Warming and snow experiment plant species composition data for Saddle snowfence, 1993 - 2000.

The International Tundra Experiment (ITEX) is a consortium of research sites seeking to understand the response of tundra plant populations to changes in growing season temperatures through a simple temperature manipulation and transplant experiment. The research goal is to examine the phenologic and reproductive responses of a set of species to experimentally-induced warming at a network of sites. The ITEX design is hierarchical, with sites participating at whatever level they are able. At the minimum, participation in ITEX requires climate monitoring (using the LTER MSR standards), a temperature manipulation using one of three possible designs, and monitoring phenologic and reproductive variables for at least one designated ITEX species or two other species. The temperature manipulation is achieved through use of conical or hexagonal open-top chambers of solar fiberglass, which have been shown to increase the air temperature at the surface approximately 3 degrees C. ITEX studies at Niwot Ridge, a logical outgrowth of the long-term phenology studies there, uses a factorial design based around the long-term snowfence experiment. Twenty cones are placed behind the snowfence, distributed at 10, 25, 45, and 75 m from the fence; each cone is paired with an adjacent plot. Beginning with the 1995 season, 24 additional plots were implemented outside of the snowfence influence. Twelve cones are distributed beyond both the north and south edges of the snowfence area, at 10, 25, 45, and 75 m behind the line of the snowfence; each cone is paired with an adjacent plot. This results in the following treatments: increased winter snow, increased summer temperature, increased snow and increased temperature, and control. Key phenologic, growth, and reproductive traits are being followed on marked individuals of Acomastylis (Geum) rossii and Bistorta (Polygonum) bistortoides, and complete species composition is being monitored. The point-quadrat technique used was identical to that described by Auerbach (1992): The point-quadrat method was used for estimating canopy stratification and plant cover. Aluminum point-quadrat frames were 1-m^2 in size, with double-layer filament spaced 10 cm apart to make a 10 x 10 cm grid for a total of 100 sample points per plot. Before sampling, the point-quadrat frame was leveled and plots were permanently marked in the following manner. Aluminum tags were nailed into the ground so that a frame could be repositioned in the same location from year to year; i.e., tags with a hole in the middle were used to define the locations for the point frame legs and four tags with a "X" stamped on them (positioned somewhere inside each of the frame corners) were used to define alignment of the frame by positioning the string crossings over these "X"s. Distances from the frame to a top canopy plant hit and to a surface layer plant hit were measured to the nearest 0.5 cm and recorded. Plant genus and species were also recorded at both hits at each point. CITATIONS. Auerbach, N. 1992. Effects of road and dust disturbance in minerotrophic and acidic tundra ecosystems, Northern Alaska. MS thesis, University of Colorado, Boulder. 253 pp.

国际冻原实验协作网（International Tundra Experiment, ITEX）是由全球多个研究站点组成的学术联盟，旨在通过标准化的温度操控与移植实验，解析冻原植物种群对生长季温度变化的响应机制。其核心研究目标为，在全球站点网络中，通过实验性增温处理，探究多类冻原物种的物候与繁殖响应特征。

ITEX的研究设计采用层级化模式，各站点可根据自身条件选择适配的参与层级。最低参与要求包括：开展遵循长期生态研究网络（Long-Term Ecological Research, LTER）MSR标准的气候监测工作、采用三种可选设计之一实施温度操控、对至少一种指定的ITEX物种或两种其他物种的物候与繁殖变量进行监测。

温度操控通过使用锥形或六边形太阳能玻璃纤维开顶式增温室（open-top chambers, OTCs）实现，此类装置可使地表空气温度提升约3摄氏度。

位于尼沃特岭（Niwot Ridge）的ITEX研究是当地长期物候研究的自然延伸，采用了基于长期雪栅栏实验的析因设计。20台锥形增温室被安置在雪栅栏后方，分布于距雪栅栏10、25、45和75米的位置，每台增温室均配有一处相邻对照样地。自1995年生长季起，研究团队在雪栅栏影响范围外增设了24个样地。另有12台增温室被布置在雪栅栏区域的南北两侧边缘之外，沿雪栅栏线后方10、25、45和75米的位置分布，每台增温室同样配有相邻样地。由此形成四类实验处理：增雪处理、夏季增温处理、增温增雪复合处理以及对照组。

研究人员对标记的山金梅属（Acomastylis，原称杨梅属Geum）rossii与拳参属（Bistorta，原称蓼属Polygonum）bistortoides个体的关键物候、生长与繁殖性状进行持续追踪，并对样地内的完整物种组成开展监测。

本研究采用的点样框法与Auerbach（1992）的描述完全一致：该方法用于估算植被冠层分层与植物盖度。铝制点样框规格为1平方米，采用双层细丝以10厘米间距编织为10×10厘米的网格，每个样地共计100个采样点。采样前，需将点样框调平，并通过以下方式对样地进行永久标记：将中部带孔的铝制标签钉入地面，用于确定点框支脚的固定位置；同时在每个样地角落内侧分别钉入一枚印有“X”标记的铝制标签，通过将点框的绳结交点对准这些“X”标记，实现样框的精准对位与年度重复定位。记录点框探针触及冠层顶部植物与地表层植物的距离，测量精度精确至0.5厘米，并同时记录每个采样点两处触及植物的属与种信息。

参考文献
Auerbach, N. 1992. 北阿拉斯加矿养与酸性冻原生态系统的道路与粉尘干扰效应. 科罗拉多大学博尔德分校硕士论文，253页。