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Dramatic drift of nymphs of the mayflies Leptophlebia Westwood, 1840 and Siphlonurus Eaton, 1868 (47 600 individuals/trap per hour) was observed between a southeastern USA river and adjacent floodplain following natural flooding events. Active movements of these nymphs against the water flow were also detected. Large numbers of leptophlebid nymphs reside in floodplains during the winter and spring, but how and why they colonize and develop in temporary habitats is uncertain. We detected few environmental advantages (i.e., temperature, food abundance or quality) for mayflies in floodplains compared with river habitats. Despite this, experiments indicated that mayflies had 36% higher growth rates in the floodplain than in the river and demonstrated tolerance to short-term drying (up to 12 d). Migration entails costs of migrating against flows during daylight when vulnerability to predation is high, colonizing a habitat subject to drying, hypoxia, and supporting amphibian predators, with few apparent benefits. Dispersal into wetlands may be attributed to avoiding swift river flows or exploiting largely fishless habitats. However, dispersal could be an evolutionary relic of behavior beneficial in more northerly habitats; our study populations of Leptophlebia mayflies were at the southern extreme of their range and perhaps operating suboptimally. Our results emphasize the importance of river-floodplain linkages to the ecology of both habitats. Une derive spectaculaire de larves d'ephemeras Leptophlebia Westwood, 1840 et Siphlonurus Eaton, 1868 (47 600 individus/piege par heure) a pu etre observee entre une riviere du sud-est des E.-U. et sa plaine de debordement adjacente a la suite d'evenements de crue naturels. Nous avons aussi detecte des deplacements actifs de ces larves contre le courant. De grands nombres de larves de leptophlebiides habitent les plaines de debordement durant l' hiver et le printemps, mais il n'est pas clair comment et pourquoi elles colonisent et se developpent dans ces habitats temporaires. Nous trouvons peu d'avantages environnementaux (par ex., de temperature, de quantite et de qualite de nourriture) pour les ephemeras dans les plaines de debordement par rapport aux habitats de riviere. Neanmoins, des experiences montrent que les ephemeres ont des taux de croissance de 36 % plus eleves dans la plaine de debordement que dans la riviere et revelent une tolerance a la dessiccation de courte duree (jusqu'a 12 jours). La migration entraine des couts de deplacement a contre-courant durant les heures du jour lorsque la vulnerabilite a la predation est elevee, pour coloniser un habitat sujet a la dessiccation et l'hypoxie et etre expose aux amphibiens predateurs, pour peu de benefices apparents. La dispersion vers les terres humides peut etre expliquee par l'evitement des forts debits de la riviere ou l'exploitation d'habitats en grande partie sans poissons. Cependant, la dispersion pourrait etre un vestige de revolution d'un comportement plus benefique dans les habitats plus nordiques; les populations d'ephemere Leptophlebia que nous etudions se situent a la marge sud extreme de leur aire de repartition et fonctionnent peut-etre de maniere suboptimale. Nos resultats soulignent l' importance des liens entre la riviere et sa plaine de debordement dans l' ecologie des deux habitats. [Traduit par la Redaction], Introduction Transitional zones between habitats, or ecotones, can be very important foci of ecological interactions and biological diversity (Risser 1995; Hufkens et al. 2009). Ecotones are found in a variety [...]

Extreme summertime flood events are expected to become more frequent in European rivers due to climate change. In temperate areas, where winter floods are common, extreme floods occurring in summer, a period of high physiological activity, may seriously impact floodplain ecosystems. Here we report on the effects of the 2002 extreme summer flood on flora and fauna of the riverine grasslands of the Middle Elbe (Germany), comparing pre-and post-flooding data collected by identical methods. Plants, mollusks, and carabid beetles differed considerably in their response in terms of abundance and diversity. Plants and mollusks, displaying morphological and behavioral adaptations to flooding, showed higher survival rates than the carabid beetles, the adaptation strategies of which were mainly linked to life history. Our results illustrate the complexity of responses of floodplain organisms to extreme flood events. They demonstrate that the efficiency of resistance and resilience strategies is widely dependent on the mode of adaptation. Key words: carabid beetles; extreme event; flood; floodplain; grassland; mollusks; resilience; resistance; river Elbe; vegetation.

