Abstract
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.
Highlights
Plant diversity is threatened across the globe by habitat loss and deterioration [1]
We studied three lowland streams in the Netherlands: the Hagmolenbeek (HM), Hooge Raam (HR) and Kleine Aa (KA) (52 ̊13’0.33" N, 6 ̊43’16.88" E; 51 ̊42’57.65" N, 5 ̊42’9.25" E; and 51 ̊35’39.92" N, 5 ̊16’38.71" E respectively)
Seed deposition following transport by stream water played a very important role in seed arrival at restored lowland stream riparian zones. Both the number of seeds and the number of species were significantly higher in seed traps that were at some point flooded by stream surface water than in non-flooded seed traps. This difference was reported in studies on seed dispersal across vegetated stream riparian zones [19,20,34] and can be explained by the additive role of hydrochory to other dominant dispersal processes such as anemochory and zoochory
Summary
Plant diversity is threatened across the globe by habitat loss and deterioration [1]. In newly created riparian zones, which are cleared of vegetation, a primary successional stage occurs in which direct seed fall from standing vegetation is still strongly reduced This provides an ideal environment for collecting information on hydrochorous seed deposition along riparian gradients and its consequences for (re-)colonization and potential restoration success. We monitored year-round seed deposition in relation to water levels of newly created riparian zones to 1) assess the relative importance of hydrochory in comparison to non-hydrochorous seed delivery to restored riparian zones, 2) improve mechanistic understanding of elevational patterns of seed deposition along riparian gradients and 3) disentangle the effects of seasonality on 1 & 2 To this purpose, we monitored the natural seed rain along riparian gradients of lowland streams that had recently been excavated to bare substrate in the context of a restoration programme. Spatial patterns of water-dispersed seeds along stream riparian gradients permanently flooded to never flooded) we could compare hydrochorous dispersal to non-hydrochorous dispersal, and study the effect of hydrochory on elevational seed deposition patterns along riparian gradients
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
