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Reservoir shorelines of regulated rivers, created by over 2.8 million dams worldwide, have experienced substantial biodiversity loss, particularly in plant communities. While actively introducing local riparian plants is a common restoration strategy, existing approaches often lack applicability and transferability across river basins. To address this, we propose a guild-based restoration framework that classifies plant species used for restoration into guilds based on shared functional traits and adaptive strategies. This approach allows for evaluating restoration outcomes across guilds along environmental gradients, optimizing restoration design.

We tested this framework along the shorelines of the Three Gorges Reservoir (TGR), characterized by steep environmental gradients. Plant guilds were identified based on shared functional traits, focusing on hydrological and geomorphological associations. The effectiveness of guild introductions was assessed across gradients of submergence intensity, topography and substrate properties by comparing outcomes to those of spontaneous colonization.

Results showed that under intermediate and high submergence intensity, active plant introduction and spontaneous colonization yielded similar restoration outcomes, with short-clonal flood-tolerant herbs naturally dominating. At low submergence intensity, the introduction of flood-tolerant woody plants increased functional diversity, whereas tall-clonal flood-tolerant herbs reduced diversity due to competitive exclusion. Actively introduced plants did not suppress invasive species. Unexpectedly, under intermediate submergence intensity, the introduction was associated with increased invasive plant presence.

Synthesis and applications: Our study validates the guild-based framework as an effective approach for shoreline vegetation restoration in regulated rivers. We show that guild identity and submergence intensity jointly shape restoration outcomes, offering insights for optimizing active plant introduction strategies in the TGR and similar reservoirs in the upper Yangtze River. Furthermore, this framework enhances the transferability of restoration practices by offering a functionally driven approach to species selection across river basins.

Over two-thirds of global rivers are subjected to flow regulation. Although it is widely recognized that flow regulation can adversely affect riparian vegetation—a critical component of river ecosystems—the specific roles of various drivers remain poorly understood. To address this gap, we conducted a broad-scale meta-analysis, aiming to elucidate how different factors mediate the adverse impacts of flow regulation on riparian vegetation. This meta-analysis encompassed 59 papers, spanning 278 dams constructed on 146 rivers. We extracted data on four key indices of riparian vegetation: species richness and abundance of all riparian species, and those indices exclusively for non-native species. Indices were compared between regulated and free-flowing or pre-damming rivers to quantify the impact of flow regulation. Our meta-analysis revealed a moderate but significant reduction in the richness and abundance of all riparian species under flow regulation, coupled with a strong increase in the abundance of non-native species. Riparian vegetation in arid and continental climate regions experienced stronger negative impacts than those in tropical and temperate climates. Furthermore, the adverse effects on riparian vegetation were more pronounced downstream of dams than upstream. Considering climate region, study identity, and relative position to the dam as random variables, it became evident that years since flow regulation emerged as the most important factor influencing species richness. Over time, richness gradually recovered from initially low levels. However, this recovery was slowed by increasing flow regulation intensity (percentage of annual runoff stored). Additionally, the impact was more evident in larger rivers. To support regulated river management, we recommend prioritizing the protection of riparian vegetation in arid and continental climates, with emphasis on areas downstream of dams, limiting flow regulation intensity, particularly in larger rivers, and monitoring non-native species to prevent disproportionate spread.

Aim: In riparian zones along rivers, plant demography is shaped by hydrologic disturbances, the dendritic structure of the river networks, and asymmetric gene flow due to the prevalence of unidirectional dispersal by hydrochory. Downstream-biased dispersal may lead to the accumulation of genetic diversity in populations situated lower within the catchment area—a phenomenon referred to as ‘downstream increase in intraspecific genetic diversity’ (DIGD). Our study aimed to test if the presence of this pattern in riparian plants depends on the species traits, sampling design and ecosystem integrity.

Location: Riparian zones along rivers worldwide.

Time Period: 1978–2023.

Major Taxa Studied: Vascular plants.

Methods: We conducted meta-analysis of population genetic studies on riparian plants to identify the factors linked to the occurrence of the DIGD pattern. We modelled the correlation between position along rivers and population genetic diversity using a dataset consisting of variables extracted from the studies, supplemented by data from plant trait databases.

Results: We found no evidence for a general trend in plant genetic diversity along rivers, but species traits and environmental factors partially explained the patterns. A downstream increase in genetic diversity was more likely to be found in species capable of hydrochoric dispersal and along the unmodified rivers which maintain habitat continuity.

Main Conclusions: Our study highlights that different patterns of genetic diversity can be linked to species traits or different levels of habitat fragmentation. Population genetic studies of riparian plants have frequently investigated patterns of genetic diversity in remnant populations in degraded riparian habitats. Although such investigations are important, more population studies of common plants in well-preserved riparian zones are needed, as these can help understanding the general mechanisms that control natural population dynamics of plant species.