Algal carbon has been increasingly recognized as the primary carbon source supporting large-river food webs; however, many of the studies that support this contention have focused on lotic main channels during low-flow periods. The flow variability and habitat-heterogeneity characteristic of these systems has the potential to significantly influence food web structure and must be integrated into models of large-river webs. We used stable-isotope analysis and IsoSource software to model terrestrial and algal sources of organic carbon supporting consumer taxa in the main channel and oxbow lakes of the Brazos River, Texas, USA, during a period of frequent hydrologic connectivity between these habitat types. Standardized sampling was conducted monthly to collect production sources and consumer species used in isotopic analysis. Predictability of hydrologic connections between habitat types was based on the previous 30 years of flow data. IsoSource mixing models identified terrestrial [C.sub.3] macrophytes (riparian origin) as the primary carbon source supporting virtually all consumers in the main channel and most consumers in oxbow lakes. Small-bodied consumers (< 100 mm) in oxbow lakes assimilated large fractions of algal carbon whereas this pattern was not apparent in the main channel. Estimates of detritivore trophic positions based on [delta][sup.15]N values indicated that terrestrial material was likely assimilated via invertebrates rather than directly from detritus. High flows in the river channel influenced algal standing stock, and differences in the importance of terrestrial and algal production sources among consumers in channel vs. oxbow habitats were associated with patterns of flooding. The importance of terrestrial material contradicts the findings of recent studies of large-river food webs that have emphasized the importance of algal carbon and indicates that there can be significant spatial, temporal, and taxonomic variation in carbon sources supporting consumers in large rivers. Key words: Brazos River, Texas, USA; floodplain; food web; IsoSource; isotopes; oxbow lakes.

Geomorphological changes can alter river hydrology and thus influence floodplain forest growth and regeneration. In this paper we quantify the effect of changes in channel elevation at the scale of four decades on hydrological conditions, overbank sediment deposits, water availability, and their impacts on common ash (Fraxinus excelsior) growth and recruitment in floodplain forests of the Ain River, France. Ash is a droughtsensitive species, and its regeneration is influenced by flood disturbance. We compared ash growth between 20 sample plots located in two contrasting geomorphological contexts using dendrochronological measurements: 11 along reaches degrading over the last 80 years and nine along stable or slightly aggrading reaches, In each context, half of the plots were located near the channel, and the remainder were within the floodplain. Ash regeneration was also quantified in each plot. This work showed that sites which undergo channel degradation are associated with less frequent overbank flows. Whereas there is no trend in either the climatic or stream flow timeseries over the last four decades, the growth patterns of ashes of these sites are significantly different as-opposed to plots located in stable or aggraded reaches (bell shaped curve vs. constant increase in tree ring width). The variance through time due to climatic or stream flow control is masked by variance due to topographical changes. Currently plots located in degraded reaches show a lower ash growth (mean of 0.20 cm/yr vs. 0.34 cm/yr over the last decade) and less frequent ash seedling establishment. We have identified a hydrologic threshold for ash growth response when stand elevation values reach 1.5-2 m above the mean annual flow stage. Our results confirm that, at a many-decade timescale, changes in channel elevation must be considered in addition to other hydrological controls of hardwood species growth and recruitment. Key words: channel degradation; common ash; dendrochronology; floodplain forests; Fraxinus excelsior; geomorphological control; sedimentation; tree growth; tree regeneration.

Abstract: Reproductive activity of seven species representing three divergent life history strategies was monitored monthly for 2 years in channel and floodplain habitats of the Brazos River, Texas, USA, to [...]

Understanding the hydraulics of flow in a compound channel with vegetated floodplains is very important for determining the stage-discharge curve and for supporting the management of fluvial processes. In this paper, the flow patterns over different types of vegetation, such as tree, shrub, and grass, are described, based on an experimental study. For vegetation on the floodplain, the authors choose plastic grass, duck feathers, and plastic straws as model grass, shrubs, and trees, respectively. A 3D acoustic Doppler velocimeter was used to measure the local flow velocities for different types of vegetation on the floodplain, and the total discharge and flume slope were measured independently. In the cases of nonvegetated floodplains, all measured streamwise velocity distributions followed the logarithmic distribution, but for vegetated floodplains, they followed an S-shaped profile, exhibiting three zones. For all cases, the fluctuating velocity followed a normal distribution. The influence of different types of vegetation on the distributions of the secondary currents, turbulence intensities, and Reynolds shear stresses were also analyzed. DOI: 10.1061/(ASCE)0733-9429(2007)133:2(148) CE Database subject headings: Channel flow: Vegetation: Flood plains: Currents: Turbulence: Reynolds stress: Shear stress.

