Replication Data for: Spatial Patterns of Water-dispersed Seed Deposition along Stream Riparian Gradients

Four worksheets in one file containing data on spatial patterns of seed arrival along stream riparian gradients, with description of column headers (worksheet 1), abiotic variables (worksheet 2), number of arrived seeds per species (worksheet 3), and species and seed traits (worksheet 4)

Fraaije et al 2018 JAPPL

Eight worksheets with data on physicochemical variables and on aquatic and riparian vegetation in restored and nearby unrestored reaches of channelized lowland streams in the Netherlands, with description of column headers (worksheet 1), data on abiotic variables of riparian zones (worksheets 2 and 3), data on abiotic variables of the in-stream habitat (worksheets 4, 5 and 6), and data on plant species percent cover per plot (worksheets 7 and 8)

Functional responses of aquatic and riparian vegetation to hydrogeomorphic restoration of channelized lowland streams and their valleys

Streams and riparian zones are highly heterogeneous ecosystems. Their high biodiversity is promoted by variable flow velocities and water depths, strong hydrological gradients and disturbance regimes. However, human interventions like damming and channelization have degraded these ecosystems world-wide. And, although restoration efforts have increased in the past decades, ecological improvement is lagging. We assessed vegetation development in channelized lowland stream valleys in the Netherlands, combining innovative restoration measures to the stream and stream valleys. This “stream valley restoration” entailed construction of narrower and shallower channels to increase flow velocities during base discharges, meandering of the watercourse to increase flow and depth heterogeneity and excavation of banks to create wide v-shaped stream valleys. We evaluated the effects on functional aspects of the developing in-stream and riparian vegetation by comparing restored stream reaches to nearby unrestored reaches. The reduced channel dimensions led to higher flow velocities, which, through interaction with meandering, triggered a higher variability in flow and depth. Combined with enlargement of the floodplain, this promoted flooding in stream valleys and created wider environmental gradients. Plant diversity strongly increased in the floodplain area, the land–water interface and the shallow water habitat at the channel margins, but decreased in the central parts of stream channels. There, higher flow velocities led to more typically lotic (running water) in-stream plant communities, indicated by a sharp decrease in floating-leaved species and an increase in trailing species. Riparian vegetation showed a higher beta-diversity across the wider valley slopes of restored reaches, with more wetland species in areas with water-tables between 0.0 and −0.6 m, and more upland species as well. Synthesis and applications. This study demonstrates that the combination of strongly reduced channel dimensions, remeandering and widening of riparian zones, is effective in restoring in-stream and riparian habitat heterogeneity. The restoration efforts lead to distinct immediate increases in total and beta-diversity of many typical stream and riparian plant species. Overall, this stresses the importance of applying restoration measures to both streams and stream valleys simultaneously, considering them as a single landscape unit

Data from: Functional responses of aquatic and riparian vegetation to hydrogeomorphic restoration of channelized lowland streams and their valleys

1. Streams and riparian zones are highly heterogeneous ecosystems. Their high biodiversity is promoted by variable flow velocities and water depths, strong hydrological gradients and disturbance regimes. However, human interventions like damming and channelization have degraded these ecosystems worldwide. And, although restoration efforts have increased in the past decades, ecological improvement is lagging. 2. We assessed vegetation development in channelized lowland stream valleys in the Netherlands, combining innovative restoration measures to the stream and stream valleys. This ‘stream valley restoration’ entailed construction of narrower and shallower channels to increase flow velocities during base discharges, meandering of the watercourse to increase flow and depth heterogeneity and excavation of banks to create wide v-shaped stream valleys. We evaluated the effects on functional aspects of the developing in-stream and riparian vegetation by comparing restored stream reaches to nearby unrestored reaches. 3. The reduced channel dimensions led to higher flow velocities, which, through interaction with meandering, triggered a higher variability in flow and depth. Combined with enlargement of the floodplain, this promoted flooding in stream valleys and created wider environmental gradients. Plant diversity strongly increased in the floodplain area, the land-water interface and the shallow water habitat at the channel margins, but decreased in the central parts of stream channels. There, higher flow velocities led to more typically lotic (running water) in-stream plant communities, indicated by a sharp decrease in floating-leaved species and an increase in trailing species. Riparian vegetation showed a higher beta-diversity across the wider valley slopes of restored reaches, with more wetland species in areas with water tables between 0.0 and -0.6 m, and more upland species as well. 4. Synthesis and applications. This study demonstrates that the combination of strongly reduced channel dimensions, remeandering and widening of riparian zones, is effective in restoring in-stream and riparian habitat heterogeneity. The restoration efforts lead to distinct immediate increases in total and beta-diversity of many typical stream and riparian plant species. Overall, this stresses the importance of applying restoration measures to both streams and stream valleys simultaneously, considering them as a single landscape unit. 27-Nov-201