Priority effects, the effects of early-arriving species on late-arriving species, are caused by niche preemption and/or niche modification. The strength of priority effects can be determined by the extent of niche preemption and/or modification by the early-arriving species; however, the strength of priority effects may also be influenced by the late-arriving species, as some species may be better adapted to deal with niche preemption and/or modification. Therefore, some combinations of species will likely lead to stronger priority effects than others. We tested priority effects for all pairwise combinations of 15 plant species, including grasses, legumes, and nonleguminous forbs, by comparing simultaneous and sequential arrival orders in a 10-week-long, controlled, pot experiment. We did this by using the competitive effect and response framework, quantifying the ability to suppress a neighbor as the competitive effect and the ability to tolerate a neighbor as the competitive response. We found that when arriving simultaneously, species that caused strong competitive effects also had weaker competitive responses. When arriving sequentially, species that caused strong priority effects when arriving early also had weaker responses to priority effects when arriving late. Among plant functional groups, legumes had the weakest response to priority effects. We also measured plant functional traits related to the plant economic spectrum, which were combined into a principal components analysis (PCA) where the first axis represented a conservative-to-acquisitive trait gradient. Using the PCA species scores, we showed that both the traits of the focal and the neighboring species determined the outcome of competition. Trait dissimilarities between the focal and neighboring species were more important when species arrived sequentially than when species arrived simultaneously. Specifically, priority effects only became weaker when the late-arriving species was more acquisitive than the early-arriving species. Together, our findings show that traits and specifically the interaction of traits between species are more important in determining competition outcomes when species arrive sequentially (i.e., with priority effects present) than when arriving simultaneously.

Key message: Seed germination responses to variation in temperature and light differed among six dry forest species, results that will inform ecological restoration and climate change adaptation projects.

Abstract: In dry forests, where opportunities for plant establishment occur in a narrow window of opportunity, seeds must respond to cues to germinate when conditions for growth are suitable. Knowledge of the strategies and adaptations of seeds to the seasonal dry-forest ecosystems, being under constant threat, is needed to guide restoration and management actions in the face of climate change. We investigated the effects of scarification, temperature and light in germination percentage, germination time and synchrony of six woody Fabaceae species. The species have ecological potential for restoration and are of cultural or economic importance for the local people in the Tehuacán-Cuicatlán Valley, Mexico. We carried out a multifactorial germination experiment with five temperatures, two light regimes and two scarification conditions for Mimosa luisana, M. polyantha, M. adenantheroides, M. lactiflua, Acaciella angustissima and Vachellia constricta. All germinated in a wide range of temperatures (10–40 °C), and mechanical scarification highly increased the germination percentage. Higher temperature increased and speeded up germination in dark conditions for most of the species, but they exist heterogeneous responses in their germination synchrony. Studied species had high germination percentages in warm temperatures, but their recruitment in nature might be negatively affected by warmer and drier conditions, and by the loss of shade and seed dispersers due to deforestation and changes in land use. It is crucial to study not just germination percentage and time but also other aspects of the germination process such as the germination synchrony, since it might reveal useful information for management actions.

Hydropower is central to renewable electricity systems, but degrades ecosystems, calling for environmental flow schemes to enhance the ecological status of river systems. Environmental flow assessments need to account for climate change, since climate-driven changes in runoff affect both hydropower operation and riverine ecosystems. Here, we quantify expected changes in hydropower production and environmental benefits of introducing environmental flows in a large regulated river system in northern Sweden in a future climate. Compared with the hydrology of 1981–2010, runoff is projected to increase with climatic conditions projected for 2040, leading to a 2.2 % increase in hydropower production with present rules for turbine and reservoir operation. Implementing environmental flows will result in lower hydropower production losses in with the 2040 climate than at present: Introducing restrictions against zero flow events, discharge to technical fishways and bypassed reaches throughout the year (with seasonal flow variation), as well as having more natural water-level variation in all run-of-river impoundments, would reduce annual hydropower production with 3.5 % with present conditions, and by 3.3 % in 2040. At the same time, the net effect of higher runoff and introducing environmental flows means that the annual hydropower production in the 2040 climate would be only 0.8 % lower compared to 1981–2010. In all scenarios, reservoir filling degree in 2040 was projected to increase compared to scenarios for 1981–2010, and flow requirements were met for both environmental flows and hydropower production over an 83-year scenario-based time series. This study demonstrates the feasibility of introducing environmental flow actions in Sweden, and other regions where increases in runoff are projected, with sustained hydropower production, having large benefits for riverine biodiversity and enhancing resilience of riverine ecosystems to climate change. For this to be successful, collaboration among stakeholders in riverine management is needed.

