep{Kevan1999}. 

Insects play a predominant role in the pollination of angiosperms,
making them key players in ecosystems. Maintaining their interactions
with flowering plants is a key part of the success of ecological
restoration \citep{Dirzo2014,Genes2022}. In the context of the
GGW, our aim is to provide baseline data on the diversity
of insect floral visitors and begin to study the impact of the
initiative's interventions on this key component of ecosystem
functioning.

The entomological literature for this region, and for the northern
Sahel in general, is scattered in various specialist publications.
There exists no synthesis of insect diversity in this region,
especially in relation to insect pollination \citep{Ollerton2017}. The
first goal of our work has thus been to characterize the diversity of
flower-visiting insects in the region and assess its current 
status\footnote{This research has produced a review of insect-flower
interactions in the Sahel \citep{Medina2025} and two papers in
preparation  (Medina-Serrano et~al., unpublished results).}.
This research is essential
for studying the impact of GGW actions on ecological restoration. To do
this, we sampled the diversity of flower-visiting insects in three
insect-pollinated tree species with significant socio-ecological
importance in the Ferlo region
\citep{Ndiaye2013,Ndong2015b,Dendoncker2020}: \textit{Balanites
aegyptiaca} (the desert date; Zygophyllaceae), \textit{Vachellia
tortilis} (Mimosoideae, Fabaceae; formerly \textit{Acacia tortilis}),
and \textit{Ziziphus mauritiana} (Rhamnaceae). 

\begin{table*}[t!]%tab1
\caption{\label{tab1}Total diversity of insects sampled at flowers of
\textit{Balanites aegyptiaca}}
\begin{tabular}{cccc}
\thead
{Order} &  {Species richness} & {Abundance} & Number of identified families \\
\endthead
Hymenoptera &  201 &  4115 &  44 (13 superfamilies) \\
Diptera &  116 &  1272 &  40 (20 superfamilies) \\
Coleoptera &  \041 &  \0275 &  16 (11 superfamilies) \\
Hemiptera &  \038 &  \0402 &  14 \\
Thysanoptera &  \012 &  \0281 &  1 \\
Lepidoptera &  \0\07 &  \0229 &  / \\
Neuroptera &  \0\04 &  \0\012 &  3 \\
Psocoptera &  \0\04 &  \0\0\07 &  / \\
Orthoptera &  \0\03 &  \0\0\07 &  3 \\
Ephemeroptera &  \0\01 &  \0\0\01 &  1
\botline
\end{tabular}
\end{table*}


The study was carried out in the Ferlo region, in the vicinity of three
villages along the Senegalese GGW layout, Ranerou, Koyli
Alpha and Widou Thiengoly. Near each village, sampling was conducted in
three kinds of sites differing in vegetation density and diversity:
inside parcels in which trees had been planted, livestock excluded, or
both; in areas that had not been planted with trees and were exposed to
grazing and browsing; and in seasonally wet depressions around
temporary ponds. We installed pan traps (yellow, white and blue) for
during 48 hours, and caught insects visiting the flowers with a hand
net during three days at different times of day \citep{Westphal2008,Wilson2008}.
These two methods give complementary information about flower-visiting
insects (for example, nocturnal insects were caught only in pan traps).
Trees near all three villages were sampled at the end of the dry
season, in May and June 2022. \textit{Balanites aegyptiaca} flowers
at different times of the year, enabling us to characterize seasonal
variation in the composition of flower visitors. Thus, in one of the
villages, Koyli Alpha, we carried out two more sampling campaigns in
the wet season in August 2022 and in the middle of the dry season in
February 2023. 


