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Biodiversity and carbon stocks in different land use types in the Sudanian Zone of Burkina Faso, West Africa

Authors:
  • African Forest Forum (AFF) - https://afforum.org/
Biodiversity
and
carbon
stocks
in
different
land
use
types
in
the
Sudanian
Zone
of
Burkina
Faso,
West
Africa
Sidzabda
Djibril
Dayamba
a,
*,
Houria
Djoudi
b
,
Mathurin
Zida
c
,
Louis
Sawadogo
d
,
Louis
Verchot
b
a
World
Agroforestry
Centre
(ICRAF),
West
and
Central
Africa
Regional
OfceSahel
Node,
BP
E5118
Bamako,
Mali
b
Center
for
International
Forestry
Research
(CIFOR),
P.O.
Box
0113
BOCBD,
Bogor
16000,
Indonesia
c
Center
for
International
Forestry
Research
(CIFOR),
06
BP
9478
Ouagadougou
06,
Burkina
Faso
d
Institut
de
lEnvironnement
et
de
Recherches
AgricolesINERA,
Département
Productions
Forestières,
03
BP
7047
Ouagadougou
03,
Burkina
Faso
A
R
T
I
C
L
E
I
N
F
O
Article
history:
Received
16
April
2015
Received
in
revised
form
21
August
2015
Accepted
19
September
2015
Available
online
xxx
Keywords:
Tropics
Land
use
Woody
species
biodiversity
Carbon
sequestration
Soil
carbon
A
B
S
T
R
A
C
T
Lack
of
data
on
carbon
stocks
hampers
implementation
of
emission
reduction
mechanisms
(e.g.,
REDD+).
Addressing
this
issue
is
relevant,
especially
when
combined
with
other
challenges
such
as
preserving
biodiversity.
The
present
study
assessed
tree
diversity
(ShannonWieners
index)
and
carbon
stocks
of
different
land
uses
in
Balé
and
Ziro
sites
in
Sudanian
zone
of
Burkina
Faso.
Aboveground
carbon
stock
was
evaluated
using
generalized
equation.
Belowground
carbon
was
assessed
by
excavating
plant
parts
in
samples
of
soil
in
each
plot.
Regarding
soil
sampling
for
C-content
assessment,
four
locations
were
selected
in
each
plot
and
soil
was
sampled
at
the
depths
of
020
cm
and
2050
cm,
using
an
auger.
The
four
soil
samples
from
each
depth
were
pooled,
thoroughly
mixed
and
a
composite
soil
sample
taken
to
the
laboratory
for
carbon
content
measurement
using
the
Black
and
Walkley
method.
The
C-content
was
then
used
for
calculating
SOC.
In
Balé
and
Ziro,
85
and
106
species,
63
and
82
genera,
29
and
35
families
were
identied,
respectively,
with
the
Leguminosae
family
as
most
dominant.
Natural
vegetation
stands
(NV)
and
fallows
showed
high
richness
and
diversity
compared
to
parklands.
Soil
was
found
the
most
important
carbon
pool.
Highest
values
of
aboveground,
belowground
and
soil
C-stocks
in
Ziro
(13.9,
14.71
and
67.1
Mg/ha)
were
recorded
in
community
managed
forests
(CMF)
logged
12
years
ago,
while
equivalent
values
for
Balé
(25.76,
14.96
and
53.02
Mg/ha)
were
recorded
in
the
dense
NV.
However,
irrespective
of
C
pool,
the
difference
between
CMFs
and
the
100
trees/ha
Vitellaria
parkland
was
not
signicant.
Correlations
were
found
between
species
richness
and
above
and
belowground
C-stocks
(R
2
=
0.22,
p
<
0.0001;
R
2
=
0.33,
p
<
0.0001).
Overall,
dense
Vitellaria
parklands,
apart
from
allowing
tree-
crop
integration,
have
real
potentials
for
C
sequestration.
Also,
C-sequestration
and
biodiversity
conservation
are
likely
not
conicting
targets.
ã
2015
Elsevier
B.V.
All
rights
reserved.
1.
Introduction
Climate
change
is
a
worldwide
concern
that
is
driven
by
increased
atmospheric
concentrations
of
greenhouse
gases
of
which,
carbon
dioxide
(CO
2
)
is
the
most
important
(Stavi
and
Lal,
2013).
Land
management
practices
that
reduce
emission
of
CO
2
or
sequester
carbon
are
being
considered
in
climate
change
mitiga-
tion
strategies
(Zomer
et
al.,
2008).
Among
the
efforts
to
sustain
emissions
reductions,
programs
like
the
Clean
Development
Mechanism
(CDM)
initiated
under
the
Kyoto
protocol
and
REDD
+
under
the
UNFCCC
are
making
nancial
resources
available
to
enhance
carbon
sequestration
and
reduce
emissions
from
land
use
change.
Through
these
mechanisms,
carbon
nance
offers
new
opportunities
to
improve
the
sustainability
of
tropical
landscapes
and
generate
social
benets
like
poverty
reduction
and
livelihood
security
(Mendis
and
Openshaw,
2004;
Ogle
et
al.,
2014).
