Increased temperature, N and snowpack experiment for north of saddle, 2006 - ongoing.

In 2006 we established a global change experiment in the Front Range
of the Rocky Mountains to investigate how manipulations of warmer
summer temperature, N deposition, and increased snowpack would
affect the growth of alpine plants. The experiment was implemented
on Niwot Ridge, where shrub cover has expanded by over 400% since
1946 (Formica et al. 2014). We established experimental plots north
of the Niwot Ridge saddle, in an area of moist meadow tundra where
willow shrub (Salix sp.) patches are present.

Within experimental plots, Salix glauca seedlings were transplanted
in 2006 and 2007 to test whether changing environmental conditions
facilitated shrub survival and growth. In 2007 and 2008,
phenological observations were recorded for all (2007) or abundant
(2008) species in experimental plots. Measurements of plant species
composition and aboveground net primary productivity (ANPP) are also
made annually or biennially (ANPP, 2017-onward). In 2021, canopy
height and NDVI began being measured annually.

In July of 2016, a community transplant experiment was implemented
to test whether changing environmental conditions support changes in
alpine tundra plant communities. Two species characteristic of (1)
dry meadow tundra (Tetraneuris acaulis, Erigeron pinnatisectus), (2)
snowbed tundra (Ranunculus adoneus, Saxifraga rhomboidea) and (3)
subalpine meadow (Trollius albiflorus, Polemonium pulcherrimum) were
transplanted into experimental plots. Survival and growth of
transplants was documented annually through 2021.

2006年，我们在落基山脉前缘（Front Range）设立了一项全球变化实验，以探究夏季增温、氮沉降（N deposition）及积雪增加的人工调控措施将如何影响高山植物的生长。本实验设于尼沃特岭（Niwot Ridge），该区域自1946年以来灌木盖度已扩张逾400%（Formica等，2014）。我们在尼沃特岭鞍部以北的湿润草甸冻土带搭建了实验样地，该区域分布有柳属（Salix sp.）灌丛斑块。

实验样地内，我们于2006年与2007年移栽了蓝叶柳（Salix glauca）幼苗，以验证环境变化是否可促进灌丛的存活与生长。2007年及2008年，我们对实验样地内的全部物种（2007年）或优势物种（2008年）开展了物候观测。植物物种组成与地上净初级生产力（aboveground net primary productivity, ANPP）的测定亦按年度或两年度周期开展（ANPP数据自2017年起采集）。2021年起，我们开始每年测定群落冠层高度与归一化植被指数（NDVI）。

2016年7月，我们启动了一项群落移植实验，以验证环境变化是否会推动高山冻土带植物群落发生改变。实验选取三类典型生境的物种：(1) 干旱草甸冻土带：无茎四蕊菊（Tetraneuris acaulis）、羽裂飞蓬（Erigeron pinnatisectus）；(2) 雪床冻土带：侧花毛茛（Ranunculus adoneus）、菱叶虎耳草（Saxifraga rhomboidea）；(3) 亚高山草甸：白花金莲花（Trollius albiflorus）、美丽花荵（Polemonium pulcherrimum），将上述物种移植至实验样地中。直至2021年，我们每年均对移植植株的存活与生长状况进行记录。