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The Ecological Significance of Annuals on a Mediterranean Grassland (Mt Ventoux, France)
Olivier Madon and Frédéric Médail
Vol. 129, No. 2 (1997), pp. 189-199
Published by: Springer
Stable URL: http://www.jstor.org/stable/20050450
Page Count: 11
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A study was carried out on a Mediterranean limestone grassland to search for the ecological significance of the occurrence of annuals. In the studied grassland, most of annuals are concentrated in patches. Authors tested if annuals (1) correspond to the R-strategy (ruderal) according to Grime's theory, i. e. they are adapted to live in disturbed, productive habitats, or (2) if they present an adaptation to a xeric climate in keeping with Raunkiaer. The correspondence analyses and the examination of plants strategies reveal that: (1) annuals are grouped with the more xerophytic perennials in the ordination, (2) the cover of annuals is higher in plots with a high cover of S species (stress-tolerators) and a lower cover of C species (competitors) and CS species (intermediate strategy). These results constitute arguments to integrate annuals of Mediterranean grasslands into stress-tolerators. In the discussion are examined the importance of patches in which annuals are preferentially located. Although patches are generated by disturbances, the presence of annuals is explained by their life cycle fitting the microclimate variations, characterized by an extreme summer drought. Their cycle is not adapted here to the frequency of disturbances (unless the summer drought is considered as annual disturbance -- this last point of view is discussed). In the studied grassland, annuals are then better thought of as highly developed stress-tolerators than as ruderals. A generalization is put forward by distinguishing two cases: in xeric habitats, annuals are stress-tolerant, and in productive habitats, they are ruderal.
Plant Ecology © 1997 Springer