INTRODUCTION
Vitellaria paradoxa Gaertn, commonly known as the shea
butter tree, is indigenous to, and part of the major component of woody flora
of the Sudan and Guinea Savannah vegetation zones (IPGRI;, 2006; Lovett & Haq, 2000; Nasare et al.,
2019). It
spreads from Senegal to Western Ethiopia and Uganda, in a belt that is 500-700
km wide, and separated from the Gulf of Guinea by forest. In Nigeria and Ghana,
it occurs within 50km from the coast (Nikiema & Umali, 2007).
In
Nigeria, shea trees grow naturally in the wild,
mostly in the northern parts from guinea to Sudano-sahelian
savannah. It normally starts fruiting at about 10-25 years of age and reach
full maturity around 20-45 years (Nikiema & Umali, 2007; Seghieri, 2019).
Shea
tree is one of the most important economic crop valued by the people of its
indigenous location (Seghieri, 2019; Tom-Dery et al., 2018) as well as the world
over. In addition to its local uses (Seghieri, 2019), it is highly
demanded in the international market for its butter which is used in the
production of chocolate as a substitute for cocoa butter (Chidiogo et al., 2013). The seed oil is
widely utilized, locally for cooking purposes and as illuminant and
industrially as skin moisturizer in lotions and lipsticks (Lovett & Haq, 2000; Tom-Dery et al., 2018) due to its excellent
quality (Okullo et al., 2010). V. paradoxa is also used in
various traditional medicine preparations for various ailments which include
jaundice, stomachache, diarrhea and headache (Popoola & Tee, 2001; Tom-Dery et al., 2018). Humans consume its
sweet pulp (Bvenura & Sivakumar, 2017; Maranz et al., 2004;
Ugese et al., 2008) and the fallen ripe
fruits can be fed to livestock (Orwa et al., 2009). Because of its high
vitamin C content, daily consumption of up to 50g can provide the needed
vitamin C supplement for both children and pregnant women (Honfo et al., 2014). Looking at its
numerous uses, V. paradoxa is
regarded as a unique resource for economic development especially in rural
areas (Chidiogo et al., 2013).
V. paradoxa
flowers develop in the axils of scale leaves, at the apices of dormant twigs (Sale et al., 2018). Inflorescences are
borne at the end of a flowering twig, normally dense fascicle, 5-7.5 cm in
diameter. The flowers are hermaphrodite, usually cross-pollinated, but can be
self-pollinated. Insects, especially bees, are important for pollination.
Flowering lasts 30-75 days and the fruits take 4-6 months to maturity which
takes place during rainy season (Orwa et al., 2009).
Oni et al. (2014) reported that
flowering in V. paradoxa took
about 45.68 ±3.77 days while fruiting took about 145.87 ±7.86 days in Nigeria.
Another research in Mali reported that V.
paradoxa flowers for about 68 days in northern guinea and Sudan zones
and 76 days in southern zone starting from November to May, whereas fruiting
commences from January to August and usually takes about 86 days and 110 days
in northern and southern zones respectively (Kelly et al., 2018).
In
Cameroon, Nguemo et al. (2014) reported that V. paradoxa flowers from November
to February in guinea savanna zone; while in Sudan savanna, the flowering is
delayed till February, and it lasts till June. The leaves, however, fall
between November and January.
The nature of phenological events such as flowering
start date and flowering synchrony (Augspurger, 1983), and the relationship between these and other phenological events such
as leaf shed may determine the reproductive success of V. paradoxa plant population (de Assis Pires et al., 2014; Hall et al.,
2018; Rawal et al., 2015; Sale et al., 2018). Flowering
synchrony directly determines the effective number of pollen donors through the
density of flowering individuals and indirectly determine the patterns of
pollen flow between trees (Delnevo et al., 2019; Murawski & Hamrick, 1992;
Stephenson, 1983), encouraging either
out-crossing or selfing, which ultimately influence
the reproductive success of the plants (de Assis Pires et al., 2014; Hall et al., 2018;
Ollerton & Lack, 1992; Poole & Rathcke, 1979; Rawal et al., 2015;
Rodríguez-Pérez & Traveset, 2016). Synchronous trees
are likely to receive pollen from more pollen donors than trees with
asynchronous flowering which may experience a reduction in reproductive output,
with the number of pollen donors and the selfing rate
being similar to those of trees found in isolated fragments (Fuchs et al., 2003).