Up to now, data have been compiled for one of the three tree species,
\textit{Balanites aegyptiaca}. Analysis of the insects collected at
flowers of the other two species is ongoing. We found unexpectedly high
insect diversity. For the one species for which insects have been
determined (\textit{B.~aegyptiaca}), we found a total of 427
morpho-species visiting its flowers. These insects belong to 10 orders,
among which Hymenoptera and Diptera predominated, accounting for 317
morpho-species  (Tables~\ref{tab1} and~\ref{tab2}).

\begin{table}[t!]%tab2
\caption{\label{tab2}Abundance of the six most abundant families of
insects at flowers of \textit{Balanites aegyptiaca}\vspace*{2pt}}
\begin{tabular}{cc}
\thead
{The six most abundant families} & {Abundance} \\
\endthead
Formicidae (Hymenoptera) &  2624 \\
Halictidae (Hymenoptera) &  \0553 \\
Chloropidae (Diptera) &  \0325 \\
Mythicomyiidae (Diptera) &  \0239 \\
Braconidae (Hymenoptera) &  \0291 \\
Phlaeothripidae (Thysanoptera) &  \0281
\botline 
\end{tabular}
\vspace*{2pt}
\end{table}

By a significant margin, the most abundant insects were ants, followed
by Halictidae, a family of solitary or subsocial bees
\citep{Danforth2002,Danforth2008}. Bees rely primarily on flowers as
food resources as both adults and larvae, while the other insects
captured at flowers can be part of several food webs. For instance,
ants at flowers may collect \mbox{nectar}, but they also hunt prey; braconid
wasps are parasitoids of other insects and use nectar to fuel their
search for hosts \citep{Jervisetal1993}. Mythicomyiidae are abundant
flower visitors in arid and desert regions throughout the world. As a
sign of how much we still have to learn about the insect fauna of the
region, very little is known about the life cycle of these abundant
flies \citep{Evenhuis2002}. Hundreds of species await description. 

\begin{table*}[t!]%tab3
\caption{\label{tab3}List of amphibian species observed in Ferlo, the
total number of observations and their conservation status according to
the IUCN \citep[unpublished data]{Licata2025}\vspace*{2pt}}
\begin{tabular}{ccccc}
\thead
{Families} &  {Species} & Number of individuals &  {IUCN status} \\
\endthead
\morerows{1}{Bufonidae}  & \textit{Sclerophrys pentoni} &  891 & LC \\
 & \textit{Sclerophrys xeros} & \0\08 & LC\vspace*{3pt} \\
\morerows{1}{Pyxicephalidae}  & \textit{Pyxicephalus edulis} & \018 & LC (but decreasing) \\
& \textit{Tomopterna milletihorsini} & \068 & DD\vspace*{3pt} \\
{Hyperoliidae} & \textit{Kassina senegalensis} & \0\09 & LC\vspace*{3pt} \\
\morerows{1}{Ptychadenidae}  & \textit{Ptychadena schillukorum} & \0\01 & LC \\
 & \textit{Ptychadena trinodis} & \0\01 & LC 
\botline
\end{tabular}
\xxtabnote{LC ${=}$ least concern; DD ${=}$ not classified owing to
insufficient data.}
\end{table*}

Our research has unveiled an unexpected diversity of flower-visiting
insects in \textit{Balanites aegyptiaca}. However, our current dataset
is insufficient to draw robust conclusions regarding the impact of the
GGW. It is imperative that research efforts continue,
including further sampling and monitoring in the Ferlo region, to
assess the current status and trends in insect diversity. Research is
also needed to determine the significance of the ecosystem services
supplied by flower-visiting insects. Is pollination a limiting factor
in fruit production by culturally and economically important trees?
What roles do \mbox{flower-visiting} insects play in the regulation of
populations of other insects?

This work aligns with the interdisciplinary research framework of the
GGW. Beyond its field applications, the project aims to
enrich our understanding of the social, ecological, and economic
dynamics of the people residing in the Sahel region. Our research and
data collection efforts are designed to make the most of this
knowledge.

\subsubsection{Amphibians and reptiles} \label{sec122}

Surveys carried out at Koyli Alpha, Widou Thiengoly,
T\'{e}ss\'{e}k\'{e}r\'{e} and Labgar, municipalities averaging about
21.3~km$^{2}$ in area (range: 17--26~km$^{2}$), revealed the presence
in the Ferlo, documented by direct observations, of seven species of
amphibians belonging to four families (Table~\ref{tab3})
\citep{Licata2025}.