Data from: Dispersal versus environmental filtering in a dynamic system: drivers of vegetation patterns and diversity along stream riparian gradients

1. Both environmental filtering and dispersal filtering are known to influence plant species distribution patterns and biodiversity. Particularly in dynamic habitats, however, it remains unclear whether environmental filtering (stimulated by stressful conditions) or dispersal filtering (during re-colonization events) dominates in community assembly, or how they interact. Such a fundamental understanding of community assembly is critical to the design of biodiversity conservation and restoration strategies. 2. Stream riparian zones are species-rich dynamic habitats. They are characterized by steep hydrological gradients likely to promote environmental filtering, and by spatiotemporal variation in the arrival of propagules likely to promote dispersal filtering. We quantified the contributions of both filters by monitoring natural seed arrival (dispersal filter) and experimentally assessing germination, seedling survival and growth of 17 riparian plant species (environmental filter) along riparian gradients of three lowland streams that were excavated to bare substrate for restoration. Subsequently, we related spatial patterns in each process to species distribution and diversity patterns after 1 and 2 years of succession. 3. Patterns in initial seed arrival were very clearly reflected in species distribution patterns in the developing vegetation and were more significant than environmental filtering. However, environmental filtering intensified towards the wet end of the riparian gradient, particularly through effects of flooding on survival and growth, which strongly affected community diversity and generated a gradient in the vegetation. Strikingly, patterns in seed arrival foreshadowed the gradient that developed in the vegetation; seeds of species with adult optima at wetter conditions dominated seed arrival at low elevations along the riparian gradient while seeds of species with drier optima arrived higher up. Despite previous assertions suggesting a dominance of environmental filtering, our results demonstrate that nonrandom dispersal may be an important driver of early successional riparian vegetation zonation and biodiversity patterns as well. 4. Synthesis: Our results demonstrate (and quantify) the strong roles of both environmental and dispersal filtering in determining plant community assemblies in early successional dynamic habitats. Furthermore, we demonstrate that dispersal filtering can already initiate vegetation gradients, a mechanism that may have been overlooked along many environmental gradients where interspecific interactions are (temporarily) reduced

Functional responses of aquatic and riparian vegetation to hydrogeomorphic restoration of channelized lowland streams and their valleys

Streams and riparian zones are highly heterogeneous ecosystems. Their high biodiversity is promoted by variable flow velocities and water depths, strong hydrological gradients and disturbance regimes. However, human interventions like damming and channelization have degraded these ecosystems world-wide. And, although restoration efforts have increased in the past decades, ecological improvement is lagging. We assessed vegetation development in channelized lowland stream valleys in the Netherlands, combining innovative restoration measures to the stream and stream valleys. This “stream valley restoration” entailed construction of narrower and shallower channels to increase flow velocities during base discharges, meandering of the watercourse to increase flow and depth heterogeneity and excavation of banks to create wide v-shaped stream valleys. We evaluated the effects on functional aspects of the developing in-stream and riparian vegetation by comparing restored stream reaches to nearby unrestored reaches. The reduced channel dimensions led to higher flow velocities, which, through interaction with meandering, triggered a higher variability in flow and depth. Combined with enlargement of the floodplain, this promoted flooding in stream valleys and created wider environmental gradients. Plant diversity strongly increased in the floodplain area, the land–water interface and the shallow water habitat at the channel margins, but decreased in the central parts of stream channels. There, higher flow velocities led to more typically lotic (running water) in-stream plant communities, indicated by a sharp decrease in floating-leaved species and an increase in trailing species. Riparian vegetation showed a higher beta-diversity across the wider valley slopes of restored reaches, with more wetland species in areas with water-tables between 0.0 and −0.6 m, and more upland species as well. Synthesis and applications. This study demonstrates that the combination of strongly reduced channel dimensions, remeandering and widening of riparian zones, is effective in restoring in-stream and riparian habitat heterogeneity. The restoration efforts lead to distinct immediate increases in total and beta-diversity of many typical stream and riparian plant species. Overall, this stresses the importance of applying restoration measures to both streams and stream valleys simultaneously, considering them as a single landscape unit

