Floodplain Forests Research Articles

Hydrological and climate intensification induces conservative behavior in the Hydrochorea corymbosa xylem production in a Central Amazon floodplain forest

IntroductionTrees from flooded forests have to adjust their xylem hydraulic structure to face the annual flooding and the climatic conditions of the atmosphere. Usually, this adjustment of anatomical tissues in the tropics is driven by drought events inducing conservative behavior and can be recorded annually in tree rings. However, how the flood pulse and the climatic conditions influence the xylem hydraulic structure in floodplain trees is unknown.MethodsTo fill this gap, we explore if flooded periods and monthly climate variation affect the annual tree growth and xylem anatomy structure for the tree species Hydrochorea corymbosa (Fabaceae) from the várzea flooded forest in the Central Amazon. We developed a 41-year ring width chronology (1971–2018) and a 30-year time series of xylem anatomy parameters (1988–2018) as mean hydraulic vessel diameter (Dh), vessel frequency (VF), and parenchyma quantity (PQ). We correlated the series with monthly hydrological and climatic data.ResultsThe hydrological regime did not correlate with annual tree growth in that species as we previously expected but showed correlations with the xylem anatomical structure. High flood levels during the end of the flooding period induced conservative patterns of the anatomical structure, with a negative correlation with Dh (rho June = −0.40, p < 0.05) and a positive correlation with the PQ (rho September/October = 0.42, p < 0.05). These responses show that these trees are responding to flooding similar to the tree responses to drought. Regarding the climatic variation, the annual tree growth showed a negative correlation with the vapor pressure deficit (VPD), after the second half of the flooded period with the strongest correlation happening during the non-flooded period (rho December = −0.66, p < 0. 01). These conservative patterns in tree behavior also happened when the maximum temperature negatively affected the vessel diameter (rho September = −0.42, p < 0.05).DiscussionIn that case, we recognized two different moments that the environment is inducing conservative patterns in the xylem structure of those trees: 1) increasing the flood levels and 2) the high evaporative demand during the non-flooded period. In this way, the intensification of the hydrological regime, as well as the strong drought conditions during the non-flooded periods, can be a risk for H. corymbosa in the Central Amazonian floodplains.

Inundation dynamics in seasonally dry floodplain forests in southeastern Brazil

AbstractFloodplains are one of the most threatened ecosystems. Even though the vegetation composition in floodplain forests is expected to reflect the variation in groundwater levels and flood duration and frequency, there is little field data on the inundation dynamics (e.g., the variability in flood duration and flood frequency), especially for the understudied seasonally dry tropics. This limits our understanding of these ecosystems and the mechanisms that cause the flooding. We, therefore, investigated six floodplain forests in the state of Minas Gerais in Brazil for 1.5 years (two wet seasons): Capivari, Jacaré, and Aiuruoca in the Rio Grande basin, and Jequitaí, Verde Grande, and Carinhanha in the São Francisco basin. These locations span a range of climates (humid subtropical to seasonal tropical) and biomes (Atlantic forest to Caatinga). At each location, we continuously measured water levels in five geomorphologically distinct eco‐units: marginal levee, lower terrace, higher terrace, lower plain, and higher plain, providing a unique hydrological dataset for these understudied regions. The levees and terraces were flooded for longer periods than the plains. Inundation of the terraces lasted around 40 days per year. The levees in the Rio Grande basin were flooded for shorter durations. In the São Francisco basin, the flooding of the levees lasted longer and the water level regime of the levees was more similar to that of the terraces. In the Rio Grande basin, flooding was most likely caused by rising groundwater levels (i.e., “flow pulse”) and flood pulses that caused overbank flooding. In the São Francisco basin, inundation was most likely caused by overbank flooding (i.e., “flood pulse”). These findings highlight the large variation in inundation dynamics across floodplain forests and are relevant to predict the impacts of changes in the flood regime due to climate change and other anthropogenic changes on floodplain forest functioning.

