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Dendrometric characteristics as indicators of pressure of Afzelia africana Sm. dynamic changes in trees found in different climatic zones of Benin

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Afzelia africana is a forest species used by local inhabitants for various purposes, especially as forage to feed cattle, as medicinal plant and its wood is used to make furniture or for cooking. Its utilisation in its current form constitutes a threat to this species. However, the lack of data on this species is a hindrance towards drawing up an efficient program for its sustainable management. In order to fill in some gaps in the knowledge of A. africana tree populations, dendrometric characteristics of this species were studied within different climatic zones where it occurs in Benin. Data collected on each of them included height and diameter, and with regard to the levels of pressure, five categories were defined namely: null, weak, moderate, severe and very severe. As far as diameter is concerned every size was taken into consideration in all the climatic zones. However, average diameter and height of the A. africana individuals varied significantly according to climatic zones. Anthropogenic pressure increased while moving from the humid zone towards the drier zone. Moreover, there was a noticeable significant change in the level and quality of pressure between trees found in the different climatic zones in the sense that the lower the height of the trees, the more severe the level of pressure exerted. Such a relationship was not significant when one considers tree diameter in accordance with the climatic zones in the country.
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Dendrometric characteristics as indicators
of pressure of Afzelia africana Sm. dynamic changes
in trees found in different climatic zones of Benin
B. SINSIN
1,
*, O. EYOG MATIG
2
, A.E. ASSOGBADJO
1
,
O.G. GAOUE
´
2
and T. SINADOUWIROU
1
1
Laboratoire d’Ecologie Applique
´e, Faculte
´des Sciences Agronomiques, Universite
´d’Abomey-Calavi,
Benin;
2
International Plant Genetic Resources Institute (IPGRI); *Author for correspondence (e-mail:
bsinsin@syfed.bj.refer.org; fax: þ229-30-30-84)
Received 5 November 2002; accepted in revised form 2 June 2003
Key words: Afzelia africana, Benin, Regeneration, Threats, Tree size
Abstract. Afzelia africana is a forest species used by local inhabitants for various purposes, especially
as forage to feed cattle, as medicinal plant and its wood is used to make furniture or for cooking. Its
utilisation in its current form constitutes a threat to this species. However, the lack of data on this species
is a hindrance towards drawing up an efficient program for its sustainable management. In order to fill in
some gaps in the knowledge of A. africana tree populations, dendrometric characteristics of this species
were studied within different climatic zones where it occurs in Benin. Data collected on each of them
included height and diameter, and with regard to the levels of pressure, five categories were defined
namely: null, weak, moderate, severe and very severe. As far as diameter is concerned every size was
taken into consideration in all the climatic zones. However, average diameter and height of the A.
africana individuals varied significantly according to climatic zones. Anthropogenic pressure increased
while moving from the humid zone towards the drier zone. Moreover, there was a noticeable significant
change in the level and quality of pressure between trees found in the different climatic zones in the
sense that the lower the height of the trees, the more severe the level of pressure exerted. Such a
relationship was not significant when one considers tree diameter in accordance with the climatic zones
in the country.
Introduction
Located in the low rainfall dry corridor named ‘Dahomey Gap’, Benin does not
have as much forest zone as its neighbouring countries of the coastal zone of
West Africa such as Co
ˆte d’Ivoire, Ghana and Nigeria. Its natural forest covers
2 538 000 ha (FAO 2001), which represents 23% of the total surface area of the
country. This low forest surface of the country is due to increased demographic
pressure with the subsequent high exploitation of Afzelia africana, a savannah
tree species, by the local population for various purposes, specifically for
feeding cattle (Sinsin 1993; Onana 1998), for traditional medicine (Kerharo and
Adam 1974; Adjanohoun et al. 1989; Ahouangonou and Bris 1997) and for
timber (Ahouangonou and Bris 1997; Bayer and Waters-Bayer 1999). Un-
controlled use of the species leads to degradation and reduction of its habitat
#2004 Kluwer Academic Publishers. Printed in the Netherlands.
Biodiversity and Conservation 1555–1570, 2004.
13:
and its population in the country. It is therefore urgent to gather data on
endangered species, such as A. africana, with a view to assess its conservation
status and also to develop effective conservation strategies.
Size class distributions have been used to understand the tree population dy-
namics (Cunningham 2001). They are considered to be a very useful predictive tool
(Geldenhuys 1992). This tool could be used to evaluate the impact of mans ac-
tivities on treespopulation (Cunningham 2001). However, several other factors
could affect the shape and the size of categories of distribution of a species (Van
Wyk et al. 1996; Sokpon and Biaou 2002).
The major aim of this study is to determine the level of pressure on A.
africana populations as a result of harvesting and utilisation of its leaves and
small branches for fodder purposes. Dendrometric parameters were therefore
collected, processed and analysed. This paper highlights the salient results of the
study.
Study sites and studied species
Study sites
The study was conducted in the three bioclimatic zones of the Republic of Benin
(112 622 km
2
), located between 68200and 128250N and 18and 38400E in West
Africa. These zones are: the sub-humid Guineo-Congolean afnity zone (from 6825
to 78300N), the Sudano-Guinean zone (from 78300to 98300N) and the Sudanian
zone (from 98300to 1280N) (White 1983). The stations surveyed in each of these
climatic zones are indicated in Figure 1.
The rainfall regime is bimodal in the Guineo-Congolean zone (from April to
June and from September to November) with a mean annual rainfall of 1200 mm.
Beyond 88N and towards the north, rainfall distribution becomes unimodal (May
October) with a mean annual rainfall above 900 mm.
The Guineo-Congolean zone has ferrallitic soils, deep and hardly fertile
(700 000 ha), alluvial soils and heavy clay soils (360 000 ha) localised in the valleys
of the Mono, Niger, Couffo and Oueme rivers, and in the Lama depression. These
soils are rich in clay, humus and inorganic elements. The quality of the countrys
vegetation has suffered severe impoverishment as a result of various intense eco-
nomic and human activities, specically in the southern region, where human
population density is high. In the southern zone, vegetation is composed of fallows
and small forest patches of less than 5 ha. The original vegetation at its early stages
was made up of semi-deciduous dense forests and Guinean savannah (Adjanohoun
et al. 1989).
