Distribution, Species Diversity and Conservation Potentials of Sacred Groves in Southwestern, Nigeria

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Onyekwelu et al.
Proceedings of 7th NSCB Biodiversity Conference, October 2020
20
Distribution, Species Diversity and Conservation Potentials of Sacred Groves in
Southwestern, Nigeria
Onyekwelu, J.C.1*; Tolorunju, M.S.1; Agbelade, A.D. 2; Lawal, A.1; Stimm, B.3 and Mosandl, R.3
1Department of Forestry and Wood Technology, Federal University of Technology, P.M.B. 704, Akure, Nigeria
2Department of Forest Resources and Wildlife Management, Ekiti State University, P.M.B. 5363, Ado Ekiti, Nigeria
3Chair of Silviculture, Technical University of Munich, Hans-Carl-von- Carlowitz-Platz 2
D- 85354 Freising, Germany
Correspondence e-mail: jconyekwelu@futa.edu.ng
ABSTRACT
This study examined the distribution, species diversity and conservation potentials of sacred groves in Southwestern,
Nigeria. Four sacred groves were selected (Osun Osogbo, Igbo Olodumare, Idanre hills and Ogun Onire sacred
groves), from three states in south west, Nigeria. Data were collected from 32 temporary sample plots of 20 m x 40
m established across the four sacred groves. A total of 18 sacred groves were located in five states, which was not
considered exhaustive due to some constraints. In these four sacred groves 34 families were enumerated at the
overstory layer of the four sacred groves, with 24, 23, 19 and 19 families occurring in Ogun Onire, Osun Osogbo,
Igbo Olodumare and Idanre hills sacred groves, respectively. Species richness varied from 32 to 58, with Ogun
Onire having a significantly higher number of species than other sacred groves. Tree density in the four sacred
groves ranged from 309 ha-1 to 417ha-1. Shannon-Wiener diversity index for overstory species ranged from 3.47 to
4.06 and was significantly different between the sacred groves, with Igbo Olodumare and Ogun Onire having the
lowest and highest values, respectively. The understory species richness at Ogun Onire (46), Idanre Hills (37), Osun
Osogbo (34) and Igbo Olodumare (23) sacred groves was generally lower than overstory species richness. Also, the
understory layer had lower Shannon-Wiener diversity index (range: 2.04 to 3.30) compared to the overstory layer in
all sacred groves. The implication of the results is that sacred groves have high potentials for biodiversity
conservation.
Keywords: Biodiversity, Conservation, Sacred groves, Species diversity, Southwestern Nigeria
INTRODUCTION
Biodiversity is an essential component of the forest
for healthy ecosystems services provision and
conservation purposes. The escalating tree species
extinction crisis is an indication that the diversity of
nature can no longer withstand the current pressure of
deforestation and reduction in ecosystem functions
(Shushma et al., 2015). Studies indicate that we have
entered into the phase of mass extinctions, which has
altered roughly half of the habitable surface of the
earth, impairing and destroying several ecosystems
(Myers, 1990; Daily, 1995; Singh, 2002). Barbault
and Sastrapradja (1995) opined that the current rates
of species extinction are 1000 –10,000 times higher
than the background rate of 10 - 7 species/year
according to fossil record. Today, it is estimated that
two to five species are being lost per hour from
tropical forests alone, which amounts to a loss of 16
million populations per year or 1800 populations per
hour (Singh, 2002). The increasing deforestation
rates are majorly responsible for plant and animal
species extinction in natural habitats (Shushma et al.,
2015). The adverse effects of biodiversity loss and
forest degradation have promoted harsh climatic
conditions. Recent adverse environmental
phenomenon (e.g. global warming, drought,
desertification, flooding, disease epidemics, etc.),
have been linked to the high rate of forest
destruction, especially tropical rainforests
(Onyekwelu, 2017).
Global deforestation rate was estimated at about 13
million ha per annum from 2000 to 2010 (FAO,
2010). It is evident that the rates of deforestation and
forest degradation must be drastically reduced or
halted if the forest ecosystem is to continue providing
its life saving goods and services. In addition, there
are dire needs of appropriate restoration and
conservation measures. Over the years, various
traditional and conventional methods of forest
conservation have evolved. Onyekwelu (2017)
opined that conventional forest conservation methods
have not been very effective in conserving
biodiversity in many tropical forests. In Africa,
various traditional conservation measures have been
practiced for centuries before the advent of
conventional conservation methods. Among the
various traditional forest conservation measures,
sacred groves, which are the most widely practiced,
have gained relevance in recent time (Berkes and
Davidson, 2006; Telly, 2006; Onyekwelu and
Olusola, 2014; Daye and Healey, 2015). Sacred

