Data from: Threshold dynamics in plant succession after tree planting in agricultural riparian zones.

1. Trajectories of plant communities can be described by different models of plant succession. While restoration projects have traditionally been framed into a clementsian (gradual continuum model) or gleasonian approach (relay floristics model), alternative succession models developed recently may better represent restoration trajectories. Threshold dynamics succession model, which predicts an abrupt species turnover after an environmental threshold is crossed, has never been used in a restoration context. This model might, however, better describe shifts in plant competitive ranking and facilitation interactions during species turnover.
2. Fifty-three riparian zones, planted with trees 3 to 17 years prior to sampling, and 14 natural riparian forests were studied in two agricultural watersheds of southeastern Québec (Canada). The cover of vegetation strata was assessed at the site-scale, and the cover of plant species was estimated in a total of 784 one square meter plots. Canopy cover was measured stereoscopically for each plot.
3. As revealed by Principal Response Curves (PRC) and broken stick models, herbaceous species composition was stable during the first 12-13 years after tree planting, but then abruptly shifted. This two-step pattern in species turnover followed the increase of canopy cover after tree planting. Once canopy cover passed a threshold of ca 40%, plant succession started and led to the re-establishment of forest communities 17 years after planting.
4. During herbaceous species turnover, the cover of ecological groups changed significantly toward covers of natural riparian forests: shade tolerant species generally increased while light-demanding and exotic species decreased. Vegetation structure was also significantly affected by tree planting: tree and shrub cover increased while monocot cover decreased.
5. Tree planting efficiently restored herbaceous forest communities in riparian zones by inducing a species turnover mediated by light availability corresponding to a threshold dynamics in plant succession. Fostering and monitoring canopy closure in tree-planted riparian zones should improve restoration outcomes and adaptive management design. The innovative statistical approach of this study aiming to identify succession patterns and their associated theoretical models can be applied to any type of ecosystem undergoing restoration around the world to bridge the gap between science and management.14-Mar-2016

1. 植物群落的演替轨迹可通过不同的植物演替模型加以描述。传统上，植被恢复项目常被归类为克莱门茨式（Clementsian，渐进连续体模型）或格莱松式（Gleasonian，接力植物区系模型）研究框架，但近年来提出的新型演替模型或许能更精准地刻画恢复轨迹。其中，阈值动态演替模型（Threshold dynamics succession model）预测当环境阈值被突破后，物种组成会发生快速更替，该模型此前从未被应用于恢复生态学研究场景中，不过它或许能更好地描述物种更替过程中植物竞争等级与促进互作的变化。
2. 本研究在加拿大魁北克东南部的两个农业流域中开展，共调查了53个于采样前3至17年栽植树木的河岸带，以及14个天然河岸林。在样地尺度上评估了植被层盖度，并在总计784个1平方米样方中估算了植物物种盖度，同时采用立体测量法测定了每个样方的冠层覆盖度。
3. 主响应曲线（Principal Response Curves, PRC）与折断棍模型（broken stick models）分析结果显示，树木栽植后的前12至13年，草本植物群落组成保持稳定，随后发生了显著转变。这种两步式的物种更替模式，与树木栽植后冠层覆盖度的增加过程相契合。当冠层覆盖度突破约40%的阈值后，植物演替正式启动，并在栽植后17年促使森林群落得以重建。
4. 在草本植物物种更替过程中，不同生态类群的盖度朝着趋近天然河岸林的方向发生了显著变化：耐阴物种盖度整体上升，而喜光物种与外来物种盖度则有所下降。植被结构同样受到树木栽植的显著影响：乔木与灌木盖度上升，而单子叶植物（monocot）盖度下降。
5. 树木栽植通过诱导由光照有效性介导的物种更替——这一过程契合植物演替的阈值动态特征——有效实现了河岸带草本森林群落的恢复。在栽植树木的河岸带中，促进并监测冠层闭合，将有助于提升恢复效果与适应性管理方案的设计质量。本研究采用的创新性统计方法，旨在识别演替模式及其对应的理论模型，该方法可推广应用于全球范围内各类正在开展生态恢复的生态系统，以弥合科学研究与管理实践之间的鸿沟。
2016年3月14日