In the Sudanian and the Sudano-Guinean zones, there are infertile mineral soils
(1 500 000 ha) and ferruginous soils (8 600 000 ha). The Sudano-Guinean transition
zone is characterised by mosaics of woodlands, dry dense forests, strewn with tree
and shrub savannahs and gallery forests. The vegetation of the Sudanian
zone consists of savannas and gallery forests with small trees and shrubs slightly
1556
covering the ground. The main activities of local communities are extensive agri-
culture, animal husbandry, and reckless exploitation of woodlands and gallery
forests.
Figure 1. Stations surveyed.
1557
Studied species
A. africana is a timber species with high potentials for fodder and medicine. In the
agro-pastoral zone of the country, the leaves are considered as important forage for
cattle during the dry season. The branches are pruned by the Fulanis to feed their
animals. The powdered bark of A. africana mixed with salt was reported to have
improved cattle intake. A. africana is used for curing several diseases such as
oedemas, intercostal neuralgias, convulsions, staturo-ponderal backwardness, and
so forth. The powdered bark is used as a febrifuge and gastro-intestinal stimulant.
When this powder is mixed with Morinda lucida, it is used as an antiseptic for
wounds. The decoction of the roots of A. africana is used to cure blennorrhoea,
stomach ache and hernias.
The timber of this species is one of the best sold in the open markets all over the
country. Because of various usages, A. africana is currently under severe human
pressure.
Methods
Six stations were selected in the Guineo-Congolean zone, nine stations in the
Sudano-Guinean zone and 12 stations in the Sudanian zone. Observations and
measurements were carried out in these stations, both in protected areas (national
parks and reserve forests) and state ranch and village zones (free zones). In each
station, one or two rectangular sample plots of 1000 m
2
were established and
considered as a centre of the plot, the rst individual of A. africana randomly
selected. A total of 669 individuals of A. africana were measured: 160 individuals
in the Guineo-Congolean zone, 198 individuals in the Sudano-Guinean zone and
311 individuals in the Sudanian zone. The parameters recorded in each plot were as
follows:
.The diameter and height of all individuals, with dbh (diameter at breast height)
above 10 cm;
.The proportion of branches cut or mutilated and the total number of branches for
each individual of A. africana, were considered and analysed in accordance with
the following ve levels of pressure:
P0 ¼null: individuals without damage (without branch neither cut nor mutilated
trunk),
P1 ¼weak: individuals with 025% of their crown pruned,
P2 ¼average: individuals with 2550% of their crown pruned,
P3 ¼severe: individuals with 5075% of their crown pruned,
P4 ¼very severe: individuals with 75100% of their crown pruned.
.The causes of mutilations on trees were identied.
1558
Data analysis consisted of analysing variations in the diameters and heights of
individuals according to climatic zones. The Newman and Keuls test of comparison
was used to compare tree diameter and height among the different climatic zones.
In addition, factorial analysis was carried out to identify the localities with similar
levels of pressure. While taking into consideration data adjustment models such as
the test of normality, of homogeneity and the independence of regression residues,
the transformation of variables was utilised to measure the height and diameter
distributions of individual trees. For each transformation process, three tests were
therefore undertaken, namely: the test of normality, the test of independence of
residual variance and the decline residual independence test of Breush-Pagan.
In addition, the impact of climatic and anthropic pressure on tree height within
each climatic zone was evaluated by studying the treesheight-class distribution.
The distribution was undertaken according to height size categories among in-
dividuals without pressure (P0) and those with moderate pressure (P1 and P2), to
the ones with severe pressures (P3 and P4) as well.
Results
Tree diameter (dbh) variations according to climatic zones
Diameter class-size distribution
Diameter class-size distribution for A. africana was not signicantly different ac-
cording to climatic zones (Figures 24). A bell-shaped distribution type was ob-
served for each climatic zone. The two extreme class-size individuals are absent in
the three zones. The slight differences in the distribution noticed are the logarith-
mic function in the Guineo-Congolean zone (log(y)¼0.0103x
3
0.2096x
2
þ
1.1379x0.2584) while it is a polynomial function in the Sudano-Guinean
zones (y¼0.0456x
5
þ1.2012x
4
10.912x
3
þ38.203x
2
36.821xþ17.267) where
individuals with a diameter between 20 and 60 cm are most predominantly
Figure 2. Diameter size-class distribution for A. africana in the Guineo-Congolean zone.
1559
represented in the stands. The small diameters are less represented at the sites.
However, the diameter distribution showed a second peak with low amplitude in the
upper diameter categories (Figure 3).
In the Sudanian zone (Figure 4), the diameter size-class distribution matches a
logarithmic function (log(y)¼0.008x
3
0.1686x
2
þ0.8848xþ0.4876). This pat-
tern reveals constant reduction in the number of A. africana individuals from the
lower diameter categories to the upper diameter categories.
The mean diameter
The mean diameter for A. africana trees varies signicantly from 42 cm in the
Sudanian zone to 48 cm in the Sudano-Guinean zone (p<0.05). The test of
NewmanKeuls classies the different climatic zones into two homogeneous
Figure 3. Diameter size-class distribution for A. africana in the Sudano-Guinean zone.
Figure 4. Diameter size-class distribution for A. africana in the Sudanian zone.
1560
groups when considering the mean diameter (Table 1). The Guineo-Congolean and
Sudano-Guinean groups are separated from the Sudanian one.
Tree height variations according to climatic zones
The height class distribution
The height class distribution for A. africana varied in accordance with specied climatic
zones (Figures 57). It was roughly a bell-shaped curve in the Guineo- Congolean zone
and tted to an increasing polynomial function (y¼5x
3
56.286x
2
þ181.71x
120.2). The median height class size varies from 12.5 to 17.5 m. In the Sudano-
Guinean zone, the distribution was truncated in the low height categories and tted a
logarithmic function (log(y)¼0.4289x
2
þ1.2616xþ1.1167; R
2
¼1). The height
size-class distribution in the Sudanian zone was different from the other zones and
tted a reverse function (1/y¼0.0351x
2
0.1455xþ0.1514; R
2
¼0.8304).