The information in Table~\ref{tab3} shows that the toad
\textit{Sclerophrys pentoni} is the most frequent species in the study
area, with 891 sightings in 25 sampling days (i.e., 89.5\% of total
sightings), followed by the frog \textit{Tomopterna milletihorsini}
with 68 sightings, i.e., 6.8\% of total sightings. The frog species
\textit{Ptychadena schillukorum} and \textit{P.~trinodis} were observed
very rarely in the study area. All species observed are classified as
``Least Concern'' (LC) on the IUCN Red List. However, the total number of
observations made for this study reveals the need for special measures
to be taken by the authorities for their conservation in Ferlo. The
species \textit{Ptychadena schillukorum} and \textit{P.~trinodis} were
observed only once each, both times at Koyli Alpha. This suggests their
rarity in the Ferlo region.

To date, 11 reptile species have been identified in the area covered by
the GGW in Senegal (Table~\ref{tab4}). These belong to two orders and
nine families. The order Squamata (lizards and snakes) is the best
represented in the area, with eight families and 10 species. The only
other reptile recorded is one turtle species. All the reptile species
recorded in the region are classified as ``Least Concern'' on the IUCN
Red List, with the exception of the Sebacean Python (\textit{Python
sebae}), which is ``Near Threatened'' (NT), and the ridged turtle
(\textit{Centrochelys sulcata}, Testudinidae), which is ``Endangered''
(EN). The ridged turtle had completely disappeared from this area of
Senegal. The population observed in this study comes from a
reintroduction of 20 individuals \citep{DiagneDiagne2019}.

\begin{table*}[t!]%tab4
\caption{\label{tab4}List of reptile species recorded in the GMV in
Senegal \citep{Thiaw2021}, their French names, and their IUCN status
\vspace*{2pt}}
\tabcolsep7pt
\begin{tabular}{ccccc}
\thead
Orders &  Famiies & Species & French name & IUCN status \\
\endthead
\morerows{9}{Squamata}  & Agamidae &  \textit{Agama agama} &  Margouillat & LC \\
& Gekkonidae & \textit{Stenodactylus petrii} & St\'{e}nodactyle de P\'{e}trie & LC \\
& Phyllodactylidae & \textit{Tarentola senegambiae} & Tarente de S\'{e}n\'{e}gambie & LC \\
& Scincidae & \textit{Chalcides delislei} & Scinque du S\'{e}n\'{e}gal & LC\vspace*{4pt} \\
& \morerows{1}{Varanidae} &  \textit{Varanus exanthematicus} & Varan de savane & LC \\
&&\textit{Varanus niloticus} & Varan du Nil & LC\vspace*{4pt} \\
 & \morerows{1}{Boidae}  &  \textit{Eryx muelleri} & Boa des sables de Muller & LC \\
&&\textit{Python sebae} & Python de S\'{e}ba & NT\vspace*{4pt} \\
 & Elapidae & \textit{Naja senegalensis} & Cobra s\'{e}n\'{e}galais & LC \\
 & Viperidae & \textit{Bitis arietans} & Vip\`{e}re heurtante & LC\vspace*{7pt} \\
Testudines & Testudinidae & \textit{Centrochelys sulcata} & Tortue sillonn\'{e}e & EN
\botline
\end{tabular}
\tabnote{LC ${=}$ least concern; NT ${=}$ near threatened; EN ${=}$ endangered.}
\vspace*{2pt}
\end{table*}

