Seed arrival, recruitment and presence in vegetation along riparian gradients

11 worksheets with data on seed arrival, experimentally studied recruitment processes (germination, seedling survival and seedling growth), and natural developing vegetation (worksheets 3-7), model predictions of seed arrival and recruitment processes (worksheets 8-11), abiotic variables (worksheet 2) and description of column headers (worksheet 1)

Fraaije et al. mesh bags control experiment

Two worksheets containing data on a control experiment which tested the effect of mesh bags on germination, with the data in worksheet 1, and description of column headers in worksheet 2

Fraaije et al. field experiments

Eight worksheets with data on experimentally studied recruitment processes (germination, seedling survival, and seedling growth: worksheet 1-3), re-structured for multivariate analyses (worksheet 4-6), soil parameters (worksheet 7) and description of column headers (worksheet 8)

Spatial patterns of water-dispersed seed deposition along stream riparian gradients

<div><p>Riparian ecosystems along streams naturally harbour a high plant diversity with many increasingly endangered species. In our current heavily modified and fragmented catchments, many of these species are sensitive to dispersal limitation. Better understanding of riparian plant dispersal pathways is required to predict species (re-)colonization potential and improve success rates of stream and riparian zone conservation and restoration. Dispersal by water (hydrochory) is an important mechanism for longitudinal and lateral dispersal of riparian species. Crucially for recruitment potential, it also influences the elevation along the riparian hydrological gradient where seeds become deposited. Due to the complex interplay between abiotic and biotic factors, however, it remains unclear how exactly patterns in seed deposition are formed. We compared hydrochorous and non-hydrochorous seed deposition, and quantified patterns of seed deposition along the bare substrate of newly created stream riparian gradients. Water levels were monitored and seed deposition was measured with seed traps along the full range of riparian hydrological conditions (from permanently flooded to never flooded). Average seed numbers and species richness were significantly higher in flooded than in non-flooded seed traps (5.7 and 1.5 times higher, respectively). Community-weighted trait means indicated that typically water-dispersed seeds were more dominant in flooded than in non-flooded seed traps and gradually decreased in concentration from the channel to the upland. Moreover, highly buoyant seeds accumulated at the average water line, and clear elevational sorting of non-buoyant seeds occurred within the floodplain. These results establish a critical role of flooding in shaping patterns of seed deposition along the riparian gradient, delivering many seeds of typical riparian species to riparian zones and depositing them at species-specific elevations as influenced by seed traits, suggesting species-specific dispersal pathways. This shows that hydrochory likely has important consequences for riparian vegetation development and that flooding forms a key process for successful restoration.</p></div

Water level fluctuations relative to the mean water level during the sampling periods for the Hagmolenbeek (HM), Hooge Raam (HR) and Kleine Aa (KA).

<p>Sampling periods are separated by vertical dotted lines. Seed trap elevation (relative to mean water level) of representative transects are indicated by horizontal lines.</p

Field study design.

<p>To monitor seed rain along the entire hydrological gradient, three replicate transects of five seed traps (squares picture left; close-up picture right) were pinned to the ground perpendicular to the stream channel. Vegetation surveys were carried out in permanent quadrats adjacent to each seed trap (rectangles; picture left). Stream water levels were registered using pressure transducers in water level gauges within 30 m of the nearest transect.</p

Overview of the number of species and number of seeds deposited in seed traps per research site, period of monitoring and season.

<p>Overview of the number of species and number of seeds deposited in seed traps per research site, period of monitoring and season.</p

Forward selections of fixed effects in (negative binomial G)LMMs explaining species number and number of seeds in the seed traps.

<p>Forward selections of fixed effects in (negative binomial G)LMMs explaining species number and number of seeds in the seed traps.</p

The effects of flooding and season on community-weighted means of seed traits of the deposited seed community.

<p>A comparison of flooded (FL) and non-flooded (Not FL) seed traps is given in the left panels (box widths proportional to number of seed traps). The effect of seed trap elevation relative to the mean water level is given in the right panels (negative values represent seed traps below the average water level, positive values represent seed traps above it). Summer and winter data are displayed in different greyscales. In the right panels, blue lines represent modelled relationships between field data (circles) and the explanatory variables season and elevation, as analyzed in LMMs. Grey ribbons indicate the 95% confidence intervals (based on fixed effects only).</p

The effects of flooding and season on the number of species of deposited seeds (upper panels) and number of seeds (lower panels).

<p>A comparison of flooded (FL) and non-flooded seed traps (Not FL) is given in the left panels (box widths proportional to number of seed traps). The effect of seed trap elevation relative to mean water level is given in the right panels (negative values represent seed traps below the average water level, positive values represent seed traps above it). Summer and winter data are displayed in different greyscales. In the right panels, blue lines represent modelled relationships between field data (circles) and the explanatory variables season and elevation, as analyzed in negative binomial GLMMs. Grey ribbons indicate the 95% confidence intervals (based on fixed effects only).</p