Phenological
studies provide information on functional rhythms of plants and plants
communities, where the timing of various phenological events may reflect biotic
and/or abiotic environmental conditions. They are also important from the point
of view of the conservation of tree genetic resource and forestry management as
they determine reproductive success of species (Sale et al., 2018) and for better
understanding of plants species and community level interactions. The aim of
this research is therefore to study the phenology in V. paradoxa and determine
the effects of some climatic conditions on some phenological events.
MATERIALS
AND METHODS
Study Area
The study
was conducted at the University of Ilorin, Nigeria, which lies between latitude
8°30´N and longitude 4° 33´E/ latitude 8.500°N and 4.550°E covering an approximate land mass of 5000 hectares. Ilorin
is situated in a transition zone between the rainforest of the South and the
Guinea savannah of the North, and it is characterized by both wet and dry
seasons. Rainy season begins from April and last till October with annual
rainfall of 990.3mm to 1318mm, while dry
season begins in November and ends in April (Olabode et al., 2014). The
relative humidity of the metropolis ranged between 28 and 57%, while daily
temperature ranges between 15 to 36 °C (Adeniran et al., 2018).
Methods
To study the phenology of V. paradoxa population,
thirty (30) shea butter trees were randomly selected
from two distinct locations tagged and followed for their
phenological events. The locations include a dense area, in which the tree
stands are found in close and continuous canopy formation with their conspecifics
and other tree species; and sparse area, in which trees occur far apart from
one another. From each selected tree, eight (8) branches, two from each of the
cardinal directions were selected, tagged and used in the research. From each
selected branch, reproductive phenological events (flower buds sprout, blooming, and
development of immature and mature fruits) and leaf phenological events
(emergence of new leaves, leaf maturation and leaf shade) were observed and
recorded
from October 2014 to July 2015. Because reproductive phenological events take
places at the apices of shoots in V. paradoxa, each event was estimated, at any given time, as the
percentage of the total number of the apical shoots on the tagged branches (Denny et al.,
2014), i.e.,
(1)
Here, Q= quantity (in percentage) of the
occurrence of any event, n= number of apical shoots with flower-buds/flower or
immature/mature fruits and N= total number of apical shoots.
Leaves phenological events, on the other hand,
were estimated as the proportion of the total canopy cover at the time of data
collection (Piepenbring et
al., 2015), i.e.,
(2)
Here, P = proportion (in percentage) of any
event, n= number of young/mature leaves and N=total number of leaves.
Phenological parameters estimated include: flowering start date, flowering
finish date, flowering duration, peak flowering date, flowering synchrony, date
of appearance of immature fruits, leaf fall start date and date of
disappearance of 50% canopy cover. Flowering synchrony index was estimated as a
percentage of the period when all the trees flower synchronously over the
entire flowering period of the population (Omondi et al.,
2016).
Data on climatic
conditions were obtained from Baseline Surface Radiation Network (BSRN)
Observatory, Department of Physics, University of
Ilorin, Nigeria.
Date analysis
The data on
phenological events were analyzed using Microsoft
Excel® 2013 and the relationship between phenological events and
climatic conditions was determined using PAST software. The results were
presented in forms of charts using means and percentages.
RESULTS
Flowering and fruiting timing
The
results of this research have revealed that the first flower buds in the
population appeared on 28 October, and continuous till
mid of March. Flower anthesis started from October
also but persisted till April (Fig. 1a). Development of immature fruits
commenced from December ending to June, while fruits maturity started from
March ending to August (Fig. 1b).
DISCUSSION
This study has revealed that some trees started flowering before others.
However the entire V. paradoxa population in the study area produce
flower from October ending to the middle of March. A similar research in Mali
shows that V. paradoxa flower from November to May (Kelly et al., 2018). Similarly, Nguemo et al. (2014) reported that V.
paradoxa flowers from November to February in guinea savanna zone; while in
Sudan savanna, the flowering is delayed till February, and it lasts till June. The little variations in flowering start and
finish dates may be attributed to genetic variation in the population as
reported by Sale & Morakinyo, (2017) or the age of the
trees themselves. However, regardless of when a tree starts flowering, most
trees take about two and a half months to complete flowering. This is in line
with the work of Kelly et al. (2018) who reported that V. paradoxa trees take about 68
days to complete flowering in northern guinea and Sudan zones of Mali.
