Data from: Extrapolating multi-decadal plant community changes based on medium-term experiments can be risky: evidence from high-latitude tundra

For most experimental studies the short-term responses to manipulation often differ from the long-term changes in the community composition, dynamics or functioning. Such discrepancy limits the translation of experimental results into key ecological topics such as global environmental change. Here we analyzed plant community dynamics from a 23-year transplant experiment in the Fennoscandian mountain tundra and explored how well the pattern of responses over the first 12 years of the experiment can predict longer-term changes. Sod-blocks of tundra heath vegetation were transplanted to a snowbed 150 m higher in elevation from their origin, where, with contrasting levels of soil wetness, half of the transplants were protected from mammalian herbivores. Throughout the experiment, community changes strongly depended on both plant functional types and experimental treatments. The first 12 years were characterized by a response to transplantation to the snowbed showing a strong increase of graminoid and a decrease of shrub abundances in the transplants. In the longer term, the community divergence increased in particular in response to grazing and soil wetness within the snowbed, while graminoid dominance disappeared. Markov Chain Models captured the main trends during the first 12 years but they failed to predict their relative abundance after 23 years. In particular, the late dominance of bryophytes in the wet snowbed, the recovery of shrubs in the dry exclosures, and the subordinate status of graminoids deviated from the extrapolation based on the medium-term trends. Despite clear community dynamical trajectories detected in the first decade, the differences in the temporal scale of both treatment effects and plant functional type responses limited their ability to extrapolate longer-term trajectories. We find that increasing focus on long-term experiments is a crucial step to understanding the processes involved in the response of plant communities to global environmental change.在多数实验研究中，人为操控下的短期响应往往与群落组成、动态及生态系统功能的长期变化存在显著差异。这类差异限制了实验结果向全球环境变化等核心生态学研究议题的推广应用。 本研究依托芬诺斯坎迪亚山地苔原开展的23年移栽实验，分析了植物群落动态，并探讨了实验前12年的响应模式能否有效预测长期变化。研究将苔原灌丛植被的草皮块移栽至距起源地海拔高150米的雪床生境中，该生境的土壤湿度存在显著干湿梯度；其中一半移栽样地设置了植食动物排除围栏，以阻挡哺乳动物植食动物的取食，另一半则未受此类防护。 整个实验周期内，群落变化强烈依赖于植物功能型（plant functional types）与实验处理两类核心因素。实验前12年的响应特征为：移栽至雪床的样地中，禾草类植物（graminoid）多度显著增加，灌木（shrub）多度则呈下降趋势。从长期来看，群落分异程度进一步加剧，这尤其与雪床生境内的放牧压力和土壤湿度密切相关，而禾草类植物的优势地位最终消失。 马尔可夫链模型（Markov Chain Models）能够捕捉实验前12年的主要动态趋势，但无法准确预测23年后各功能群的相对多度。具体而言，湿润雪床生境中苔藓植物（bryophytes）的后期优势地位、干旱围栏样地内灌木的恢复，以及禾草类植物的次要地位，均偏离了基于中期趋势的外推结果。 尽管实验前十年已观测到清晰的群落动态轨迹，但实验处理效应与植物功能型响应的时间尺度存在差异，这限制了基于短期结果外推长期动态轨迹的能力。 本研究表明，加大对长期实验的关注力度，是理解植物群落响应全球环境变化相关过程的关键环节。