But in the three zones, individual trees with up to 30 m height were observed.
The mean height
This study shows that in Benin, the mean height of A. africana varies from 9 m in
the Sudanian zone to 13 m in the Guineo-Congolean zone. With regard to the
Table 1. Bioclimatic zones classications based on diameter of A. africana trees.
Climatic zone Mean diameter
a
(cm) Number of individuals measured
Sudano-Guinean zone 48 A 198
Guineo-Congolean zone 47 A 160
Sudanian zone 42 B 311
a
There is no signicant difference between mean diameters followed by the same letter.
Figure 5. Height size-class distribution for A. africana in the Guineo-Congolean zone.
1561
stations, the lowest mean height is observed in Penessoulou (4 m) located in the
Sudanian zone while the highest is observed in the reserve forest of Lama (17 m)
located in the Guineo-Congolean zone.
Analysis of variations of the mean heights of A. africana trees (Table 2) showed a
signicant difference from one climatic zone to another (p<0.05). The mean
height decreases progressively from the humid (Guineo-Congolean) to the driest
Figure 6. Height size-class distribution for A. africana in the Sudano-Guinean zone.
Figure 7. Height size-class distribution for A. africana in the Sudanian zone.
Table 2. Mean heights comparison for A. africana between the climatic zones.
Climatic zone Mean heights
a
(m) Number of individuals measured
Guineo-Congolean zone 13 A 160
Sudano-Guinean zone 10 B 198
Sudanian zone 9 C 311
a
The letters A, B and C indicate signicant differences between the three zones
with respect to height (p<0.05).
1562
zones (Sudanian). In fact, the tallest individual trees were found in the Guineo-
Congolean zone (e.g. in the Lama Forest Reserve (17 m) and in Pobe
`(16 m)).
While in Penessoulou, Sudano-Guinean zone and in Segbana, Sudanian zone, in-
dividual trees observed measured 4.20 and 5.25 m, respectively.
Levels of pressure on A. africana in the climatic zones
The levels of pressure varied according to climatic zones (Figure 8). Pressure was
low in the Guineo-Congolean zone and gradually increased when moving towards
the Sudanian zone. The highest frequencies of the pressure levels P3 (severe
pressure) and P4 (very severe) were recorded in the Sudano-Guinean and Sudanian
zones. On the contrary, in the Guineo-Congolean zone, the highest frequencies
were recorded for the levels of pressure null (P0) and low (P1). The Sudano-
Guinean zone presented an intermediate situation. Indeed, in the Guineo-Congolean
zone, more than 60% of the trees measured were neither pruned nor debarked.
Almost all the trees of A. africana recorded in the Sudanian and Sudano-Guinean
zones were mutilated. The Sudano-Guinean zone has the highest frequencies of
severe pressure on trees (55% against 52% in the Sudanian zone).
Influence of pressure on tree heights
Figures 9 and 10 compare the tree heights with and without pressures in the
Guineo-Congolean zone. The impact of the pressure is both on the number of
individuals and on the height, where the height size class 2030 m disappears with
very severe pressures. For the Sudano-Guinean zone the 1015 m height size class
no longer exists under very severe pressure conditions (Figures 11 and 12). In the
Figure 8. Frequencies of level of pressure in the different climatic zones. The gures P0P4 indicate
the different levels of pressure (P0¼null, P1 ¼weak, P2 ¼average, P3 ¼severe, P4 ¼very severe).
1563
Figure 9. Height size-class distribution for A. africana in the Guineo-Congolian zone without pressure
(P0).
Figure 10. Height size-class distribution for A. africana in the Guineo-Congolian zone with pressure
(P1P4).
Figure 11. Height size-class distribution for A. africana under weak and average pressure in the
Sudano-Guinean zone (P1 and P2).
1564
Sudanian zone, with minimum pressure (P0P2), a good distribution of heights
from 5 to 30 m is observed but there are no more individuals of height size class
2025 m under severe pressure (Figures 13 and 14). The number of individuals per
height size class is relatively low. Within the parameters ranging from severe to
very severe pressures, the maximum heights observed are 15 m. But the number of
individuals is higher than under low pressure conditions.
In conclusion, in virtually all the climatic zones, various pressures inuence the
growth of A. africana.
The factorial analysis (Figure 15) of the matrix crossing the 25 surveyed stations,
coupled with the different levels of pressure (P0P4), identied three homogeneous
groups of stations according to their levels of pressure.
Figure 12. Height size-class distribution for A. africana under severe pressure in the Sudano-Guinean
zone (P3 and P4).
Figure 13. Height size-class distribution for A. africana under null and average pressure (P0, P1 and
P2) in the Sudanian zone.
1565
Group I (GI), including the reserve forests of Lama, Ketou and Pobe, the ranch of
Samiondji and forest patches at Lonkly and Azove
`in Kouffo province, is mainly
composed of the stations located in the Guineo-Congolean zone. It is well corre-
Figure 15. Factorial analysis for the level of pressure and the localities surveyed. The gures P0P4
indicate the different levels of pressure (P0¼null, P1¼weak, P2 ¼average, P3 ¼severe, P4 ¼very
severe).
Figure 14. Height size-class distribution for A. africana under severe pressure (P3 and P4) in the
Sudanian zone.
1566
lated with the lowest levels of pressure (P0 and P1) (Figure 8). It regroups stations
where A. africana trees were undergoing relatively low pressure. Indeed, in these
stations, 66% of the individuals recorded were intact and less than 10% of in-
dividuals were subjected to severe or very severe pressures.
Group II (GII) is composed of the following stations: Tasso, Sakabansi, Kere-
mou, Okpara, Beterou, Segbana, Bense
´kou, Agbassa, Dogo, Toui and Bessassi. In
these clustered stations important pressures occurred with regard to mutilations on
the branches of A. africana. This group was correlated with the average (P2) and
severe (P3) levels of pressure (Figure 8). Intact individuals in these stations were
absent or rare.
Group III (GIII) comprises the stations Bassila, Penessoulou, Perma, Bembereke,
Firou, Gbeba, Pikire, Birni and Toucountouna. In these stations individual trees
were under very severe level of pressure (P4), and intact trees (P0) were rare.