Implementation
of
these
mechanisms
is
constrained
by
the
availability
of
data
on
carbon
stocks
and
emissions
associated
with
different
land
uses
and
land
use
change
in
tropical
countries
(Wertz-Kanounnikoff
et
al.,
2008;
Verchot
et
al.,
2012).
Over
the
last
decades,
the
conservation
of
biodiversity
has
become
an
objective
of
international
conventions,
national
governments,
state
agencies,
nongovernmental
organizations,
local
communities,
school
clubs,
and
individuals
(Redford
and
Richter,
1999).
Indeed,
changes
in
components
of
biodiversity
*
Corresponding
author.
E-mail
addresses:
d.dayamba@cgiar.org
(S.D.
Dayamba),
h.djoudi@cgiar.org
(H.
Djoudi),
m.zida@cgiar.org
(M.
Zida),
sawadogo_ls@hotmail.com
(L.
Sawadogo),
l.verchot@cgiar.org
(L.
Verchot).
http://dx.doi.org/10.1016/j.agee.2015.09.023
0167-8809/ã
2015
Elsevier
B.V.
All
rights
reserved.
Agriculture,
Ecosystems
and
Environment
216
(2016)
6172
Contents
lists
available
at
ScienceDirect
Agriculture,
Ecosystems
and
Environment
journal
homepage:
www.elsev
ier.com/locate
/agee
cause
concern
for
ethical
and
aesthetic
reasons,
but
they
also
have
a
strong
potential
to
alter
ecosystem
properties
and
the
goods
and
services
they
provide
to
humanity
(Hooper
et
al.,
2005).
In
the
context
of
Burkina
Faso
with
dry
forest
ecosystems,
biodiversity
needs
to
be
promoted
to
improve
regulation
services
at
the
landscape
level
(soil
fertility,
water
inltration,
etc.)
and
also
because,
the
goods
and
services
provided
by
the
ecosystems
is
important
for
local
people's
livelihoods,
their
food
security
and
their
adaptation
to
climate
changes.
Biodiversity
is
under
the
inuence
of
many
biotic
and
abiotic
factors
which
are
themselves
under
the
inuence
of
human
activities/practices.
In
the
current
context
of
climate
changes,
these
practices
are
changing
to
allow
increased
resilience
and
adaptation
to
new
environmental
conditions
and
to
seek
ways
for
mitigation.
Moreover,
it
is
believed
that
climate
change,
deforestation,
forest
degradation,
and
biodiversity
are
interlinked
to
each
other
(Mandal
et
al.,
2013)
and
for
some
ecosystems,
biodiversity
was
shown
to
often
promote
stability
and
primary
productivity,
and
therefore
carbon
stocks
(Hicks
et
al.,
2014).
However,
no
clear
global
relationship
between
biodiversity
and
carbon
sequestration
is
apparent;
and
it
is
also
not
understood
how
local
and
landscape
level
changes
in
biodiversity
might
alter
carbon
cycling.
All
this
limit
more
mature
policy
development
for
their
co-management
(Midgley
et
al.,
2010).
In
the
Sudanian
zone
of
West
Africa
in
general
and
in
Burkina
Faso
particularly,
different
land
uses
and
management
systems
are
encountered
ranging
from
State
forests
(managed
by
central
administration)
to
Community
managed
forests
and
to
Natural
vegetation
not
under
dened
management
per
se
(known
as
protected
forest
forêts
protégées)
(Sawadogo,
2006).
Plantation
forests,
initiated
some
decades
ago
(1970s)
using
exotic
species
such
as
Eucalyptus
camaldulensis
Denh.,
Gmelina
arborea
Roxb.,
and
Tectona
grandis
L.f.,
although
not
widely
spread
today,
are
still
encountered,
but
the
new
trend
is
towards
tree
crop
species
like
cashew
and
mango
(Anacardium
occidentale,
Mangifera
indica).
Other
common
tree-related
land
use
types
in
the
country
are
parklands,
which
are
agroforestry
areas,
similar
to
natural
savannah
where
mature
trees
of
a
range
of
species
(Vitellaria
paradoxa,
Parkia
biglobosa,
Adansonia
digitata,
Faidherbia
albida)
are
preserved
and
among
which
annual
crops
are
planted
(Bayala
et
al.,
2014).
In
the
past
parklands
were
used
in
a
rotational
spatial
dynamic,
shifting
from
agriculture
land
to
fallows
and
vice
versa.
Recently,
the
practice
of
fallows,
whether
in
Burkina
Faso
or
elsewhere
in
sub-Saharan
Africa,
which
allowed
the
restoration
of
soil,
has
received
little
attention
from
farmers
due
to
the
increasing
population
pressure
on
arable
land
(Kumar
and
Nair,
2011).
Tree-related
land
use
practices,
namely
agriculture/agroforestry
and
forestry,
can
contribute
to
mitigating
increasing
atmospheric
CO
2
concentrations
because
of
their
high
capacities
for
capturing
and
storing
atmospheric
CO
2
in
vegetation,
soils,
and
biomass
products
(Kumar
and
Nair,
2011;
Jose
and
Bardhan,
2012).
They
could,
therefore,
contribute
to
consolidate
the
global
development
of
carbon
markets
and
associated
trading
options
such
as
Payment
for
Environmental
Services
in
forests.