The
research reported that fruiting in V. paradoxa in the study area
commenced from December ending all through to August. This agrees with the work
of Kelly et al. (2018) and Nguemo et al. (2014) who reported that
the fruiting period in V. paradoxa
is from January to August in Mali.
The
result has revealed that trees in the sparse areas started flowering earlier
than those in the dense area. This could be attributed to the fact that those
in the sparse areas have more access to solar radiation, wind and even insects
pollinators as there may be no competition. This indicated that space is required for early flowering in V.
paradoxa plant since trees in the disturbed area are found solitary with
zero completion for light and space (Sale et al., 2018).
Furthermore,
some trees started flowering early, some started late, but majority of the
trees started sometimes halfway between the two extremities. This is what bring
about the high level of synchrony and it can enhance and encourage outcrossing (Ollerton & Lack, 1992; Poole & Rathcke, 1979) which in turn could
bring about improved fruitfulness as observed by Sale et al. (2018).
The
results reported that V. paradoxa
shed their leaves from November to March. This is perhaps due to the fact that
those months form the core of dry season in the study area, and by April, all
the trees produced new leaves. This means there was no enough water for the
trees to sustain their leaves from November to March and therefore the leaves
are shed for the trees to survive the stress. This does not agree with the work
of Nguemo et al. (2014) who reported that
leaves shed between November and January. The leaves sprout in April due to
commencement of rain. Similar findings was also reported by Okullo et al. (2010).
The
variation in the timing and degree of leaf shed across different trees could be
attributed to genetic variation within the population or even age as older
trees may have longer root to reach more water than younger ones, and therefore
the old ones may tend to sustain more leaves or delay shedding.
Trees also
differed in the degree to which leaves are shed in different locations. Trees
in dense area seemed to shed larger percentage of leaves than those in the
sparse area, with some of the trees in the sparse area not shading their leaves
completely. This is perhaps due to the facts that in the sparse areas there is
little competition for water around the rhizosphere, therefore the trees have
access to enough water to retain certain percentage of their leaves.
The results of the relationship between leaf fall and climatic conditions
revealed positive linear relationship with temperature, wind speed and
rainfall; and negative relationship with relative humidity. This is because
temperature and wind speed increase dehydration in both the soil and plants
which in turn cause more leaf shed. Wind speed also increase
the mechanical leaf shedding. Relative humidity, on the other hand, does
exactly the opposite of wind speed and temperature.
Acknowledgements
This research received no specific grant from any funding agency in the
public, commercial, or not-for-profit sectors.
Conflict of Interests
The
authors declare that there are no conflicts of interest related to this article
REFERENCES
Adeniran, J. A., Aremu, A. S., Saadu, Y. O., &
Yusuf, R. O. (2018). Particulate matter concentration levels during intense
haze event in an urban environment. Environmental Monitoring and Assessment,
190(41). https://doi.org/10.1007/s10661-017-6414-4
Augspurger, C. K. (1983). and Fruit Set of Six Neotropical
Shrubs1. Biotropica, 15(4), 257–267.
http://www.jstor.org/stable/2387650
Bvenura, C., & Sivakumar, D. (2017). The role of wild
fruits and vegetables in delivering a balanced and healthy diet. Food
Research International, 99(1), 15–30.
https://doi.org/10.1016/j.foodres.2017.06.046
Chidiogo, I., Peter, A., & Adedapo, M. (2013). Developing
the Shea Value Chain for Wealth Creation in Nigeria. Journal of Biology,
Agriculture and Healthcare, 3(5), 45–54.
de Assis Pires, J. P., da Silva, A. G., & Freitas, L.
(2014). Plant size, flowering synchrony and edge effects: What, how and where
they affect the reproductive success of a Neotropical tree species. Austral
Ecology, 39(3), 328–336. https://doi.org/10.1111/aec.12082
Delnevo, N., van Etten, E. J., Byrne, M., & Stock, W. D.