The greenery of floodplain meadows in arid regions, such as Mongolia, is influenced by climate, hydrology, and land use. In this study, we analyzed the NDVI (Normalized Difference Vegetation Index) of two floodplain meadows located along the South Tamir and Tamir Rivers using LANDSAT images. Our goal was to observe NDVI spatial changes, variations, and mean values in mid-August every six years from 1991 to 2015 and to identify the factors driving these differences. To achieve this, we conducted variance analysis to identify changes in NDVI and implemented Principal Component Analysis to determine the influence of hydro-meteorological factors and grazing intensity. Our findings indicate a significant decrease in greenness, as measured by pixel-scale NDVI, during the late summer period. This decrease was consistently observed, except for a series of harsh winters that followed relatively dry summers, resulting in a disastrous event called dzud, which led to the death of livestock. The decrease in NDVI was amplified by lower precipitation in June, higher temperatures and wind speed in July, and increased precipitation in August, along with a higher frequency of days with convective rain. Our findings have important implications for managing grazing in Mongolia’s grasslands, promoting sustainable land use, and mitigating sandstorms. The variance and average values of NDVI at the pixel level can serve as reliable markers of sustainable pasture management in areas where other vegetation measures are limited.

The globalization in plant material trading has caused the emergence of invasive pests in many ecosystems, such as the alder pathogen Phytophthora ×alni in European riparian forests. Due to the ecological importance of alder to the functioning of rivers and the increasing incidence of P. ×alni-induced alder decline, effective and accessible decision tools are required to help managers and stakeholders control the disease. This study proposes a Bayesian belief network methodology to integrate diverse information on the factors affecting the survival and infection ability of P. ×alni in riparian habitats to help predict and manage disease incidence. The resulting Alder Decline Network (ADnet) management tool integrates information about alder decline from scientific literature, expert knowledge and empirical data. Expert knowledge was gathered through elicitation techniques that included 19 experts from 12 institutions and 8 countries. An original dataset was created covering 1189 European locations, from which P. ×alni occurrence was modeled based on bioclimatic variables. ADnet uncertainty was evaluated through its sensitivity to changes in states and three scenario analyses. The ADnet tool indicated that mild temperatures and high precipitation are key factors favoring pathogen survival. Flood timing, water velocity, and soil type have the strongest influence on disease incidence. ADnet can support ecosystem management decisions and knowledge transfer to address P. ×alni-induced alder decline at local or regional levels across Europe. Management actions such as avoiding the planting of potentially infected trees or removing man-made structures that increase the flooding period in disease-affected sites could decrease the incidence of alder disease in riparian forests and limit its spread. The coverage of the ADnet tool can be expanded by updating data on the pathogen's occurrence, particularly from its distributional limits. Research on the role of genetic variability in alder susceptibility and pathogen virulence may also help improve future ADnet versions.

Restaurering av Juktån är ett samverkansprojekt som har drivits på frivillig basis av den ideella föreningen Samverkan Umeälven (www.umealven.se) tillsammans med Umeälvensvattenregleringsföretag, Vattenfall och Umeå Universitet. Juktån är en 60 kilometer lång torrfåra med minimitappning om 12% av det oreglerade flödet (MQ) vid reglerings. I produktionssystemet har den en funktion som spillfåra. Projektets ambition och mål var att Juktån skulle återfå ekologisk funktion med fungerande reproduktion av öring och harr, mer naturlig och bredare strandvegetation och svämskogar, mer naturlig artsammansättning av makrofyter samt en sedimentationsprocess med mindre deponering av silt och finsediment. Juktånprojektet har kartlagt och genomfört biotopåtgärder samt restaurerat huvudfåran sträckan nedströms Tjangarn och sidofåran Lickotgrenen under 2019 och 2020. Totalt har dryga 35 kilometer torrfåra restaurerats, hundratals trösklar och flottledsobjekt har rivits ut. Juktåprojektet ansökte hos Mark och Miljö Domstolen (MMD) om att ändra den relativt statiska minimitappningen till en säsongsanpassad minimitappning, vilket beviljades i augusti 2020 och infördes våren 2021. Metoderna för att genomföra restaureringen bygger på restaureringsekologi och sambandet till naturlig flödesregim. Juktåns restaurering har inneburit en komplex restaurering från utrivning av grunddammar och trösklar, restaurering av den fysiska miljön för att gynna öring, harr, makrofyter, strandvegetation och processer. Vi har utgått från ekologi i oreglerade vattendrag och utvecklat metoder speciellt anpassat för torrfåror med minimitappning. Preliminära resultat visar på en ökad reproduktion av öring, mer naturliga processer kopplat till flöde, sedimentation, vattenhastighet och som har påverkat både makrofyter samt strandvegetation.