Particularly,
since
the
adoption
of
the
Marrakech
Accords
in
2001
under
the
Kyoto
Protocol,
agroforestry
has
gained
increased
attention
as
a
strategy
to
sequester
carbon
(C)
and
mitigate
global
climate
change
(Albrecht
and
Kandji,
2003).
However,
although
the
system
is
spread
over
one
billion
ha
in
diverse
ecoregions
around
the
world
(Kumar
and
Nair,
2011),
our
understanding
of
C
sequestration
in
specic
agroforestry
practices
from
around
the
world
is
rudimentary
at
best
(Jose
and
Bardhan,
2012).
We
hypothesized
that
(i)
some
land
use
types
in
this
Sudanian
ecosystems
would
have
far
better
carbon
sequestration
potentials
and
be
potential
candidates
for
mitigation
perspective;
(ii)
land
use
types
with
high
carbon
sequestration
potential
would
not
show
biodiversity
preserving
ability
(which
is
also
a
pressing
regional
challenges;
see
Batjes
(2001))
in
the
sense
that
only
few
species
would
be
contributing
to
the
majority
of
biomass.
Therefore
the
Fig.
1.
Vegetation
map
of
Burkina
Faso
and
location
of
the
two
study
sites.
(Adapted
by
CTIG/INERA/Burkina
Faso
November,
2013,
after
Fontès
and
Guinko,
1995).
62
S.D.
Dayamba
et
al.
/
Agriculture,
Ecosystems
and
Environment
216
(2016)
6172
present
paper
aimed
at
comparing
the
carbon
stocks
and
species
diversity
of
different
land
uses
and
providing
scientic
evidence
for
decision
making
regarding
land
use
plans
and
policies.
2.
Materials
and
methods
2.1.
Study
sites
The
study
was
conducted
in
different
land
use
types
in
the
Ziro
(11
35
0
N;
01
55
0
W)
and
Balé
(11
42
0
N;
03
10
0
W)
provinces
respectively
in
the
Center
West
and
Boucle
du
Mouhoun
regions
of
Burkina
Faso.
Phyto-geographically,
both
sites
are
located
in
the
south
Sudanian
ecological
zone
(Fig.
1),
mostly
dominated
by
savanna
communities
(Fontès
and
Guinko,
1995).
The
climate
is
tropical
with
a
unimodal
rainy
season,
lasting
for
about
6
months
from
May
to
October.
Based
on
data
collected
from
in
situ
mini-
weather
station,
the
mean
annual
rainfall
for
the
period
1993
2011
was
904
144
mm
(mean
SD)
for
Ziro
while
for
Balé,
records
made
at
a
station
30
km
away
(village
of
Laba)
gave
924
157
mm
for
the
same
period.
The
temperature
ranged
from
16
to
32
C
in
DecemberJanuary
and
2640
C
in
MarchApril.
Ziro
is
dominated
by
hydromorphic
leached
ferruginous
soils,
associated
with
reshufed
tropical
ferruginous
soils
and
lithosols
while
in
Balé,
the
most
dominant
type
is
leached
hardened
ferruginous
tropical
soils,
leached
ferruginous
tropical
soils
with
spots
and
concretions
and
hydromorphic
leached
ferruginous
tropical
soils
(Bunasols,
2001,
2006).
In
both
regions,
the
main
land
management
encountered
are
parklands
of
different
tree
densities
depending
on
the
practice
of
the
farmer.
Fallowing,
although
less
common
in
some
areas
(for
lack
of
space),
is
still
encountered
as
soil
recovery
practice.
Natural
vegetation
remains
in
both
sites
and
in
Ziro,
part
of
it
is
under
community
management
since
more
than
20
years
which
practice
had
consisted
in
dividing
forest
area
into
plots
and
logging
a
plot
each
year
following
a
rotational
period
of
20
years.
With
regards
to
plantation,
although
not
common
practice,
it
exists
in
Ziro
and
is
made
in
general
of
the
species
Anacardium
while
in
Balé,
only
an
old
Eucalyptus
plantation
was
found.
In
the
natural
vegetation
of
the
two
regions,
as
in
general
in
the
Sudanian
zone,
re
is
a
prominent
feature,
and
it
is
estimated
that
2550%
of
the
area
is
burnt
annually
(Delmas
et
al.,
1991 ),
and
all
areas
burn
every
23
years
primarily
due
to
anthropogenic
causes
(Menaut
et
al.,
1991 ).
2.2.
Experimental
design
For
the
needs
of
this
study,
we
selected
different
tree
densities
of
Vitellaria
parklands
(10,
50,
100
trees/ha),
different
age
categories
of
fallow
lands
(4
categories
in
Ziro
and
3
in
Balé),
plots
with
different
histories
of
selective
cutting
in
community
managed
forest
(cutting
conducted
2,
12
and
23
years
ago),
different
ages
of
tree
plantations
(3,
7
and
10
years
old
A.
occidentale
plantation,
3
years
old
mango
plantation
and
30
years
Table
1
Different
land
use
types
in
Ziro
and
Balé
provinces
and
their
mean
basal
area
and
tree
densities.