Additional data to the historical breeding of the Eurasian Woodcock in the Carpathian Basin

Abstract The Eurasian Woodcock is a regular breeder in the wooded areas of the Carpathian Basin. In the past, several literature reviews on the distribution and breeding biology of the species in the Carpathian Basin have been published, but these have ignored the annual reports on spring returns collected between 1894 and 1926 under the coordination of the Hungarian Ornithological Centre. These included 379 nesting records from the present area of Austria, Croatia, Hungary, Romania, Serbia, Slovakia, Slovenia, and Ukraine. The majority of the data came from the Carpathians, with a smaller number from forested areas in the lower mountains and hills. It was particularly rare in lowland areas, with most of the records coming from floodplain forests. The spatial distribution of the data is somewhat at odds with that described in recent summary works. From the Northern Carpathians and the Eastern Alps, however, these sources report fewer nestings, and most of the data come from Transylvania. The temporal distribution of the data is consistent with previously published results. In some cases nestings were found in late February and early March. The peak of nesting was in April, with only a small number of nestings reported in the second half of May. Breeding occurred significantly later in areas at higher altitudes. Nevertheless, it can be concluded that knowledge of the species’ nesting in the Carpathian Basin is still incomplete.

Effects of canopy gaps on microclimate, soil biological activity and their relationship in a European mixed floodplain forest

Forest canopy gaps can influence understorey microclimate and ecosystem functions such as decomposition. Gaps can arise from silviculture or tree mortality, increasingly influenced by climate change. However, to what degree canopy gaps affect the buffered microclimate in the understorey under macroclimatic changes is unclear. We, therefore, investigated the effect of forest gaps differing in structure and size (25 gaps: single tree gaps up to 0.67 ha cuttings) on microclimate and soil biological activity compared to closed forest in a European mixed floodplain forest. During the investigation period in the drought year 2022 between May and October, mean soil moisture and temperature as well as soil and air temperature fluctuations increased with increasing openness. In summer, the highest difference of monthly means between cuttings and closed forest in the topsoil was 3.98 ± 9.43 % volumetric moisture and 2.05 ± 0.89 °C temperature, and in the air at 30 cm height 0.61 ± 0.35 °C temperature. For buffering, both the over- and understorey tree layers appeared as relevant with a particularly strong influence of understorey density on soil temperature. Three experiments, investigating soil biological activity by quantifying decomposition rates of tea and wooden spatulas as well as mesofauna feeding activity with bait-lamina stripes, revealed no significant differences between gaps and closed forest. However, we found a positive significant effect of mean soil temperature on feeding activity throughout the season. Although soil moisture decreased during this period, it showed no counteracting effect on feeding activity. Generally, very few significant relationships were observed between microclimate and soil biological activity in single experiments. Despite the dry growing season, decomposition rates remained high, suggesting temperature had a stronger influence than soil moisture. We conclude that the microclimatic differences within the gap gradient of our experiment were not strong enough to affect soil biological activity considerably.

Critical linkages among floodplain hydrology, geomorphology and ecology along a lowland meandering river, Illinois, USA

AbstractThe ecology of forested floodplains is intricately linked to river hydrology through the frequency, magnitude, timing and duration of floodplain inundation. Spatial variability in inundation characteristics is influenced by the geomorphic template of a floodplain, both in terms of the topography of floodplain features and connectivity of these features to the main river channel. Spatial variability in inundation, in turn, has the potential to produce spatial variability in forest ecological characteristics. This study examines the influence of floodplain geomorphic features on spatial variability in inundation frequency as well as the relationship between these geomorphic features and the ecological characteristics of a floodplain forest. The frequencies of floods of different magnitudes are determined from flow‐duration analysis of over 100 years of discharge data for a lowland meandering river in Illinois, USA. Data on discharge, stage, and topography are then used to calibrate a two‐dimensional hydraulic model of flow across the floodplain at different levels of inundation. Integrating the frequency and inundation data yields mapping of average annual inundation frequency for different parts of the floodplain. Significant differences in inundation frequency correspond to three distinct floodplain geomorphic features: secondary channels (frequency = 12%), closed depressions (frequency = 4%) and the floodplain surface (frequency = 3%). Tree density is similar among the three types of geomorphic features, but tree species composition and canopy density differ significantly between secondary channels and the floodplain surface. The results provide insight into linkages among hydrology, geomorphology and tree characteristics of forested floodplains of lowland meandering rivers.