Soil profiles in 10 persistently bare areas (i.e. scalds), mainly located in coastal backswamps of New South Wales, Australia, were examined for chromium-reducible sulfur content and selected chemical properties. At 5 of the sites, the adjacent paddocks with vegetation cover were also examined. All of the tested sites had been affected by the extensive drainage of the surrounding acid sulfate soil (ASS) landscapes and the consequent oxidation of pyrite. All sites had low pH values in the surface soil layers and these low pH values extended for up to 150 cm into the underlying unoxidised blue/grey pyritic estuarine gels. This can be attributed to the downward diffusion of acidity, either produced in the overlying oxidised zones of these soils or transported laterally across the landscape to these low-lying areas. Acidified unoxidised pyritic zones 120 cm thick can evidently form within several decades after drainage disturbance. At the scalded sites the depth from the soil surface to the main pyritic zone varied from the surface to >200 cm depth, indicating that this variable is not critical to ASS scald formation. For most of the sites examined, the chromium-reducible sulfur contents in the surface soil layers were appreciably higher than those in the immediately underlying soil layers. In most of the vegetated sites the chromium-reducible sulfur content in the surface layers was considerably higher than for the adjacent scalded site. The conditions necessary for pyrite formation (i.e. adequate supplies of organic matter, soluble iron, sulfate, and waterlogging) were found to exist at all sites, and the pyrite accumulations in these surface soil layers are considered to be neo-formed. The vegetated soil-profile pyrite and pH results were very similar to their scalded counterparts except that they had an extra 20-40 cm layer of vegetation and mulch that was missing from the scalded profiles. This indicates that there is considerable potential for more extensive scalding in these ASS areas. Additional keywords: subsurface pyrite, surface pyrite, pyrite oxidation, pyrite re-formation, acid sulfate soil pH, backswamp management, backswamp drainage., Introduction Acid sulfate soil (ASS) scalds are persistently bare areas of land associated with pyrite oxidation and ASS formation in drained coastal floodplains. In Australia, ASS scalds have not previously [...]

The observations presented in this paper illustrate that significant amounts of monosulfidic black oozes (MBO) were eroded from flood mitigation drainage canals and redistributed across a coastal floodplain during a flood event associated with extreme deoxygenation and a massive fish kill. MBO are organic materials enriched in iron monosulfides and thick layers can accumulate in drains affected by acid sulfate soils. Laboratory studies have demonstrated that MBO can react rapidly when brought into suspension to completely consume dissolved oxygen. The abundance of MBO in flood mitigation drains and their extreme reactivity implicated MBO in the acute deoxygenation of the Richmond River, north-eastern New South Wales, Australia, following a major flood in February 2001. The field observations of MBO redistribution provide valuable evidence to help explain how these materials may interact and contribute to the deoxygenation of floodwaters. Additional keywords: iron sulfides, pyrite, monosulfides, acid volatile sulfur, deoxygenation, MBO., Introduction Monosulfidic black oozes (MBO) are organic materials enriched in iron monosulfides. Thick layers of MBO accumulate in many canals that drain acid sulfate soil (ASS) landscapes (Bush et al. [...]

By using the established hydraulic relationships among flood frequency, flood magnitude, and river-channel capacity, we develop a scale-independent assessment of the hydrogeomorphic impacts of 21 dams across the United States that have broad ranges in function and contributing drainage area. On the basis of generalized extreme value (GEV) analysis of pre- and post-dam hydrologic records, our analysis indicates that the 2 yr discharge has decreased ~60% following impoundment, exceeding the magnitude of climatically triggered discharge reductions occurring during the Holocene. Reductions in the frequency of the pre-dam 2 yr discharge have been equally profound. The pre-dam 2 yr flood has occurred on average twice per site, whereas statistical analysis indicates that it should have occurred ~20 times. Furthermore, floods greater than bankfull have been essentially eliminated by dams, completely disconnecting the riparian zone from riverine influence. Our analyses herein suggest that a critical threshold of disconnectivity exists and corresponds approximately to the pre-dam 5 yr flood. This similar recurrence probability exists independent of region, dam type, of catchment size. Keywords: dams, hydrologic regime, floods, riparian.

Interstitial flow of river (hyporheic) water influences algal productivity, benthic assemblages, and locations of fish spawning. However, little is known of the effects of hyporheic flow on the growth of riparian vegetation. By increasing water availability and nutrient delivery, regional upwelling of hyporheic water may increase the growth of terrestrial vegetation. We tested and accepted the hypothesis that cottonwood trees (Populus trichocarpa) in a gaining reach of an alluvial floodplain grow faster than trees in a losing reach by comparing basal areas and ages on an expansive floodplain in western Montana (USA). Trees in the gaining reach had basal areas twice the size of the trees in the losing reach, after correcting for tree age. In addition, the carbon-to-nitrogen ratios in leaves were 16% lower in the gaining reach. Lower cottonwood stem densities, deeper layers of fine sediments, and a higher water table occurred in the gaining compared to the losing reach. Each of these variables was significantly correlated with tree growth and likely interacted to influence the productivity of cottonwoods. We concluded that hydration and fertilization of riparian trees likely is mediated by hyporheic flow. Key words: cottonwood; dendrochronology; floodplain; groundwater; growth; hyporheic; interstitial flow; Montana, USA; Populus; riparian; tree rings.