Ziro
Balé
Land
use
type
Code
used
Basal
area
at
the
base
(m
2
/ha)
Density
of
individual
with
10
cm
Dbh
(N/ha)
Land
use
type
Code
used
Basal
area
at
the
base
(m
2
/ha)
Density
of
individual
with
10
cm
Dbh
(N/ha)
Community
managed
forest
exploited
2
years
ago
CMF02
14.87
0.64
152
35
Natural
vegetation
with
intermediate
degradation
NVID
8.36
2.81
77
30
Community
managed
forest
exploited
12
years
ago
CMF12
13.93
1.36
156
32
Natural
vegetation
with
low
degradation
NVLD
21.37
3.30
316
33
Community
managed
forest
exploited
23
years
ago
CAF
23
13.57
1.54
223
99
Natural
vegetation
with
high
degradation
NVHD
1.15
0.26
23
7
Natural
vegetation
with
low
degradation
NVLD
13.98
3.63
258
49
Fallow
land
2
years
old
Fall2
1.96
0.34
18
3
Natural
vegetation
with
intermediate
degradation
NVID
12.68
0.84
181
42
Fallow
land
4
years
old
Fall4
2.30
0.55
11
5
Natural
vegetation
with
high
degradation
NVHD
10.62
0.71
117
12
Fallow
land
6
years
old
Fall6
4.03
0.89
4
0
Fallow
land
one
year
old
Fall1
11.42
1.25
40
16
Vitellaria
paradoxa
parkland
(10
tree/ha)
VPark10
1.91
0.52
14
2
Fallow
land
2
years
old
Fall2
6.63
1.43
27
4
Vitellaria
paradoxa
parkland
(100
tree/ha)
VPark100
8.55
0.85
116
16
Fallow
land
3
years
old
Fall3
9.59
1.55
53
9
Vitellaria
paradoxa
parkland
(50
tree/ha)
VPark50
3.37
0.66
52
4
Fallow
land
7
years
old
Fall7
7.87
1.34
46
11
Eucalyptus
camaldulensis
plantation
30
years
old
Eucal30
28.14
5.16
101
12
Vitellaria
paradoxa
parkland
(10
tree/ha)
VPark10
1.45
0.24
12
0
Vitellaria
paradoxa
parkland
(100
tree/ha)
VPark100
10.85
4.49
95
4
Vitellaria
paradoxa
parkland
(50
tree/ha)
VPark50
5.15
0.72
52
0
Anacardium
occidentale
plantation
10
years
old
Anac10
7.03
0.9
63
18
Anacardium
occidentale
plantation
3
years
old
Anac3
0.77
0.22
13
5
Anacardium
occidentale
plantation
7
years
old
Anac7
4.41
1.29
40
11
Mangifera
indica
plantation
3
years
old
Mang3
1.99
0.42
22
7
Values
in
the
table
are
means
standard
errors.
S.D.
Dayamba
et
al.
/
Agriculture,
Ecosystems
and
Environment
216
(2016)
6172
63
old
E.
camaldulensis
plantation).
Moreover,
we
also
included
in
the
sampling,
protected
forests
not
under
management
with
different
degrees
of
degradation
(low,
intermediate
and
high)
that
we
characterized
using
the
density
of
trees
with
dbh
>
10
cm,
and
basal
area
measured
at
the
base
of
the
tree.
Each
land
use
type
had
four
replicate
plots
(50
m
50
m)
(Table
1).
In
this
eld
experiment,
identication
of
replicates
was
challenging.
However,
effort
was
made
to
ensure
that
in
each
land
use
category,
replicates
were
as
identical
as
possible
(sometimes
belonging
to
the
same
large
stand;
i.e.,
in
natural
vegetation)
but
as
separate
as
possible
from
each
other
to
take
into
consideration
the
problem
of
pseudo-replication.
2.3.
Data
collection
and
analysis
2.3.1.
Inventory
of
ligneous
component
For
woody
vegetation,
all
individuals
in
the
plots
were
systematically
surveyed.
The
following
parameters
were
recorded:
species
name,
number
of
stems
per
individual,
total
stem
height,
height
of
the
stem
from
the
soil
surface
to
the
beginning
of
the
crown,
girth
at
stump
level
(for
stems
>10
cm)
and
girth
at
breast
height,
diameters
of
the
crown
in
two
perpendicular
directions.
Small
tree
individuals
(<10
cm
girth)
were
all
identied
to
species
level,
counted
and
the
height
recorded.
The
inventory
data
were
rst
used
to
characterize
the
vegetation
in
the
study
area.
Identication
of
species
and
families
of
plants
follows
the
International
Plant
Names
Index
(http://www.ipni.org
[accessed
24th
of
September
2013]).
Richness,
relative
density,
relative
dominance
and
diversity
of
species
were
computed
for
each
replicate
in
each
land
use
type.
Species
richness
was
dened
as
total
number
of
species
encountered
per
plot.
Relative
density
=
(number
of
individuals
of
a
species/total
number
of
individuals)
100.
Relative
dominance
=
(total
basal
area
for
a
species/total
basal
area
of
all
species)
100.
Species
diversity
was
assessed
using
ShannonWieners
diversity
index
(H
0
),
calculated
using
the
following
equation:
H
0
¼
Xp
i
lnp
i
;
where
p
i
is
the
relative
abundance
of
species
i
in
a
plot
(Magurran,
2004).
2.3.2.
