1 INTRODUCTION

A forest herbaceous layer plays a critical role in mediating carbon sequestration, energy flow and efficient nutrient recycling (Muller, 2014; Neufeld & Young, 2014; Welch et al., 2007). Although it represents only less than 1% of the plant biomass of temperate forests, it includes more than 90% of a total plant species richness (Gilliam, 2007). The level of light received by herbaceous species in the forest understorey is seasonally controlled by the chronology of leaf initiation of canopy trees. In temperate deciduous forests, this is a crucial factor for establishing adaptive differentiation of plant phenological cohorts, starting with shade-intolerant species in the spring and progressing to shade-tolerant species in the summer (Rathcke & Lacey, 1985). Spring flowering species must start their life cycle before leaf development of canopy trees, because their photosynthetic output is not sufficient under reduced photosynthetic radiation (Kudo et al., 2008). In contrast, summer species, that is species growing and blooming later in the shade of the canopy, have a more efficient photosynthesis at lower light levels (Sparling, 1967).

The temporal environmental changes may cause specific species to increase or decrease their presence depending on the phenological cohort (hereafter referred to as phenological guilds, or PhGs). We define a PhG as a group of species that co-occur over time in a given phenophase. Due to existing pre-adaptations, with respect to the use of seasonally available resources, shifts in seasonally available resources can reshape patterns of PhG co-occurrence within the plant community. This may affect seasonal peaks in diversity and overall abundance in the forest understorey by promoting performance or excluding specific PhGs through environmental filtering. Changes in seasonal environmental filters can also narrow or lengthen the period during which rich and abundant herbaceous vegetation is present (hereafter referred to as seasonal evenness in diversity and abundance of PhGs; Menzel & Fabian, 1999; Oehri et al., 2017). Although these phenology-specific environmental effects remain poorly understood, they have a potentially strong impact on nutrient cycling and the performance of other trophic guilds in forest ecosystems (Beard et al., 2019; Rafferty & Ives, 2012).

There is some evidence that the abundance of spring species, that is species with significant biomass development and onset of flowering in the months before tree leafing, has increased in recent decades (Dierschke, 2013; Heinrichs & Schmidt, 2017). Spring species are particularly sensitive to an earlier onset of the growing season, and with a warmer climate in spring, their growth period may be extended (De Frenne et al., 2010). Increasing winter temperatures may promote their rhizome growth (Philipp & Petersen, 2007), alongside with increasing winter and spring precipitation may even promote their performance and population spread (Dierschke, 2013). These factors may contribute to the increased diversity and abundance of spring species. In contrast, stable (Bernhardt-Römermann et al., 2015; Chase et al., 2019; Dornelas et al., 2014; Vellend et al., 2013) or declining (Chudomelová et al., 2017; Hédl et al., 2010) diversity and abundance have been found in studies that include summer species. For temperate forest ecosystems, atmospheric pollution, increased shading following abandonment of traditional forestry practices and game pressure are the most commonly cited drivers of vegetation composition and diversity change (Bernhardt-Römermann et al., 2015; Chudomelová et al., 2017; Hédl et al., 2010; Keith et al., 2009; Staude et al., 2020). In addition, climate change, manifested by a reduction in summer rainfall followed by subsequent desiccation, is allowing some drought-tolerant species to survive at the expense of more water-demanding summer species (Feeley et al., 2020; Garssen et al., 2014).

The negative effects of climate change may not be as obvious, at least for the summer phenological cohort in forest ecosystems, as the canopy microclimate has been shown to mitigate the detrimental effects of the macroclimate (De Frenne et al., 2013; Zellweger et al., 2020). The microclimate in the forest is determined by the three-dimensional canopy structure, which promotes shading, air mixing and evaporative cooling (Atkinson, 2003), thus buffering against extreme heat and drought (De Frenne et al., 2019). However, today's temperate forests are suffering from more unpredictable weather, characterised by more extreme droughts and heavy rainfall (Anderegg et al., 2013; Gonzalez et al., 2010). This is accompanied by the spread of pathogens such as Phytophthora alni and Hymenoscyphus fraxineus, resulting in higher tree mortality of alder and ash (Bjelke et al., 2016; Grosdidier et al., 2020), which are among the dominant tree species in floodplain forests. This interaction of the aforementioned factors is still yet unknown in floodplain vegetation (Havrdová et al., 2023).

To enhance forest recovery, silvicultural management involving clearcutting and mechanical soil preparation with the application of herbicides prior to new tree planting is often used, which can have a negative effect on the diversity of spring and summer species (Newmaster et al., 2007; Šebesta et al., 2021). Increased drought and pathogens causing tree mortality and logging of woody biomass open forest canopies and accelerate thermophilisation—the onset of warm-adapted species (Stevens et al., 2015; Zellweger et al., 2020) that include competing tall species with higher biomass or dominance (De Frenne et al., 2015; Govaert et al., 2021). It follows that the effects of climate change on forest plant communities must interact strongly with the forest management practices applied in particular locations. Given the current global trend of natural forest opening due to repeated drought events and the spread of pathogens, the impact of clearcutting interventions on the forest understorey should be clearly assessed compared to no intervention.