Expansion of Typha domingensis into areas previously dominated by Cladium jamaicense in the Florida Everglades has been linked to anthropogenie phosphorus (P) enrichment and increased hydroperiod. The principal stress factor for plants in flooded soils is biochemical reduction, the intensity of which is measured as redox potential (Eh). The objective of this study was to assess the growth response of C. jamaieense to Eh (-150, +150, and +600 mV) and P availability (10, 80, and 500 [micro]g P/L). Plants were grown hydroponically in a factorial experiment using titanium ([Ti.sup.3+]) citrate as an Eh buffer. Treatment effects on growth, biomass partitioning, and tissue nutrients were recorded. Growth approximately doubled in response to a 50-fold increase in P availability. Low redox significantly reduced growth and tissue P concentration. While plant P concentrations increased 20-fold between the 10 and 500 [micro]g P/L treatments, P concentrations were 50 100% higher at +600 mV than at -150 mV within each phosphate level. At high Eh, C. jamaieense appears well adapted to low nutrient environments because of its low P requirement and high retention of acquired P. However, at low Eh the ability to acquire or conserve acquired P decreases and as a consequence, higher phosphate levels are required to sustain growth. Findings of this study indicate that young C. jamaicense exhibits low tolerance to strongly reducing conditions when phosphate is scarce. Key words: Cladium jamaicense; Cyperaceae; Everglades; micronutrients: nutrient acquisition; nutrient allocation; nutrient use efficiency; photosynthesis; sawgrass; Typha domingensis.

1 The structure and functioning of riverine ecosystems is dependent upon regional setting and the interplay of hydrologic regime and geomorphologic processes. We used a retrospective analysis to study recruitment along broad, alluvial valley segments (parks) and canyon segments of the unregulated Yampa River and the regulated Green River in the upper Colorado River basin, USA. We precisely aged 811 individuals of Populus deltoides ssp. wislizenii (native) and Tamarix ramosissima (exotic) from 182 wooded patches and determined the elevation and character of the germination surface for each. We used logistic regression to relate recruitment events (presence or absence of cohort) to five flow and two weather parameters. 2 Woody plant establishment occurred via multiple pathways at patch, reach and segment scales. Recruitment occurred through establishment on (1) vertically accreting bars in the unregulated alluvial valley, (2) high alluvial floodplain surfaces during rare large flood events, (3) vertically accreting channel margin deposits in canyon pools and eddies, (4) vertically accreting intermittent/abandoned channels, (5) low elevation gravel bars and debris fans in canyons during multi-year droughts, and (6) bars and channels formed prior to flow regulation on the dammed river during controlled flood events. 3 The Yampa River's peak flow was rarely included in models estimating the likelihood that recruitment would occur in any year. Flow variability and the interannual pattern of flows, rather than individual large floods, control most establishment. 4 Regulation of the Green River flow since 1962 has had different effects on woody vegetation recruitment in canyons and valleys. The current regime mimics drought in a canyon setting, accelerating Tamarix invasion whereas in valleys the ongoing geomorphic adjustment of the channel, combined with reduced flow variability, has nearly eliminated Populus establishment. 5 A single year's flow or a particular pattern of flows over a sequence of years, whether natural or man-made, produces different recruitment opportunities in alluvial and canyon reaches, in diverse landforms within a particular river reach, and for Populus and Tamarix. The design of flows to restore riparian ecosystems must consider these multiple pathways and adjust the seasonal timing, magnitude and interannual frequency of flows to match the desired outcome. Key-words: Colorado, dams, floods, Green River, Populus, regulated river, riparian, Tamarix, tree ageing, unregulated river, Utah, Yampa River. Journal of Ecology (2003) 91, 182-196

Paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from Glacial Lake Missoula, Montana, entered Washington's Yakima and Walla Walla Valleys during the last glaciation. In these valleys, the field evidence for hiatuses between floods is commonly subtle. However, paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at Zillah, Touchet, and Burlingame Canyon display consistent secular variation that correlates serially both within and between sections. The secular variation may further correlate with paleomagnetic data from Fish Lake, Oregon, and Mono Lake, California, for the interval 12,000-17,000 [sup.14]C yr B.P. Deposits of two successive floods are separated by two tephras derived from Mount St. Helens, Washington. The tephras differ in age by decades, indicating that a period at least this long separated two successive floods. The beds produced by these two floods are similar to all of the 40 beds in the slack-water sediment sequence, suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years. Keywords: Glacial Lake Missoula, jokulhlaups, tephra, paleomagnetic secular variation.

