Abstract: Efficient in situ and ex situ conservation strategies are urgently needed in biodiversity hotspots, where high concentrations of endemic plant species are undergoing exceptional loss of habitat. In particular, determining seed desiccation sensitivity is a key prerequisite to design storage methods useful for ex situ programs. In this study, we explored seed desiccation sensitivity and its link with phenological and morphological traits as well as with the environmental variables for 45 New Caledonian plant species. Desiccation sensitivity was quantified through RH50, that is, the relative humidity at which 50% of initial viable seeds died. RH50 was found to be positively associated with the initial seed water content, seed mass, precipitation seasonality, precipitation of the warmest quarter, and presence in rainforest habitats. In contrast, the ability of species to endure desiccation increased in drier habitats such as dry forest. We also found that desiccation sensitivity was consistent at the genus level. These new data provide the basis to establish conservation plans for a large array of plant species in New Caledonia. Moreover, this study may help us to better understand the underlying mechanisms of desiccation sensitivity and to predict desiccation sensitivity of other taxa within the New Caledonian flora on the basis of taxonomy, functional traits and environmental features.

Keywords: South Pacific, tropical biodiversity, conservation, hotspot, storage

**********

NEW CALEDONIA IS AN ARCHIPELAGO in the South Pacific Ocean recognized as one of the global biodiversity hotspots (Myers et al. 2000, Roberts et al. 2002). This ca. 18,000 [km.sup.2] archipelago hosts 3371 native plant species, 73% of which are endemic (Jaffre et al. 2001, Morat et al. 2012). The flora of New Caledonia also stands out among other floras for its very distinctive nature: the presence of several primitive groups including the emblematic Amborella trichopoda which is sister to all other extant angiosperms (Soltis et al. 2008), the importance of families belonging to the core Eocene flora, and the presence of intense speciation (Morat et al. 2012). This exceptional biological richness results from a complex biogeographical history and a wide variety of environments including an extreme diversity and specificity of edaphic conditions (Jaffre 1993, Morat 1993, Pillon et al. 2010). The geological history of New Caledonia, with its phase of total submersion at the end of the Eocene, its covering by a slice of oceanic lithospheric mantle during emersion and its sudden re-emersion 37 million years ago, led to the presence of ultramafic substrates now covering more than one third of the main island (Paris 1981, Pelletier 2006), with a flora that has adapted to these edaphic conditions (Jaffre 1996, Pillon et al. 2010, Morat et al. 2012, Isnard et al. 2016).

The climate of New Caledonia is affected by tropical and temperate influences. The latter are however reduced by the maritime environment and the quasi-permanent presence of the trade wind (Maitrepierre 2012). There are two main seasons in New Caledonia: a hot or cyclonic season, from January to March, and a cool season, from June to September. Transitions between these two...