Ecosystem type affects how Amazonian tree species invest in stem and twig wood

Abstract Wood density (WD) is a key functional trait for its importance in tree performance and in biomass calculations of forests. Yet, the variation of WD among different woody tree parts, how this varies across ecosystems, and how this influences estimates of forest carbon stocks remains little understood, particularly for diverse tropical forests such as the Amazon. We assembled a dataset on stem and twig wood density from 119 tree species in three different Amazonian ecosystem types that differ considerably in soil nutrition and flooding: non‐flooded forest (Terra Firme), white‐water floodplain forest (Várzea) and black‐water floodplain forest (Igapó) to investigate (i) variation of stem and twig wood density across ecosystems, (ii) the relationships between stem and twig wood density and how these relationships vary across ecosystems. Wood density varied substantially across ecosystems. Várzea species showed lower mean WD for stems compared to Terra firme, while Igapó species showed higher WD for twigs compared to the other ecosystems. Twig and stem wood density were positively related (R2adj = 0.47) with similarly increasing rates across ecosystems, although average WD values differed between Terra firme and Igapó. For any given twig density, stem density tends to be lower in floodplain environments but higher in Terra firme, a habitat‐specific pattern of wood density variation within trees that may emerge from differences in the function of stem and twig wood for growth and survival in ecologically differentiated environments. Our results show how ecosystem has strong impacts on how trees allocate resources to different woody tissues, suggesting contrasting ecological strategies linked to ecosystem constraints. Our results suggest that greater consideration of the variation of WD within trees and how these changes across ecosystems might lead to more accurate estimates of above‐ground biomass in Amazonia. Read the free Plain Language Summary for this article on the Journal blog.

USE OF MACHINE LEARNING, FIXED AND MIXED MODELS FOR VOLUME ESTIMATION IN FLOODPLAIN FOREST IN THE AMAZON ESTUARY

The present study aimed to evaluate the performance of artificial neural networks (ANNs), support vector machines (SVM), and fixed and mixed models to estimate the volume of individual trees in an Amazonian estuary floodplain forest. The forest inventory was conducted in an area located in the district of Itatupã - Gurupá, Pará, Brazil. The Schumacher and Hall linear model was used in its fixed and mixed form to estimate the volume. A total of 240 ANNs and 32 SVM configurations were trained, with 4 variations of the input variables: diameter at breast height (D), commercial height (hm), diameter classes (CCD), commercial height classes (CChm),) and species (SP), with the volume (V) being the output variable. The ANNs were trained in the Neuro 4.0.6 software program, and the analyses of the fixed and mixed regression models and SVM were performed in the R software program. The AIC (Akaike’s Information Criterion) and BIC (Bayesian Information Criterion) information criteria were used for the regression models, while the following were used for comparisons of all models: correlation coefficient (rYŶ), bias, root mean squared error (RMSE), and residual distribution analysis. The best statistical metrics were obtained by the ANN of the RPROP- algorithm with D+hm+CCD+CChm inputs, with eight neurons in the hidden layer and hyperbolic tangent activation function, with 0.9827 of rYŶ RMSE of 0.2439, bias of 0.0080 and residual graphic distribution tending to homogeneity.

Sustainable energy production and resilience towards floods by using hydro and solar photovoltaic energy

Unexpected and intense floods have become more frequent recently; this is related to extreme weather events that are difficult to predict accurately. This necessitates new solutions to decrease the risk of flooding urban and rural areas. Moreover, such solutions should have negligible impact on the environment. There are several concepts, tools, and technical measures for preventing floods, one of which is the ‘monkey cheek’ concept for flood protection, used in Thailand for protection from river and sea floods. Monkeys collect food in their mouths and eat subsequently in stages. In a similar manner, excess water from floods could be collected and stored in reservoirs, sags, canals, floodplain forests, and unused space. Collected water could then be used for irrigation. In most cases, collected water must be pumped to distant or higher locations compared to the location where the water was collected. This requires electric energy for the pumps. This paper analyses a case study for the presented concept for the town of Ludbreg in Croatia, currently undergoing real-site measurements and calculations. A rescaled adjusted partial sums method is applied for the analysis. It has been shown that the energy potential of the local, small river Bednja in the observed location could be approximated using the “monkey cheek’’ concept. Within this, using the produced electricity from small hydropower plants and solar photovoltaic systems has been proven promising. The solution avoids building dams for flood protection, satisfying the environmental aspects.