Interferometric processing of a Space Shuttle-based swath of synthetic aperture radar (SAR) data collected over the central Amazon floodplain reveals one-day decreases in water levels ranging from 1 to 11 cm in mid-October 1994. The decreases, plotted in a geographic information system (GIS), do not appear to be related to water-body size. Instead, the drops correlate with distance between measured location and main river channel. Because the flow routes connecting observed water bodies to a river channel are convoluted, stream network extraction algorithms operating within a GIS are ideally suited to identify flow-path distances. High-resolution digital elevation models (DEMs) are not available for the Amazon Basin; instead, extraction algorithms are applied to a basin-wide mosaic of raster-based SAR amplitude data. SAR amplitudes mimic topography with weak radar returns over open water lying in low elevations and strong returns over non-flooded, higher elevations. As flow-path distance increases, there is a general decrease in the floodplain water level drops. This functional relationship is used to extrapolate the swath of interferometrically based observations beyond their ~ 15-percent coverage of the central Amazon floodplain. If the extrapolation is correct, the decreases in water levels sum to a storage change of 4,600 [m.sup.3]/s from an area of 11,800 k[m.sup.2] across the floodplain during midrecessional flow. This value is about 30 percent less than the storage change estimates previously derived from flood routing. The difference likely results from the model-based assumption that water-level fluctuations across the floodplain are equivalent to those in the main river channel. The interferometric observations suggest that this equivalence does not appear to be correct for mid-October 1994. Key Words: floodplains, flow networks, GIS, interferometric SAR.

1 Summer floods whose severity is affected by flooding duration, submergence depth and underwater light availability, have a large impact on the zonation of riparian plant species. 2 We analysed the range and variability of these flooding components in the River Rhine and quantified their effects on the ability of Arrhenatherum elatius, Achillea millefolium, Rumex acetosa and Rumex crispus, to survive periods of submergence under experimental conditions. 3 Survival characteristics were used to model species' lower distribution boundaries for extreme and average floods and were compared with the current field distribution. Different light conditions were simulated by implementing three scenarios of suspended load. 4 Extreme deep Rhine floods are characterized by very low median light transmission levels (i.e. below 0.5%). The largest survival responses in the experiment were observed at such low levels (0.4-3.5 [micro]mol [m.sup.-2] [s.sup.-1]). Strong effects of light were found in R. crispus and A. millefolium, but responses were weaker in A. elatius and R. acetosa. Submergence depth also affected survival, but not as strongly as light. 5 For the flood intolerant species (A. millefolium and A. elatius) the average flood was predicted to have little effect on field distributions under normal light conditions. However, their actual field distributions in 2000 corresponded to the predicted lower boundaries in the extreme years. This suggests that extreme years determine the distributions of these species for many years. The suspended load scenarios significantly modified the predicted lower boundaries in both extreme and average years, implying that plant lower distribution limits may be significantly shifted upwards or downwards depending on the suspended load of the river system. 6 The predicted lower boundaries of the intermediately tolerant R. acetosa and the highly tolerant R. crispus for both extreme and average years were below the actual field distribution in 2000. This suggests that their current distribution is only partly influenced by major flood disturbances and that other factors, either proximate or historical, may play a prominent role. Keywords: Disturbance, flooding regime, submergence, survival, floodplain zonation, suspended load, light attenuation.

Pristine floodplain forests are virtually nonexistent in the eastern United States, requiring that preservation efforts focus on relatively intact representatives of these unique ecosystems, many situated where hydrologic modifications are the norm. This article examines the vegetation dynamics for one such natural area, a wilderness island in northwestern Pennsylvania, to assess how the ecological processes of a riparian preserve are affected by changes to the surrounding environment. Ordination of a vegetation sample identifies several landscape patches on the island; the structure and historical development of these communities are analyzed using tree ring patterns, aerial photography, and the flood regime characteristics preceding and following construction of a large dam upstream. Research on natural riparian sites has emphasized the role of floods as a disturbance that generates early successional habitat. Here, however, moderation of the hydrologic regime has shifted the impact of floods from disturbance to stressor. Peak flows are no longer sufficient to open sites for colonization, while the duration of flooding has increased. Without flood disturbance, later stages of succession become more widely represented, and species regeneration occurs in the context of competitive--rather than open--sites. The altered disturbance regime thus favors species with life history characteristics atypical of the pre-dam environment, including nonnative species, resulting in altered composition and vegetation dynamics. Managerial expectations that natural successional processes will eventually restore degraded riparian habitats in these modified settings are therefore unlikely to be fulfilled. Key Words: dam impacts, disturbance regime, flooding, natural area management.

Nutrient and organic matter dynamics were evaluated for a glacial river-floodplain system in the Swiss Alps (Val Roseg). Glacial melt water was the primary source of particulate organic and inorganic matter; hillslope groundwater was richest in DOC and Si[O.sub.2]; and pulses in dissolved nitrogen were identified during spring snowmelt. Calculations of temporal coherency revealed that hydrological processes within the catchment-floodplain complex controlled nutrient and organic matter species along the main channel; however, local hydrological and/or biogeochemical processes played a major controlling role in most floodplain channels. DON and N[O.sub.3]-N were the only variables that were in average significantly correlated across all sampling sites. Comparisons of measured concentrations and concentrations based on a two end member mixing model indicated that the floodplain served as a major sink for particulate phosphorous and suspended matter but was never a source for nutrients or organic matter. Annual area-specific export rates from the Val Roseg catchment were 7.6 kg [ha.sup.-1] [yr.sup.-1] for TOC (47% DOC), 4.3 kg for TP (98% particulate phosphorus), and 4.1 kg for TN (78% N[O.sub.3]-N).