The stations in groups II and III are generally characterized by a high mutilation
pressure on A. africana and are located in the Sudanian or Sudano-Guinean zones.
Group II encompasses not only several stations of the Sudano-Guinean zone such as
Okpara, Toui, Beterou and Agbassa, but also stations from the Sudanian zone,
including Keremou, Segbana, Sakabansi and Bensekou.
Discussion
The tree diameter and height size-class variations according to climatic zones
It was noticed in general that most of the diameter shape categories are represented
within each climatic zone. This could be explained by the presence of protected
areas within each surveyed zone. In protected areas, the pressure on A. africana is
low. In all climatic zones, there was a high concentration of individuals in the
diameter classes ranging from 20 to 50 cm. This low amplitude reveals the existing
pressure on the individuals of the other diameter classes. These pressures are
mainly due to the commercial logging of individuals with diameters above 50 cm,
followed by the high foliage pruning and the de-barking of trees for traditional
medicine purposes. These pressures were accentuated in the Sudanian zone, which
is the main transhumance zone at country level, and where illegal and uncontrolled
logging activities of high diameter trees were observed.
In general, trees are shorter in the Sudano-Guinean zone where most of the trees
are within a narrow range of class height (520 m). In the Guineo-Congolean zone,
greater tree heights such as 1728 m in Lama reserve forest (68550N), and 1520 m
at Pobe
`station (78N) were recorded. This fast growth could be explained inter
alias, on one hand, by the protected area status of these stations where Afzelia trees
are protected from pruning; and on the other hand by the more favourable rainfall
regime occurring in these areas situated in the Guineo-Congolean climatic zone
where bush re is rare in forest patches.
Several authors (Paradis and Houngnon 1997; Cunningham 2001; Sokpon and
Biaou 2002) have used the diameter size-class distribution as a eld method to
1567
assess the impact of harvest practices on the regeneration of the species. It is also a
valid tool for assessing the pressure undergone by a tree species population.
However, it is important to take into consideration the species temperament and the
development stage of the population when analysing its diameter or height size-
class distribution.
It was observed in this study that in the three climatic zones, the species has a
bell-shaped curve for its diameter size-class distribution. The same distribution was
observed by Paradis and Houngnon (1997) in Lama Reserve, Benin. This dis-
tribution was also found by Sokpon and Biaou (2002) in another forest reserve in
Benin (Bassila reserve forest). According to Cunningham (2001), the bell-shaped
curve indicates either light required or competition-intolerant species or low
numbers of seeds due to an unusual reproductive strategy. But A. africana is known
as a shade-intolerant species. According to Sokpon and Biaou (2002), its diameter
size-class distribution indicates the absence of young trees with less than 20 cm
diameter and also difculty for its recruitment in a heavy clayed-soil forest such as
the Lama Reserve. The absence of individuals with larger diameters mainly in the
Sudanian zone could be explained by logging activities where the trees are facing
very severe pressure, which can lead to the extinction of the population of the
species. Indeed, the big trees are the best seed-bearers of the population, which
ensures the production of seeds and thus supports the regeneration of the species.
The scarcity in the stands of an optimum density of sexually mature individuals
(sexually mature diameter trees) will accordingly be a weakness for the re-
generation of the population.
Impact of pressure on the tree height and diameter within climatic zones
The comparison made for the tree heights in the same climatic zone, such as the
Guineo-Congolean zone without pressure (Figure 9) and under pressure (Figure
10), shows that the height class size 2030 m is no longer represented within the
areas under pressure. The species height varies from 4.20 m (Penessoulou) in the
Sudanian zone to 17.20 m (Lama Reserve) in the Guineo-Congolean zones. This
trend is in accordance with the data collected (810 m) in savannah by Ahouan-
gonou (1997) on the same species. Kerharo and Adam (1974) indicated that the
species could grow up to 2530 m under favourable conditions while it is short and
stocky in Senegal (dry zone). This means that climatic conditions inuence the
species growth (the height of the species). Climatic conditions are not the single
factor that inuences the height of the species, as the study shows individual trees
with up to 30 m height within the three climatic zones. This study also demon-
strated the reduction in the same climatic zone of tree population heights in severe
and very severe pressure conditions. Pressure (pruning, debarking, etc.) inuences,
amongst others, the growth of A. africana.
Repeated tree crown pruning observed between 88N and 128N, in a region after
bush res during the dry season, is the main cause of the pressures on A. africana.
This pruning practice reduces the growth of the tree. Bayer and Water-Bayer (1999)
1568
note that pruning and coppicing strongly inuence the quantity of leaves propor-
tionate to the branches and in accordance with the growth of trees. The species is
also used in traditional medicine and as timber species. Onana (1998) observed in
the northern part of Cameroon that this practice of regular pruning and coppicing
performed by herdsmen, the frequent bush res and the regular browsing of the
seedlings, already jeopardise many populations of A. africana in the Sudano-Sa-
helian zone. This is the reason why FAO has also selected this species for a
conservation programme in Cameroon (Palmberg 1987). In Benin, no relevant
conservation strategies have been put in place for this tree species that is under
increasing severe pressures. Its conservation becomes more than ever urgent.
Conclusions
The size-class distribution and the average values of A. africana tree height and
diameter allowed the assessment of the level of pressure affecting the populations
of this species within the different climatic zones of Benin. The height and the
diameter of the species varied signicantly from one climatic zone to another. The
lowest diameter was observed within the latitudes ranging from 88Nto128N. This
area includes the localities where A. africana is facing very strong pressure. On the
contrary, the big individuals of A. africana were recorded in the Guineo-Congolean
zone (extending from 68250Nto78300N) with recorded lowest pressures. In certain
ecosystems such as the reserve forest of Lama, which are well-protected areas, are
found very good individuals of A. africana because of the absence of the various
forms of human pressure.
In situ conservation measures of the species should be taken in areas where the
species is facing low pressures. In addition, measures focussing on the enrichment
of the impoverished forests with the species should be one of the major concerns of
Benin forest managers. Silvicultural techniques successfully experimented on the
species in other African countries could be adapted to Benin conditions, as was the
case for Tectona grandis (teak).