Assessment
of
aboveground
biomass
and
carbon
stock
Individual
assessment
of
the
biomass
of
each
tree
species
was
not
feasible
because
of
unavailability
of
species
specic
equations
in
the
GlobAllomeTree
database
(Henry
et
al.,
2013).
However,
Chave
et
al.
(2005)
developed
generalized
biomass
equation
for
different
ecosystems
and,
which
are
used
by
authors
when
destructive
methods
are
not
selected
(Sist
et
al.,
2014).
In
the
current
study,
we
used
the
equation
proposed
for
dry
forest
which
predicts
tree
aboveground
biomass
(AGB,
kg)
as
a
function
of
tree
diameter
at
breast
height
(D
in
cm),
tree
height
(H
in
m)
and
wood
specic
density
(r
in
g/cm
3
)
as
follows:
AGB
¼
0:112
rD
2
H
0:916
Values
for
wood
specic
density
were
taken
from
the
global
wood
density
database
(Zanne
et
al.,
2009).
For
species
that
lacked
a
direct
measurement
of
specic
gravity
in
that
database,
genus-
level
averages
were
used
wherever
possible.
In
a
few
cases
where
up
to
genus
level,
the
species
was
not
represented
in
the
data
base
a
site-averaged
value
of
wood
specic
gravity
had
to
be
used.
This
equation
was
developed
based
on
data
where
maximum
tree
diameter
was
63.4
cm.
In
our
data,
6
individuals
in
the
Ziro
and
8
individuals
in
the
Balé
exceeded
this
dbh
limit,
but
were
not
excluded
from
the
calculation.
After
calculating
biomass,
the
carbon
stock
was
estimated
to
be
50%
of
the
total
biomass
(Losi
et
al.,
2003).
In
this
study,
herbaceous
biomass
was
not
taken
into
account.
Although
in
Sudanian
zone,
the
herbaceous
layer
can
be
an
important
component
of
the
aboveground
biomass,
reaching
a
maximum
standing
crop
of
around
46
t/ha
(Fournier,
1994;
Sawadogo
et
al.,
2005),
it
is
a
dynamic
and
seasonal
biomass.
Indeed,
the
herbaceous
stock
is
degraded
quickly
during
the
dry
season
through
res,
grazing,
and
decomposition
(Seghieri
et
al.,
1995).
Carbon
cycles
through
this
pool
relatively
quickly
and
is
not
a
long-term
storage
pool.
2.3.3.
Assessment
of
belowground
biomass
and
carbon
stock
Belowground
biomass
was
estimated
as
a
plot
level
measure-
ment
where
two
soil
depths
(020
cm
and
2050
cm)
were
considered.
For
each
plot
and
depth,
four
(04)
sample
pits
were
excavated
using
a
sharp-edged
metal
cube
of
the
size
25
cm
25
cm
20
cm.
The
sampling
points
in
the
plot
were
selected
based
on
the
heterogeneity
of
the
vegetation
in
the
plot
but
selection
of
point
was
made
to
avoid
standing
herbaceous
vegetation
to
maximize
chance
of
only
assessing
ligneous
belowground
biomass.
Roots
were
manually
removed
from
the
soil
samples
and
fresh
weight
was
assessed
using
a
balance
of
maximum
24.1
kg
(1
g)
(SB24001
DR
METTLER
TOLEDO,
made
in
Switzerland).
Dry
weight
was
determined
after
oven-drying
at
105
C
for
48
h.
For
each
soil
depth,
dry
root
biomass
per
sample
was
determined
and
extrapolated
to
whole
surface
area
of
each
plot.
To
take
into
account
ne
roots
that
could
not
be
manually
isolated
in
the
eld,
a
sub-sample
of
the
excavated
soil
was
taken
to
the
lab
and
wet-
sieved
to
isolate
ne
roots.
The
fresh
weight
of
these
roots
was
determined
using
a
balance
of
maximum
210
g
(0.01
g)
(PL203-S/
00
METTLER
TOLEDO,
made
in
Switzerland)
and
they
were
then
dried
to
assess
dry
weight.
The
total
belowground
biomass
in
each
plot
was
then
assessed
by
summing
the
weights
of
the
coarse
and
ne
roots.
Carbon
stock
was
estimated
as
above.
The
sampling
scheme
(limited
to
a
depth
of
50
cm)
could
lead
to
some
underestimate
of
the
total
root
biomass,
but
the
part
of
the
root
biomass
below
50
cm
is
inconsequential
to
understanding
the
effects
of
land
use
on
carbon
stocks.
Indeed
several
authors
have
noted
that
the
predominance
of
the
root
biomass
in
the
Sudanian
zone
is
in
the
upper
40
cm
(Seghieri,
1995;
Foumier
and
Planchon,
1998)
for
two
main
reasons:
(i)
lack
of
water
penetration
to
deeper
layers
during
the
rainy
season;
and
(ii)
the
presence
of
an
indurated
lateritic
horizon
in
ferruginous
soils
(as
in
our
sites;
see
Section
2.1
description
above)
that
inhibits
deep
root
penetration.
2.3.4.
Assessment
of
SOC
stock
In
each
plot
(50
m
50
m),
four
sampling
locations
were
selected
following
the
distribution
of
vegetation
(sampling
was
done
in
beneath
vegetation
and
outside
tree
cover
[if
any
in
the
plot]).
