SEV-LTER Mean - Variance Experiment Quadrat Plant Species Cover and Height

We designed novel field experimental infrastructure to resolve the relative importance of changes in the climate mean and variance in regulating the structure and function of dryland populations, communities, and ecosystem processes. The Mean - Variance Climate Experiment (MVE) adds three novel elements to prior designs that have manipulated interannual variance in climate in the field (Gherardi & Sala, 2013) by (i) determining interactive effects of mean and variance with a factorial design that crosses reduced mean with increased variance, (ii) studying multiple dryland biomes to compare their susceptibility to transition under interactive climate drivers, and (iii) adding stochasticity to our treatments to permit the antecedent effects that occur under natural climate variability. This new infrastructure enables direct experimental tests of the hypothesis that interactions between the mean and variance of precipitation will have larger ecological impacts than either the mean or variance in precipitation alone. This dataset includes plant species cover and height data measured in 1 m x 1 m quadrats at all Mean - Variance experiment sites. Quadrat locations span five important ecosystems of the American southwest: blue grama-dominated Plains grassland (est. fall 2019), black grama-dominated Chihuahuan Desert grassland (est. fall 2020), creosotebush dominated Chihuahuan Desert shrubland (est. fall 2021), juniper savanna (est. fall 2022) and pinon-juniper woodland (est. fall 2023). Data on plant cover and height for each plant species are collected per individual plant or patch (for clonal plants) within 1 m x 1 m quadrats. These data inform population dynamics of foundational and rare plant species. The cover and height of individual plants or patches are sampled twice yearly (spring and fall) in permanent 1m x 1m plots within each site or experiment. This data package includes plant cover and height only -- for species biomass estimates per quad see package knb-lter-sev.350.

本研究构建了新型野外实验平台，以厘清气候均值与方差变化在调控旱地种群、群落及生态系统过程的结构与功能时的相对重要性。
均值-方差气候实验（Mean - Variance Climate Experiment, MVE）在既往野外操控气候年际方差的实验设计（Gherardi & Sala, 2013）基础上，新增三项创新要素：其一，通过降低气候均值与增大方差的析因交叉设计，明确气候均值与方差的交互效应；其二，开展多旱地生物群系研究，对比其在交互气候驱动因子下的群落转型敏感性；其三，为实验处理引入随机性，以还原自然气候变率下的前置效应。
该新型实验平台可直接验证如下科学假说：降水均值与方差的交互作用，其生态影响将显著大于单独的降水均值或降水方差效应。
本数据集涵盖均值-方差气候实验所有样地内1m×1m样方中测得的植物物种盖度与高度数据。样地分布于美国西南部五类典型生态系统：以蓝格兰马草（blue grama）为主的平原草原（2019年秋季建站）、以垂穗格兰马草（black grama）为主的奇瓦瓦沙漠草原（2020年秋季建站）、以石炭酸灌木（creosotebush）为主的奇瓦瓦沙漠灌丛（2021年秋季建站）、桧木稀树草原（2022年秋季建站）以及松-桧木林地（2023年秋季建站）。
本研究针对每个植物物种，在1m×1m样方内按单株或克隆植物的斑块采集盖度与高度数据，相关数据可为建群种与稀有植物物种的种群动态研究提供支撑。
每个实验站点的永久1m×1m样地内，每年于春季与秋季两次采样单株或斑块的盖度与高度。
本数据包仅包含植物盖度与高度数据——若需获取单个样方的物种生物量估算数据，请查阅数据集knb-lter-sev.350。