Onyekwelu et al.
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groves are tracts of virgin forests harbouring rich
biodiversity; they are repositories of rare and
endemic species, remnant of primary forests that are
protected by the local people who live around them
based on their culture, religious beliefs, and taboos
(Rajasri et al., 2014; Khan et al., 2008). Oftentimes,
resources extraction in sacred groves is restricted by
a variety of rules to placate the deity (Khan et al.,
2008). Sacred groves feature in various cultures
(Africa, Asia, Europe, America and Australia) and
occur in various forms such as sites for religious and
cultural festivals, remnants of old forests, burial
grounds for chiefs and sites of ancestral worship
(Onyekwelu and Olusola, 2014). Several
communities in Nigeria had traditional methods
(sacred grove) of protecting both plant and animal
species in their habitat before the advent of
conventional forest conservation methods in the
country in late 19th century (Okali, 1997). Specific
myths, taboos, folklore and rules are attached to
sacred groves and used to protect the forest from
encroachments such as illegal logging, farming
activities, etc. Sacred groves are often found in many
communities but under different names and different
sizes, thus many of them often go undocumented and
relatively unknown. This is true in Nigeria where
there is no known documentation of the distributions
of sacred groves. To bridge this knowledge gap, this
study was designed to map the distribution of sacred
groves in southwestern Nigeria and investigate their
species diversity and conservation potentials using
some selected sacred groves with the view of
examining their contributions to biodiversity
conservation.
MATERIALS AND METHODS
The Study Area
This study was conducted in south-western region of
Nigeria, which is comprised of six states: Ekiti,
Lagos, Ogun, Oyo, Osun and Ondo. The area lies
between longitude 2º31′ and 6º00′ E and latitude
6º21′ and 8º 37′ N. The region is dominated by
tropical rainforest ecosystem but has some derived
savanna and mangrove/swamp forest ecosystems.
The climate is tropical, with distinct rainy and dry
seasons and characterized by high mean annual
temperature (21 - 34ºC) and well distributed high
annual rainfall (1400 mm - 4000 mm). Rainfall
begins late March and ends in November while dry
season occurs between December and early March.
Soils are predominantly ferruginous, typical of the
variety found in intensively weathered areas of
basement complex formations in the rainforest zone
of south-western Nigeria (Onyekwelu et al., 2008).
Method of Data Collection
Out of the six (6) states in southwestern Nigeria, five
states were visited with the aim of locating sacred
groves. Lagos state was not visited due to its complex
and highly developed nature, which tended to suggest
that there may be no sacred grove in the city. The
coordinates of each identified sacred grove was taken
using a hand-held Global Positioning System (GPS).
Out of the identified sacred groves, four were
selected for inventory based on their
prominence/significance, accessibility and
permission to conduct inventory in them. It was
ensured that selected sacred groves were not
concentrated in one section of southwestern Nigeria.
The selected sacred groves were: Osun Osogbo
(Osun State), Idanre hills (Ondo State), Igbo
Olodumare (Ondo State) and Ogun Onire (in Ekiti).
Two line transects of 1000 m each in length with a
distance of at least 1000 m from each other were laid
approximately at the middle of each sacred grove.
Four temporary sample plots of 40m × 20m were laid
at alternate sides along each transect at every 250m
interval, resulting in 4 plots per transect, 8 plots per
sacred grove and 32 plots for this study. Within each
plot, all living trees with Dbh ≥ 10 cm were identified
and their Dbh and total heights measured. For tree
sapling (Dbh >1.0 cm but < 10 cm) enumeration,
10m × 10m sub-plot was laid at the middle of each 40
m x 20 m plot. All saplings were identified and their
dbh measured. A 5m × 5m quadrant was laid within
the 10m × 10m sub-plot for seedlings (Dbh < 1.0 cm)
enumeration. Frequencies of identified seedling
species were recorded.
Data Processing and Analyses
Distribution map of Sacred Groves
The field coordinates of identified sacred groves were
exported to Microsoft Excel spreadsheet in a tabular
format and the values converted to decimal degrees
by dividing the longitude and latitude values with 60
minutes. The converted data were imported into Arc-
GIS software environment for further analyses.
Southwestern Nigerian map was extracted to a new
layer for analysis. Afterwards, the coordinates of the
sacred groves were imported into the Arc-GIS by
adding XYZ data. The digital map was then exported
and saved in picture format.
Basal Area Estimation
The basal areas of all trees in the sample plots were
calculated using equation 1.
)1.(........................................
4
2
D
BA


Where BA = Basal Area (m2), D = Diameter at Breast
Height (m) and  = Pie (3.142).

