Reproductive traits affect the rescue of valuable and endangered multipurpose tropical trees
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Reproductive traits affect the rescue of valuable and endangered multipurpose tropical trees
Viviane Sine´ bou 0 1
Muriel Quinet 1
Bonaventure C. Ahohuendo 0
Anne-Laure Jacquemart 1
Associate Editor: Dennis F. Whigham
0 De ́partement de Productions Ve ́ge ́tales, Faculte ́ des Sciences Agronomiques, Universite ́ Abomey-Calavi , Cotonou 01 BP 526 , Benin
1 Research Group Genetics , Reproduction, Populations , Earth and Life Institute - Agronomy, Universite ́ Catholique de Louvain , Croix du Sud 2 Box L7.05.14, B-1348 Louvain-la-Neuve , Belgium
Conservation strategies are urgently needed in Tropical areas for widely used tree species. Increasing numbers of species are threatened by overexploitation and their recovery might be poor due to low reproductive success and poor regeneration rates. One of the first steps in developing any conservation policy should be an assessment of the reproductive biology of species that are threatened by overexploitation. This work aimed to study the flowering biology, pollination and breeding system of V. doniana, a multipurpose threatened African tree, as one step in assessing the development of successful conservation strategies. To this end, we studied (1) traits directly involved in pollinator attraction like flowering phenology, flower numbers and morphology, and floral rewards; (2) abundance, diversity and efficiency of flower visitors; (3) breeding system, through controlled hand-pollination experiments involving exclusion of pollinators and pollen from different sources; and (4) optimal conditions for seed germination. The flowering phenology was asynchronous among inflorescences, trees and sites. The flowers produced a large quantity of pollen and nectar with high sugar content. Flowers attracted diverse and abundant visitors, counting both insects and birds, and efficient pollinators included several Hymenoptera species. We detected no spontaneous self-pollination, indicating a total dependence on pollen vectors. Vitex doniana is self-compatible and no inbreeding depression occurred in the first developmental stages. After extraction of the seed from the fruit, seed germination did not require any particular conditions or pre-treatments and the seeds showed high germination rates. These pollination and breeding characteristics as well as germination potential offer the required conditions to develop successful conservation strategies. Protection, cultivation and integration in agroforestry systems are required to improve the regeneration of the tree.
Bees; breeding system; conservation biology; mating system; pollinator efficiency; seed germination
Introduction
Global biodiversity is decreasing at an unprecedented
rate as a complex response to several human-induced
changes
(Sala et al. 2000)
. Land use change is the driver
that has the largest global impact on biodiversity, mostly
due to habitat destruction and fragmentation. Land use
change is particularly the most important driver in
tropical forests
(Sala et al. 2000)
. The African forests are
subject of haphazard modification following
anthropogenic pressures including tree cutting and clearing
for agriculture. In West Africa, logging and seasonal
fires set by farmers and hunters have increased
deforestation, destroying an average of 870 000 ha/year
between 2000 and 2010
(FAO 2011)
. Consequently, several
food and medicinal tree species have been declared
locally endangered and are priorities for conservation
(Eyog-Matig et al. 2002; FAO 2011)
. Forest harvesting
directly decreases the rates of survival, growth and
reproduction of individual trees, affecting the structure and
dynamics of harvested populations (Oumorou et al.
2010). In harvested stands, only large, old trees and a
few seedlings and saplings generally survive
(Oumorou
et al. 2010)
. Maintaining these local remnant populations
will require informed management and conservation
practices.
Vitex doniana, commonly called black plum, is one of
the most important wild-harvested, multipurpose trees
in tropical Africa
(Akoe`gninou et al. 2006; N’Danikou
et al. 2015)
. The tree is widely used for food, medicinal
purposes and as firewood
(Achigan-Dako et al. 2011)
.
The species also has a great socio-cultural and
mythological importance for local people
(Dadjo et al. 2012;
N’Danikou et al. 2015)
.
Despite its high value for local populations, there is no
evidence of any conservation initiatives from harvesters
(N’Danikou et al. 2011)
. People usually harvest the
desired resources without considering regeneration and
management or attempting silvicultural practices (e.g.
planting and sowing)
(Dadjo et al. 2012; N’Danikou et al.
2015)
. Mainly due to overexploitation, V. doniana is one
of the most-threatened food tree species with high
priority for conservation in Benin, Kenya, Niger and Burkina
Faso
(Eyog-Matig et al. 2002; Oumorou et al. 2010;
N’Danikou et al. 2015)
.
The threats to the (...truncated)