(2019). Floral display and habitat fragmentation: Effects on the reproductive
success of the threatened mass-flowering Conospermum undulatum (Proteaceae). Ecology
and Evolution, 9(19), 11494–11503. https://doi.org/10.1002/ece3.5653
Denny, E. G., Gerst, K. L., Miller-Rushing, A. J., Tierney,
G. L., Crimmins, T. M., Enquist, C. A. F., Guertin, P., Rosemartin, A. H.,
Schwartz, M. D., Thomas, K. A., & Weltzin, J. F. (2014). Standardized
phenology monitoring methods to track plant and animal activity for science and
resource management applications. International Journal of Biometeorology,
58(4), 591–601. https://doi.org/10.1007/s00484-014-0789-5
Fuchs, E. J., Lobo, J. A., & Quesada, M. (2003). Effects
of Forest Fragmentation and Flowering Phenology on the Reproductive Success and
Mating Patterns of the Tropical Dry Forest Tree Pachira quinata. Conservation
Biology, 17(1), 149–157.
Hall, E. S., Piedrahita, L. R., Kendziorski, G., Waddle, E.,
Doak, D. F., & Peterson, M. L. (2018).
Climate and synchrony with conspecifics determine the effects of
flowering phenology on reproductive success in Silene acaulis . Arctic,
Antarctic, and Alpine Research, 50(1), e1548866.
https://doi.org/10.1080/15230430.2018.1548866
Honfo, F. G., Akissoe, N., Linnemann, A. R., Soumanou, M.,
& Van Boekel, M. A. J. S. (2014). Nutritional Composition of Shea Products
and Chemical Properties of Shea Butter: A Review. Critical Reviews in Food
Science and Nutrition, 54(5), 673–686.
https://doi.org/10.1080/10408398.2011.604142
IPGRI; (2006). Descriptors for Shea tree (Vitellaria
paradoxa). Instituto Nacional de Investigacióny Tecnología Agrariay
Alimentaria. https://www.bioversityinternational.org/fileadmin/user_upload/online_library/publications/pdfs/1130.pdf
Kelly, B. A., Poudyal, M., & Bouvet, J. (2018).
phenophases along the north-south gradient in Mali. Research
in Plant Biology 8, 5–12.
https://doi.org/10.25081/ripb.2018.v8.3466
Lovett, P. N., & Haq, N. (2000). Diversity of the Sheanut
tree ( Vitellaria paradoxa C . F . Gaertn .) in Ghana. Genetic
Resources and Crop Evolution 47: 293–304.
Maranz, S., Kpikpi, W., Wiesman, Z., Sauveur, A. D. Saint,
& Chapagain, B. (2004). Nutritional Values and Indigenous Preferences for
Shea Fruits ( Vitellaria Paradoxa C . F . Gaertn . F .) in African
Agroforestry. Economic Botany, 58(4), 588–600.
https://doi.org/doi.org/10.1663/0013-0001(2004)058[0588:NVAIPF]2.0.CO;2
Murawski, D. A., & Hamrick, J. L. (1992). Mating system
and phenology of Ceiba pentandra (Bombacaceae) in central Panama. Journal of
Heredity, 83(6), 401–404.
https://www.cabi.org/ISC/abstract/19931636099
Nasare, L. I., Kwapong, P. K., & Doke, D. A. (2019).
Insect pollinator dependence of shea (Vitellaria paradoxa C.F. Gaertn.) in the
Guinea Savanna zone of Ghana. Ecological Processes, 8(48).
https://doi.org/10.1186/s13717-019-0211-7
Nguemo, D. D., Mapongmetsem, P. M., Tchuenguem, F.,
Gounhagou, D., & Yougouda, H. (2014). Flower biology of a beeplant
Vitellaria paradoxa ( Sapotaceae ) in the sudano- sahalian zone of Cameroon. Annals
of Experimental Biology 2(3), 41–51.
Nikiema, A., & Umali, B. E. (2007). Vitellaria
paradoxa C.F. Gaertn, Protabase. http://database.prota.org/search.htm
Okullo, J., Omujal, F., Agea, J., Vuzi, P., Namutebi, A.,
Okello, J., & Nyanzi, S. (2010). Physico-Chemical characteristics of shea
butter(Vitellaria paradoxa C.F. Gaertn.) oil from the Shea district of
Uganda. African Journal of Food, Agriculture, Nutrition and Development,
10(1). https://doi.org/10.4314/ajfand.v10i1.51484
Olabode, A. D., Ajibade, L. T., & Yunisa, O. (2014).