Soil
was
sampled
at
the
depths
of
020
cm
and
2050
cm,
using
an
auger.
The
four
soil
samples
from
each
depth
were
pooled,
thoroughly
mixed
and
a
composite
soil
sample
taken
to
the
laboratory
for
carbon
content
measurement.
All
soil
carbon
content
analyses
were
made
following
the
method
of
Walkey
and
Black
(1934).
Soil
bulk
density
was
measured
using
an
8
cm
diameter
metal
ring.
The
ring
was
driven
into
the
soil
using
a
hammer.
It
was
then
carefully
lifted
to
prevent
loss
of
its
soil
content.
Excess
soil
of
the
ring
was
cut
using
a
trowel.
The
content
of
the
ring
was
then
placed
in
a
plastic
bag,
the
fresh
weight
determined
in
the
eld
and
the
sample
brought
to
the
lab
for
dry
weight
assessment
after
oven-
drying
at
105
C
for
48
h.
Proportion
of
ne
soil
was
determined
by
drying,
grinding,
reducing
to
powder
and
sieving
with
2
mm
mesh
size,
soil
samples
taken
at
the
depth
of
020
and
2050
cm
in
each
plot.
The
64
S.D.
Dayamba
et
al.
/
Agriculture,
Ecosystems
and
Environment
216
(2016)
6172
proportion
of
ne
soil
was
then
determined
as
the
weight
of
the
soil
passing
through
the
2
mm
mesh
divided
by
the
total
weight
of
the
soil
sample.
Soil
carbon
stock
was
determined
using
the
following
calculations
(Aynekulu,
2003)
and
then
converted
to
conventional
expression
in
mass
per
area
(Mg
C
ha
1
):
Total
volume
of
soil
in
the
plot
(m
3
)
=
plot
area
(m
2
)
soil
depth
(m)
Weight
of
soil
in
the
plot
(Mg)
=
Volume
of
soil
in
the
plot
(m
3
)
soil
bulk
density
(Mg/m
3
)
Weight
of
ne
soil
in
the
plot
(Mg)
=
Weight
of
soil
in
the
plot
(Mg)
Proportion
of
ne
soil
(%)
Weight
of
SOC
(Mg/plot)
=
Weight
of
ne
soil
(Mg/plot)
%
C
concentration.
As
our
plots
were
of
0.25
ha
in
size,
the
weight
of
SOC
in
a
plot
was
multiplied
by
4
to
have
the
SOC
in
one
(1)
ha.
In
this
study,
soil
carbon
stock
was
evaluated
based
on
ne
soil
fraction
and
to
a
depth
of
50
cm.
It
is
known
from
the
literature
(Zabowski
et
al.,
2011)
that
coarse
soil
fraction
(2
mm)
and
deeper
soils
(>50
cm)
might
contain
a
substantial
amount
of
C.
Our
sampling
scheme
here
could
underestimate
total
SOC
stocks.
But,
it
serves
as
a
good
basis
for
comparing
the
different
land
uses.
2.3.5.
Data
analysis
Prior
to
statistical
analyses,
all
data
were
checked
for
meeting
the
assumptions
of
normality
using
KolmogorovSmirnovs
test
(and
by
inspecting
the
histogram
of
distribution)
and
homogeneity
of
variance
using
Levenes
test.
In
cases
where
some
assumptions
(normality
and/or
homogeneity)
were
violated,
log
transformed
data
were
used
for
the
analyses.
We
used
one
way
analysis
of
variance
(model
1)
to
determine
if
there
was
signicant
difference
in
land
use
types
with
respect
to
species
richness,
diversity
and
aboveground
C-stock.
Y
i
¼
m
þ
L
i
þ
e
i
ðModel1Þ
where
Y
i
is
the
response
variable
for
the
species
richness,
diversity
and
aboveground
C
stock,
m
was
the
overall
mean,
L
i
was
the
effect
of
land
use
and
e,
the
error
term.
For
belowground
carbon
and
soil
carbon
stocks,
a
two
way
analysis
of
variance
(Model
2)
was
used
since
soil
depth
was
considered
as
a
study
factor
together
with
land
use
type.
Y
ij
¼
m
þ
L
i
þ
D
j
þ
LD
ij
þ
e
ij
ðModel2Þ
where
Y
ij
is
the
response
variable
for
belowground
carbon
and
soil
carbon
stocks,
m
was
the
overall
mean,
L
i
was
the
effect
of
land
use,
D
j
the
effect
of
soil
depth,
LD
ij
the
interaction
effect
and
e,
the
error
term.
Because
the
factor
soil
depth
had
two
levels
of
different
sizes
(020
and
2050
cm),
for
the
sake
of
comparing
the
two
depth,
we
standardized
the
parameters
(soil
and
belowground
C
stock)
measured
at
these
depths
by
dividing
the
value
found
at
the
020
cm
depth
by
2
and
the
one
found
at
the
2050
cm
by
3.
When
signicant
differences
were
found
between
study
factors
(land
use
types),
a
pairwise
comparison
was
made
using
Tukeys
test
at
5%
level
of
signicance.
Results
of
the
statistical
analyses
were
considered
signicant
if
p
<
0.05
and
to
show
tendency
if
0.05
<
p
<
0.1.
