Species traits and recolonization processes after flood disturbances in riverine macrophytes

Macrophyte recolonization after two major flood disturbances (winter 1990 and autumn 1991) was studied for 3 years in 11 contiguous permanent quadrats located along a transect from one bank to the other across a former channel of the Rhône River. Floods induced changes in substrate grain-size from fine to coarser sediment and swept away all the plants present before disturbance. Re-establishment of species started on or near the banks in fine sediment areas that can act as refuges for propagules during disturbance or as regeneration niches for propagules brought in by floods. From the banks, the species expanded towards the center of the channel in coarse sediment. The transect was fully colonized by macrophytes the second year after a major flood. All these species, as well as those observed before the 1990 flood, can be considered as pioneer species adapted to frequent disturbances. Information identified from personal previous observations and collected in literature concerning selected species traits was analysed statistically using a fuzzy-coding technique and confronted with date of re-establishment of each species after disturbance. Species composition before disturbance and selected species traits allow us to predict species composition in disturbed areas. The first species to re-establish were able to produce turions or other non-subterranean vegetative organs. Species that disseminate both by lateral spread and regeneration by stem fragments re-establish later, before helophytes that also disseminate by lateral spread but flower each year.Abbreviations CA Correspondence Analysis Species abbreviations used in figures and tables are listed in Appendix 1     

Exotic invasive black willow (Salix nigra) in Australia: influence of hydrological regimes on population dynamics

Floodplain vegetation occupies disturbance prone habitats vulnerable to exotic plant invasion. Black willow (Salix nigra Marshall) is a flood-tolerant tree native to the southeastern United States and recently invasive in Australia, where it is considered detrimental to riparian environments. Effective management of S. nigra requires understanding the impacts of hydrological conditions on population dynamics at each stage of the plant’s life cycle. The influence of inundation events (timing, duration, and recession rates) on S. nigra stand dynamics and relative growth rate (RGR) was quantified across a hydrological gradient on the shorelines of Blowering Dam reservoir (NSW, Australia). Successful recruitment (sexual and asexual) and establishment is highly dependent on the position of S. nigra recruits above reservoir water levels and exposure to flooding during the first few years of establishment. Recruitment was ubiquitous along the hydrological gradient but a greater number of asexual recruits were found at higher elevations where inundation events are less frequent. Juvenile mortality was highest at lower elevations, which experienced greater depth and duration of inundation. Mean RGR was greatest in S. nigra stands experiencing no inundation over the study period and declined as inundation duration increased. Flooding events inhibit adult growth, but create suitable conditions for seedling recruits, provided the depth and duration of the flood does not exceed complete submersion for more than 30 days. To investigate relative tolerance to water table decline rooted S. nigra cuttings were grown in rhizopods, controlled growth devices that allow water-table manipulation. Water-table decline rates of 0, 1, 2, 4, and 8 cm day⁻¹ were applied and the response of leaf abscission measured. S. nigra cuttings were not significantly impacted at water-table decline rates of between 1 and 4 cm day⁻¹. Spatial location of S. nigra recruits in Australian floodplains represents a trade-off among hydrological conditions that promote recruitment without inducing mortality, resulting in a narrow spatial and temporal regeneration window critical to successful establishment. Future distribution and abundance of S. nigra in Australia will be determined by propagule availability and the degree to which current and future flow regimes create suitable hydrological conditions for successful establishment.     

A comment on “Changing estuaries,changing views”

The provision of flood safety is of paramount importance in densely populated deltaic regions. The Dutch rely on flood defences to protect their lives and livelihoods from large-scale floods. The paper “Changing estuaries, changing views” (Smits et al., Hydrobiologica 565:339–355, 2006) criticizes this strategy and presents an alternative that could be summarized as a proposal to leave deltas untouched and to rely on natural sedimentation to reduce the impact of floods. It seems questionable, however, whether such a strategy will often be compatible with population pressures and efforts to stimulate economic growth. Moreover, it presupposes morphological conditions that seem highly unrealistic, not just in the Netherlands but also in many other sediment-starved coastal systems. Other than recommending countries not to implement the Dutch flood protection strategy and to leave deltas untouched, it should be recommended that solutions be tailored to local circumstances. The choice of a flood protection strategy should be based on a balanced evaluation of alternatives, including a realistic assessment of physical conditions.

Ichthyoplankton transport in relation to floodplain width and inundation and tributary creek discharge in the lower Savannah River of Georgia and South Carolina

We report the results of a 3-year study of ichthyoplankton in the lower Savannah River and its coastal plain tributaries. Sampling was weekly from February through July in 1983, 1984 and 1985. Ichthyoplankton transport was used as an estimate of ichthyoplankton production. Ichthyoplankton transport in the river, for both total and most common taxa, was highest in 1983 and lowest in 1985. Ichthyoplankton transport into the river from tributary streams was also highest in 1983 and lowest in 1985. Ichthyoplankton transported from these tributaries sometimes comprised a significant percent of the larval transport at the next river station downstream from the tributary mouth. The highest larval transport occurred when the spring flood pulse was most elevated for the longest time, and larval transport at particular river stations or creeks was correlated with floodplain width in 1983 and 1984, years when flood pulses were high enough so that the adjacent floodplain was inundated during or following spawning. In 1985 the flood pulse was brief, inundation levels were low, and inundation occurred in February before most fish had spawned. Except for American shad and sunfishes, larval transport for all common taxa was greatly reduced in 1985 compared to 1983.     