\subsubsection{Birds}\label{sec123}

A number of studies have been carried out in the past in the Senegal
River valley \citep{Morel1978}, particularly in the Djoudj National
Bird Park and in the northern Ferlo, but none have focused on the GGW
route area. These studies have shown the presence of significant avian
biodiversity in this part of the country. In fact, of all the different
regions of Senegal, the Ferlo has the highest concentrations of
migratory birds during the migration period 
\citep{Zwarts2012,Zwarts2018,Zwarts2023a,Zwarts2023b}.  
Thus, following the observation of the importance of
birds in ecosystems, the OHMi has been interested in bird biodiversity
in Ferlo since 2011 \citep{Roux2012,Diop2020,Diop2023,Diop2024a}. 
We have \mbox{currently} identified 217 bird species, including 
60~waterbird species. Almost half of the species identified are migratory
(106 species), with palearctic migrants predominating. Examples include
the Black-tailed Godwit (\textit{Limosa limosa}), Turtle Dove
(\textit{Streptopelia turtur}) and Eurasian Spoonbill (\textit{Platalea
leucorodia}). Some species are classified at high protection levels on
the IUCN's Red List of Threatened Species. These include the
Black-tailed Godwit \textit{(Limosa limosa}), Savannah Boater
(\textit{Terathopius ecaudatus}), Abyssinian Bucorva (\textit{Bucorvus
abyssinicus}), Turtle Dove (\textit{Streptopelia turtur}), Scavenger
Vulture (\textit{Necrosyrtes monachus}), the African Vulture
(\textit{Gyps africanus}), R\"{u}ppell's Vulture (\textit{Gyps
rueppelli}) and the Scavenger Vulture (\textit{Necrosyrtes monachus})
\citep{Diop2020,Diop2023,Diop2024b}. Owing to disturbances noted in the
area of the Djoudj National Bird Park as a result of climate change and
the development of rice cultivation in the Ferlo, some species such as
pelicans, spoonbills and storks, which used to migrate only to this
park, now come as far south as the Lac de Guier tributary south-east of
Keur Momar Sarr, very near the Koyli Alpha community nature\break reserve.

\subsubsection{Micromammals}\label{sec124}

\paragraph{Study of rodent populations}

The results are based on trapping carried out between 2009 and 2016 in
different habitats in three villages (Labgar, T\'{e}ss\'{e}k\'{e}r\'{e} and
Widou-Thiengoly) along the GGW route in Senegal: inside plots initially
fenced off to exclude livestock and encourage the regeneration of woody
vegetation (protected plots; two per locality), outside these plots
(more or less degraded savannah areas and fields) and at the ecotone
(edge) between these two habitats  \citep[see][for details of the
methodology]{Granjon2019}.

\begin{table*}[t!]%tab5
\caption{\label{tab5}Trapping effort  \citep[in number of nights
effective traps, cf.][]{Granjon2019}, results of trapping carried out
in and outside of defended plots between 2009 and 2016 along the GGW in
Senegal, and Shannon diversity indices for each species assemblage}
\tabcolsep3pt
\begin{tabular}{cccccccc}
\thead
&\parbox[t]{2.3cm}{\centering Trapping effort (trapnight number)} &  
\parbox[t]{1.7cm}{\centering \textit{Arvicanthis
niloticus}} &  \parbox[t]{1.3cm}{\centering \textit{Gerbillus nigeriae}} &  
\parbox[t]{2cm}{\centering\textit{Mastomys erythroleucus}} &  
\parbox[t]{1.4cm}{\centering \textit{Taterillus pygargus}} &  
\parbox[t]{1.6cm}{\centering Total number of captures} &  
\parbox[t]{1.4cm}{\centering H$'$ \mbox{(Shannon)}} \vspace*{2pt}\\
\endthead
{Fenced areas} &  1510 &  60 &  93 &  0 &  59 &  212 &  2.47 \\
\parbox[t]{2.2cm}{\raggedright Surrounding habitat matrix} &  1096 &  60 &  92 &  2 &  
15 & 169 &  1.39 \vspace*{2pt}
\botline
\end{tabular}
\vspace*{-2pt}
\end{table*}

To test the hypothesis of an effect of fenced plots (and therefore of
woody regeneration) on populations of terrestrial small rodents, we
compared trapping results and the diversity of species assemblages
between the ``fenced'' (i.e., fenced plots and their edges) and
``non-fenced'' (savannah and field habitat matrix) sets. The results
(Table~\ref{tab5} and Figure~\ref{fig2}) show no significant difference
in stand composition between these two groups. \textit{Gerbillus
nigeriae}, \textit{Arvicanthis niloticus} and \textit{Taterillus
pygargus} are, in that order of abundance, the species present, with a
fourth species, \textit{Mastomys erythroleucus}, having only been
caught twice near a small pond outside the defended plots. On the other
hand, the relative abundances of the three dominant species appear to
be more \mbox{equitable} on the defended plots, resulting in a much higher
diversity index for this category of plots (H$'$\ ${=}$\ 2.47 vs.\ 1.39
outside the defended plots).

