Importance of hydrochory in structuring plant communities along rivers

Abstract

NILSSON, C., GARDFJELL, M., and GRELSSON, G. 1991. Importance of hydrochory in structuring plant communities along rivers. Can. J. Bot. 69: 2631-2633. Using wooden cubes as experimental seed mimics we tested whether differences in seed deposition among riverbank sites predictably affect the structure of riparian vegetation. Although cube deposition was not interpretable in terms of environmental variables like current velocity, riverbank width, and substrate, it was related to species composition of the riparian vegetation. We found an excess of species with short-floating seeds among those that were most frequent in sites capturing few cubes and an excess of species with long-floating seeds among those that were most frequent in sites capturing many cubes. This result provides the first evidence that water dispersal interacting with floating time may play a role in smallscale structuring of riparian plant communities. hydrochory in structuring plant communities along rivers. Can. J. Bot. 69 : 2631-2633. En utilisant de petits cubes de bois comme modele experimental pour imiter les graines, les auteurs ont vCrifiC si les differences dans la dCposition des graines de long des rives de la rivikre permettrait de prCdire la structure de la vegetation riparienne. Bien que la deposition des cubes ne soit pas interprktable en terme de variable environnementale, telle que la vtlocitC du courant, la largeur des rives et le substrat, elle est cependant relike a la composition des especes de la vCgCtation riparienne. Les auteurs ont trouvC une plus grande quantitC d'espkces ayant des graines de courte flotabiliti, parmi celles qui se retrouvent le plus souvent dans les sites oh Cchouent les cubes et un surplus d'especes avec des graines a longue floatabilite parmi celles qui Ctaient des plus frCquentes dans les sites oh on retrouve un grand nombre de cubes. Ce rCsultat donne la premikre preuve que la dispersion par I'eau, en interaction avec la ptriode de flotabilitk, pourrait jouer un r61e dans la structuration a petite Cchelle des communautCs de plantes ripariennes.

Species richness in a riparian plant community along the banks of the Xiangxi River, the Three Gorges region

“…However, ecological conditions vary greatly along the river network as a function of hydrologic regime and human interventions (Nilsson et al 1991). Several studies have suggested that vascular species richness along riverbanks reaches a maximum at the midreach of streams (Nilsson et al 1989(Nilsson et al , 1991Decamps and Tabacchi 1992;Tabacchi et al 1996). We found similar results for the Xiangxi River watershed (Figure 3).…”

“…Because riparian ecotones are transitional between aquatic-terrestrial ecosystems, they contain species belonging to each distinct environment as well as species typical of a humid environment (Hupp and Osterkamp 1996;Sagers and Lyon 1997). However, ecological conditions vary greatly along the river network as a function of hydrologic regime and human interventions (Nilsson et al 1991). Several studies have suggested that vascular species richness along riverbanks reaches a maximum at the midreach of streams (Nilsson et al 1989(Nilsson et al , 1991Decamps and Tabacchi 1992;Tabacchi et al 1996).…”

Consequences of propagule dispersal and river fragmentation for riparian plant community diversity and turnover

“…In addition, regional species pools have equal access to tranquil and turbulent reaches of the Vindel River. Higher species richness along turbulent reaches is likely due in part to higher substrate heterogeneity (Reno¨fa¨lt et al 2007), which provides more microhabitats to accommodate a wider range of species and more opportunities due to higher propagule trapping ability (Nilsson et al 1991b, which act in concert to enhance species richness.…”

“…Levine (2003) noted that most patches along a river in California were colonized by propagules from sources within only 100 m upstream. Structurally complex rivers (such as the Vindel River) are efficient at trapping water-dispersed seeds along hydraulically complex reaches and areas with many emergent objects (e.g., cobbles and plant stems; Schneider and Sharitz 1988, Nilsson et al 1991b, Merritt and Wohl 2002, Gurnell et al 2007). Areas of high propagule trapping efficiency have been associated with more species-rich plant communities both in simulations (Merritt and Wohl 2002) and in field experiments (Andersson et al 2000b).…”

“…Some of these are from local sources (,100 m; Levine 2003) and others are transported far (e.g., hundreds of kilometers) by water (Andersson et al 2000b, Boedeltje et al 2003. As a consequence, rivers are unique landscape elements in that they biologically (mainly through hydrochory) connect otherwise disconnected meta-populations or meta-communities (Boudell and Stromberg 2008), accelerate colonization, and possibly enhance potential diversity through transporting propagules long distances from throughout a catchment (Nilsson et al 1991b, Andersson et al 2000b). Water dispersal is a secondary dispersal mechanism for many riparian species, but deposition in water can enhance a propagule's chances of reaching a safe site for establishment through dispersing farther from parent plants (decreasing intraspecific competition; i.e., Janzen-Connell effect; Bever 2003).…”