A reconstruction of flood events using scarred trees in the Tatra Mountains, Poland

In this paper we reconstructed flood events in a small mountain stream (6.6 km long, elevation 1100–1950 m a.s.l.) in the Dolina Waksmundzka Valley in the Tatra Mountains in the Western Carpathians. This reconstruction was based on cross-dated flood scars found in Norway spruce trees growing along stream banks. The scars were most likely formed by woody debris and stones transported during flood events. Reconstructed flood years were then compared with climatic records collected at the nearest meteorological station.Fifty-eight scars were cross-dated indicating 17 years with flood events in the period between 1928 and 2005. The large number of reconstructed flood events proves that the Potok Waksmundzki stream discharge can be highly variable. The high mid-summer rainfall (approximately 300 mm or more per month) peaks in June, July, August and this period coincides with some of the flood scar formation. The high winter and spring precipitation (December–May) does not seem to induce floods. The rate of snow melting seems to be more important. The highest number of scars (33%) was formed in dormant season of 1957/1958. In April and May 1958 there was an unusually large difference between mean monthly temperatures, the highest recorded in the twentieth century. This probably led to an abnormally rapid snow melt. No one single climatic factor can be held responsible for all flood events. Intensive mid-summer rainfall as well as rapid snow melting may induce floods in the Dolina Waksmundzka Valley. Cross-dated scars have enabled past flood events to be detected, which are otherwise invisible from climatic data alone.     

Effects of flooding and artificial burning disturbances on plant species composition in a downstream riverside floodplain

Our objective was to detect environmental and disturbance factors that determine plant species composition in a downstream riverside floodplain of the Shinano River, where both natural flooding and artificial fire disturbances predominate. We classified the natural vegetation into five types by physiognomy, i.e., burnt field, intact (unburnt) field, early-successional forest, later-successional forest, and margin of channel. We deployed 14 transect belts containing 713 plots of 1 m × 1 m at these sites. In the plots, we determined plant occurrences and values of five environmental (soil moisture, soil texture, relative elevation above the river, horizontal distance from the river, and light conditions) and two disturbance factors (scouring of plants by flooding and fire). Plant species compositions and environmental and disturbance factors were different among the sites. Logistic regression analysis showed that burning stimulated the occurrences of herbaceous annuals and conversely constrained those of woody and fern species, suggesting that fire disturbance resets the succession. Scouring of plants by flooding also affected the occurrences of many species, and had a positive influence on that of herbaceous winter annuals in particular. Canonical correspondence analysis indicated that the distributional characteristics of the plant species in the riverside floodplain were influenced primarily by distance from the river, reflecting the magnitude of flood disturbance. We conclude that (1) magnitude of flood disturbance is the primary factor determining plant species composition, and (2) burning maintains early successional vegetation and simultaneously creates a unique plant species composition by stimulating the germination of buried viable seeds transported by flood.     

Larval and juvenile fishes occurring with flood tides on an intertidal mudflat in the Tama River estuary, central Japan

Intertidal movements of fish larvae and juveniles on a mudflat in the Tama River estuary, central Japan, were investigated by comparing the abundance and sizes of fishes caught in the intertidal zone during flood tides with those in the subtidal zone during low tides. A total of 28465 individuals, belonging to 9 families and 20 species, were collected by small purse seine. Among the abundant species, planktonic larvae and juveniles of gobiids and Konosirus punctatus were more abundant in the intertidal zone at flood tide than the subtidal zone at low tide. Similar occurrence patterns were found in juvenile Plecoglossus altivelis altivelis and Lateolabrax japonicus, having fully developed swimming abilities. In contrast to these species, much higher abundances of epibenthic juveniles of 2 gobiids (Acanthogobius flavimanus and Gymnogobius macrognathos) were found in the subtidal zone at low tide, although they also utilized the intertidal zone at flood tide.     

Re-creation of a lowland flood-plain meadow: management implications for invertebrate communities

Intensification of framing practices after the Second World War has led to wide scale loss of semi-natural grasslands throughout the UK. Flood-plain meadows (NVC MG4 Alopecurus pratensis–Sanguisorba officinalis grassland) suffered under these changes in agricultural management, and now cover an area of <1500 ha in England and Wales. In 1985, an experiment was initiated at Somerford Mead, Oxford, with the target of re-creating MG4 grassland. The grassland was established with a sown seed mixture harvested from local MG4 grassland. A replicated block experiment was set up to look at the effects of sheep, cattle and no grazing on the establishment of the target floral community. In 2002, the effects of these management regimes on beetle communities were investigated. Grazing regime was seen to be the primary determinant of abundance, species richness and species assemblage of the beetle population. Vegetation structure was also found to influence beetle diversity. The percentage cover of the legume Trifolium repens had important effects on beetle community assemblage, whilst Trifolium pratense was strongly correlated with the abundance of three common phytophagous beetles. This study provides a preliminary investigation into the responses of beetle communities to management intended for the re-creation of the plant communities of this threatened grassland habitat.     

Seed deposition of Eragrostis curvula, an invasive alien plant on a river floodplain

To test the hypothesis that nonbuoyant seeds transported by river water are deposited with mineral sediment particles that have a similar fall velocity through water, we examined the relationship between the size of sediment deposited by a flood and the density of the deposited seeds of a invasive alien plant, Eragrostis curvula. The average estimated fall velocity of the seeds was 2.93 cm/s, and this value was similar to the fall velocity through water of fine sand (about 0.18 mm in size). Most seeds deposited by a flood pulse caused by a typhoon were observed in sites where fine sand and silt had accumulated on the surface. Over the course of two study years, the number of the seeds found in sediment deposited at microsites correlated significantly with the proportion of sediment particles <0.25 mm in size. Our results suggest that floodplain areas where fine sand is deposited by floods have a high risk of invasion by E. curvula. An erratum to this article can be found at