The role of hydrochory in structuring riparian and wetland vegetation

Abstract

Hydrochory, or the passive dispersal of organisms by water, is an important means of propagule transport, especially for plants. During recent years, knowledge about hydrochory and its ecological consequences has increased considerably and a substantial body of literature has been produced. Here, we review this literature and define the state of the art of the discipline. A substantial proportion of species growing in or near water have propagules (fruits, seeds or vegetative units) able to disperse by water, either floating, submerged in flowing water, or with the help of floating vessels. Hydrochory can enable plants to colonize sites out of reach with other dispersal vectors, but the timing of dispersal and mechanisms of establishment are important for successful establishment. At the population level, hydrochory may increase the effective size and longevity of populations, and control their spatial configuration. Hydrochory is also an important source of species colonizing recruitment-limited riparian and wetland communities, contributing to maintenance of community species richness. Dispersal by water may even influence community composition in different landscape elements, resulting in landscape-level patterns. Genetically, hydrochory may reduce spatial aggregation of genetically related individuals, lead to high gene flow among populations, and increase genetic diversity in populations receiving many propagules. Humans have impacted hydrochory in many ways. For example, dams affect hydrochory by reducing peak flows and hence dispersal capacity, altering the timing of dispersal, and by presenting physical barriers to dispersal, with consequences for riverine plant communities. Hydrochory has been inferred to be an important vector for the spread of many invasive species, but there is also the potential for enhancing ecosystem restoration by improving or restoring water dispersal pathways. Climate change may alter the role of hydrochory by modifying the hydrology of water-bodies as well as conditions for propagule release and plant colonization.

Restoring macrophyte diversity in shallow temperate lakes: biotic versus abiotic constraints

“…Capers (2003) found that about 60% of the individuals that colonised bare soil in freshwater tidal areas originated from vegetative propagules. Genetic studies, however, show that recruitment from vegetative propagules versus seeds and oospores is very species specific (Nilsson et al, 2010;Bornette & Puijalon, 2011).…”

Plant species diversity in a Neotropical wetland: patterns of similarity, effects of distance, and altitude

“…In these types of areas, diversity is usually higher and species composition may vary in short distances (Scheiner andRey-Benayas 1994, RodriguesIturbe et al 2009), whereas large distances may decrease similarity for several reasons, such as variations in the gradient and differences in niche occupation and dispersal limitation (Necola and White 1999, Boedeltje et al 2003, Nilsson et al 2010. These variations may influence the pattern of species colonization, mainly due to dispersal strategies such as hydrochory (Barrat-Segretain 1996, Wittmann and Junk 2003, Riis and SandJensen 2006, Hopfensperger and Baldwin 2009.…”

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

“…Sediment transport has the potential to increase the available propagule bank within riparian zones, since propagules are also transported at times of flood (Nilsson et al 2010) and deposited along with sediment in low energy environments. Patches of freshly deposited sediment thus represent gaps characterised by high levels of nutrients, organic matter and high densities of viable propagules (Nilsson and Svedmark 2002).…”