Department of Ecology and Environmental Sciences, University of Umeå, SE-90187, Umeå, Sweden.
Section of Ecology, Department of Biology, University of Turku, FI-20014, Turku, Finland.
Glob Chang Biol. 2015 Sep;21(9):3379-88. doi: 10.1111/gcb.12970. Epub 2015 Jun 19.
Climate change is resulting in a rapid expansion of shrubs in the Arctic. This expansion has been shown to be reinforced by positive feedbacks, and it could thus set the ecosystem on a trajectory toward an alternate, more productive regime. Herbivores, on the other hand, are known to counteract the effects of simultaneous climate warming on shrub biomass. However, little is known about the impact of herbivores on resilience of these ecosystems, that is, the capacity of a system to absorb disturbance and still remain in the same regime, retaining the same function, structure, and feedbacks. Here, we investigated how herbivores affect resilience of shrub-dominated systems to warming by studying the change of shrub biomass after a cessation of long-term experimental warming in a forest-tundra ecotone. As predicted, warming increased the biomass of shrubs, and in the absence of herbivores, shrub biomass in tundra continued to increase 4 years after cessation of the artificial warming, indicating that positive effects of warming on plant growth may persist even over a subsequent colder period. Herbivores contributed to the resilience of these systems by returning them back to the original low-biomass regime in both forest and tundra habitats. These results support the prediction that higher shrub biomass triggers positive feedbacks on soil processes and microclimate, which enable maintaining the rapid shrub growth even in colder climates. Furthermore, the results show that in our system, herbivores facilitate the resilience of shrub-dominated ecosystems to climate warming.
气候变化导致北极地区的灌木迅速扩张。研究表明，这种扩张受到正反馈的加强，这可能使生态系统走上另一条更具生产力的轨道。另一方面，食草动物被认为可以抵消气候同时变暖对灌木生物量的影响。然而，人们对食草动物对这些生态系统弹性的影响知之甚少，即系统吸收干扰的能力，以及仍然保持相同状态，保留相同的功能、结构和反馈。在这里，我们通过研究森林-苔原交错带长期实验性变暖停止后灌木生物量的变化，研究了食草动物如何影响以灌木为主的系统对变暖的弹性。正如预测的那样，变暖增加了灌木的生物量，而且在没有食草动物的情况下，苔原上的灌木生物量在人工变暖停止后的 4 年内继续增加，这表明变暖对植物生长的积极影响甚至可能持续到随后的寒冷时期。食草动物通过将系统恢复到森林和苔原栖息地的原始低生物量状态，为系统的弹性做出了贡献。这些结果支持了更高的灌木生物量引发土壤过程和小气候正反馈的预测，从而使快速的灌木生长即使在较冷的气候条件下也能维持。此外，结果表明，在我们的系统中，食草动物促进了以灌木为主的生态系统对气候变暖的弹性。