Acknowledgements
This work was completed with the nancial support of the United Nations En-
vironment Programme (UNEP) provided by the Sub Saharan African Forest Ge-
netic Resources Programme (SAFORGEN) of the International Plant Genetic
Resources Institute (IPGRI). We would like to thank these institutions.
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... Previous studies described the species population structure and associated drivers (Mensah et al. 2014;Assogbadjo et al. 2017;Nacoulma et al. 2017;Amahowe et al. 2018;Atanasso et al. 2019). There are consitent reports of poor natural regeneration and a recruitment bottleneck of the species even in protected areas (Sinsin et al. 2004;Bonou et al. 2009;Amahowe et al. 2018). Bationo et al. (2001) suggested this is linked to the sensitivity of the species seedling to fire, grazing, and drought stress that prevail in the Sudanian zone (Nacoulma et al. 2017;Amahowe et al. 2018). ...
... Our results showed higher A. africana tree density in the hunting zone as compared to the edge of the core zone and the core zone, which could be linked to the low density of wildlife among which elephants (Atanasso et al. 2019). Our findings of less than 1% juveniles in all sites also support previous studies that consistenly reported a recruitment challenge at juvenile stage (Sinsin et al. 2004;Bonou et al. 2009;Amahowe et al. 2018 attributed to the sensitivity of the species seedling to fire, grazing, and drought stress that prevail in the Sudanian zone (Nacoulma et al. 2017;Amahowe et al. 2018). Potential effects of several other factors such as natural enemies and competition have been extensively discussed in Atanasso et al. (2019) and Mensah et al. (2020). ...
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Background and aims – Understanding the spatial patterns and associations of tree species with their conspecific and heterospecific neighbours is critical for sustainable management of their stands. This study assessed the intra- and interspecific spatial structure of six life stages in Afzelia africana, a keystone multipurpose and endangered tree species in a tropical savanna of Benin.Material and methods – Three plots of 4 ha each were demarcated on three sites along a conservation gradient (hunting zone – core conservation zone). Individuals of A. africana (irrespective of their diameter at breast height) and heterospecific trees (dbh ≥ 5 cm) were mapped. Tree spatial patterns and associations were determined using univariate and bivariate pair correlation functions. The distance to the nearest neighbour was further used to assess tree-to-tree distance.Key results – We found variable spatial patterns across sites. In the core zone where wildlife density is high, most life stages had a random distribution. In contrast, in the hunting zone where wildlife density is low, the species spatial distribution changed from a predominantly aggregative pattern during early stages to a less aggregative or random spatial pattern for very large adults. Most pairs of life stages showed neutral associations, except for small and large adults, which had positive association between themselves on two sites. We also found that A. africana tree spatial distribution was unrelated to heterospecific trees.Conclusion – We suggest that bush fire, seed dispersion, predation, and local environment would have contributed to the observed patterns.
... The species undergoes anthropogenic and natural disturbances and shows very low potential of natural recruitment even in strictly protected areas (Bonou et al. 2009;Houehanou et al. 2013;Mensah et al. 2014;Atanasso et al. 2019). In natural habitats, the species regenerations are rare despite the presence of International Society for Tropical Ecology many adult trees within stands (Bationo et al. 2001;Sokpon and Biaou 2003;Sinsin et al. 2004;Bonou et al. 2009;Ouédraogo and Thiombiano 2012). Many previous studies reported very rare saplings with recruitment and growth difficulties of A. africana in natural stands (e.g. ...
... Afzelia africana, african oak is an endangered tree species highly preferred for the good quality of its timber (Sinsin et al. 2004). It belongs to the Fabaceae-Caesalpinioideae family (White 1983). ...
Article
Understanding abiotic and biotic factors affecting the survival of seedlings of threatened species such as Afzelia africana is fundamental for restoration and sustainable management purposes. This study used seedling individual-level morphological data and plot-level data to assess the effect of abiotic (season, elevation, soil type and terrain slope) and biotic (seedling initial density, basal diameter, height and number of leaves, insect and fungal infection, insect herbivory, mammal herbivory, vegetation type, adult conspecific density and diameter, and heterospecific density and diameter) factors on the survival probability (at individual level) and survival rate (at plot level) of seedlings of A. africana in the Pendjari Biosphere Reserve. Generalized Linear Mixed Models (GLMMs) were used for data analyses. At individual level, we found that the survival probability of A. africana seedlings increased with initial height, but decreased from wet to dry season. At plot level, the survival rate of A. africana seedlings also decreased from the wet season (0.72 ± 0.05) to the dry season (0.18 ± 0.04) and was inversely proportional to seedling basal diameter (P = 0.024) and density of conspecific adults (P = 0.016). There were also positive effects of seedling initial height (P = 0.026) and mean diameter of conspecific adults (P = 0.037) on survival rate. Among abiotic factors, only terrain slope showed significant and negative effect (P = 0.028) on the survival rate, suggesting higher survival rate on flat terrain. Our findings suggest that sustainably managing seedlings of A. africana would require accounting for conspecific neighboring effect, terrain slope and season-specific actions. Practical aspects of these factors were further discussed.
... as a threatened (Nacoulma et al., 2011) or endangered species (Sinsin et al., 2004). These pressures reduce the occurrence and the geographic range of the species. ...
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Afzelia africana Sm – a multipurpose leguminous tree species – is threatened in West Africa – a climate change hotspot region. Yet, although the impacts of land use on this species dynamics have been widely reported, there is a little literature on the impacts of climate change on its spatial distribution. This study aimed to predict the impacts of climate change on the geographic distribution of A. africana in Burkina Faso. A total of 4,066 records of A. africana was compiled from personal fieldwork and vegetation database. Current and future bioclimatic variables were obtained from WorldClim website. For future climatic projections, six global climate models (GCMs) were selected under two emission scenarios (RCP 4.5 & RCP 8.5) and two horizons (2050 & 2070). Presence data and bioclimatic variables were processed in ArcGIS software and used in the algorithm MaxEnt (maximum of entropy) to predict the species distribution. Findings showed that maximum temperature of warmest month and mean temperature of coldest quarter mostly affect the habitat suitability of A. africana. About 25.54% of Burkina Faso land surface was currently suitable for A. africana conservation. Under future climatic projections, all the climate models predict climate-driven habitat loss of the species with a southward range shift. Across the two emission scenarios, the spatial extent of suitable habitats was predicted to decline from 9.43 to 23.99% and from 12.29 to 25% by the horizons 2050 and 2070, respectively. Habitat loss and range shifts predicted in this study underline the high vulnerability of A. africana to future climate change. Reforestation actions and the protection of predicted suitable habitats are recommended to sustain the species conservation.