Constraints on nitrogen fixation are the ultimate causes of N limitation of primary production, but hypotheses concerning limitations to [N.sub.2] fixation remain largely untested in natural terrestrial ecosystems. We examined limitations to [N.sub.2] fixation by thinleaf alder (Alnus tenuifolia) in two stages of primary forest succession on the Tanana River floodplain (interior Alaska, USA) and focused on the hypothesis that [N.sub.2] fixation was limited by low soil P availability. Paired control and P fertilized plots were established at four replicate early successional alder stands and four later successional poplar (Populus balsamifera) stands (dense alder understories with mature poplar overstories) and [N.sub.2] fixation was estimated with an acetylene reduction assay. In alder stands, P fertilization increased total nodule dry biomass and increased total ecosystem N inputs, but it had little effect on nitrogenase activity per unit nodule dry mass (specific acetylene reduction activity, ARA). Specific ARA increased only in late July when soil temperature and ARA were at their maximum values. In contrast, fertilization had no effect on these measures in poplar stands where reduced soil moisture may have superseded limitation by P. We detected no differences in specific ARA, total nodule biomass, or N inputs, between alder and poplar stands but all of these measures were highly variable. Leaf area of the alder canopy emerged as the best predictor of ecosystem inputs of fixed N among control plots. Alders resorbed high amounts of P but little N (consistent with low P availability and a high P demand and a high N availability in alder), and P fertilization reduced P resorption but had no effect on N resorption. The timing of [N.sub.2] fixation and N resorption indicate that late-season increases in leaf N, following a midseason reduction in leaf N, were driven by [N.sub.2] fixation in excess of plant N demands as nodules continued fixing N while alder leaves senesced. These results have shown that P limits [N.sub.2] fixation in alder stands in this nitrogen-limited sere, but that factors limiting [N.sub.2] fixation can change over short successional time scales. Key words: Alaska; alder; Alnus; allelopathy; nitrogen fixation; nitrogen retention; nodule biomass; phosphorus; Populus; primary, succession; resorption; Tanana River floodplain.

A method is presented for determining morphological relationships within river basins. The method incorporates systematic interaction between basin steepness, relief and size, interpreted in an intermediate limit process framework bounded by spatial scales.

An analysis is presented on the augmentation of particle trapping tendencies within flood-dominated estuary systems due to the interplay between tidal asymmetries and buoyancy. The effects of slow and long ebbs, tidal straining, weak vertical mixing, turbulence and horizontal advection and dispersion are also discussed.

Research on floodplain ecology in the southwestern US indicates that the native cottonwood species Populus deltoides is sufficiently dominant to withstand the potential introduction of the invasive species saltcedar, or Tamarix ramosissima. Although both are responsive to natural flooding cycles, Populus was found to have superior competitive ability.

1 The objective of this study was to examine how increasing water depth in the field affects the aeration achieved by convective gas flow in an emergent aquatic sedge (Eleocharis sphacelata). 2 We compared internal pressurization, convective gas flow, changes in internal gas composition, and differences in plant morphology at three depths (0.75-0.90 m, 1.40 m, and 2.15-2.65 m) in an oligotrophic lake. 3 Internal pressures generated in the aerial tissue of the influx culms were similar at all depths, but the convective inflows increased with depth due to lower resistances to convective flow in the plants growing in deeper water. In contrast, rates of flow returning up the efflux culms decreased with depth, due to a decrease in ratio of influx: efflux culms with depth. 4 Respiration lowered the oxygen concentration in the stagnant internal gas at night, with predawn concentrations highest at the shallowest site and lowest at the deepest site. Low oxygen concentrations also persisted longer after dawn in plants at the deep site than at the other sites due to the large volume of stagnant gas that had to be expelled relative to the flow rates. 5 By 14.00 h, the stagnant gas had been flushed from the plants at all depths, and oxygen concentrations were close to atmospheric values throughout. The two factors apparently responsible for maintaining high oxygen concentrations when convective flow was operating were (i) morphological changes at the deep site that reduced the resistance to flow, and (ii) dissolution of carbon dioxide produced in respiration into the external medium. 6 The data indicate that the average oxygen concentration maintained internally over a 24-h cycle by convective flow decreases significantly with depth, suggesting that oxygen stress due to gas transport limitations may be one of the factors limiting depth penetration in this species and other emergent aquatic plants. Keywords: emergent macrophyte, flooding, oxygen, respiration, wetland

An overview is presented on the Kissimmee-Okeechobee-Everglades restoration project in Florida, focusing on the partnership between resource management and scientific research. Topics include the environmental effects of nutrient loading, biotic variables, algal bloom frequencies, floodplain ecology, turbidity and storm water runoff.

