•The number of Lecythidaceae individuals decreased by > 1000, but basal area and biomass did not change significantly over 30 years.•Mortality is highest in the lower-lying, wetter habitats.•The most ...abundant species in the plot do not overlap in their habitat associations, nor do sister species.
In this study, we analyze the demographic rates and biomass dynamics of Lecythidaceae in a 100-ha permanent forest plot in the Central Amazon. We characterize habitats in the plot, analyze the effect of habitat on tree density, species richness, and biomass and demographic dynamics, and quantify significant species habitat associations. The plot experienced a 13.2 % net loss of Lecythidaceae individuals (n = 1023) but aboveground biomass (AGB; Mg ha−1) did not differ between the two censuses. Growth rates averaged 1.2 mm year−1 with high intraspecific variation and differed significantly among species height classes. Stem density and species richness decreased in all six terra firme habitats and were significantly lower in both years in the flood disturbed habitat. Only the flood disturbed areas experienced a significant loss in AGB, along with the highest annual mortality, recruitment, and growth rates across the plot. The lower-lying habitats experienced higher mortality rates than the slopes and plateaus, suggesting too much moisture is a higher risk to Lecythidaceae individuals than drought in this plot. There were no overlapping habitat associations among sister species, or among the seven most abundant species, which suggests that terra firme habitat association provides a niche partitioning mechanism for closely related Lecythidaceae species. As intended with its establishment, this plot continues to provide integral baseline data for one of the most ecologically dominant and culturally significant tree families in the Amazon region.
Artificial high flows attempt to simulate natural flood pulses in flow-regulated rivers with the intent to improve their ecological integrity. The long-term use of such high flow events have shown ...beneficial ecological effects on various rivers globally. However, such responses are often non-linear and characterized by underlying feedback mechanisms among ecosystem components. The question arises as to what happens when such high flow releases are disrupted or even discontinued. Here, we used the long-term (22 years) monitoring dataset from the river Spöl to examine whether discontinuation (2016–2021) of the flood program (annual artificial high flows from 2000 to 2016) resulted in the ecological degradation of the river. We used monitoring data of physico-chemistry, periphyton, benthic organic matter, macroinvertebrates and fish (brown trout, Salmo trutta fario L.) in the analysis. The flood program had no long-term effect on water physico-chemistry with most parameters showing typical variations associated with season and inter-annual weather patterns. The floods were effective at mobilizing bed sediments that reduced periphyton biomass and benthic organic matter following each flood. Increases in periphyton biomass and benthic organic matter occurred between floods, but both parameters showed no significant increase with discontinuation of the flood program. Floods reduced macroinvertebrate densities, but with density increases occurring between floods. The pulsed disturbances, and the progressive change in the habitat template, resulted in shifts in community assembly by reducing densities of Gammarus fossarum, a dominant crustacean, which allowed other taxa to colonize the system. Macroinvertebrate densities remained low after discontinuation of the floods, although G. fossarum densities have increased substantially while other taxa, especially some stoneflies, remained low in abundance. Notably, community assembly returned to a pre-flood composition with discontinuation of the floods. The abundance of brown trout increased substantially during the flood program but returned to low pre-flood numbers with discontinuation of the floods. We conclude that the flood program was beneficial to the ecology of the river Spöl and discontinuation of the floods resulted in degradation of the system after a relatively short lag period. However, the system showed high resilience to an earlier perturbation, a sediment spill in 2013, suggesting a rapid positive response by biota with resumption of the flood program.
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•Artificial floods mobilized bed sediments, reducing biofilms and benthic organic matter.•Floods reduced macroinvertebrate densities with quick recovery between floods.•Floods shifted community assembly to be more alpine in character.•Floods increased spawning habitat for brown trout, increasing abundances.•Flood discontinuation shifted assemblages to pre-flood conditions.•Flood discontinuation resulted in degradation of the system.
We conducted a systematic review of literatures on biodiversity in retarding basins to grasp the status of knowledge regarding effects of constructions and managements of them on biodiversity. Six ...taxonomic groups (birds, amphibians, fish, insects, shellfish, and plants) were included in the review to examine multi-taxonomic responses. Totally 9,183 literatures were reviewed, and 242 were selected for this systematic review. The total number of sites in the selected literature was 33, which cover only 22 ％ of the number of retarding basins in Japan. Birds were reported most frequently (94) whereas amphibians were most scarce (6). For all the taxa, reports on the occurrence of rare species or invasive species, and new record of species distribution, were common. Only 15 studies were based on the BACI design, suggesting a lack of scientific knowledge regarding biodiversity assessments in retarding basins. Thus, we could not fully clarify the effects of retarding basins on biodiversity. However, some studies suggested that the artificial disturbances, wetland creation, vegetation management, and soil excavation, had positive effects on many taxa.