\begin{figure}
\vspace*{2pt}
\includegraphics{fig02}
\caption{\label{fig2}Trapping yields 
(numbers of captures in relation
to the effective trapping effort, expressed as percentages, see details
in \citet{Granjon2019}) for the four rodent species captured in
and outside the protected plots in the developed areas of the 
GGW in Senegal (villages of Labgar, T\'{e}ss\'{e}k\'{e}r\'{e} and Widou
Thiengoly).}
\vspace*{-2pt}
\end{figure}

In the GGW area of Senegal, due to environmental changes
associated with the period of rainfall deficit from the 70s to the 90s
as well as anthropogenic activities in the Sahel 
\citep{Lebel2009,Miehe2010,Gonzalez2012,Bodian2014,Brandt2014,Walther2016},
significant changes in the
structure of local communities of small mammals have been observed over
the last few decades \citep{Granjon2019}. Today, species adapted to
aridity (Gerbillinae and among them species of the genus
\textit{Gerbillus}) or to habitats created/modified by man 
(\textit{A.~niloticus} in hedgerows around fields) dominate the Ferlo stand, where
the majority of species 40 years ago was a species \mbox{typical} of Sahelian
savannahs \citep[\textit{T.~pygargus},][]{Poulet1972}. The two species
that dominate today's assemblage (\textit{G.~nigeriae} and
\textit{A.~niloticus}) are known to be harmful to crops and stored
goods, as well as being potential reservoirs of pathogens transmissible
to humans and livestock \citep{GranjonDuplantier2009,Dahmana2020}.

\subsubsection{Larger wild mammals}\label{sec125}

Work on large wild mammals (LWM) began in 2015 with numerous surveys at
Widou Thiengoly, T\'{e}ss\'{e}k\'{e}r\'{e}, Labgar and then Koyli Alpha
\citep{NiangNdiaye2021,Niang2023a}. We based our work on the
classification of \citet{Kassa2022}, who define as large mammals those
whose average weight is ${\geq}$2~kg. Several study methods were used
during the surveys: surveys of local populations, line transects,
reconnaissance transects, fixed points, and camera trapping. Surveys
were mostly conducted during the day, with nocturnal surveys on a few
occasions. This was the first study of LWM in this part of the Ferlo.
In further work, the team has concentrated on Koyli Alpha and the
surrounding area. This work has shown the presence of nine species of
LWM, eight of which are nocturnal (Table~\ref{tab6}).

\begin{table*}[t!]%tab6
\caption{\label{tab6}Repertory of the large wild mammals encountered in
the GGW area. Indications to~evaluate their relative
abundance are presented in two publications
\citep{NiangNdiaye2021,Niang2023a}\vspace*{-2pt}}
\begin{tabular}{ccccc}
\thead
Orders & Families & Species & 
French name & UICN red list category \\
\endthead
\morerows{6}{Carnivora}  & \morerows{1}{Canidae}  & \textit{Canis aureus} & Chacal dor\'{e} & LC \\
 &  & \textit{Vulpes pallida} & Renard des sables & LC\vspace*{4pt} \\
 & Felidae & \textit{Felis silvestris} & Chat sauvage & LC \\
 & Herpestidae & \textit{Atilax paludinosis} & Mangouste des marais & LC\vspace*{4pt} \\
 & \morerows{1}{Mustelidae}  & \textit{Ictonyx striatus} & Zorille & LC \\
 &  & \textit{Mellivora capensis} & Ratel & LC\vspace*{4pt} \\
 & Viverridae & \textit{Genetta genetta} & Genette commune & LC\vspace*{8pt} \\
Lagomorpha & Leporidae & \textit{Lepus capensis} & Li\`{e}vre & LC \\
Primates & Cercopithecidae & \textit{Erythrocebus patas} & Singe patas & NT
\botline
\end{tabular}
\tabnote{LC ${=}$ least concern; NT ${=}$ near threatened; DD ${=}$ not
classified.\vspace*{-2pt}}
\end{table*}

