Plant Ecology

, Volume 198, Issue 1, pp 73–87 | Cite as

Distribution, shape and clonal growth of the rare endemic tree Olea europaea subsp. laperrinei (Oleaceae) in the Saharan mountains of Niger

  • Fabien Anthelme
  • Afane Abdoulkader
  • Guillaume Besnard
Article

Abstract

The populations of the Laperrine’s olive (Olea europaea subsp. laperrinei) are located in three main areas corresponding to the mountains of northern Niger (Aïr), southern Algeria (Hoggar), and north-western Sudan (western Darfur). The populations native of Niger were found to occur in very fragmented patches from 1550 to 1850 m in five isolated mountains with population sizes not exceeding 100 trees each, except in the Tamgak. Samples in the Tamgak and the Bagzane mountains were studied by combining field observations with identification of genets (using highly variable DNA marker analyzes). Trees were relatively small and multi-stemmed like those in the Hoggar, and were associated with some tropical species as in the western Darfur. They were found on borders of “wadis”, i.e., temporary water courses, in ravines and on hillsides. They were unable to rely on sexual reproduction, which was found to be ineffective. In contrast, 28% of the genetic profiles found (ngenet = 98) were represented with two or more trees without aboveground connections. Molecular and morphological data both demonstrated that the populations used clonal growth (CG) to survive in the current unfavorable period of hyper-aridity, and thus are likely to be remnant populations. Signs of human-related disturbances, recorded on 43% of the sampled trees, should be a determining factor of distribution as well. In the Bagzane mountains especially, where human activities are more intense than in the Tamgak mountains, trees developed preferentially on hillsides and ravines with low access rather than on wadi borders with better edaphic conditions but easier access for livestock/people. CG may be therefore, a survival strategy both against aridity and human-related disturbances. Sexual reproduction may be triggered during a less arid period, following the model of multiple demographic strategies, widespread in arid environments. However, survival would be affected by browsing and cuttings. Lastly, the absence of an efficient sexual strategy coupled with the high fragmentation of very small populations and a narrow altitudinal range of distribution indicates that today the populations of O. e. laperrinei in the Aïr mountain range are more endangered than those from southern Algeria and north-western Sudan.

Keywords

Arid Isolation Habitat fragmentation Human activities Microsatellite markers Multiple demographic strategy Remnant population 

Notes

Acknowledgements

The authors thank Salouhou Djibrilla, Rhissa Bagzanamas, Vincent Simont and Haidara Attefock for their help in the field, Jean Maley for his advises on the manuscript, Luc Descroix for hydrologic support, and D. Taylor and D. Manley for linguistic advises.

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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Fabien Anthelme
    • 1
  • Afane Abdoulkader
    • 2
  • Guillaume Besnard
    • 3
  1. 1.IRD, UR 136 and UMR 1097Montpellier cedex 5France
  2. 2.Département de GéographieUniversité Abdou MoumouniNiameyNiger
  3. 3.Department of Ecology and Evolution, BiophoreUniversity of LausanneLausanneSwitzerland

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