Onyekwelu et al.
Proceedings of 7th NSCB Biodiversity Conference, October 2020
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Basal area per hectare was obtained by multiplying
the mean plot total basal area by 12.5 (i.e. number of
20m x 40m plots in one hectare).
Volume Estimation
Volumes of individual trees were estimated using
Newton‟s formula (equation 2).
24 )( 222 DtDmDb
hV 


……… (2)
Volume per hectare was obtained by first computing
the mean plot total volume and then multiplying the
mean plot total volume by 12.5. (i.e. number of 20m
x 40m plots in one hectare).
Biodiversity Indices
Species Relative Density (RD (%)), which is an index
for assessing species relative distribution, was
computed using equation 3 while species Relative
Dominance (RDo (%)) was estimated using equation
4.
100 N
n
RD i
……………………… (3)



n
i
OBa
Ba
RD 100
……………………………
………… (4)
Where RD = relative density; RDo = relative
dominance; ni = number of individuals per species; N
= total number of all individual trees of all species in
the entire population; Bai = basal area of individual
tree belonging to the it species; Ban = stand basal
area.
Shannon-Wiener Diversity Index (H′) was calculated
using using equation 5 while species evenness in
each plot was determined using Shannon‟s
equitability (EH)(equation 6).
Where H′ = Shannon diversity index, S = the total
number of species in the community, Pi = proportion
S (species in the family) made up of the ith species;
ln = natural logarithm.
Tree species richness was calculated using the
Margalef Index (d) (equation 7); Family (FIV) and
Species (IVI) Importance Value Index were
computed using equations 8 and 9 while species
similarity index between two sites, A and B, was
estimated using Sorensen‟s Species Similarity Index
(SI) (equation 10).
S-1/ln N (2)…………………………… (7)
(8) ...................
2 RDo) + (RD
FIV
(9) ....................
2 RDo) + (RD
IVI
(10) ...................... 100 x
ba
2ab 






SI
Where: S = Total number of Species, N = Total
number of individuals of all species; RD and RDo are
as previously defined; a and b = number of species at
sites A and B, respectively.
RESULTS
Distribution of Sacred Groves in Southwestern
Nigeria
A total of 18 sacred groves were located in the five
states (Figure 1). Our experience in the field was that
obtaining information about existence of sacred
grove was often difficult as the people were not
willing to give information for various reasons,
ranging from fear to taboo. A good number of the
sacred groves were found in Ekiti, Osun and Ondo
States. Generally, the sacred groves are small in size;
from a few hectares to 75 ha, the biggest being Osun
Osogbo with a core area of 75 ha and buffer zone of
47 ha. All sacred groves were guided by local laws
and customs, taboos and deities. Access into sacred
groves were highly regulated, access is preceded by a
formal permission by responsible authorities. In some
cases, access to the public is prohibited except by
high priest(s)/priest(s) to perform rituals or for
community festival(s) celebration(s). The systems of
administration of sacred groves are quite developed
and complex. Some sacred groves are community
sites (Ogun Onire), others are state heritage sites
(Idanre Hills and Igbo Olodumare) whileOsun
Osogbo is a national monument and UNESCO World
Heritage site. All the sacred groves have rich cultural
history and have existed for hundred(s) of years.
There were indications that the sacred groves are
becoming tourist attraction centres (Osun Osogbo
and Idanre Hills), with thousands of visitors every
year.
)5..(..........)( ln
1
'

 S
iii ppH
(6) ........
)ln(
)ln(
1
'
S
PP
H
H
E
S
iii
Max
H




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Proceedings of 7th NSCB Biodiversity Conference, October 2020
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Figure 1: Map of southwestern Nigeria showing the locations of sacred groves
Tree Growth and Yield
The maximum Dbh of individual trees in each sacred
grove was 185cm, 150.80cm, 131.50cm and 105cm
for Idanre hills, Osun Osogbo, Ogun Onire and Igbo
Olodumare sacred groves, respectively. Mean Dbh
varied from 24.4cm to 31.9cm and was highest at
Idanre hills and lowest in Ogun Onire sacred groves
while mean height \was highest at Ogun Onire
(13.7m) and lowest at Osun Osogbo sacred groves
(9.76m) (Table 1). Maximum height of individual
trees was 32.40m at Ogun Onire and Igbo Olodumare
sacred groves while it was 30.80m and 26.80m at
Idanre hills and Osun Osogbo sacred groves,
respectively. Basal area per hectare was highest at
Igbo Olodumare (51.83 m2ha-1) sacred grove
followed by Idanre Hills (44.85 m2ha-1), Ogun Onire
(40.7 m2ha-1) and Osun Osogbo (32.69 m2ha-1).
Idanre Hills recorded the highest stand volume of
389.52 m3ha-1 followed by Ogun Onire with 319.57
m3ha-1, Igbo-Olodumare with 302.74 m3ha-1 and Osun
Osogbo sacred grove with has 270.83 m3ha-1.
Diameter and Height class distribution
In all the sacred groves, tree diameter distribution
followed inverse-J shape (Figure 2). The results
revealed that as tree dbh decreases, number of trees
increases while as dbh increases, the number of tree
reduces. Majority of the trees in the four sacred
groves fell within the dbh range of 10cm - 20cm,
followed by 20cm - 30cm class; only few trees were
encountered within the diameter class of 100 cm and
above (Figure 2). Figure 3 indicated that a high
number of the trees in the four sacred groves were
found within height class of 0 - 10 cm and 10-20m.
Only very few trees were found to have heights that
are greater than 20 m (Figure 3).
Biodiversity Indices of the Sacred Groves
The results indicated that 34 families were
enumerated in the four sacred groves, with 24, 23, 19
and 19 families occurring in Ogun Onire, Osun
Osogbo, Igbo Olodumare and Idanre hills sacred
groves, respectively (Tables 1). Number of tree per
hectare ranged from 309 to 417. Osun Osogbo sacred
grove had the significantly highest tree density (417
ha-1) while the significantly lowest tree density (309
ha-1) was recorded in Idanre hills sacred grove while
there was no significant difference in tree densities at
Igbo Olodumare and Ogun Onire groves (Table 1).
Shannon-Wiener diversity index (H′) for the
overstory layers (range: 3.47 to 4.06) followed the
order Ogun Onire > Idanre Hills > Osun Osogb >
Igbo Olodumare sacred groves, with Igbo-Olodumare
and Ogun Onire sacred groves having the lowest and
highest values, respectively. Margalef index (species
richness: 8.05 - 10.24) followed the order Ogun
Onire > Osun Osogbo > Idanre Hills > Igbo
Olodumare sacred groves while species evenness
ranged from 0.52 to 0.86 and was also similar across
the sacred groves expect for Igbo Olodumare.

