Data from: The abundance and distribution of guilds of riparian woody plants change in response to land use and flow regulation

1. Many riparian ecosystems in Mediterranean Europe are affected by land use and flow alteration by dams. We focused on understanding how these stressors and their components affect riparian forests in the region. We asked: (i) are there well-defined, responsive riparian guilds?; (ii) do dam-induced stream flows determine abundance and distribution of riparian guilds? and (iii) what are the main drivers governing composition and cover of riparian guilds in regulated rivers? 2. We inventoried the cover of riparian woody species in free-flowing rivers and downstream of dams. We performed a cluster analysis and ordination to derive riparian guilds, using abundance data from 66 riparian woody species and 26 functional plant traits. We used a reduced set of principal components for the environment, land use and hydrology, and general linear modelling to explore the effect of these factors (separately and combined) on riparian guilds. 3. We found that: (i) four dominant guilds are responsive to disturbance in Southwestern European streams, namely the obligate riparian, water-stress tolerant, deciduous competitive, and Mediterranean evergreen guilds ; (ii) a set of land use and hydrological variables differentially affect the diverse co-occurring riparian guilds; (iii) frequency and duration of high flow pulses and the low-flow conditions were major drivers of change in landscapes dominated by intensive agriculture and forestry; (iv) storage reservoirs reduced the cover of obligate riparian and Mediterranean evergreen guilds, and increased the abundance of water-stress tolerant and deciduous competitive guilds, while run-of-river dams, having limited water storage, reduced both obligate and deciduous competitive guilds. 4. Synthesis and applications. Future research, especially in Southwestern Europe, should address the resilience of riparian guilds and the effects of interacting landscape factors and stressors on guild distribution. Stream flow regulations downstream of reservoirs should focus on specific flow components, namely the magnitude of flows, and frequency and duration of extreme flow events. For successful mitigation of the dam-induced effects on riparian vegetation, river management plans must incorporate the environmental and land use site-specific contexts.

1. 地中海欧洲的诸多河岸生态系统均受到土地利用变化与水坝引发的径流改变的影响。本研究旨在探明此类干扰因子及其组分对该区域河岸森林的作用机制，并提出三项核心科学问题：(1) 是否存在界定清晰且响应性强的河岸功能群（riparian guilds）？(2) 水坝调控的河川径流是否决定了河岸功能群的丰度与分布格局？(3) 在受人工调控的河流中，主导河岸功能群组成与盖度的核心驱动因子是什么？
2. 本研究对自由流动河流及水坝下游的河岸木本物种盖度开展了系统调查。基于66种河岸木本植物的丰度数据与26项植物功能性状，研究通过聚类分析（cluster analysis）与排序分析（ordination）推导得到河岸功能群。此外，本研究选取环境、土地利用与水文变量的主成分降维子集，结合一般线性模型（general linear modelling），分别及联合探究上述因子对河岸功能群的影响效应。
3. 研究结果表明：(1) 欧洲西南部溪流中的4个优势河岸功能群对干扰具有显著响应，分别为专性河岸型、耐旱型、落叶竞争型与地中海常绿型功能群；(2) 一系列土地利用与水文变量对共存的不同河岸功能群产生了差异化影响；(3) 高流量脉冲的频率与持续时长，以及枯水期水文条件，是集约化农林业主导景观中植被变化的核心驱动因子；(4) 蓄水型水库（storage reservoirs）会降低专性河岸型与地中海常绿型功能群的盖度，同时提升耐旱型与落叶竞争型功能群的丰度；而蓄水能力有限的径流式水坝（run-of-river dams）则会同时降低专性河岸型与落叶竞争型功能群的丰度。
4. 综合与应用展望。未来的研究（尤其是在欧洲西南部开展的相关工作）应聚焦于河岸功能群的恢复力，以及景观因子与干扰因子的交互作用对功能群分布的影响。水库下游的径流调控应重点关注特定径流组分，即径流总量与极端水文事件的发生频率及持续时长。若要有效减缓水坝对河岸植被造成的负面影响，河流管理规划必须结合研究区域的环境与土地利用的特定场地情境。