Propagule input, transport and deposition in riparian environments: the importance of connectivity for diversity

Abstract

Question: How important is hydrochory for dispersing propagules along riverbanks and to what extent do the quantity and species composition of deposited propagules reflect the riparian vegetation, represent “new” species that are not present in the vegetation, and vary with river flow and season? Location: River Frome, Dorset, UK. Methods: Over 13 consecutive 6‐week time periods, during which river water levels were continuously monitored, aerial inputs of propagules to riverbanks were sampled using funnels, hydrochorous propagule transport was sampled using drift nets, and deposition across the riverbanks was sampled using astroturf mats. A survey of the riparian vegetation enabled comparison between samples and the standing vegetation, so that “new” species could be identified. Differences in propagule abundance and diversity between sampling methods, time periods and locations were tested using Mann‐Whitney U‐tests and Kruskall‐Wallis ANOVA. DCA established contrasts in the floristic composition of all deposited propagules and “new” propagules between different sample types, time periods and locations. Results: Aerial seed fall generated few propagules of low species richness. Hydrochory introduced large numbers of propagules and new species, resulting in high propagule deposition on the riverbank. The number and diversity of deposited propagules was governed by seasonal patterns of seed release and the hydrological regime. Propagule deposition was significantly greater on the most frequently inundated parts of the riverbank and autumn floods were particularly important for transporting “new” species to the study site and for remobilizing previously released propagules. Conclusions: The abundance and diversity of propagules deposited along riverbanks is dependent upon high river flows, which facilitates connectivity between the channel and the riparian zone.

Aquatic Plant Dynamics in Lowland River Networks: Connectivity, Management and Climate Change

“…More specific predictions at the level of traits (e.g., trade-offs) or combination of attributes could be tested experimentally (e.g., [23,53,113,[134][135][136]). A more mechanistic and experimental approach could lead to more predictive species distribution and associated community structure against our changing climate and management practices [34,137].…”

The changing role of ecohydrological science in guiding environmental flows

“…We have begun to assess connectivity upstream/downstream under the river continuum concept (Vannote et al 1980), which can be important, for example, for input, transport and deposition of sediments and propagules in riparian environments (Moggridge et al 2009), and utilization of different habitats through a life-cycle (Fausch et al 2002). Moreover, integrated operation of multiple dams to optimize ecosystem services throughout a large basin requires regional ecohydrological assessment, as the US Army Corps of Engineers and others are demonstrating in the Connecticut River basin, USA .…”

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

“…One of the most important physical functions of riparian areas is to trap and buffer the transfer of sediment . Riparian vegetation modifies sediment transport either by altering channel hydraulics or by physically entrapping materials, most significantly in lowland environments (Moggridge et al 2009). There is growing interest in sedimentation processes in rivers and the link to flood events , partly driven by climate-related changes in flow regime and increased awareness of the link between land management and fine sediment entry to rivers.…”