A computer model for epilithic algae and grazer biomass in streams is modified to better predict the effects of temperature and is calibrated for diatoms and mayflies. Mayflies are predicted to maintain low diatom biomass provided that (1) temperatures remain within their preferred range (10-20 degrees C); and (2) mayfly populations are not adversely affected by floods. Algal blooms are predicted to occur in mayfly-dominated streams above 20 degrees C - temperatures common in pasture streams over summer. We hypothesize that mobile bed streams are susceptible to blooms during summer low flows following floods because (1) they usually lack temperature tolerant snail grazers; and (2) mayfly recovery lags behind algal regrowth, and there is a short period when algae escape from 'top-down' grazer control.

Phosphorus (P) availability in the Parana flood plain lakes of Argentina is discussed. Its influence of pH and phosphate buffering by fluvial sediments was studied in three geologically different rivers. Phosphate-buffering properties and P chemistry of suspended particulate matter (SPM) in three rivers are compared and distinctive P-buffering capacities were related to the chemical composition of SPM. Loading of fluvial sediments to the lakes and the acidic dissolving of calcium-bound P likely can explain the permanent excess of dissolved phosphate-P in the waters in question.

Introduction This study of grazing on the Murrumbidgee River's flood plain had its origins in a larger project which aimed to investigate the environmental impacts of cattle on riparian land. [...]

Possible health risks related to exposure to heavy metals in river bank soils have been investigated for the River Meuse, which was flooded at the end of 1993. Soil and deposit samples and corresponding arable and fodder crops were analyzed for heavy metals. Soils of the floodplain appeared to be severely polluted by the flooding, mostly by cadmium (Cd) and zinc (Zn), but heavy metal concentrations in the crops grown on the soils were within background ranges. A potential health risk does exist for bank dwellers of this river which floods on the average every 2 years.

The successive construction of large dams has had a significant impact on reservoir biogeochemistry along the Rio Negro in Uruguay. Among a total of 30 woody species identified in the floodplain forests studied, there was a significant decrease in tree height, stem density, wood biomass and basal area from the riparian forest to patch and transition forests. There were also changes in nutrient concentrations in wood along the floodplain. In riparian forests, phosphorous was higher than in other forest types. There was a rise in N from the riparian to patch and transition forests.

We compared small-mammal communities between inactive floodplain and actively flooded terraces of riparian habitat in the Verde Valley of central Arizona. We used species diversity, abundance, weight of adult males, number of juveniles, number of reproductively active individuals, longevity, residency status, and patterns of microhabitat use to compare the two communities. Although abundances of small mammals tended to be higher in the active floodplain, species diversity was greater in the inactive floodplain. Results were inconsistent with our initial prediction that actively flooded riparian habitat acts as a species source, whereas inactive floodplain acts as a sink or dispersal site for small mammals. Within each habitat type, we found evidence of significant microhabitat separation among the three most abundant small-mammal species (Peromyscus boylii, P. eremicus, and Neotoma albigula). Percent cover by annual and perennial grasses and shrubs, substrate, and frequency of shrubs, trees, and debris were significant determinants of small-mammal distribution within a habitat type. We found that the three most abundant species selected a nonrandom subset of available habitat. Nonrandom use of habitat and microhabitat separation were the two most important mechanisms structuring small-mammal communities in riparian habitat of central Arizona. Key words: small-mammal communities, riparian floodplains, inactive floodplains, source-sink dynamics, habitat selection, Arizona

In forest understories, tree seedlings that germinate and emerge early in the growing season have significant survival advantages. We hypothesized that (a) early emergence is related to seed size and half-sib family, and (b) increased survival is due to reduced competition for resources. To test these hypotheses, we collected seeds of Acer rubrum from four half-sib families and planted them in the understory of a South Carolina floodplain forest. In one experiment, date of emergence was not related to seed size or half-sib family. However, our method of seed collection may have underestimated variability among half-sib families. In a second experiment, seeds were spread onto 20 understory plots, half of which were trenched to reduce root competition with overstory trees. One-year survival and biomass were greater for early- than for later-emerging cohorts. Trenching changed biomass distribution among aboveground parts and may have increased total biomass, but had essentially no impact on survival or root mass. Variation in plot flooding resulted in large differences in timing of emergence, survival, and biomass. For Acer rubrum, the survival advantage accorded by early emergence may be more related to flooding, light conditions, and genetic heterogeneity than to seed size or avoidance of root competition. Key words: Acer; Aceraceae; flooding; forest understory; forested wetlands; germination; half-sib family; microsites; root competition; seeds.

