Quelles origines à l’asylvatisme des îles volcaniques australes Crozet et Saint-Paul (Terres Australes et Antarctiques Françaises, océan Indien) ?

• Published in: Cybergeo
• Main Authors: Larrue, Sébastien, Chadeyron, Julien, Faucon, Frédéric
• Format: Article in Journal/Newspaper
• Language: French
• Published: UMR 8504 Géographie-cités 2018
• Subjects: biogéographie; île; végétation; géographie physique; géohistoire; biogeography; island; physical geography; geohistory; geo; hist; Antarctic; Indian; Saint-Paul; The Antarctic; Antarc*; Antarctique*; Saint-Paul Island
• Online Access: http://journals.openedition.org/cybergeo/28917

亚南极火山岛圣保罗群岛（Saint-Paul）和克罗泽特群岛（Crozet）上没有原生树木或灌木。考虑到在“愤怒的50年代”一些南部岛屿有原生木本植物，因而原生树木在这两个群岛上的缺位就更加令人惊讶了。克罗泽特群岛和圣保罗群岛“与世隔绝” 的状况是否能解释这一现象的起源？我们研究了对包括克罗泽特群岛和圣保罗群岛在内的26个亚南极火山岛上的木本植物数量产生影响的8个地理因素。我们的研究结果表明，年平均温度解释了所研究岛屿上木本植物的23.7％的数量变化。 克罗泽特群岛没有树木和灌木，一定程度上与年均气温低于6°C有关。然而，南方木本植物的扩散能力和其种子到达这些岛屿的难度似乎也起着很关键的作用。主要成分分析（MCA）表明，圣保罗群岛的隔绝状况和其他有原生木本植物分布的岛屿并无区别。圣保罗无原生木本植物的状况无法由其特殊的隔绝状况来解释。1626年和1633年在圣保罗曾观察到灌木，但在进行第一次植物调研之前，17世纪晚期的火山活动可能已摧毁圣保罗的原生木本植物。 Remote islands of Saint-Paul and Crozet (Indian Ocean) are among the most isolated islands in the world. Neither native trees nor shrubs have been reported on these Subantarctic Islands. Both regular and high wind speed that characterize these southern latitudes are considered the main factor to explain the origin of these treeless islands. However, this explanation seems unlikely because some southern islands in the “Roaring Forties” harbor many native woody species. In this article, we studied the insular context of Crozet archipelago and Saint-Paul island by means of eight geographic factors compared to 26 other Subantarctic Islands harboring native woody species or not. Factors used as potential predictors that may contribute to the naturally treeless island included island area (km²), island elevation (km), mean daily temperature (°C) and precipitation (mm), as well as the distance from the nearest continent (km), the distance to the nearest similar island (km), the distance to the Antarctic, and index of isolation (UNEP). Spearman’s rank correlation coefficient, stepwise regression analysis and bar diagrams were used to assess the relative influence of these factors on woody native species richness. Results show that the spatial pattern of woody species richness was significantly influenced by mean daily temperature (R² = 0.237, P = 0.014) with a threshold of treeless island phenomenon below ca. 6°C. However, seed dispersal abilities of woody southern species could play an important role to explain these naturally treeless islands. Principal Component Analysis (PCA) shows that ...