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大坝径流调控的影响。本研究聚焦于阐明此类扰动因子及其组分对该区域河岸森林的影响机制，并提出三个科学问题：(i) 是否存在界定清晰且对扰动具有响应性的河岸功能群（riparian guilds）？(ii) 大坝调控的溪流径流是否决定了河岸功能群的多度与分布格局？(iii) 在受调控河流中，支配河岸功能群组成与盖度的核心驱动因子是什么？
2. 本研究对天然无调控河流及大坝下游的木本河岸物种盖度进行了调查。我们基于66种木本河岸物种的多度数据与26个植物功能性状，通过聚类分析与排序分析推导得到河岸功能群。此外，我们选取环境、土地利用与水文变量的主成分降维子集，并结合一般线性模型，探究了此类因子（单独作用与联合作用）对河岸功能群的影响效应。
3. 本研究结果表明：(i) 西南欧洲溪流中存在4类对扰动具有响应性的优势河岸功能群，分别为专性河岸类群、耐旱类群、落叶竞争类群与地中海常绿类群；(ii) 一系列土地利用与水文变量对多种共存的河岸功能群产生了差异化影响；(iii) 高流量脉冲的频率与持续时长，以及枯水期水文条件，是集约化农业与林业主导景观发生变化的核心驱动因子；(iv) 蓄水型水库会降低专性河岸与地中海常绿类群的盖度，同时提升耐旱类群与落叶竞争类群的多度；而储水能力有限的径流式大坝则会同时降低专性河岸类群与落叶竞争类群的多度。
4. 总结与应用展望。未来的研究（尤其是在西南欧洲地区）应聚焦于河岸功能群的恢复力，以及景观因子与扰动因子的交互作用对功能群分布的影响。水库下游的溪流径流调控应针对性关注径流的量级、极端水文事件的发生频率与持续时长。若要有效减缓大坝对河岸植被的负面影响，河流管理规划必须纳入针对具体位点的环境与土地利用背景条件。