According to the IUCN's Red List of Threatened Species, of these nine
species only the Patas monkey is classified as ``Near Threatened
(NT)'', all others being of minor concern. However, while several
widely distributed species such as the Cape hare, the pale fox and the
golden jackal are globally of ``least concern'', the poor state of
conservation of their current habitats in Senegal makes it clear that
special attention needs to be paid to the conservation of these species
to avoid the risk of their disappearance in Senegal. There is a need to
draw up a local red list of endangered species for better biodiversity
\mbox{management} at the national level. In the course of our works, we have
identified a loss of biodiversity in the Ferlo zone. We reported in
\citet{NiangNdiaye2021a,NiangNdiaye2021} the decline of five species of LWM in Ferlo
zone, among them the dorcas gazelle, the striped hyena and the leopard,
which are classified as ``Vulnerable'', ``Near \mbox{Threatened}'' and ``Critically
Endangered'' respectively. The dorcas gazelle was disappeared from the
Ferlo area for many years but, an attempt to reintroduce a few
individuous from captivity has permited the repopulation of northern
Ferlo. In this context, it is important to have information on locally
extinct species so as to be able to envisage their reintroduction as
part of the restoration of degraded ecosystems. This is the context in
which the Sahelo-Saharan antelope Oryx algazelle (\textit{Oryx dammah})
is being reintroduced into the Koyli Alpha Community Nature Reserve
\citep{Niang2023a}. The herd is currently adapting well to the
reserve's environmental conditions. In fact, at least four births a
year have been recorded so far, for a herd of six individuals starting
out in May 2020. This example shows that reintroduction can also be
possible for other species that have disappeared from the area. The
reintroduction of Gazelle dorcas (\textit{Gazella dorcas}), Oryx
algazelle and Gazelle dama (\textit{Nanger dama}) into the Katan\'{e}
enclosure in Ferlo Nord \citep{Abaigar2013} is a good model on
which to base such actions along the GGW route.

\subsection{Intra- and interspecific interactions}

A return to rainier conditions \citep{Bodian2014} and the
rehabilitation of more treed habitats, for \mbox{example} via the GGW
initiative \citep{DiaDuponnois2012,Boetsch2019}, could
offer opportunities to rebalance the small mammal community, but more
generally to help re-establish more diverse animal communities. The
restoration of more complex ecological relationships, including
parasitism, competition and predation, could in turn help the natural
regulation of populations of rodents in the region 
\citep{Krebs1999,Bianchi2006}, following the example of what has been observed in
temperate zones \citep{BenedekSirbu2018,Meyer2019} and in
southern Africa \citep{Starik2020}. With regard to predation, the
increase in tree density associated with the regeneration of woody
species, an action at the heart of the GGW, should encourage the
establishment of raptors that prey on small rodents such as the barn
owl \citep[\textit{Tyto alba},][]{Thiam2008}, which would thus benefit from more
perches and nesting sites. The contribution of these predators to the
control of small mammal populations 
(see \citet{Krebs1999} and \citet{Labuschagne2016} for discussions
on this subject), would fit in completely with the logic of ecological
management in the framework of the operational expectations of the GGW
\citep{DiaNiang2012}. 

The ecosystem interactions between restoration actions and the presence
of insect and small mammal populations have therefore been studied and
documented, thanks to the work of OHMi T\'{e}ss\'{e}k\'{e}r\'{e}. A
final major aspect of animal biodiversity has also played an important
role: the study of bird populations. Insects and rodents form a large
part of the diet of various predators, including birds, some of which
feed exclusively on insects or rodents \citep{Morel1978}. In fact,
studies carried out at OHMi T\'{e}ss\'{e}k\'{e}r\'{e} have shown that
birds are more numerous in fenced plots (more Palearctic and
intra-African migrants and vultures), as these plots offer better
conditions for nesting, an abundance of food (insects for the
black-billed hornbill, for example, and rodents for raptors)
\citep{Roux2012}. On the other hand, these plots are less frequented
by granivorous birds, which prefer open-ground territories. Studies
have also shown that fenced plots constitute refuge areas for resting
and breeding for many species of birds and large mammals
\citep{Diop2020,Diop2023,Diop2024a,Diop2024b,Niang2023a}. Thus, from a
bioecological point of view, the reforested perimeters, in addition to
improving bioclimatic conditions, also contribute to the conservation
of both animal and plant biodiversity.