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Figure 2: Tree diameter distribution (cm) in (a) Osun Osogbo, (b) Igbo Olodumare, (c) Idanre hills and Ogun Onire Sacred groves
(a)
(b)
(c)
(d)

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Figure 3: Tree height (m) distribution in (a) Osun Osogbo; (b) Igbo Olodumare; Idanre hills and Ogun Onire Scared groves
(a)
(b)
(c)
(d)

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Table 1: Biodiversity Indices (Overstory and Understory) and Tree Growth Variables of the Sacred Groves
Biodiversity Indices and Growth
variables
Sacred Groves
Osun Osogbo
Igbo Olodumare
Idanre Hill
Ogun Onire
Overstory Species
Number of Families
23a
19b
19b
24a
Number of Individual Trees Ha-1
417a
408b
309c
408b
Number of Species
46b
32c
43b
58a
Shannon-Wiener's Evenness
0.84
0.52
0.86
0.85
Shannon's Diversity Index
3.83
3.47
3.76
4.06
Simpson Concentration (λ)
0.07
0.4
0.06
0.05
Species Richness (Margalef index)
8.05
5.57
7.94
10.24
Basal Area Ha-1 (m2)
32.69
51.83
44.85
40.70
Volume Ha-1 (m3)
270.83
302.74
389.52
319.57
Mean Dbh (cm)
24.39
31.68
31.89
28.00
Mean Height(m)
9.76
11.95
13.50
13.74
Maximum Dbh (cm)
150.80
105.00
185.00
131.50
Maximum Height (m)
26.80
32.50
30.80
32.50
Understory Species
Number of Species
34
23
37
46
Number of Individual Trees Ha-1
381
193
207
273
Shannon-Wiener's Index
2.9
2.04
3.22
3.3
Shannon-Wiener's evenness
0.85
0.65
0.89
0.86
Shannon's diversity Index
3.53
3.14
3.61
3.83
Simpson concentration
0.08
0.27
0.05
0.06
Species richness(Margalef index)
5.55
4.18
6.75
8.02