The importance of tree species identity and trait-based winter foraging ecology of bark-foraging bird species in a large Central European floodplain forest

Beyond preferences for particular species of tree, bark-foraging birds are associated with various tree characteristics such as decay stage, trunk diameter, or bark roughness. Our objectives were to study the winter foraging ecology of different bark-foraging bird species in the highly diverse floodplain forests of Donau-Auen National Park (Austria) by examining the importance of tree species and characteristics. We used 'first-foraging' observations on the great spotted woodpecker (Dendrocopos major), middle spotted woodpecker (Leiopicus medius), Eurasian nuthatch (Sitta europaea), treecreepers (Certhia spp.), great tit (Parus major), Eurasian blue tit (Cyanistes caeruleus), and marsh tit (Poecile palustris). We examined bird-tree relationships with a bird-plant network approach, where we compared traits of trees and their preferences among avian species. The five most important tree species relative to distance-weighted fragmentation were European white elm (Ulmus laevis), pedunculate oak (Quercus robur), common ash (Fraxinus excelsior), and white and black poplar (Populus alba, P. nigra). Avian taxa differed only in the use of tree condition, where woodpeckers used decayed and dead trees more than tits. Most species preferred trees of larger trunk diameter with rougher bark. We suspect that changes in these highly diverse floodplain forest stands will eventually lead to changes in bark-foraging bird assemblages. For the protection of such highly diverse floodplain forests, conservation-based water management practices will be crucial to maintaining a sufficient groundwater table. Our findings also suggest that forest management practices should focus on more diverse commercial forest stands with a critical amount of secondary tree species, a variety of size classes, varying tree conditions, and species with different bark roughness classes.

Contrasting responses of forest phenological guilds to complex floodplain change

Abstract Understanding the seasonal dynamics of the forest herb layer and the factors that influence it is essential for predicting how the forest ecosystem, including mutualistic interactions, will respond to global change. However, to date, no research has investigated how understorey phenological guilds respond to major environmental threats and forest interventions. We showed the marked changes in the phenological structure of floodplain forest plant communities over half a century at a multi‐regional scale in Central Europe. Unlike previous studies focusing on individual species' responses to climate change, we examined shifts in species richness, frequency and abundance between phenological guilds within the plant community. We examined the effects of temporal variation in climate, hydrology, soil conditions and canopy structure, and assessed the effects of non‐intervention and intervention management on phenological guild responses. Our results show a significant loss of local species richness and a decline in species frequency in the forest understorey vegetation, associated with species exhibiting summer phenology. In contrast, an increase in abundance and richness of spring flowering species was observed, attributed to high nutrient loads and reduced flooding, respectively. The abundance of spring species increased only in stands where canopy cover increased over time, probably due to the suppression of summer flowering species, allowing spring flowering species to spread on open, bare ground. The community experienced a shift in maximum flowering plant richness from June to May. Despite management interventions such as clearcutting and tree planting, our data show similar temporal trajectories in intervention and non‐intervention forests, indicating that changes in phenological structure are largely independent of recent management activities. Synthesis. We propose that a complex interplay of environmental factors, rather than climate change alone, is shaping shifts towards earlier phenological guilds in floodplain forests. This study highlights the importance of considering a comprehensive view of phenological guild dynamics and the impact of environmental factors on forest plant community structure in the face of global change.

