Waterlogging and canopy interact to control species recruitment in floodplains

Abstract

Summary 1.The extent to which seedling recruitment contributes to local functional diversity depends on the environmental filters operating in a plant community. Classical community assembly models assume that habitat constraints and competition act like hierarchical filters with habitat filtering as the dominant one. Alternative models assume a synergic interaction since responses to environmental stress and competition may impose physiological trade-offs in plants. 2. River floodplains are an ideal system to test the relationship between habitat and competition filtering in community (re)assembly, as flooding causes changes in both habitat stress (waterlogging, resulting in anoxia and toxicity) and competition (dieback of vegetation) on one hand and acts as an effective seed dispersal vector on the other hand. 3. We conducted a mesocosm experiment on early community assembly from a pool of 34 floodplain species covering a wetness gradient. Seed mixtures were sown in a full factorial design with water level, canopy and mowing as controlling factors. We measured the biomass of all species after one growing season and determined germination and seedling growth traits, both outside (response to waterlogging ⁄ no waterlogging) and in a growth-chamber (response to light ⁄ darkness). 4. Species recruitment was analysed in relation to the controlling factors and measured functional traits using co-inertia analysis. Furthermore we analysed the effects of the controlling factors on several aspects of functional diversity. 5. There was no establishment in grass sward, unless mowing was applied. Species-rich communities only developed when germination and early establishment phases occurred on waterlogged bare soil. High water level did not suppress establishment but reduced the total biomass and lowered inter-specific competition. The effect of mowing on species richness depended upon the interplay between waterlogging and canopy. 6. Establishment success under canopy required seedling strategies to tolerate shade. The elimination of typical wetland specialists from oxic mesocosms was clearly an effect of their poorer and ⁄ or slower germination and lower competitive abilities in comparison to non-wetland plants, leading to their disappearance in this low-stress environment. 7. Our results indicate that single stress factors can enhance species richness and functional diversity through limiting competition but a synergic interaction of different stresses can lead to reduced richness.

Climate change and floodplain vegetation—future prospects for riparian habitat availability along the Rhine River

“…However, as the calculations of overlap for the different projections in relation to floodplain area revealed, suitable habitat for some vegetation types and river stretches will be available only to a very little extent. Since the hydrologic conditions act as only one abiotic filter besides others and biotic constraints such as dispersal limitation or competition further reduce the amount of habitat that can actually be inhabited (Donath et al 2003;Kotowski et al 2010;Radtke et al 2012), special emphasis concerning these species and river sections should be given from a nature conservation point of view. In any case, the partially large differences between the river sections clearly demonstrated that potential habitat developments need to be evaluated for each river stretch individually since differences in the flow regime, geomorphic structure of the floodplain as well as land use occur along the river.…”

Quantifying flooding regime in floodplain forests to guide river restoration

“…These lower surfaces include channel bars, point bars, channel shelves, backswamps, sloughs, swales and oxbows (Hupp, 2000). Further, upland species may in some cases readily tolerate infrequent flooding of short duration, allowing these species to co-occur with or exclude flood-dependent species, preventing the development of a distinct floodplain vegetation (Shankman, 1993;Kotowski et al, 2010). Finally, relationships between flooding and vegetation composition may be profoundly affected by the relative flood tolerances of invasive species (Tickner et al, 2001;Cooper et al, 2003;Stromberg et al, 2007), many of which are favored by the high level of disturbance associated with floodplain habitats (Zedler and Kercher, 2004;Richardson et al, 2007).…”

Influence of flood variation on seasonal floodplain vegetation communities in the Okavango Delta, Botswana

“…Light availability is a limiting resource for understorey species' primary production (Lite et al 2005). Kotowski et al (2010), in their experimental study on waterlogging and canopy interactions as controls on floodplain plant species recruitment in the Netherlands, found that canopy presence prevented the establishment of understorey plant species, probably due to high light attenuation.…”