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A total of 98 species were identified and enumerated
in the understory layers across the four sacred groves.
The understory species encountered across the sacred
groves were: 46 in Ogun Onire, 37 in Idanre Hills, 34
in Osun Osogbo and 23 in Igbo Olodumare,
respectively. The understory layer has a range of
species per hectare between 381/ha to 193/ha. Total
number of understory cover for individual treeis
381/ha which is fully represented in Osun Osogbo
with 193/ha in Igbo Olodumare, Idanre hill (207/ha)
and Ogun onire (273/ha). Shannon-Wiener diversity
index (H′) for the understory followed the order
Ogun Onire > Idanre Hills > Osun Osogbo > Igbo
Olodumare sacred groves and ranged from 2.04 to
3.30 in all sites, with Igbo Olodumare sacred grove
and Ogun Onire sacred groves having the lowest and
highest values, respectively (Table 1). Shannon-
Wiener species evenness ranged from 0.65 to 0.89
and was also similar across the sacred groves expect
for Igbo Olodumare, whose species evenness was
clearly lower compared to the evenness in other
sacred groves. Margalef index (species richness)
followed the order: Ogun Onire > Idanre Hills >
Osun Osogbo > Igbo Olodumare sacred groves
(Table 1).
Table 2: Families Importance index Value for Osun Osogbo Sacred Grove
Family
Basal area ha-1
Volume ha-1
RD%
RDo%
FIV%
Apocynaceae
0.61
15.13
4.35
6.52
5.43
Fabaceae
0.54
130.13
23.91
41.9
32.91
Moraceae
0.07
59.21
6.52
19.43
12.97
Rubiaceae
0.25
4.03
8.7
2.41
5.55
Sterculiaceae
0.02
19.35
6.52
9.92
8.22
Table 3: Families Importance index Value for Igbo Olodumare Sacred Grove
Family
Basal area ha-1
Volume ha-1
RD%
RDo%
FIV%
Euphorbiaceae
4.02
24.39
9.09
7.76
8.42
Fabaceae
2.22
15.30
15.15
4.29
9.72
Meliaceae
0.70
3.91
6.06
1.36
3.71
Moraceae
2.87
35.49
6.06
5.54
5.80
Sterculiaceae
36.27
186.92
18.18
69.99
44.08
Table 4: Families Importance index Value for Idanre hill Sacred Grove
Family
Basal area ha-1
Volume ha-1
RD%
RDo%
FIV%
Apocynaceae
9.31
78.22
9.09
20.76
14.93
Fabaceae
17.45
168.18
18.18
38.9
28.54
Malvaceae
5.40
43.97
9.09
12.04
10.57
Meliaceae
0.29
1.75
11.36
0.65
6.01
Moraceae
6.87
67.80
11.36
15.31
13.34
Table 5: Families Importance index Value for Ogun Onire Sacred Grove
Family
Basal area ha-1
Volume ha-1
RD%
RDo%
FIV%
Fabaceae
1.49
10.37
15.25
3.66
9.45
Malvaceae
5.87
46.58
5.08
14.43
9.76
Moraceae
7.46
70.22
10.17
18.33
14.25
Sterculiaceae
7.19
58.10
11.86
17.67
14.77
Ulmaceae
8.53
70.78
1.69
20.96
11.33

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The Family Importance Value (FIV) indices for the
sacred groves are presented in Tables 2-5. The results
indicated that the most important families across the
sacred groves were Sterculiaceae, Fabaceae,
Ulmaceae and Moraceae and Malvaceae. In Osun
Osogbo sacred grove, the most important families
were Fabaceae, Moraceae and Sterculiaceae with FIV
of 32.91%, 12.97% and 8.22%, respectively (Table
2). It was different in Igbo Olodumare sacred grove
where Sterculiaceae had was the highest FIV of
44.08%, followed by Fabaceae (9.72%) and
Euphorbiaceae (8.42%) (Table 3). The highest FIV
Index in Idanre Hills sacred grove was recorded for
Fabaceae (28.54%), followed by Apocynaceae
(14.93%) and Moraceae (13.34%) (Table 4). In
Ogun-Onire sacred grove, the Sterculiaceae family
accounted for 14.77% of trees families, while
Moraceae (14.25%) and Ulmaceae (11.33%) had
high FIV (Table 5). The FIV index above 20% across
the sacred groves were Sterculiaceae and Fabaceae
families while the FIV index below 10% were
Phyllanthaceae, Meliaceae, Combretaceae.
In Osun Osogbo grove, the species with the highest
importance value index were Brachystegia eurycoma
(13.16), Angylocalyx oligophyllus (11.37) and Cola
hispida (11.31%) (Table 6). Hildegardia barteri was
found to be very important in the floristic
composition of Igbo Olodumare grove with IVI of
62.75%, Sterculia tragacantha (6.42%) and
Ricinodendrum heudelotii (4.21%) were also
important in this sacred grove (Table 7). In Idanre
Hills sacred grove, the most important tree species
were Ceiba pentandra (11.95%), Cassia siamen
(11.93%) and Cola gigantea (9.16%) (Table 8). Ogun
Onire sacred grove had Blighia sapida (11.25%),
Celtis zenkerii (8.31%) and Diospyros dendo (5.81%)
as the most important species (Table 9).
Results of species similarity index were as follows
Idanre Hills and Osun Osogbo: 47.2%; Idanre Hills
and Ogun Onire: 45.5%; Ogun Onire and Osun
Osogbo: 40.4), Igbo Olodumare and Ogun Onire:
40%, Igbo Olodumare and Osun Osogbo: 38.5%;
Igbo Olodumare and Idanre Hills: 37.3%. It was
observed that the similarity values across the four
sites were found to be low. Though, results from
Idanre Hills and Osun Osogbo groves (47.2%) as
well as Idanre Hills and Ogun-Onire groves (45.5%)
showed that tree species are more similar in these
sites than any other site combination while others
such as Igbo-Olodumare and Idanre Hills groves
showed that only 37.3% of the species in these sites
were similar. The low similarity of species across the
four sacred groves may be due to rarity of some
species, genetic and site differences.
DISCUSSION
Distribution and status of sacred groves in
southwestern Nigeria
Sacred groves occur in various forms such as sites for
place of deity/ancestral worship, cultural festivals,
coronation of kings, burial grounds for chiefs/kings,
etc. However, their methods of management vary
depending on their intrinsic nature, distribution and
local beliefs. Sacred groves are found in many
countries across the globe but are more common in
Asia and Africa (Bhagwat and Rutte, 2006; Aniah
and Yelfaanibe, 2016). Globally, India has the
highest numbers of sacred natural sites, with 100,000
–150,000 groves spread across 19 of the 28 Indian
states (Malhotra, et al., 2001; Ormsby, 2012a).
Ghana has about 1,900 sacred groves, which makes it
the country with the highest sacred groves in Africa
(Ormsby, 2012b).
It has been documented that almost all southeastern
and southwestern communities in Nigeria have at
least one sacred grove and that sacred groves are
symbols of identity for most Yoruba People in
southwestern Nigeria (NCMM, 2005; Borokini,
2016; Adeyanju, 2020). Consequently, higher
number of sacred than what was reported in this
study was expected. It is therefore expected that the
list of sacred groves presented in this study would be
updated as more are identified. Among the
importance of sacred groves as tool for biodiversity
conservation is their widespread distribution (Laird,
1999). Thus, though most sacred groves are relatively
small in size, the cumulative area occupied by sacred
groves in a locality/country is usually large when
their individual areas are summed up. Research
studies (Mgumia and Oba 2003, Khan et al. 2008)
have observed that the area of sacred groves could
vary from as low as 0.001 ha to as high as 26,326 ha,
which is collaborated by the results of this study.
With core area of 75 ha and buffer zone of 47 ha,
Osun Osogbo sacred grove is the largest in Nigeria
(Onyekwelu and Olusola, 2014; Agbelade and Ojo,
2020). This implies that Nigerian sacred groves are
small in size, considering the thousands of hectares
occupied by natural forests. Also, Nigerian sacred
groves are generally smaller when compared with
their counterparts in some parts of the world (Khan et
al. 2008). The local laws and customs as well as
regulation/prohibition of access into sacred groves in
southwestern Nigeria could explain the lack of or low
encroachment into the groves. Onyekwelu and
Olusola (2014) noted that through respect and fear of
taboos and deity, people keep away from the sacred
grove and refrain from felling trees while Borokini
(2016) and Adeyanju (2020) reported that some
sacred groves in southwestern Nigeria are still intact.