Reservoirs have altered the flow regime of most rivers on the globe. To simulate the natural flow regime, experimental floods are being implemented on regulated rivers throughout the world to improve ...their ecological integrity. As a large-scale disturbance, the long-term sequential use of floods provides an excellent empirical approach to examine ecosystem regime shifts in rivers. This study evaluated the long-term effects of floods (15 floods over eight years) on a regulated river. We hypothesized that sequential floods over time would cause a regime shift in the ecosystem. The floods resulted in little change in the physicochemistry of the river, although particulate organic carbon and particulate phosphorus were lower after the floods. The floods eliminated moss cover on bed sediments within the first year of flooding and maintained low periphyton biomass and benthic organic matter after the third year of flooding. Organic matter in transport was reduced after the third year of flooding, although peaks were still observed during rain events due to tributary inputs and side slopes. The floods reduced macroinvertebrate richness and biomass after the first year of floods, but density was not reduced until the third year. The individual mass of invertebrates decreased by about one-half after the floods. Specific taxa displayed either a loss in abundance, or an increase in abundance, or an increase followed by a loss after the third year. The first three flood years were periods of nonequilibrium with coefficients of variation in all measured parameters increasing two to five times from those before the floods. Coefficients of variation decreased after the third year, although they were still higher than before the floods. Analysis of concordance using Kendall's W confirmed the temporal changes observed in macroinvertebrate assemblage structure. An assessment of individual flood effects showed that later floods had ~30% less effect on macroinvertebrates than early floods of similar magnitude, suggesting that the new assemblage structure is more resilient to flood disturbance. We conclude that the floods caused an ecosystem regime shift that took three years to unfold. Additional long-term changes or shifts are expected as new taxa colonize the river from other sources.
The roots of some coastal and wetland trees grow peculiar vertical protrusions, the function of which remains unclear. Here, using computational simulations based on first-principles fluid and ...sedimentation dynamics, we argue that the protrusions work together to create an elevated patch of sediment downstream of the tree, thereby creating its own fertile flood-protected breeding grounds for the seedlings. In our simulations, we vary the vertical root diameter, root spacing and total root area and show that there is an optimal vertical root spacing that depends on root thickness. Next, we quantify and discuss the cooperative effects between adjacent vertical root patches. Lastly, by varying vertical root spacing of a patch of trees, we estimate a maximal vegetation density for which vertical-root production has a beneficial geomorphological response. Our hypothesis suggests that vertical roots, such as the 'knee roots' of baldcypress trees, have an important role in shaping riparian geomorphology and community structure.
AbstractIt is reported that the magnitudes of flood events in riverine systems have been increasing due to global climate change. Because flood events could displace fish species downstream and/or ...increase the mortality of fish, it is important to know how the increased floods can affect fish in river networks. In this study, we focused a hatchery-raised amphidromous fish, Ayu Plecoglossus altivelis altivelis in a mainstem-tributary network in Japan and examined the relative fish abundance changes before and after the recordable massive flood using the environmental DNA (eDNA) analysis. We also examined the spatiotemporal patterns of the Ayu eDNA concentrations and the relationships with tributary discharge, width, and depth to examine if the relative abundance changes could be related to tributary size. Our results indicated that Ayu tended to inhabit large, deep tributaries more than small, shallow tributaries even after the flood event. Further, the eDNA concentrations of Ayu have decreased in most study sites after the flood; however, the eDNA concentrations in certain tributaries with lower tributary size have increased during the study period. These results suggest that (1) the habitat conditions could be important for the maintenance of Ayu populations before and after flood events, (2) increase in flood magnitude along climate changes could have impacts on Ayu populations, and (3) not only large tributary, but also small tributaries could be important habitats for the target species to avoid flood disturbances.
1. In river corridors, water plays a key role in connecting various landscape patches. This `hydrological connectivity' operates on the four dimensions of fluvial hydrosystems: longitudinal, lateral, ...vertical, and temporal. The present review focuses on: (1) lateral connectivity that links the main course of a river with floodplain waterbodies; and (2) vertical connectivity, the exchanges between the surface and groundwater via infiltration into the alluvial aquifer and exfiltration of phreatic water from the hillslope aquifer.
2. The biocomplexity of fluvial hydrosystems results from interactions between processes operating at various spatial and temporal scales. Differences in the nature and intensity of hydrological connectivity contribute to the spatial heterogeneity of riverine floodplains, which results in high alpha, beta and gamma diversity. Differences in connectivity also provide complementary habitats that are required for the parts of life cycles and life‐cycles of some species. Hydrological connectivity also produces antagonistic effects, even within the same waterbody.
3. Two temporal scales are distinguished in connectivity dynamics. River level fluctuations within years lead to a pulsing connectivity that drives the functioning of floodplain ecosystems, namely the exchange of organic matter and inorganic nutrients and the shift between production and transport phases. On the scale of decades to centuries, the interactions between various processes increase the biocomplexity of floodplains; for example, river dynamics, which create highly connected waterbodies, compensate for succession that tends towards disconnection. Alternatively, river‐bed incision leads to the reduction of fluvial dynamics and to the disconnection of waterbodies, although river incision may increase vertical connectivity where waterbodies are supplied by the hillslope aquifer.
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