The Baobabs of the Comoro Islands: Some Biogeographical Factors Towards the Protection and Conservation of a Neglected Asset
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The baobabs of the Comoro Islands: some biogeographical factors towards the protection and conservation of a neglected asset Maoulida Mohamed Abdillahi, Cyrille Cornu, Raïma Fadul, Michel Charpentier, Edmond Roger, Bakolimalala Rakouth, Jean-Michel Tropical Ecology Leong Pock Tsy, et al. ISSN 0564-3295 Trop Ecol DOI 10.1007/s42965-019-00046-9 1 23 Your article is protected by copyright and all rights are held exclusively by International Society for Tropical Ecology. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. 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The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Tropical Ecology International Society https://doi.org/10.1007/s42965-019-00046-9 for Tropical Ecology REVIEW ARTICLE The baobabs of the Comoro Islands: some biogeographical factors towards the protection and conservation of a neglected asset Maoulida Mohamed Abdillahi1,2 · Cyrille Cornu3 · Raïma Fadul4,5 · Michel Charpentier6 · Edmond Roger2 · Bakolimalala Rakouth2 · Jean‑Michel Leong Pock Tsy3,9 · Pascal Danthu3,7,8 Received: 22 July 2019 / Revised: 17 September 2019 / Accepted: 10 November 2019 © International Society for Tropical Ecology 2019 Abstract This study aims to provide some information about the area of presence and geographical breakdown of baobabs belonging to the Adansonia digitata species on the four Comoro Islands. Two of the eight known species of baobabs in the world are present in the Comoro Islands. Whilst they have asset value, a thorough study of their geographical distribution has yet to be produced and there is very little existing action to protect and conserve the asset. An inventory of the A. digitata populations on the islands (Grande Comore, Mohéli, Anjouan and Mayotte) and islets of the archipelago was carried out. From this, it was possible to map the geographical breakdown and analyse the spacial distribution of the baobabs. Their distribution seems to be strongly associated to their proximity to the coastline, suggesting the seeds are dispersed by marine hydrochory. The ecological status of this species based on IUCN status assessment, is known from the threats and pressures incurred and its distribution according to their ecological preferences. The species is categorized as Endangered (ER). The data from this study should contribute to improved management and conservation of the Adansonia species in the Comoros, a growing requirement in the light of concerns about anthropogenic pressure. Keywords Adansonia digitata · Baobab · Comoros’archipelago · Conservation · Dispersal · Flora · Hydrochory Introduction There are eight species of baobab (Adansonia genus) in the * Maoulida Mohamed Abdillahi world (Fig. 1). Adansonia digitata L. is the most common [email protected] and certainly the most widely studied species (see synthesis by Wickens and Lowe 2008). It is present in its natural state 1 INRAPE, National Institute of Research in Agriculture Fisheries and Environment, Moroni, Comoros in the Sahelian strip from Senegal to Somalia, in East Africa and Australasia, the Comoro Islands and the north-west of 2 Faculty of Sciences, University of Antananarivo, BP 906, Antananarivo, Madagascar Madagascar (Baum 1995; Wickens 2008; Leong Pock Tsy et al. 2009). A recent study (Leong Pock Tsy et al. 2009) 3 DP Forest et Biodiversity, BP 853, Antananarivo, Madagascar showed that the species originated in West Africa and took a migratory route from the west of the African continent 4 UMR C53. PVBMT, Faculty of Sciences et Technologies, University of Réunion, BP 7151, 97715 Saint-Denis Cedex 9, to the east and then to the south and on to Madagascar. A La Réunion, France new, possible ninth, species, distinct from A. digitata by 5 its degree of ploidy, is thought to have been discovered in DAF Mayotte, BP 103, 97600 Mamoudzou, Mayotte, France 6 East Africa (Douie et al. 2015; Pettigrew et al. 2012) and is Les Naturalistes de Mayotte, 10, rue Mamawé, Kawéni, BP Adansonia kilima 1391, 97600 Mamoudzou, France named . However, a new study (Cron et al. 2016) seems to invali- 7 CIRAD, UPR HortSys, 34398 Montpellier cedex 5, France date this discovery, suggesting that Adansonia kilima is 8 HortSys, CIRAD, University of Montpellier, Montpellier, synonymous with A. digitata, causing a controversy which France nonetheless, a priori, does not concern the populations of A. 9 Drfgrn-Foffa, Ambatobe, Boite Postale 1690, Antananarivo, digitata in the Comoro Islands and Madagascar. Madagascar Vol.:(0123456789)1 3 Author's personal copy Tropical Ecology Fig. 1 Distribution species of baobab (Adansonia genus) in