Analysis of Flood Risk Zones ( Frzs ) Around Asa River in Ilorin Using
Geographic Information System ( GIS ). International Journal of Innovative
Science, Engineering & Technology, 1(9), 621–628.
Ollerton, J., & Lack, A. J. (1992). Flowering
Phenology : An Example of Relaxation of Natural Selection ? Tree,
7(8), 274–276.
Omondi, S. F., Odee, D. W., Ongamo, G. O., Kanya, J. I.,
& Khasa, D. P. (2016). Synchrony in Leafing , Flowering , and Fruiting
Phenology of Senegalia senegal within Lake Baringo Woodland , Kenya :
Implication for Conservation and Tree Improvement. International Journal
of Forestry Research 2016. http://dx.doi.org/10.1155/2016/6904834
Oni, P. I., Jimoh, S. O., & Adebisi, L. A. (2014).
Management of indigenous medicinal plants in Nigeria using phenological
information. Journal of Medicinal Plant Research, 8(16), 619–631.
https://doi.org/10.5897/JMPR2013.5108
Orwa, C., Mutua, A., Kindt, R., Jamnadass, R., & Anthony,
S. (2009). Agroforestree Database:a tree reference and selection guide
version 4.0.
http://www.worldagroforestry.org/sites/treedbs/treedatabases.asp
Piepenbring, M., Hofmann, T. A., Miranda, E., Cáceres, O.,
& Unterseher, M. (2015). Leaf shedding and weather in tropical dry-seasonal
forest shape the phenology of fungi - Lessons from two years of monthly surveys
in southwestern Panama. Fungal Ecology, 18, 83–92.
https://doi.org/10.1016/j.funeco.2015.08.004
Poole, R. ., & Rathcke, B. (1979). Regularity,
randomness, and aggregation in flowering phenologies. Science, 203(4379),
470–471. https://doi.org/https://doi.org/10.1126/science.203.4379.470
Popoola, L., & Tee, N. T. (2001). Potentials of Vitellaria Paradoxa Gaertn F. in
Agroforstry systems in Benue state. Nigerian Journal of Ecology, 16,
20–24.
Rawal, D. S., Kasel, S., Keatley, M. R., & Nitschke, C.
R. (2015). Herbarium records identify sensitivity of flowering phenology of
eucalypts to climate: Implications for species response to climate change. Austral
Ecology, 40(2), 117–125. https://doi.org/10.1111/aec.12183
Rodríguez-Pérez, J., & Traveset, A. (2016). Effects of
flowering phenology and synchrony on the reproductive success of a
long-flowering shrub. AoB PLANTS, 8.
https://doi.org/10.1093/aobpla/plw007
Sale, S., & Morakinyo, J. A. (2017). Morphological
characterization and varietal delineation of Vitellaria paradoxa (Shea Butter)
Trees found on the University of Ilorin Campus. Bima Journal of Science and
Technology, 1(1), 131–139. http://bimajstgsu.org.ng/publications.php
Sale, S., Morakinyo, J. A., & Abba, H. M. (2018). Effects
of density and phenology on fecundity in Vitellaria paradoxa. International
Journal of Agriculture and Environmental Research, 04(03), 820–829.
www.ijaer.in
Seghieri, J. (2019). Shea tree (Vitellaria paradoxa Gaertn.
f.): from local constraints to multi-scale improvement of economic, agronomic
and environmental performance in an endemic Sudanian multipurpose agroforestry
species. Agroforestry Systems, 93(6), 2313–2330.
https://doi.org/10.1007/s10457-019-00351-1
Stephenson, A. G. (1983). Sexual selection in hermaphroditic
plants. Nature, 305, 765–766.
Tom-Dery, D., Eller, F., Reisdorff, C., & Jensen, K.
(2018). Shea (Vitellaria paradoxa C. F. Gaertn.) at the crossroads: current
knowledge and research gaps. Agroforestry Systems, 92(5),
1353–1371. https://doi.org/10.1007/s10457-017-0080-y
Ugese, F. D., Baiyeri, P. K., & Mbah, B. N. (2008). Mineral
Content of the Pulp of Shea Butter Fruit ( Vitellaria Paradoxa C . F . Gaertn
.) Sourced from Seven Locations in the Savanna Ecology of Nigeria. Tree and
Forestry Science and Biotecnology, 2, 40–42.