In addition, recent eutrophication of forest soils may favour the growth of spring species more than summer species. In the past, European temperate deciduous forests have been overexploited by human practices such as tree coppicing, litter raking and grazing, all of which remove biomass, leading to severe soil nutrient limitation (Glatzel, 1991). However, the cessation of regular nutrient removal from forest ecosystems in the 20th century and the massive use of NPK fertilisers in the countryside led to a replenishment of nutrients. Specifically, floodplain forests located on the banks of large rivers were particularly affected by excessive nutrient inputs (Havrdová et al., 2023). Spring species appear to be quite nutrient demanding due to their rapid growth strategy and high photosynthetic rates that require high nitrogen and phosphorus inputs (Anderson & Eickmeier, 2000; Lapointe & Lerat, 2006; Merryweather & Fitter, 1995). The presence of underground storage organs such as bulbs and rhizomes allows nutrients to be taken up and remobilised from the leaves throughout the year, which can also be essential for spring growth (Fichtner et al., 2018; Rothstein & Zak, 2001; Stolle, 2004). An alleviation of soil nutrient limitation may have increased their abundance and diversity in recent decades. The spring species relocate and store nutrients in below-ground organs before summer species become active (Anderson & Eickmeier, 2000; Lapointe & Lerat, 2006; Nault & Gagnon, 1988). They may therefore have an advantage over summer species in capturing nutrients released by leaf decay and accumulated by early spring flooding (Anderson & Eickmeier, 2000; Muller & Bormann, 1976; Tessier & Raynal, 2003).

In this study, we test the effects of temporal changes in climate, hydrology, soil conditions and canopy structure on PhGs of floodplain forests in terms of herbaceous species richness and abundance under non-intervention management compared to intervention. Floodplain forests are a suitable model system for our study because they contain up to 10% of the spring species of total species richness in their herbaceous layer (Douda et al., 2016; Vymazalová et al., 2016). We monitored changes in vegetation at 117 selected sites established in the 1950s and 1960s in several river basins. We then evaluated the effects of the above environmental factors both without and with clearcutting management. We did this by monitoring the original sites, without intervention, with nearby new plots that had been recently logged. This approach makes it possible to determine the interaction between the effects of environmental changes and the management interventions applied in the forests. We hypothesised that spring and summer PhGs will respond differently to environmental changes represented by forest management and succession, climatic and hydrological changes over about 60 years in floodplain forests. This is due to the lower dependence of spring PhGs on changes in forest understorey light conditions and the potential effects and interactions with other environmental factors such as changes in climate, nutrients and hydrological regime.

中文翻译：

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森林物候协会对复杂洪泛区变化的对比响应

 1 简介

森林草本层在调节碳固存、能量流动和有效养分循环方面发挥着关键作用（Muller，2014；Neufeld & Young，2014；Welch 等，2007）。虽然它只占温带森林植物生物量的不到 1%，但它包含了植物物种总丰富度的 90% 以上（Gilliam，2007）。森林下层草本物种接收到的光水平受冠层树木叶子萌生时间的季节性控制。在温带落叶林中，这是建立植物物候群适应性分化的关键因素，从春季不耐荫的物种开始，到夏季发展到耐荫的物种（Rathcke＆Lacey，1985）。春季开花的物种必须在冠层树木的叶子发育之前开始其生命周期，因为在光合辐射减少的情况下，它们的光合输出不足（Kudo et al., 2008）。相比之下，夏季物种，即在树冠阴影下生长和开花较晚的物种，在较低光照水平下具有更有效的光合作用（Sparling，1967）。

时间环境变化可能会导致特定物种的存在增加或减少，具体取决于物候群（以下称为物候群或 PhG）。我们将 PhG 定义为在给定物候期随时间共同出现的一组物种。由于现有的预适应，关于季节性可用资源的使用，季节性可用资源的变化可以重塑植物群落内 PhG 共现的模式。这可能会通过环境过滤提高性能或排除特定的 PhG，从而影响森林下层多样性和总体丰度的季节性峰值。季节性环境过滤器的变化也会缩短或延长草本植被丰富的时期（以下称为 PhG 多样性和丰度的季节性均匀性；Menzel & Fabian，1999；Oehri 等人，2017）。尽管人们对这些物候特定的环境影响仍知之甚少，但它们对森林生态系统中的养分循环和其他营养群的表现具有潜在的强烈影响（Beard 等，2019；Rafferty & Ives，2012）。