The
relationships
between
the
individual
carbon
pools
and
between
the
carbon
pools
and
diversity
were
investigated
using
regression
analysis
and
Pearson's
product
moment
correlation
coefcients.
Preliminary
analyses
were
performed
to
ensure
no
violation
of
the
assumptions
of
normality,
linearity
and
homosce-
dasticity.
When
some
assumptions
were
violated,
log
transformed
values
were
used.
All
statistical
analyses
were
performed
with
SPSS
20
software
(SPSS,
Chicago).
3.
Results
3.1.
Vegetation
characterization
In
Ziro,
vegetation
stands
were
characterized
as
lowly,
intermediately
and
highly
degraded
with
respectively,
258
49
trees/ha
and
13.98
3.63
m
2
/ha
basal
area,
181
42
trees/ha
and
12.68
0.84
m
2
/ha
as
basal
area,
117
12
trees/ha
and
10.62
0.71
m
2
/ha
as
basal
area.
Equivalent
values
in
Balé
were
316
33
trees/ha
and
21.37
3.30
m
2
/ha
as
basal
area,
77
30
trees/ha
and
8.36
2.81
m
2
/ha
as
basal
area
and,
23
7
trees/ha
and
1.15
0.26
m
2
/ha
as
basal
area
(Table
1).
In
total,17
and
10
land
use
types
which
could
be
grouped
into
natural
vegetation
stands
(managed
and
not
under
management),
fallow
lands,
parklands
and
plantations,
were
sampled
in
the
two
provinces.
Detailed
characteristics
(relative
species
density
and
relative
dominance)
of
the
vegetation
in
the
different
land
use
types
are
given
in
Appendices
A1
and
A2.
Table
2
Species
richness
and
diversity
in
different
land
uses
in
the
Ziro
and
Balé
provinces.
Ziro
Balé
Land
use
Species
richness
(N)
Shannon
diversity
index
(H
0
)
Land
use
Species
richness
(N)
Shannon
diversity
index
(H
0
)
CMF02
39
1
2.50
0.07
NVID
47
3
2.80
0.08
CMF12
48
2
2.53
0.06
NVLD
45
3
2.70
0.13
CMF23
47
1
2.61
0.23
NVHD
6
1
1.17
0.09
NVLD
45
1
2.84
0.23
Fall2
25
4
2.50
0.09
NVID
43
2
2.99
0.14
Fall4
17
1
2.03
0.13
NVHD
36
1
2.61
0.20
Fall6
24
2
2.22
0.20
Fall1
38
2
2.44
0.21
VPark10
12
2
2.13
0.07
Fall2
39
1
2.71
0.12
VPark100
17
2
2.36
0.17
Fall3
40
3
2.81
0.1
VPark50
22
4
2.45
0.22
Fall7
28
1
2.46
0.11
Eucal30
28
3
2.23
0.25
VPark10
6
1
1.07
0.46
VPark100
13
1
1.75
0.12
VPark50
9
2
0.81
0.27
Anac10
23
2
1.90
0.21
Anac3
7
1
1.23
0.15
Anac7
30
2
2.88
0.06
Mang3
23
1
2.45
0.24
Values
in
the
table
are
means
standard
errors.
S.D.
Dayamba
et
al.
/
Agriculture,
Ecosystems
and
Environment
216
(2016)
6172
65
3.2.
Species
richness
and
diversity
Overall,
in
Balé
and
Ziro
provinces,
85
and
106
species
belonging
to
63
and
82
genera
and
29
and
35
families
were
identied,
respectively.
The
Leguminosae
family
was
the
dominant
group
(24
species
in
Balé
and
28
in
Ziro),
followed
by
the
Combretaceae
(11
species
in
the
two
sites)
and
the
Rubiaceae
(8
species
in
the
two
sites).
Moreover
species
richness
varied
signicantly
with
land
use
types
in
Ziro
(F
=
23.231;
P
<
0.0001)
with
community
managed
forest
(CMF),
natural
vegetation
(NV)
and
fallow
lands
(Fall)
having
signicantly
higher
richness
compared
to
parklands
and
plantations.
In
general,
parklands
(VPark),
irrespective
of
tree
density,
and
the
3
years
old
Anacardium
plantation
had
very
low
richness
(Table
2)
while
substantial
richness
was
found
in
the
other
Anacardium
and
mango
plantations.
The
difference
in
richness
was
also
signicant
in
the
Balé
province
(F
=
32.627,
P
<
0.0001)
where
intermediately
degraded
natural
vegetation
(NVID)
displayed
the
highest
richness
followed
by
lowly
degraded
natural
vegetation
(NVLD)
(Table
2).
Here,
the
tendency
of
parklands
having
lower
richness
was
not
very
pronounced
and
appeared
even
counterbalanced
by
the
50
trees/ha
density
parkland
where,
on
average
22
species
were
encountered.
The
lowest
richness
(6
species)
was
shown
by
the
highly
degraded
natural
vegetation
(NVHD).
With
respect
to
diversity,
there
was
signicant
difference
in
land
use
types
in
Ziro
province
(F
=
12.304;
p
<
0.0001).
As
for
species
richness,
parklands
(notably,
those
with
lower
tree
density;
10
and
50)
and
the
youngest
Anacardium
plantation
showed
signicantly
lower
diversity
compared
to
CMF,
NV
and
fallow
lands
(Table
2).