Influence of Floodplain Forest Structure on Overbank Sediment and Phosphorus Deposition in an Agriculturally Dominated Watershed in Iowa, USA

Influence of Floodplain Forest Structure on Overbank Sediment and Phosphorus Deposition in an Agriculturally Dominated Watershed in Iowa, USA

Vipers in the state of Acre, western Brazilian Amazon: a review

Snakes of the family Viperidae are distributed in many different ecosystems, generally being the most abundant species in snake surveys and studies on snake assemblages in Brazil. These species are medically important as they can cause snakebites and are responsible for approximately 99% of envenomings in humans in Brazil. Considering the ecological importance of snakes in terrestrial ecosystems, mainly as important predators in food webs, and in public health due to the risks of snakebites, here we review the information available in the literature about vipers in the state of Acre, western Brazilian Amazon. Six species of vipers were already recorded for Acre, with Bothrops atrox being the most abundant, present in various types of habitats and being the main species involved in snakebites. Bothrops bilineatus is the most common snake found in a floodplain forest in the protected area Japiim Pentecoste, a factor probably associated with prey availability. The other four species of vipers (Bothrocophias hyoprora, Bothrops brazili, B. taeniatus and Lachesis muta) are less frequent and associated with unflooded forests. Although we found in the literature several studies involving vipers in Acre, there is a need for more studies on these snakes in the region, addressing their ecology, ethno-herpetological questions and snakebites, including research on their ecology and behavior in the field, genetic variation and differentiation among populations and species, and biochemical composition of venoms.

Occurrence of the golden jackal (Mammalia, Caninae, Canis aureus Linnaeus, 1758) in the Saratov region, expansion of its range in the region against the background of its expansion in Europe and Russia

The history of golden jackal dispersal in Russia and adjacent countries, as well as in southern, central, eastern and northern Europe, is considered. Data confirming the demographic explosion of this species on the European continent territory are given. Materials on the dispersal of golden jackals in the European Russia are considered in more detail. The main emphasis is made on the study of the process of golden jackal penetration into the territory of Saratov region, from its first sightings in the Saratov Volga region in the late 1980s – early 1990s in the Dyakovsky (Saltovsky) forest to dispersal in adjacent territories. The penetration of the species into the Saratov Right Bank and its further dispersal throughout the region on both banks of the Volga river is described. It is shown that the areas of the modern jackal range are approximately the same both in the Right Volga Bank and Left Volga Bank of the Saratov region. However, the number of jackal is currently higher in the areas of the region located on the right bank of the Volga river. Probably, this is explained by more favorable conditions for the golden jackal habitat in this part of the region, associated with its higher afforestation. Gold en jackals breed in the southern districts of the Saratov region, located on both banks of the Volga river. However, golden jackals are also found in the northernmost parts of the region, and most likely there, as well as in the south of the region, its stable reproductively active groups appear. In the Saratov Volga region, in spite of its very low forest cover, the golden jackal is recorded both in the south-eastern and north-eastern areas, but its numbers are high enough only in the vicinity of the forest on the Prieruslan sands and in areas along the Volga river, where there are areas of floodplain and bairn forests. In the Right Volga Bank of the Saratov region the golden jackal is most abundant in upland oak forests of the Privolzhskaya Upland, occurs in floodplain forests of the Medveditsa river and in the Medveditsa–Khopyor interfluve.

Structure and vulnerability of the ichthyochory network in wetland forests of Central Amazonia

AbstractThe interaction between fish and plants is vital for the dynamics of ecosystems since it influences plant distribution and regeneration patterns. In the floodable areas of the Amazon, these interactions are mainly structured by the flood pulse, which enables seed dispersal via water (hydrochory) and fish (ichthyochory), and which contributes to the formation of complex mutualistic networks. Our study evaluated the structure (modularity, nestedness, specialisation, and robustness) of the network of dispersal of seeds by frugivorous fish in a floodplain forest in Central Amazonia. We expect the binary network to have a nested pattern, while the weighted network is expected to have a non‐nested structure; that generalist frugivorous species should constitute the core of the network, while specialist frugivorous species will be peripheral; that the size of fish and seeds is related to specialisation, and that the robustness of the network weakens as generalist frugivorous fish are removed. We found 5012 intact seeds from 49 plant species in the digestive tracts of 11 species of frugivorous fish. A nested and modular pattern was found for the binary and weighted networks, albeit with a low degree of nestedness. Our network proved relatively robust when the frugivores were removed, whereby all the fish and plant species became peripheral. No relationship was found between the size of the fish and the seeds and the degree of specialisation. Considering the anthropogenic impacts that can cause modifications in seed dispersal networks, knowing the structure of mutualistic networks is fundamental in order to be able infer the vulnerability of the interactions as a result of changes in the ecosystem.