... The annual average is 1200 mm. All over the year, the temperature varies between 25 °C and 29 °C with a ratio between 69% and 97% [14] . In the study area, agricultural practices impacted heavily the forest coverage area [15] . ...
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Since the time of our ancestors, natural products issued from plant play a therapeutic crucial role. About 25-30% of all medicines (drugs) available for the treatment of diseases are derived from natural products (from plants, animals, bacteria and fungi) or are derivatives of natural products. The aim of this research was to scientifically identify and supply tangible documentation on these two plants employed in the traditional medicine. From November 2020 to February 2021, an ethnobotanical survey was conducted within four markets at the south of Benin, employing a semi-structured questionnaire. Two hundred respondents including 80% of females and 20% of males were interviewed. The 2 studied plants are mainly used for different types of sickness related to infections. Females' herbalists are the most represented. From this research, it appears that the 2 plants are widely used for the treatment of severe infections. On the market, 95% of the leafy steam are sold against 5% of the roots for both plants. The main preparation way is decoction. Oral use is reported to be common in all region. The value of samples sold varies from 200F CFA (Financial Cooperation of Africa) to 1000F CFA. The decoctions are usually obtained through one of a mix of different types of plants. Traditional knowledge is transmitted from one generation to another by oral education. Till today there was no record found. During our study, we did no record prohibition or side effect related to these plants' use. These medicinal plants occupy a crucial place within the therapeutic arsenal of west Africa. Our results constitute a vital tool to determine the true potentials of these plants. These results could lead to new improved traditional medicine.
... Along this water availability gradient, three contrasting biogeographical zones evolved, namely: Guineo-Congolian region, Sudano-Guinean transition zone and Sudanian region (White 1983). The Guineo-Congolian region typically is made of fallows and small forest patches in the wetland, mosaics of subhumid woodlands while the two dryer areas are covered by savannas and gallery forests (Sinsin et al. 2004). Main soil types include hydromorphic soils, well-drained soils and lithosols in Sudanian region. ...
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Background: Ophidian envenomation is a public health problem in the tropics and subtropics. Expensive cost of antivenoms forces most of the population to resort to medicinal plants as a first-line treatment. The present study aimed to contribute to a better knowledge of medicinal plants used in the treatment of snakebite envenomation in Benin. Methods: Ethnobotanical information was collected from 339 people (hunters and traditional healers) across various sociolinguistic groups using a structured interview and the snowball technique. Knowledge was quantitatively assessed using the Relative Citation Frequency. The R software (cran.r�project.org) and Microsoft Excel were used to produce graphs and/or charts. Results: A total of 109 plants species belonging to 51 botanical families were reported as being used in the treatment of snakebite envenomation. Distribution of these species by family showed that Leguminosae (20.18%), Euphorbiaceae (9.17%), Asteraceae (4.59%), Annonaceae (3.67%) were mentioned the most. The dominant life forms were herbs and shrubs collected mainly from savannas and fallows. Roots and leaves were the most used plant parts in the preparation of remedies. Conclusion: In-depth pharmacological and toxicological studies must be carried out to validate reported medicinal plants, to contribute to the well�being of local communities in developing countries. Keywords: Ethnobotanical survey, ophidian envenomation, antivenom, medicinal plants, well�being.
... Plusieurs types de produits sont quotidiennement recherchés par les agriculteurs. Il s'agit entre autres de noix comestibles, champignons, fruits, herbes, épices, gommes, plantes aromatiques, gibier, bois, fourrage et produits végétaux ou animaux aux usages médicinaux, cosmétiques, alimentaires et/ou culturels (Sinsin et al., 2004). L'exploitation plus raisonnée et durable de ces produits pourrait contribuer non seulement à la préservation de leur diversité biologique, mais également à l'amélioration des conditions de vie de nombreuses communautés locales (FAO, 2009). ...
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Les espèces ligneuses jouent un rôle important dans la vie des populations locales. Parmi les espèces couramment utilisées au Niger figurent Balanites aegyptiaca et Ziziphus mauritiana. Ces deux espèces sont exploitées comme sources alimentaires et pour divers produits médicinaux, avec comme conséquence une réduction de leurs peuplements. La présente étude vise à analyser la structure des peuplements et les modes de régénération des deux espèces dans deux secteurs agro-écologiques contrastées de la région de Maradi au centre sud du Niger. Au total, 60 relevés ont été délimités, d’une part dans des formations naturelles dominées par ces espèces, et d’autre part dans les systèmes agrosylvopastoraux des secteurs sahélien et sahélo-soudanien. Dans chaque placette et sur chaque arbre, le diamètre à 1,30 m au rasdu sol , la hauteur totale et deux diamètres perpendiculaires de houppier ont été mesurés. L’inventaire de la régénération a été effectué dans 5 placeaux. La nature de la régénération (drageon, marcotte, semis naturel), la hauteur totale et le nombre de tiges de chaque plantule ont été notés. La densité de B. aegyptiaca ne varie significativement entre sites et entre secteurs. Par contre, la densité de Z. mauritiana varie significativement entre sites et entre secteurs. En effet, le site de Birni Lallé, situé dans le secteur sahélien strict, et le site de Kegil dans le secteur sahélo-soudanien ont les densités les plus élevées de Z. mauritiana avec respectivement 66,4 ± 52,5 et 77,5 ± 61,4 arbres/ha. L’analyse de la distribution