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Proceedings of 7th NSCB Biodiversity Conference, October 2020
29
Table 6 Summary of growth characteristics and diversity indices of three most important species Osun Osogbo Sacred Grove
Family
Species
Density
Ha-1
Mean
Dbh(cm)
Mean
Ht (m)
Mean
BA (m2)
Mean
Vol (m3)
RD
(%)
RDo
(%)
IVI
(%)
Sterculiaceae
Cola hispida
70
17.47
7.38
0.03
0.14
16.85
5.77
11.31
Fabaceae
Brachystegia eurycoma
27
41.96
13.96
0.25
2.56
6.37
19.94
13.16
Fabaceae
Angylocalyx oligophyllus
16
17.05
9.65
0.02
0.16
3.75
19
11.37
Table 7 Summary of growth characteristics and diversity indices of three most important species in Igbo Olodumare Sacred Grove
Family
Species
Individual
Tree Ha-1
Mean
Dbh (cm)
Mean
Ht (m)
Mean
BA (m2)
Mean
Vol (m3)
RD
(%)
RDo
(%)
IVI
(%)
Sterculiaceae
Hildegardia barteri
253
33.22
11.35
0.13
0.67
62.04
63.46
62.75
Sterculiaceae
Sterculia tragacantha
23
20.72
10.29
0.06
0.28
5.74
7.09
6.42
Euphorbiaceae
Ricinodendrum heudelotii
17
44.78
13.86
0.21
1.29
4.21
4.21
4.21
Table 8 Summary of growth characteristics and diversity indices for three most important species in Idanre Hills Sacred Grove
Family
Species
Individual
Tree Ha-1
Mean
Dbh (cm)
Mean
Ht (m)
Mean
BA (m2)
Mean
Vol (m3)
RD
(%)
RDo
(%)
IVI
(%)
Apocynaceae
Holarrhena floribunda
4.69
109.93
21.57
1.52
12.99
7.63
21.93
14.78
Moraceae
Antiaris africana
9.38
97.97
22.77
1.00
10.50
6.80
14.39
10.60
Moraceae
Morus mesozygia
1.56
105.20
30.80
0.87
13.05
7.31
12.52
9.92
Table 9 Summary of growth characteristics and diversity indices of three most important species Ogun Onire Sacred Grove
Family
Species
Individual
Tree Ha-1
Mean
Dbh (cm)
Mean
Ht (m)
Mean
BA (m2)
Mean
Vol (m3)
RD
(%)
RDo
(%)
IVI
(%)
Ulmaceae
Celtis zenkerii
67
32.23
15.53
0.13
1.05
16.48
0.14
8.31
Sapindaceae
Blighia sapida
6
65.28
13.68
0.47
2.82
1.53
20.96
11.25
Ebenaceae
Diospyros dendo
2
10.00
5.30
0.01
0.01
0.38
11.24
5.81