A project on the scale of the GGW necessarily entails changes in many
aspects of the environment and society, not just effects on flora and
fauna. These changes, socio-economic and demographic, primarily concern
human populations, and include the opening up of the area and
associated transport infrastructure. Another important transformation
is the increase in the number of boreholes, as well as the increased
transport of water from boreholes to near hamlets and other residential
areas. The widespread availability of water causes piosphere gradients
\citep{Shahriary2021} to flatten or disappear, with widespread heavy
grazing, as more and more of the savannah is close enough to water to
allow heavy grazing and browsing. The research carried out by OHMi
T\'{e}ss\'{e}k\'{e}r\'{e} has highlighted the importance of these
transformations, which are indirectly linked to the installation of the
GGW, leading to a co-construction between researchers from the
disciplines of ecology and the humanities and social sciences.

\subsection{Relations between people and their environment}

The relationship between human populations and their environment in
Senegal's GGW zone is complex and multifaceted. The GGW 
is a project aimed at combating desertification and
restoring degraded ecosystems in the Sahel region. In general, local
populations rely heavily on ecosystem goods and services such as crop
production, fishing, livestock breeding, hunting and gathering for
their food security. Ecotourism is not yet well developed in this part
of the Senegalese Sahel, but the establishment of the Koyli Alpha
Community Nature Reserve suggests that it could play a major role in
the economy of this part of the country, in addition to its functions
in restoring degraded ecosystems. It is with this in mind that the
Agence S\'{e}n\'{e}galaise de la Reforestation et de la Grande Muraille
Verte (Senegalese Agency for Reforestation and the GGW) is
joining the drive to multiply the number of community nature reserves
along the route of the project to promote ecotourism and green
employment in the Ferlo.

Indeed, according to \citet{Ngom2014}, each type of ecosystem
corresponds to different functions and services, which in turn depend
on the health of the ecosystem, the pressures exerted on it, and the
use made of it by societies in a given biogeographical and geo-economic
context. Human societies use ecosystems, modifying them both locally
and globally \citep{Chevassus2009}. In turn, societies
adjust their uses to the modifications they experience. This dynamic
interaction characterizes what are known as socio-ecosystems
\citep{Walker2002}. Several ethnobotanical studies in arid and
semi-arid zones of Africa have shown the vital importance of vegetation
for the well-being of local communities
\citep{Lykke2004,Diop2005,Ayantunde2009,Cheikhyoussef2011,Sop2012,Dendoncker2013,Gning2013,Sarr2013,Sagna2014,Sene2018}.

Land restored through the GGW can provide more productive
farmland and pasture for livestock, helping to improve food security.
Village multi-purpose gardens in the Ferlo are a good example of an
institutional initiative in the fight against rural precarity and for
land restoration \citep{Billen2015}. Indeed, according to
\citetalias{Billen2015}, the establishment of gardens offers a solution to
two dimensions of women's precarity in the Senegalese Ferlo: it enables
an improvement in the quantity and quality of their diet, and promotes
access to capital.

Access to fresh water is essential for local populations, both for
human consumption and for livestock watering. Ecosystem services linked
to \mbox{watershed} and water resource management are crucial to ensuring an
adequate water supply. Water management will involve seeking a balance,
assuring the water needs of people while minimizing the impact of
widespread water availability on grazing pressure and pasture quality.
In the Ferlo region, ponds play a key role in supplying local
populations with water. In an area covering 3360 ha in the village of
Widou, 244 ponds can be detected via satellite images \citep{Faye2019}.
The density and cover of woody plants in ponds are higher in all areas
studied (204.38 ind/ha and 39.41\% in degraded areas; 201.86 ind/ha and
57.06\% in advanced areas), and lower on slopes (38.8 ind/ha and
6.02\%; 29.39 ind/ha and 7.62\%) and plateaus (23.89 ind/ha and 2.85\%;
17.87 and 4.53\%). Creating pond-like habitats near boreholes could
help compensate for increased grazing pressure near these artificial
watering points.