des tiges par classe de diamètre montre que pour les deux espèces, les individus jeunes sont bien représentés. Cela suggère une bonne régénération de ces espèces. L’analyse de la densité et nature de régénération montre que les deux espèces se régénèrent essentiellement par drageonnage. En réponse au ramassage des fruits pour diverses utilisations, les espèces B. aegyptiaca et Z. mauritiana ont développé des stratégies alternatives de propagation en zone sahélienne. Cette aptitude à la propagation végétative permet aux deux espèces de s’adapter en zones arides caractérisées par la sécheresse et les hautes températures. MOTS CLÉS : DISTRIBUTION DES ESPÈCES LIGNEUSES, B. AEGYPTIACA, Z. MAURITIANA, MARADI, NIGER, SAHÉLO-SOUDANIEN [83] afrika focus — Volume 33, Nr. 1, 2020 — pp. 83-104 RABIOU HABOU, MOUSSA MASSAOUDOU, TOUGIANI ABASSE, MAHAMANE ALI, MAHAMANE LARWANOU & PATRICK VAN DAMME Wood species play an important role in the life of local communities. Among the species commonly used in Niger, are Balanites aegyptiaca and Ziziphus mauritiana. This species are exploited as food sources and as various medicinal products, with a consequent reduction in their populations. The present study aims to analyze the stand structure and the regeneration modes of the two species in two contrasting agro-ecological sectors of the Maradi region in south central Niger. A total of 60 surveys were delineated in natural formations dominated by these species and in agrosilvopastoral system in the Sahelian and Sahelo-Sudanian zones. On each tree, the diameter at 1.30 m from the ground, the total height and two perpendicular tree crown diameters were measured. The inventory of natural regeneration was carried out in 5 plots delineated in each plot. The mode of reproduction of the regeneration (suckers, marcots, natural seedlings) was recorded as well as the total height and the number of stems of each juvenile were. The density of B. aegyptiaca does not vary significantly between sites and between sectors. The Birni Lallé site, located in the strict Sahelian zone, and the Kegil site in the Sahelo-Sudanese sector stand out in terms of Z. mauritiana density with respectively 66.4 ± 52.5 and 77.5 ± 61.4 trees. /Ha. The analysis of the diameter class structure shows that for both species, young individuals are well represented. This suggests strong regeneration among these species. The analysis of the density and nature of regeneration shows that the two species regenerate mainly by suckering. In response to the collection of fruits for various uses by local populations, B. aegyptiaca and Z. mauritiana have developed alternative propagation strategies in the Sahelian zone. This ability to propagate vegetatively allows these two species to adapt to arid areas characterized by drought and high temperatures. KEY WORDS: DISTRIBUTION OF WOODY SPECIES, B. AEGYPTIACA, Z. MAURITIANA, MARADI, NIGER, SAHELO-SUDANESE
... Ces nombreux usages cités ci-dessus, engendrent une pression sans cesse croissante sur le peuplement de K. anthotheca à l'état naturel à l'exemple d'autres espèces de plantes à usages multiples. Les études, sur certaines espèces telles que Afzelia africana (Sinsin et al., 2004), K. senegalensis (Gaoue et Ticktin, 2007) et de nombreuses plantes ligneuses d'Afrique centrale et occidentale (Traoré et al. 2011 ;Baye-Niwah et al., 2020) ont montré par exemple que l'exploitation des Produits Forestier Non Ligneux (PFNL) comme K. anthotheca peut affecter les paramètres vitaux, agissant sur la structure de leurs populations. Ces pressions anthropiques et autres facteurs de diverses natures agissent constamment sur la structure des populations de l'espèce sans que d'importantes actions spécifiques de conservation ne soient effectuées (Gbesso et al., 2014). ...
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RESUME: L'objectif de cette étude est d'apporter des informations scientifiques nécessaires à la préservation et gestion durable de Khaya anthotheca dans le sud-ouest de la République Centrafricaine via l'amélioration des connaissances sur son écologie. Pour y parvenir, des inventaires forestiers ont été effectués dans les Permis d'Exploitation et d'Aménagement (PEA) des entreprises forestières CentraBois (PEA 192) et Timberland (PEA188). Pour toutes les caractéristiques dendrométriques calculées en fonction des concessions et des classes de diamètre, le PEA 188 de Timberland est largement dominant. La densité moyenne des individus adultes est de 0,10 pieds/ha sur le PEA 192 et de 12 pieds/ha sur le PEA 188 avec le même coefficient de variation (cv) de 112,7%. La surface terrière (m 2 /ha) varie de 0,86 sur le PEA 192 à 3,78 sur le PEA 188 avec des cv respectifs de 60,2% et 66,4%. La densité de régénération moyenne varie de 3,52 plants/ha sur le PEA 192 à 12,19 plants/ha sur le PEA 188. Les courbes dendrométriques sont exponentielles décroissantes dans les deux concessions. Des travaux de recherches sur la régénération artificielle de K. anthotheca sont importantes pour définir des mesures de préservation dans ces zones. ABSTRACT The objective of this study is to provide scientific information necessary for the preservation and sustainable management of Khaya anthotheca in the southwest of the Central African Republic by improving knowledge of its ecology. To achieve this, forest inventories were carried out in the Logging and Management Permits (PEA) of the forestry companies CentraBois (PEA 192) and Timberland (PEA188). For all dendrometric B. DEGUENE et al. / Int. J. Biol. Chem. Sci. 14(7): 2491-2505, 2020 2492 characteristics calculated according to concessions and diameter classes, Timberland's PEA 188 is largely dominant. The average density of adult individuals is 0.10 tree/ha on PEA 192 and 12 tree/ha on PEA 188 with the same coefficient of variation (CV) of 112.7%. The basal area (m 2 /ha) varies from 0.86 on PEA 192 to 3.78 on PEA 188 with respective coefficient of variation of 60.2% and 66.4%. The average regeneration density varies from 3.52 plant/ha on the PEA 192 to 12.19 plant/ha on the PEA 188. The dendrometric curves are exponentially decreasing in both concessions. Research on artificial regeneration of K. anthotheca is important to define preservation measures in these areas.
