Data from: Short-term herbivory has long-term consequences in warmed and ambient high Arctic tundra

Climate change is occurring across the world, with effects varying by ecosystem and region but already occurring quickly in high-latitude and high-altitude regions. Biotic interactions are important in determining ecosystem response to such changes, but few studies have been long-term in nature, especially in the High Arctic. Mesic tundra plots on Svalbard, Norway, were subjected to grazing at two different intensities by captive Barnacle geese from 2003–2005, in a factorial design with warming by Open Top Chambers. Warming manipulations were continued through 2014, when we measured vegetation structure and composition as well as growth and reproduction of three dominant species in the mesic meadow. Significantly more dead vascular plant material was found in warmed compared to ambient plots, regardless of grazing history, but in contrast to many short-term experiments no difference in the amount of living material was found. This has strong implications for nutrient and carbon cycling and could feed back into community productivity. Dominant species showed increased flowering in warmed plots, especially in those plots where grazing had been applied. However, this added sexual reproduction did not translate to substantial shifts in vegetative cover. Forbs and rushes increased slightly in warmed plots regardless of grazing, while the dominant shrub, Salix polaris, generally declined with effects dependent on grazing, and the evergreen shrub Dryas octopetala declined with previous intensive grazing. There were no treatment effects on community diversity or evenness. Thus despite no changes in total live abundance, a typical short-term response to environmental conditions, we found pronounced changes in dead biomass indicating that tundra ecosystem processes respond to medium- to long-term changes in conditions caused by 12 seasons of summer warming. We suggest that while high arctic tundra plant communities are fairly resistant to current levels of climate warming, underlying ecosystem processes are beginning to change. In addition, even short bouts of intense herbivory can have long-term consequences for some species in these communities.

全球范围内均正经历气候变化，其影响因生态系统与区域而异，但在高纬度与高海拔地区，气候变化已快速显现。生物相互作用是决定生态系统对这类气候变化响应的核心因子，但相关长期研究仍较为匮乏，在高北极地区尤为如此。2003年至2005年，研究团队在挪威斯瓦尔巴群岛设置中湿苔原样地，以析因实验设计开展处理：由圈养的白颊黑雁（Barnacle geese）以两种不同强度对样地进行放牧，并采用开顶式增温箱（Open Top Chambers）实施增温处理。增温处理持续至2014年，当年我们测定了该区域中湿草甸的植被结构、组成，以及3个优势物种的生长与繁殖状况。与对照样地相比，增温样地内的维管植物枯体生物量显著更高，且不受过往放牧历史的影响；但与多数短期实验结果不同的是，样地内活体生物量并未出现显著差异。这一结果对养分循环与碳循环具有重要意义，且可能反向影响群落生产力。优势物种在增温样地中的开花率有所提升，尤其是曾接受放牧处理的样地。然而，这类有性繁殖的增加并未转化为植被盖度的显著变化。无论放牧与否，增温样地内的杂类草（Forbs）与灯心草均略有增加；而优势灌木极地柳（Salix polaris）的盖度通常会下降，其影响程度依赖于放牧强度；常绿灌木仙女木（Dryas octopetala）的盖度则在曾经历高强度放牧的样地中出现下降。实验处理对群落多样性与均匀度均无显著影响。因此，尽管活体总丰度未发生变化——这是环境变化下的典型短期响应——我们仍观测到枯体生物量出现了显著变化，表明苔原生态系统过程会对12个夏季增温季所引发的中长期环境变化产生响应。我们认为，尽管高北极苔原植物群落对当前水平的气候增温具有较强的抗性，但潜在的生态系统过程已开始发生改变。此外，即便高强度放牧的持续时间较短，也会对该群落中的部分物种产生长期影响。