Biodiversity in the region plays a key role in the provision of
ecosystem services. Local species of plants provide resources for local
species of animals that contribute to pollination, pest regulation and
other ecological services. Biodiversity conservation is therefore an
important aspect of the relationship between local populations and
their environment. The woody stand contributes to the provision of six
categories of provisioning ecosystem services: human food, fodder,
traditional pharmacopoeia, energy wood, construction wood and craft
wood \citep{Ngom2014,Niang2014,Sagna2014,Sall2019,Sene2018}.

Local populations play a central role in the management of natural
resources such as land, water and vegetation. Sustainable management of
these resources is essential to preserve ecosystem services in the long
term. Climate change is having a significant impact on the Sahel region
and in particular on the Ferlo, with more frequent droughts and more
pronounced variations in rainfall. Local populations face challenges in
adapting to these changes and maintaining their standard of living. The
GGW involves land restoration actions, such as tree
planting, fencing and other measures to combat desertification. These
actions can have an impact on the way local populations use and manage
their land.

In summary, the relationships between local populations and their
environment in the context of Senegal's GGW are deeply
linked to the ecosystem services provided by local ecosystems. The
sustainability of these relationships depends on the judicious
management of natural resources, the conservation of biodiversity, and
adaptation to the challenges of climate change. Promoting sustainable
agricultural and land management practices is essential to ensure that
local populations benefit from ecosystem services while preserving the
environment.

\section{Conclusion}

In view of the complexity of the ecological interactions between trees
and other plants and their biotopes, great caution is called for in the
management of ecosystems in the GGW zone. It is in this
sense that the main results obtained from the ecological study of
Sahelian ecosystems in Senegal could be considered as starting tools to
support restoration activities. For Senegal, which hosted the GGW's
first experiments, the results are encouraging; however, corrections
are needed to achieve the objectives and expected results.

Once these multidisciplinary research foundations have been laid (those
relating to plant and animal populations and their interactions), it
becomes possible to envisage the implementation of much more
interdisciplinary projects, thanks to the exchanges made possible by
the operation of research structures such as the Observatoires
Hommes-Milieux. In fact, by enabling all the researchers involved to
work on the same research subject (i.e., the GGW in the case of OHMi
T\'{e}ss\'{e}k\'{e}r\'{e}), they enable the players to resonate with
each other's research, to receive insights from other points of view,
and thus to bring out disciplinary issues in a more enlightened way.

This is the case in particular for the interactions between insect
pollinator species and woody plants in the GGW, a project currently
underway to analyze the structure of the pollinator community and its
influence on the structure of the territory, as a function of the
restoration of woody plants within the GGW  \citep[and papers in
\mbox{preparation}]{Medina2025}. Combining entomology, ecology and genetics,
this project is the result of interaction between researchers working
on the same subject. In addition, a project combining ecology, zoology
and human and social sciences is also the fruit of this research: this
project aims to reconstitute, document and compare the memory of the
environment as experienced by local populations and researchers 
\citep{Juillard2022,Guisse2024,Juillard2024a}.

Finally, as the GGW project involves local populations, the results of
the research carried out by the OHMi are regularly communicated to them
through popularized presentations made by the project leaders. These
presentations enable local populations to grasp the scientific issues
behind the research projects carried out in their territory, and are
also an opportunity for researchers to integrate the questions raised
by local populations into their research \citep{OHMi2022,OHMi2024}.

\section*{Acknowledgments}

This work was funded by the Labex DRIIHM, French programme
``Investissements d'Avenir'' (ANR-11-LABX-0010), which is managed by
the ANR (French National Research Agency). The authors thank all the
authorities of the Labex DRIIHM and the OHMi T\'{e}ss\'{e}k\'{e}r\'{e},
the local populations, particularly those of Koyli Alpha, and the 
GGW agency in Senegal (ASERGMV) for their help during this
study. We also wish to thank the authorities of Cheikh Anta Diop
University for the use of facilities during this work. 

\CDRGrant[ANR]{ANR-11-LABX-0010}

\section*{Declaration of interests}

The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\back{}

\printbibliography
\refinput{crgeos20240602-reference.tex}

\end{document}