Article
Detarium microcarpum Guill & Perr. and Detarium senegalense J.F.Gmel. are two species of wild trees that contribute significantly to the livelihoods of local communities in sub-Saharan Africa. Exploration of the ecological patterns of their population structure is, therefore, necessary to ensure long-term management. The aims of this study were to: (i) determine the floristic composition of the habitats of D. microcarpum and D. senegalense, (ii) assess the population structure of both species, and (iii) assess the influence of biotic and abiotic drivers on the structural parameters of these species. A total of 177 plots were installed in eight sites in Benin. The data collected included the dbh1.30m, the crown diameter, the total height, and the type of regeneration (generative, sprout, and sucker). The topographical and soil parameters of the plots were also recorded. A generalized linear model (binomial negative regression) and ANOVA were used for the analysis of density and morphological features data, respectively. The floristic composition of D. microcarpum habitats was found to be relatively distinct (p = 0.001) from one zone to another. A significant difference (p = 0.001) in heterospecific individuals was also observed between the habitats of both species. The density of individuals of D. microcarpum decreased significantly from the Sudanian zone (4594 ± 207 stems/ha) to the Guinean zone (93.60 ± 11.90 stems/ha; p < 0.001). In the Sudano-Guinean zone where both species were found, the density of D. senegalense was very low (19.07 ± 7.64 stems/ha). The density of adult individuals of D. microcarpum was significantly high on gravelly soils. The regeneration of the species was negatively correlated with the slope, soil texture and basal area of heterospecific individuals. In D. senegalense, its regeneration was negatively correlated with elevation and positively with the density of its adult individuals. The height of both species of Detarium was positively associated with altitude. This study showed the effect of biotic and abiotic factors determining the population dynamics of Detarium spp. species and could be considered in the sustainable management of these species.
Article
The exploitation of non-timber forest products contribute considerably to local livelihoods for subsistence in developing countries. The study aims to assess the structure and fruit production of C. procera natural populations in harvesting and non-harvesting sites and to compare the structure characteristics and fruits yields of the two sites. The study was carried out in Burkina Faso on both, harvesting and non-harvesting sites. Eighty fruits bearing trees (40 per site) were sampled, from each, all the fruits were counted. Dendrometric parameters were measured in 80 plots of 1000 m². In each plot, diameter at breast height (dbh) and total height of trees were measured. Density, basal area, mean diameter and height were computed for each site. Analyses of variance were performed to test differences between sites based on measured variables. Weibull theoretical model was used on size class distribution to analyze trees structure in both sites. The results showed that the production of fruits reach a mean of 6462.73 ± 4237.51 fruits/ha and 9103.44 ± 7631.88 fruits/ha, respectively in non-harvesting and harvesting site. Significant differences (p < 0.05) were found for tree densities, basal area and tree height between sites with highest values in the harvesting site. The size class distribution of trees showed in both sites the existing of potential regeneration with the dominance of young trees (1 < c < 2) with some survival difficulties during the growth stages. C. procera populations exhibit a high potential of fruit production and natural regeneration but are influenced by pressures impact.
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Afzelia africana, Entada africana, and Pterocarpus erinaceus are economically important tropical tree species in Africa. In this study, we performed morphological and molecular analyses to examine the mycorrhizal status of these species in their natural habitat in Benin, West Africa. Fine roots were examined using trypan blue staining. Putative arbuscular mycorrhizal fungi (AMF) were identified by extracting root DNA and sequencing the large subunit region of ribosomal DNA. Operational taxonomic units (OTUs) were positioned on a consensus phylogenetic tree produced using maximum likelihood and neighbor-joining models. Morphological analyses revealed vesicles, arbuscules, and inter-and intracellular hyphae in roots of all three tree species. Molecular analyses revealed 39 AMF OTUs, among which 18 were from roots of E. africana, 15 from P. erinaceus, and 9 from A. africana. These OTUs belonged to Glomus, Nanoglomus, Rhizoglomus, Sclerocystis, Septoglomus, and Scutellospora; two unidentified species belonged to the family Glomeraceae. This is the first study to report AMF in roots of A. africana, E. africana, and P. erinaceus in Benin, and opens new avenues for future studies.
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One of the fundamental basis in the development of sustained-use management systems is the determination of the minimal logging diameters (MLD) and the felling cycle compatible with sustainable logging operations. The method used in the present study to determine the MLD and felling cycle is based on the growth rate and the diameter class distributions of the most important merchantable species in Bassila forest reserve, North Benin. The calculations of the MLD and cutting cycle are done using both the class distribution of the stem diameter and basal area of nine valuable timber species selected within the most important commercial species of this forest reserve, in order to assess the difference between these two approaches.Values of MLD and cutting cycle duration obtained using the stem class distribution or the basal area class distribution are in general the same. The MLD calculated for nine timber species varies from 35 to 65cm. The cutting cycle period obtained is 18 years for the bell-shaped type species and 24 years for the inverse J-shaped type species. For the bell-shaped type species, the mean percentage of recruitment obtained with 18 years felling cycle is about 60% considering the number of the loggable stems and 34% of the loggable basal area. As far as the inverse J-shaped type species are concerned, 24 years felling cycle will allow 55% of mean recruitment considering the number of the loggable stems and 19% of the loggable basal area. For the whole forest stand, 22 years cutting cycle is obtained allowing 57% recruitment of the loggable stems and 23% recruitment of the loggable basal area.
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Copyright: 1996 Bureau for Scientific Publishers The composition and dynamics of Dukuduku coastal lowland forest were investigated by means of ordination techniques. Size-class distributions on data from 200 plots were analysed and we also interpreted aerial photographs. An initial classification suggested that there were six widespread communities. Ordination of data of potential canopy species, found in the canopy and in the sub-canopy, was done separately for five of the six communities. A successional trajectory became apparent from this analysis. Understorey composition in a particular community was often similar to the canopy composition in the next community in the hypothesized time sequence, than to the composition of its own canopy. Analysis of size-class distributions of canopy species for each community supported the concept of a successional gradient. Common canopy species found in early successional community tended to have negative exponential size-class distributions, whereas these same species were less frequent and had flatter size-class distributions in the later successional stages. Based on the results of the ordinations and size-class analysis, a conceptual model of forest dynamics is presented. It is hypothesized that large-scale disturbances, such as fire, are the dominant forces driving the dynamics of this coastal lowland forest.
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Contains 3 folded maps (scale 1:5.000.000), and a legend Map(s) inclu.
La gestion des fourrages
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