In
Balé
province
also,
land
use
types
had
effect
on
diversity
(F
=
8.647;
p
<
0.0001)
and
the
highly
degraded
natural
vegetation
showed
signicantly
lower
diversity
compared
to
all
other
land
use
types
(Table
2).
However,
contrary
to
Ziro,
where
parklands
showed
the
lowest
diversity,
in
Balé,
no
signicant
difference
was
observed
between
parklands
and
the
other
land
use
types
(except
NVHD
mentioned
above).
3.3.
Aboveground
carbon
stock
Aboveground
carbon
stocks
differed
between
land
uses
in
Ziro
province
(F
=
14.033,
P
<
0.0001).
The
treatment
comparisons
are
presented
in
Appendix
A3.3.
CMF
and
NV
(irrespective
of
degree
of
degradation)
had
signicantly
higher
aboveground
C-stock
com-
pared
to
young
fallows
(1
and
2
years
old),
less
dense
parklands
(10
trees/ha)
and
young
plantations
(3
and
7
years
Anacardium
and
3
years
mango).
It
could
be
noted
that
the
difference
between
CMF
and
dense
parklands
was
not
signicant.
However,
differ-
ences
were
observed
when
comparing
older
fallows
(3
and
7
years)
and
parklands
to
young
plantations.
Overall,
three
subgroups
of
the
land
use
types
could
be
identied
based
on
their
aboveground
carbon
stocks:
group1
with
aboveground
biomass
C
<
5
Mg/ha
was
composed
of
13
years
old
fallows,
3
and
7
years
old
Anacardium
plantations,
3
years
old
mango
plantation
and
the
less
dense
(10
trees/ha)
parkland.
Group2
with
5
<
C
<
10
Mg/ha
was
composed
of
10
years
old
Anacardium
plantation,
highly
degraded
natural
vegetation,
7
years
old
fallow
land
and
community
managed
forest
logged
2
years
ago.
Group3
with
C
>
10
Mg/ha
was
composed
of
community
managed
forest
logged
12
and
23
years
ago,
intermediately
and
lowly
degraded
natural
vegetation
stands
and
more
dense
(50
and
100
trees/ha)
parklands
(Table
3).
Aboveground
carbon
stock
was
also
signicantly
different
between
the
land
use
types
in
the
Balé
(F
=
8.89,
P
<
0.0001)
and
NVLD
produced
the
highest
aboveground
C-stock
(25.76
Mg/ha)
followed
by
the
30
years
old
Eucalyptus
plantation.
The
three
classes
of
aboveground
carbon
values
contained
the
following
land
use
types:
Group1
(C
<
5
Mg/ha),
NVHD,
the
fallow
lands
(2,
4
and
6
years
old),10
and
50
trees/ha
parklands;
Group2
(5
<
C
<
10
Mg/ha)
was
composed
of
intermediately
degraded
natural
vegetation
and
the
dense
(100
trees/ha)
parkland.
Group3
(C
>
10
Mg/ha)
was
composed
of
the
30
years
old
Eucalyptus
plantation
and
the
less
degraded
natural
vegetation
(Table
3).
3.4.
Belowground
carbon
stock
Belowground
carbon
stock
in
Ziro
differed
signicantly
between
land
use
types
(F
=
7.410;
p
<
0.0001),
soil
depth
(F
=
4.903;
p
=
0.029)
and
the
interaction
between
land
use
types
and
soil
depth
(F
=
1.895;
p
=
0.029)
(Fig.
2).
Belowground
carbon
stock
for
the
soil
depth
020
cm,
was
1.68
0.17
Mg/ha
for
every
10
cm
of
soil
while
the
equivalent
value
for
the
soil
depth
2050
cm
was
1.30
0.13
Mg/ha.
In
pair-wise
comparison
of
the
land
use
types
in
the
Ziro,
CMF
and
NV
(except
the
highly
degraded
one)
showed
signicantly
higher
belowground
C-stocks
compared
to
Table
3
Aboveground,
belowground
and
soil
C
stocks
in
the
different
land
use
types
in
Ziro
and
Balé
provinces.
Ziro
Balé
Land
use
Aboveground
C
stock
Belowground
C
stock
to
50
cm
depth
Soil
C
stock
to
50
cm
depth
Total
C
stock
Land
use
Aboveground
carbon
stock
Belowground
C
stock
to
50
cm
depth
Soil
C
stock
to
50
cm
depth
Total
C
stock
Mg
ha
1
Mg
ha
1
CMF02
9.18
1.22
12.21
1.77
52.56
3.49
73.95
4.21
NVID
5.14
1.73
14.85
8.55
38.91
1.67
58.90
8.91
CMF12
13.9
2.3
14.71
2.13
67.10
9.14
95.71
9.63
NVLD
25.76
5.51
14.96
2.75
53.02
3.19
93.74
5.36
CMF23
12.07
1.25
12.33
3.01
60.06
2.58
84.46
4.27
NVHD
0.52
0.14
1.10
0.32
49.05
10.04
50.67
10.06
NVLD
11.5
3.4
8.93
1.63
45.77
5.55
66.20
6.35
Fall2
2.21