One sixth of Amazonian tree diversity is dependent on river floodplains.

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.

Comparison of spatial dispersion of epigeic fauna between alluvial forests in an agrarian and Dunajské luhy protected landscape area, southern Slovakia

Abstract The spatial distribution of the epigeic fauna of floodplain ecosystems (willow-poplar floodplain forest, regenerated poplar forest), in the conditions of the natural environment of the Dunajské luhy Protected Landscape Area (PLA, hereinafter) and agrarian landscape was studied. The Dunajské luhy PLA, hereinafter (Slovak Republic) is the part of the system of protected areas of the European Union. During the three years 2020–2022, 24,169 individuals belonging to 19 taxa at 6 locations using the pitfall traps method were recorded. Through spatial modeling, the preference of most taxa for floodplain forests located in the Dunajské luhy PLA was found. We also observed a significant difference in number of individuals of epigeic fauna in floodplain forests betvween Dunajské luhy PLA area and agrarian landscape during all three years 2020 (p = 0.0070), 2021 (p = 0.0077) and 2022 (p = 0.04624). Thus, agroecosystems in the neighborhood of alluvial forests had a negative impact on the taxonomic diversity and abundance of epigeic fauna. In order to maintain a balance between the production of food, wood and the preservation of natural forest stands, it is important to optimally allocate areas and set up their management. For example, by creating forest islands in agricultural crops, to increase the epigeic fauna.

Distribution, density and trends of the Eurasian eagle owl (Bubo bubo) population breeding in March-Thaya floodplain forests: impact of owlets on sustainability of natural nests

Abstract In this study, we investigated the Eurasian eagle owl (Bubo bubo) breeding in lowland forests in the trans-border area between western Slovakia, eastern Austria, and southern Moravia. The research provides new information on the reuse of nests by eagle owls and presents initial insights into population density and trends of eagle owls in the March-Thaya floodplains. Our 19-year monitoring has shown that the eagle owl has become a widespread breeder over the study area, with an increasing population trend. A total of 151 breeding attempts by eagle owls have been identified, occupying 82 natural nests (originally built by at least nine species of birds) and 12 artificial nests. With an average of 6.2 active nests per 100 km2 and a maximum of 17 active nests found in 2021 (~10.6 pairs per 100 km2), our findings represent one of the highest eagle owl breeding densities found, especially in comparison with core populations nesting in the mountains (the Carpathians, north-eastern Alps and the Bohemian Massif). Regarding the dynamics of nest reuse, our results reveal that only a third of nests used by eagle owls were reused by other raptors or storks (Ciconia sp.). Almost 50% of the natural nests in which eagle owl bred, subsequently disintegrated after the owlets had fledged. Lastly, black stork (Ciconia nigra) nests re-used by eagle owls were twice as likely to have disintegrated after the owlets had fledged than nests built by other bird species. Our results suggest that black stork nests in the March and Thaya floodplain forests are most susceptible to destruction.

