Complex biotic interactions drive long-term vegetation dynamics in a subarctic ecosystem

Predicting impacts of global warming requires understanding of the extent to which plant biomass and production are controlled by bottom-up and top-down drivers. By annually monitoring community composition in grazed control plots and herbivore-free exclosures at an Arctic location for 15 years, we detected multiple biotic interactions. Regular rodent cycles acted as pulses driving synchronous fluctuations in the biomass of field-layer vegetation; reindeer influenced the biomass of taller shrubs, and the abundance of plant pathogenic fungi increased when densities of their host plants increased in exclosures. Two outbreaks of geometrid moths occurred during the study period, with contrasting effects on the field layer: one in 2004 had marginal effects, while one in 2012 severely reduced biomass in the control plots and eliminated biomass that had accumulated over 15 years in the exclosures. The latter was followed by a dramatic decline of the dominant understory dwarf-shrub Empetrum her...

预测全球变暖的影响，需要明确植物生物量与生产力在多大程度上受上行调控（bottom-up）与下行调控（top-down）因子的控制。本研究通过在北极某点位对放牧对照样地与无草食动物围栏样地的群落组成开展长达15年的年度监测，揭示了多种生物间相互作用：周期性啮齿动物种群波动以脉冲形式驱动地表层植被生物量的同步变化；驯鹿会影响较高灌木的生物量；而在围栏样地中，植物病原真菌的丰度会随宿主植物密度的升高而增加。研究期间共发生两次尺蛾（geometrid moths）暴发事件，对地表层植被产生了截然不同的影响：2004年的暴发仅产生微弱影响，2012年的暴发则大幅降低了对照样地的生物量，并彻底清除了围栏样地中积累15年的生物量。此次暴发后，林下优势矮灌木岩高兰（Empetrum her...）出现了急剧衰退。