Institute of Landscape Ecology and Resource Management, Research Centre for BioSystems, Land Use and Nutrition, Justus-Liebig-University Gießen, Heinrich-Buff-Ring 26-32, DE-35392 Gießen, Germany.
Ann Bot. 2011 Jul;108(1):177-83. doi: 10.1093/aob/mcr097. Epub 2011 May 30.
A meta-analysis of global change experiments in arctic tundra sites suggests that plant productivity and the cover of shrubs, grasses and dead plant material (i.e. litter) will increase and the cover of bryophytes will decrease in response to higher air temperatures. However, little is known about which effects these changes in vegetation structure will have on seedling recruitment of species and invasibility of arctic ecosystems.
A field experiment was done in a bryophyte-dominated, species-rich subarctic heath by manipulating the cover of bryophytes and litter in a factorial design. Three phases of seedling recruitment (seedling emergence, summer seedling survival, first-year recruitment) of the grass Anthoxanthum alpinum and the shrub Betula nana were analysed after they were sown into the experimental plots.
Bryophyte and litter removal significantly increased seedling emergence of both species but the effects of manipulations of vegetation structure varied strongly for the later phases of recruitment. Summer survival and first-year recruitment were significantly higher in Anthoxanthum. Although bryophyte removal generally increased summer survival and recruitment, seedlings of Betula showed high mortality in early August on plots where bryophytes had been removed.
Large species-specific variation and significant effects of experimental manipulations on seedling recruitment suggest that changes in vegetation structure as a consequence of global warming will affect the abundance of grasses and shrubs, the species composition and the susceptibility to invasion of subarctic heath vegetation.
对北极苔原地区的全球变化实验进行的荟萃分析表明，植物生产力以及灌木、草本植物和死植物物质（即凋落物）的覆盖面积将增加，而苔藓植物的覆盖面积将减少，这是对更高空气温度的响应。然而，对于这些植被结构变化将对物种幼苗补充和北极生态系统的入侵性产生哪些影响，人们知之甚少。
在苔藓植物占主导地位、物种丰富的亚北极石楠灌丛中，通过在析因设计中操纵苔藓植物和凋落物的覆盖范围，进行了一项野外实验。在播种到实验小区后，分析了草本植物高山瞿麦和灌木矮桦的幼苗补充的三个阶段（幼苗出苗、夏季幼苗存活、第一年补充）。
苔藓植物和凋落物去除显著增加了两个物种的幼苗出苗率，但植被结构的操纵对补充后期阶段的影响差异很大。高山瞿麦的夏季存活率和第一年的补充率显著更高。虽然苔藓植物去除通常会提高夏季存活率和补充率，但在去除苔藓植物的小区中，矮桦的幼苗在 8 月初死亡率很高。
大的物种特异性变化和实验处理对幼苗补充的显著影响表明，全球变暖导致的植被结构变化将影响亚北极石楠灌丛植被的草和灌木的丰度、物种组成和易感性。