Framework for comprehensive assessment of ecological water conveyance based on long-term evolution forecast of riparian forests in arid floodplains: synergistic consideration of flood inundation and groundwater

Ecological water conveyance (EWC) is a crucial measure to address ecological degradation in arid regions. To scientifically formulate ecological water conveyance pattern (WCP), and provide a basis for ecological flow management of reservoirs, this study proposes a framework to assess the effect of EWC, and applied it to the Irtysh River basin as a case study. Following the framework, we first developed a calculation method to assess the evolution of the reproduction and growth of riparian forests caused by hydrological variations. Additionally, simulations of surface water and groundwater conditions under different scenarios of water resources development were conducted based on hydrodynamic and groundwater models. The study further predicted the long-term evolution of riparian forest reproduction and growth based on the simulation results. The results indicated that when EWC was not carried out (reservoirs operating according to the designed rules), after 30 years, floodplain flood (FF) inundation area decreased by 47%, duration shortened by 73%, and groundwater levels in 80% of the region declined by 1.5–2 m, causing severe and moderate impacts on the reproduction and growth of riparian forests, respectively. Alternatively, adopting EWC (reservoirs operating according to ecological rules) led to a 24% decrease in FF inundation area, a 63% reduction in its duration, and a groundwater level decline of 0.5–1 m in 87% of the region, and these changes caused severe impacts on riparian forest reproduction, while growth remained unaffected. These findings indicate that the current EWC effectively safeguards the growth of riparian forests but fall short of mitigating the impacts of water conservancy project construction and operation on the reproduction of riparian forests. Given the current trajectory, riparian forests are anticipated to undergo a gradual decline. Consequently, a sustainable EWC should ensure that the water volume discharged into the region exceeds 53% of the natural inflow and urgently requires measures to extend the duration of FF inundation. This study can provide new insights for the early evaluation, comparison and optimization of various WCPs before their implementation.

Relict of riparian floodplain forests: Natural distribution and ecology of Ulmus laevis in Switzerland

European white elm (Ulmus laevis Pallas) is a typical species of riparian forest. In Switzerland, at the margin of its distribution range, this tree is rare and poorly known. Its naturalness was often debated, and the species was seen most often as only cultivated. We aimed to clarify its status, ecology and distribution with extensive field work and surveys in Switzerland, as well as historical investigations. Ulmus laevis has a scattered distribution along large rivers and lakes of Switzerland. It is found mainly on coarse, moderately calcareous soils with good fertility. It generally occurs in hardwood riparian forests and occasionally in softwood forests in more dynamic systems. Our findings indicate that U. laevis grows naturally in Switzerland. However, the channelization of the large rivers and stabilization of water levels of the main lakes during the 19th century have altered the alluvial dynamics necessary for U. laevis’ natural regeneration and thus its long-term survival. Therefore, U. laevis occurs today mainly as a relict species in ancient floodplain forests with altered dynamics. In this context, regeneration occurs only to a very limited extent and is scarcely sufficient for species persistence. With a total population of less than 1000 naturally occurring individuals, it belongs to the rarest and most threatened trees of Switzerland. By demonstrating the fact that this species was actually present originally in this country, we exemplify the need for a multi-faceted approach to answering questions on the original occurrence versus introduced character of a species, which is very important in regard to land use planning, conservation, and wise use of local plant resources.

Leaf turgor loss point varies among tree species, habitats, and seasons in a bottomland hardwood forest

Key messageTree species in a temperate floodplain forest had leaf turgor loss point values similar to those of upland forest trees, suggesting physiological drought tolerance in this generally non-water-limited system.Leaf turgor loss point (TLP) is a key plant trait associated with drought tolerance. In the bottomland hardwood (BLH) forests that grow in floodplains of the southeastern USA, drought stress is generally low but may increase with climate change. To address drought tolerance among BLH trees, we measured TLP among 20 species in a BLH forest in Louisiana, USA. We tested whether (1) TLP is higher in BLH tree species than in upland temperate-zone trees; (2) lower TLP is associated with higher drought tolerance among BLH species; (3) TLP drops during the growing season within BLH trees; and (4) within species, TLP is lower in more water limited, non-flooded BLH habitats than in seasonally flooded habitats. Among BLH tree species, TLP was −2.23 ± 0.28 (mean ± SD) and, contrary to our hypothesis, weakly positively correlated with drought tolerance. Within BLH species, TLP was lower in non-flooded habitats than seasonally flooded habitats and TLP decreased between the early and late growing season, more so in the non-flooded habitat. Overall, our results show that TLP among BLH trees is relatively low and plastic for a system that is generally not water limited, which may contribute to drought tolerance in future scenarios.