the world (Wickens 2008) A. digitata is not currently considered as an endangered make it easier to defne the modes of management and the species within its entire area of presence and does not feature conservation of baobab population and help to defne the on the IUCN red list [IUCN (International Union For The zones of ring-fencing taking account of determinants associ- Conservation of Nature) 2015, 2019]. As far as the Union ated with the biology of baobabs, the constraints of dispersal of Comoros is concerned (Map 1), whilst there are many in a context of insularity but also demographic dynamics and baobabs in the Mohéli marine park (the country’s largest urban expansion. protected space), Adansonia digitata does not feature on Our approach is based on an inventory of the baobab pop- the list of protected species published in decree n° 01/031/ ulations, which is as precise as is possible to enable refer- MPE/CAB of 14 May 2001 relating to the protection of the ence maps of presence and to relate the distribution observed Comoros’ wild fauna and fora (Louette 2004). In Mayotte to explanatory factors such as ecological (biology of bao- (Map 1), A. digitata does not feature either on the list of babs and modes of dispersal), geographical (topographical, protected species, whereas the species Adansonia madagas- in particular) and human (demographic and dynamics of cariensis, of which there are a few rare subjects, features urbanisation) factors. (Barthelat et al. 2006; IUCN Comite Français 2013). The natural marine park, created in 2010 ensures the lagoon’s protection but its area is limited by the upper foreshore (limit Materials and methods of the publicly-owned seafront). Elements of the land fora, in particular baobabs, are not included. The few specimens Inventory methods and measured variables on the isle of Mbouzi are protected since the island’s 82 hectares of land was designated a natural reserve in 2007. This study is based on a series of land inventories of baobabs Whilst the baobab is emblematic of the fora of Comoro and in the Comoro islands that were as exhaustive as possible. Mayotte, it currently receives very little, if any, protection A set of data was collated for each including the following: and is threatened by certain human activities, particularly urbanisation (Fig. 2). – geographic coordinates and altitude were measured using This lack of conservation status can be directly related to GPS; a gap in the knowledge. The present study aims to fll this – diameter at breast height (DBH), taken from measure- gap by providing information on the area of presence and ments of the circumference with a tape measure; geographic breakdown of baobabs of the Adansonia digitata – height of bole (Hf) and total height (Ht) of tree, measured species on the four Comoros Islands. This knowledge should with a clinometer; 1 3 Author's personal copy Tropical Ecology Map 1 Location of the Comoro Islands in the Indian Ocean bole. It should be noted that in these inventories, the number of young baobabs (individuals of small calibre with a DHP and/or Hf ≤ 1 m) is very likely underestimated as these indi- viduals are difcult to locate and identify in the context of rugged, overgrown terrain. Where Mayotte and the surrounding isles were con- cerned, the inventories were carried out between February and April 2010, and resulted in the localisation of 2007 bao- babs on Mayotte (Fadul 2010). This study was based on two prior inventories, which it complemented. The frst was car- ried out in 2006 by the Environmental and Forestry service of Mayotte’s Agricultural and Forestry Department (DAF), who collated an inventory and mapped out 776 baobabs in Fig. 2 Baobab felled to make way for construction of a house at Fom- the south east of the island and 31 on the beach at N’Gouja. boni The second was carried out by the national botanical con- servatory of Mascarin (CBNM) on Mayotte, who formulated a distribution map of 699 baobabs. – the shape of each tree was noted and in particular the Concerning the islands of the Union of the Comoros, single-stemmed or multi-stemmed organisation of the (Grande Comore, Anjouan and Mohéli), the inventories 1 3 Author's personal copy Tropical Ecology were carried out between January 2009 and July 2010 and – Categories and Criteria of the IUCN Red List: Version continuously updated until 2016. They relied on prelimi- 3.1 (2012), (www.uicn.fr/La-Red-Red-of-Species.html ). nary localisation of the baobabs by photo-interpretation – Guidelines for the Application of the IUCN Red List Cri- of very high spatial resolution satellite imagery based on teria at Regional and National Levels: Version 4.0 (2012) and adapted from the method described by Vieilledent (www.uicn.fr/La-Red-Red-Speci es.html).