有一些证据表明，近几十年来，春季物种（即生物量显着发展并在树木长叶前几个月开始开花的物种）的丰富度有所增加（Dierschke，2013；Heinrichs & Schmidt，2017）。春季物种对生长季节提前开始特别敏感，随着春季气候变暖，它们的生长期可能会延长（De Frenne 等，2010）。冬季气温升高可能会促进其根茎生长（Philipp＆Petersen，2007），而冬季和春季降水量的增加甚至可能会促进其表现和种群扩散（Dierschke，2013）。这些因素可能有助于增加春季物种的多样性和丰富度。相反，稳定（Bernhardt-Römermann 等人，2015；Chase 等人，2019；Dornelas 等人，2014；Vellend 等人，2013）或下降（Chudomelová 等人，2017；Hédl 等人， 2010）在包括夏季物种在内的研究中发现了多样性和丰富性。对于温带森林生态系统，大气污染、放弃传统林业做法后遮荫增加以及狩猎压力是最常被提及的植被组成和多样性变化的驱动因素（Bernhardt-Römermann 等，2015；Chudomelová 等，2017；Hédl 等）等人，2010；基思等人，2009；斯塔德等人，2020）。此外，气候变化（表现为夏季降雨量减少和随后的干燥）使一些耐旱物种能够生存，但牺牲了更多需水的夏季物种（Feeley 等人，2020 年；Garssen 等人， 2014）。

气候变化的负面影响可能并不那么明显，至少对于森林生态系统的夏季物候群而言，因为冠层小气候已被证明可以减轻大气候的有害影响（De Frenne 等，2013；Zellweger 等） .，2020）。森林中的小气候是由三维树冠结构决定的，它促进遮阳、空气混合和蒸发冷却（Atkinson，2003），从而缓冲极端炎热和干旱（De Frenne等，2019）。然而，今天的温带森林正遭受更加难以预测的天气，其特点是更加极端的干旱和暴雨（Anderegg等，2013；Gonzalez等，2010）。伴随着赤霉疫霉和白蜡树等病原体的传播，导致桤木和白蜡树死亡率较高（Bjelke等人，2016年；Grosdidier等人，2020年），这些树种是洪泛区的优势树种森林。上述因素在洪泛区植被中的相互作用尚不清楚（Havrdová et al., 2023）。

为了加强森林恢复，经常采用包括砍伐和机械整地以及在种植新树之前使用除草剂的造林管理，这可能对春季和夏季物种的多样性产生负面影响（Newmaster 等人，2007 年；Šebesta）等人，2021）。干旱和病原体的增加导致树木死亡和木质生物量的砍伐，开放森林冠层并加速嗜热作用——适应温暖的物种的出现（Stevens等人，2015年；Zellweger等人，2020年），其中包括具有更高生物量或更高的竞争性高树种主导地位（De Frenne 等人，2015；Govaert 等人，2021）。由此可见，气候变化对森林植物群落的影响必须与特定地点采用的森林管理实践密切相关。鉴于当前全球因干旱事件反复和病原体传播而导致天然林开放的趋势，应明确评估与不采取干预措施相比，砍伐干预措施对森林下层植被的影响。

此外，最近森林土壤的富营养化可能比夏季物种更有利于春季物种的生长。过去，欧洲温带落叶林被人类过度开发，如树木修剪、垃圾耙和放牧，所有这些都消除了生物量，导致严重的土壤养分限制（Glatzel，1991）。然而，20世纪森林生态系统养分去除的停止以及农村大量使用氮磷钾肥料导致了养分的补充。具体而言，位于大河沿岸的洪泛区森林尤其受到过度养分输入的影响（Havrdová et al., 2023）。春季物种似乎对养分的需求量很大，因为它们的快速生长策略和高光合速率需要大量的氮和磷输入（Anderson & Eickmeier, 2000; Lapointe & Lerat, 2006; Merryweather & Fitter, 1995）。球茎和根茎等地下储存器官的存在可以全年从叶子中吸收和重新调动养分，这对于春季生长也至关重要（Fichtner et al., 2018; Rothstein & Zak, 2001; Stolle, 2004）。近几十年来，土壤养分限制的缓解可能增加了它们的丰富度和多样性。在夏季物种开始活跃之前，春季物种会在地下器官中重新定位和储存养分（Anderson & Eickmeier, 2000；Lapointe & Lerat, 2006；Nault & Gagnon, 1988）。因此，它们在捕获叶子腐烂释放的养分和早春洪水积累的养分方面可能比夏季物种具有优势（Anderson & Eickmeier, 2000; Muller & Bormann, 1976; Tessier & Raynal, 2003）。

在本研究中，我们测试了气候、水文、土壤条件和冠层结构的时间变化对漫滩森林 PhG 的影响，包括非干预管理与干预下草本物种丰富度和丰度的影响。洪泛区森林是我们研究的合适模型系统，因为它们的草本层含有高达物种总丰富度的 10% 的春季物种（Douda 等，2016；Vymazalová 等，2016）。我们监测了 20 世纪 50 年代和 1960 年代几个流域内 117 个选定地点的植被变化。然后我们评估了没有和有皆伐管理时上述环境因素的影响。我们通过在没有干预的情况下监控原始地点以及最近记录的附近新地块来做到这一点。这种方法可以确定环境变化的影响与森林中应用的管理干预措施之间的相互作用。我们假设春季和夏季的 PhG 对泛滥平原森林约 60 年来以森林管理和演替、气候和水文变化为代表的环境变化会有不同的反应。这是由于春季 PhG 对森林林下光照条件变化以及与其他环境因素（如气候、养分和水文状况变化）的潜在影响和相互作用的依赖性较低。