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Proceedings of 7th NSCB Biodiversity Conference, October 2020
30
Tree growth and yield characteristics
The density of trees in the studied sacred groves is
similar or lower than the density recorded in some
studies conducted in southwestern, Nigeria. Lawal
and Adekunle (2013) and Adekunle et al. (2014)
reported densities of 406/ha and 500/ha, respectively
for tropical forests in Nigeria, which are comparable
to our results. Onyekwelu et al. (2008) reported
higher densities of 508 to 671 for some degraded and
primary forests in southwestern Nigeria. The
estimated volume for these sacred groves range
between389.52 m³ha-1 and 270.83 m³ ha-1 and is
similar to the volume estimated for some protected
forests. Adekunle et al. (2013) estimated volume of
387 m³ha-1 for Akure Strict Nature Reserve (SNR),
Adekunle et al. (2014) obtained volume of 287.49
m³ha-1 for Eda protected forest, Wittmann et al.
(2008) reported volume of 312 m³ha-1 for Southern
Pantanal, Brazil. Banda et al. (2006) and Munishi et
al. (2011) found that management activities had
significant influence on tree species growth
characteristics, density and volume. Tree diameter
distribution is an indication of how well the forest is
regenerating and making use of site resources
(Olajuyigbe and Jeminiwa, 2018). The inverse-J
diameter distribution of trees in all the four sacred
groves in this study is typical of natural tropical
forest ecosystems (Onyekwelu et al., 2008) and an
indication of good regeneration status and healthy
forest ecosystem (Onyekwelu and Olusola, 2014;
Sundarapandian and Subbiah, 2015). The tree height
distributions graphs revealed that a high proportion of
trees were within the height class of 10 – 20m, with
only few trees in 30 – 40m height class. This is
similar to the report of Adekunle et al. (2013) that
64% of the trees in an SNR in Akure, Nigeria fell
within the height class of 11m - 20m while only
about 4% of the trees were found in 26m – 30m
height class.
Biodiversity status of the Sacred Groves
One of the important characteristics of tropical
rainforest ecosystems is their richness in floristic
composition. Biodiversity indices are usually
estimated to bring the floristic diversity and
abundance in different habitats to similar scale for
comparison, which is important for conservation
purposes. The higher the value of Shannon-Wiener
diversity index, the higher the species richness of
such ecosystem. The Shannon-Wiener diversity
indices (H′) of the four sacred groves under study
ranged from 1.80 to 3.46, which is similar to the
range of H′ (2.82 to 3.66) for some tropical rainforest
ecosystems in southwestern, Nigeria (Adekunle
2006; Onyekwelu et al., 2008; Onyekwelu and
Olusola, 2014). The high diversity indices (3.19 to
3.46) of three sacred groves in this study compares
favourably with the values reported for some primary
forests in Nigeria (Adekunle et al., 2013; Onyekwelu
et al., 2008; Onyekwelu and Olusola, 2014).
Adekunle et al. (2013) reported H′ of 3.74 for an
SNR in Nigeria while Onyekwelu et al. (2008)
reported H′ of 3.31 and 3.12 for Omo Biosphere
reserve and Oluwa primary forest, respectively. The
diversity indices of the three sacred groves in this
study were higher than those of some degraded
forests and similar with those of others (Onyekwelu
et al., 2008; Onyekwelu and Olusola, 2014). The
Shannon-Wienner diversity indices for this study are
similar to the range of 2.94–3.96 for sacred groves in
south-eastern Ghats, India (Rao et al. (2011) but
higher than values obtained for sacred groves in
Tamil Nadu Indian (1.69-2.33) and Tanzania (1.2–
1.4) (Mgumia and Oba, 2003; Sundarapandian and
Subbiah 2015). The high diversity indices of the
sacred groves in this study could be an indication of
the effectiveness of sacred groves as traditional
biodiversity conservation measure. The high diversity
indices of the sacred groves could be attributed to the
strict traditional method (taboo) of conservation and
the prohibition of activities in and around the sacred
groves. Sundarapandian and Subbiah, (2015); Khan
et al., (2008) revealed that religious beliefs and
taboos were central to the protection of sacred groves
in India resulting in the increase in tree species
diversity. The good conservation status of Osun-
Osogbo sacred grove was attributed to fact that the
people see it as home of deity, place of worship and
cultural site (Onyekwelu and Olusola, 2014), which
is similar to the situation in Tanzania (Mgumia &
Oba 2003). Onyekwelu and Olusola (2014) attributed
the low species diversity index of Igbo-Olodumare
sacred grove to its “low sacredness” and revealed that
only 5% of community dwellers see it as home of
deity and place of worship. Thus, the people are no
longer afraid of the deity and taboos associated with
this grove, which may have led to encroachments in
recent times. The low diversity index of Igbo-
Olodumare sacred grove can also be attributed to its
rockiness (Onyekwelu and Olusola, 2014) and its
dominance by fewer tree species. Our results
revealed that Hildegardia barteri had relative
dominance and IVI of 63.46% and 62.75%,
respectively in Igbo-Olodumare sacred grove, with
162 individual trees. The slight reductions in
biodiversity indices of Osun-Osogbo sacred grove
compared to past studies may be attributed to some
practices at the sacred grove site. Adeyanju (2020)
reported that the high influx of worshipers and
tourists to Osun-Osogbo sacred grove for the yearly
Osun annual festival celebration contributes to
negative pressure on the environmental and cultural

