Department of Biology, NTNU, Norwegian University of Science and Technology, Høgskoleringen 5, 7491, Trondheim, Norway.
Norwegian Institute for Nature Research, P.O. Box 5685, Torgarden, 7485, Trondheim, Norway.
BMC Ecol. 2018 Aug 30;18(1):29. doi: 10.1186/s12898-018-0185-9.
Shrub cover in arctic and alpine ecosystems has increased in recent decades, and is predicted to further increase with climate change. Changes in shrub abundance may alter ecosystem carbon (C) sequestration and storage, with potential positive feedback on global C cycling. Small and large herbivores may reduce shrub expansion and thereby counteract the positive feedback on C cycling, but herbivore pressures have also changed in the alpine-arctic tundra; the increased shrub cover together with changes in herbivore pressure is leading to unpredictable changes in carbon sequestration and storage. In this study we investigate the importance of herbivory and shrub introduction for carbon sequestration in the short term. We measured standing biomass and daytime mid-growing season carbon fluxes in plots in a full factorial design where we excluded small and large mammalian herbivores and introduced Salix by planting Salix transplants. We used three study sites: one Empetrum-dominated heath, one herb- and cryptogam-dominated meadow, and one Salix-dominated shrub community in the low-alpine zone of the Dovre Mountains, Central Norway.
After 2 years, significant treatment effects were recorded in the heath community, but not in the meadow and shrub communities. In the heath community cessation of herbivory increased standing biomass due to increased biomass of dwarf shrubs. Cessation of herbivory also reduced biomass of bryophytes and ecosystem respiration (ER). Except for an increase in biomass of deciduous shrubs caused by the Salix introduction, the only effect of Salix introduction was an increase in biomass of graminoids in the heath.
Our short-term study demonstrated that herbivore exclusion had small but still significant effects on heath vegetation, whereas such effects were not apparent in the herb-and cryptogam-dominated meadow and the Salix-dominated shrub community. Following the treatments over more years is needed to estimate the long-term effects on community structure and the consequences for C sequestration in the three plant communities. Such data are important for predicting the impact of shrub expansion on C budgets from alpine regions.
近年来，北极和高山生态系统中的灌木覆盖面积增加，预计随着气候变化还会进一步增加。灌木丰度的变化可能会改变生态系统的碳（C）固存和储存，从而对全球 C 循环产生潜在的正反馈。小型和大型食草动物可能会减缓灌木的扩张，从而抵消对 C 循环的正反馈，但高山-北极冻原的食草动物压力也发生了变化；增加的灌木覆盖面积加上食草动物压力的变化，导致碳固存和储存的不可预测变化。在这项研究中，我们研究了食草作用和灌木引种对短期碳固存的重要性。我们在一个完全因子设计的样地中测量了立木生物量和日间中生长季碳通量，其中我们排除了小型和大型哺乳动物食草动物，并通过种植柳移植来引入柳。我们使用了三个研究地点：挪威中部多夫雷山脉低海拔地区的一个以石南花为主的石南灌丛、一个草本植物和隐花植物为主的草地以及一个以柳为主的灌丛群落。
2 年后，在石南灌丛群落中记录到了显著的处理效应，但在草地和灌丛群落中没有记录到。在石南灌丛群落中，由于矮灌木生物量增加，停止食草作用增加了立木生物量。食草作用的停止还减少了苔藓植物和生态系统呼吸（ER）的生物量。除了柳引种导致落叶灌木生物量增加外，柳引种的唯一影响是石南灌丛中的禾本科生物量增加。
我们的短期研究表明，食草动物的排除对石南植被有较小但仍有显著的影响，而在草本植物和隐花植物为主的草地和柳为主的灌丛群落中则没有明显的影响。需要对这些处理进行更多年的跟踪，以估计对三个植物群落的群落结构和碳固存的长期影响。这些数据对于预测高山地区灌木扩张对 C 预算的影响很重要。