Directed dispersal by an abiotic vector: wetland plants disperse their seeds selectively to suitable sites along the hydrological gradient via water

Plant species around the world invest in seed dispersal by producing large numbers of seeds, with a wide range of morphological adaptations that facilitate dispersal. Not all dispersed seeds reach suitable sites, however, and plants can significantly improve their fitness by increasing the proportion of seeds arriving at suitable sites for germination and establishment. Disproportionate dispersal to suitable sites is known as ‘directed dispersal’. Yet, mechanisms of directed dispersal are only known for a limited number of animal-dispersed plant species. We tested the hypothesis that directed dispersal can also be driven by abiotic vectors, such as water or wind. We used a tiered approach, combining analyses of experimental, field and literature data on wetland plant species and evaluating the potential for evolution of directed dispersal with a spatially explicit individual-based model. The data collected demonstrate that wetland plants produce seeds with adaptations to promote transportation and deposition by water towards microsites along the hydrological gradient where they germinate and establish best. Aquatic species produce seeds that sink and are transported by water as bed load towards inundated sites. In contrast, shoreline species produce seeds that float for very long periods of time so that they are eventually entrapped by shoreline vegetation or deposited at the waterline. Our model simulations confirm that the patterns we observed in nature can evolve under natural selection through adaptations in seed buoyancy. For wind dispersal, the situation is more complex. Wind does not provide directed dispersal in the strictest sense but, rather, simply appears to be the best available dispersal vector for more terrestrial wetland plant species to reach drier areas in a wet environment. Synthesis. We show that directed dispersal towards specific, suitable microsites is not exclusive to animal-dispersed plant species, but may be far more common in plants – also in species dispersed by abiotic vectors, in particular water. As water and wind are very common dispersal vectors throughout the plant kingdom, directed dispersal (and not just dispersal distance) seems to be of general importance for the ecology of plants. A lay summary is available for this article

Data from: Early plant recruitment stages set the template for the development of vegetation patterns along a hydrological gradient

1. Recruitment processes are critical components of a plant's life cycle. However, in comparison with later stages in the plant life cycle (e.g. competition among adults), relatively little is known about their contribution to the regulation of plant species distribution. Particularly little is known about the individual contributions of the three main recruitment processes—germination, seedling survival, and seedling growth—to community assembly, while quantitative information on these contributions is essential for a more mechanistic understanding of the regulation of plant species distribution and biodiversity. 2. Riparian zones along streams provide a globally-relevant case study for evaluating the importance of the different stages of plant recruitment. The natural hydrological gradients of stream riparian zones are currently being restored after a period of worldwide habitat degradation. To identify how recruitment contributes to vegetation patterns and biodiversity in riparian zones, we carried out field experiments at restored lowland streams. We quantified the germination of introduced seeds, and survival and growth of introduced seedlings of 17 riparian plant species across a gradient from the stream channel to upland. 3. The hydrological gradient of riparian zones acted as a strong environmental filter on all three recruitment processes, through imposing an abiotic limitation (excess water) at low elevations and a resource limitation (water shortage) at higher elevations. Other variables, such as soil organic matter content and nutrient availability, only affected recruitment marginally. 4. Species-specific patterns of environmental filtering initiated niche segregation along the riparian gradient during all three recruitment processes, but particularly during germination and seedling growth. These recruitment niches appeared strongly related to indicator values for adult distribution optima, suggesting that at least some riparian plant species may have evolutionary adaptations that promote recruitment under favourable hydrological conditions for adult growth and reproduction. 5. Our results suggest that strong environmental filtering during germination and seedling growth plays an important role in determining later adult distributions, by forming the spatial template on which all subsequent processes operate. In addition to well-known mechanisms, such as competitive exclusion at the adult stage, environmental filtering during early recruitment stages already strongly affect plant distribution and diversity