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Proceedings of 7th NSCB Biodiversity Conference, October 2020
31
integrity of sacred site. For example, due to the high
influx of people into the grove, understory species
that are to contribute to tree species diversity might
be trampled upon and thus affect the survival of the
species. Oftentimes, rituals rites and sacrifices to the
gods may involve ground clearing and ground fires
by the traditional priests and visiting devotees. This
may adversely affect tree density in the sacred
groves, especially density of saplings and seedlings,
thereby, having negative influence on natural
regeneration and species richness in the sacred
groves. This may explain the comparatively lower
number of species in understories (32 to 46) than the
over stories (32 to 58) of the four sacred groves
investigated in this study. The Hmax values for this
study, which ranged from 3.47 to 4.06 were higher
than those of some previous studies (1.80 to 3.46)
(Onyekwelu et al. 2008; Onyekwelu and Olusola
2014; Agbelade and Ojo 2020). This implies that
most of the species encountered in the sites do not
have equal area abundance (Onyekwelu et al. 2008).
Species richness is one of the most widely used
indices for measuring biodiversity of an ecosystem.
Igbo-Olodumare sacred grove had the lowest
overstory tree species richness (5.57) when compared
with the Margalef indices of Idanre Hills (7.94),
Osun Osogbo (8.05) and Ogun-Onire (10.24) sacred
groves. Igbo-Olodumare also had the lowest species
richness at the forest understory. Adekunle et al.,
2013 estimated higher Margalef index of 64.72 for
Akure SNR, Nigeria. The distribution of few tree
species per hectare is mostly responsible for poor tree
species richness in most Nigerian forest ecosystems.
Osun Osogbo, Idanre Hills and Ogun Onire sacred
groves had similar species evenness values of 0.84,
0.86, and 0.85, respectively while Igbo Olodumare
grove had low evenness of 0.52, which agrees with
some published results. Adekunle et al. (2013)
obtained species evenness value of 0.82 for Akure
SNR; Agbelade and Ojo, (2020) reported species
evenness of 0.45 for Eda forest reserve while
Onyekwelu et al. (2008) estimated species evenness
for Elephant forest (0.57), Oluwa forest (0.65) and
Queen‟s forest (0.66) in south western Nigeria. This
implies that tree species are similarly evenly
distributed across the three sites while tree species in
Igbo-Olodumare were not evenly distributed
probably because of the dominance of the site by
Hildegardia barteri. Connell and Lowman (1989)
affirmed that forest that has 50-80% of its canopy
covered by only few species is considered a low
diversity forest. IUCN (2004) opined that a species is
considered endangered if reduction in population size
in time is greater than 80% over the last ten years or
projected reduction in the future if the estimation in
numbers of matured individuals is less than 2,500
individuals and if projected extinction of least 20%
within the next 20 years.
CONCLUSION AND RECOMMENDATION
The results of this study suggest that sacred groves
are effective in the conservation of trees species. The
high biodiversity indices of the sacred groves are
attributed to the fact that the taboos guiding these
groves are still held in high esteem, thus curtailing
anthropogenic influences on the sacred groves. The
diameter distributions curve of trees in the four
sacred groves gave an indication that the sacred
groves have good regeneration potentials. Species
similarity between pairs of sacred groves was
generally low. The low similarity of species between
groves may be due to dominance by few species, to
rarity of some species and site differences. The
biodiversity conservation gains of sacred groves
should be incorporated into state managed forests.
This could be achieved through community based
forest management system, wherein communities are
actively involved in forest management. Government
should encourage in-situ conservation through
assisted regeneration and by strengthening the
traditional laws and regulations guiding the sacred
groves. Cultural values and indigenous knowledge
should be incorporated into the policy framework of
conservation. Efforts should be made to regenerate,
protect and conserve endangered and vulnerable tree
species in the sacred groves to avoid risk of
extinction.
ACKNOWLEDGEMENT
This study is part of a wider study on “Status and
drivers of biodiversity conservation in sacred groves
in southwestern Nigeria” under the sponsorship of
Alexander von Humboldt Foundation (AvH), Bonn,
Germany. The authors are grateful to the AvH for
providing the funding for this work under the
institutional research group linkage programme of the
AvH.
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