Between 1987 and 1990, we estimated seedfall and recorded age, growth, and survival of 10 933 tree and vine seedlings growing in the understories of four bottom-land hardwood forests in South Carolina. The forests differed in flood frequency, soils, and vegetation structure but had a number of woody plant species in common. Several demographic processes were consistent for all four forests as well as for flood-plain forests described in other published studies. Smaller seeded species had larger numbers of seeds dispersed, germinants, and established seedlings. Seed size, however, was not clearly related to seedling survival. Published rankings of shade and flood tolerances were also unrelated to survival, at least during the first growing season after germination. Seedling survival rates were least during the first growing season and greater in subsequent years. Within a growing season, early germinants had greater survival. For some species, survival was negatively related to basal area of neighboring conspecific adult trees. Some aspects of the regeneration process were more site specific. Within species, seedfall densities relative to adult tree abundance differed across forests by an order of magnitude. First-year seedling mortality rates were significantly affected by site and site X species interactions. Mortality in subsequent years was also significantly affected by site. Although the role of flooding in site-specific mortality was not clear, small elevation changes within flooded sites were correlated with changes in germination and survival for some species.

In northwestern Quebec, black ash (Fraxinus nigra Marsh.) is found mostly in floodplains bordering lakes and rivers. In this habitat, population dynamics are largely controlled by spring water level, and sexual regeneration is more abundant in sites less exposed to flooding. The hypothesis tested in this study is that sexual regeneration of black ash in sites slightly exposed to flooding is influenced by fluctuations of spring flood water level. The age structure of two sapling populations (

Palaeosols (fossil soils) are abundant in the alluvial late Silurian-early Devonian Moor Cliffs Formation and Rat Island Mudstone (Freshwater West Formation) of south Dyfed, South Wales. The palaeosols occur in thick mudstones deposited on floodplains under a seasonal, semi-arid climate, and represent Vertisol-type soils. Simple, single profiles are rare and most of the mudstone intervals exhibit complex overprinted profiles. However, a major difference exists between the palaeo-Vertisols in each of the two units studied. The Moor Cliffs Formation contains thick floodplain intervals with evidence of frequent erosion and reactivation of earlier soil horizons. The associated coarser channel deposits mainly represent ephemeral streams. The alluvial system was unstable, flashy and prone to extensive stripping of stored floodplain sediment. Arroyos (unstable ephemeral stream channels) probably developed during this interval. Evidence for any marine influence on soil development is missing and previous speculations that the formation may represent deposition in an upper-intertidal or supratidal system are not supported. The Rat Island Mudstone represents a complete contrast in that there was little or no stripping of floodplain sediments. The channel deposits are typically of the fining-upwards type representing more stable, low sinuosity channels and with ephemeral-stream floods. By integrating the palaeosols, a more detailed picture of the geomorphic history of these units can be formulated. Comparison with contemporary drainage basins indicates that a change in climate was a possible cause for the differences between the two units, less frequent and more severe storms occurring during the deposition of the Rat Island Mudstone.

Effective management of the Amazon's commercial fish populations requires an understanding of the factors controlling their production. A fundamental step in the investigation of fish production is to identify the plant groups that contribute energy to fish foodwebs. Stable isotope data for plants and 35 fish species were used to identify autotrophic carbon sources for the central Amazon fish community. Adult fish, aquatic macrophytes, tree parts, periphyton, and phytoplankton were collected in lakes and other flooded environments along the central Amazon floodplain and analyzed for carbon stable isotope composition (delta-13C) by mass spectroscopy. Delta-13C values for plants ranged from -39.4 to -11.9% with averages of -33.3, -28.8, -27.6, -26.2, and -12.8% for phytoplankton, flooded forest trees, C3 aquatic macrophytes, periphyton, and C4 macrophytes, respectively. The average for all C3 plants (phytoplankton, trees, C3 macrophytes, and periphyton) was -29.1%, while the average for C4 plants (mainly C4 macrophytes) was -12.8%. Mean delta-13C values for adult fish ranged from -37.0 to -19.8% with an average of -28.8%. Fish and plant data were used in an isotope mixing model to estimate the relative contribution of different plant groups to fish carbon. C4 macrophytes, which contributed over half of the primary production on the floodplain, accounted on average for only 2.5-17.6% (minimum to maximum) of the carbon in fish. The C3 plants, as a group, were the primary carbon source for 34 fish species, and accounted for an average of 82.4-97.5% of the carbon in all species. Phytoplankton, a minor C3 producer, accounted for a minimum of 36.6% of fish carbon on average, and was the principal carbon source for the commercially important characiform detritivores. Several alternative hypotheses are proposed to explain the apparent selective transfer of C3 carbon through Amazon fish foodchains.

1. A large-scale outdoor experiment was carried out to study the effect of flooding on growth, survival and reproduction in relation to developmental stage in three short-lived species. Several cohorts of Chenopodium rubrum, Rumex maritimus and R. palustris were raised in accordance with a flooding regime which was based on the average flooding conditions of their natural habitats in river forelands. 2. Survival of submergence in the pre-reproductive phase was high in both species of Rumex, but relatively low in C. rubrum. Biomass reduction following flooding depended on plant size before flooding and on the mean temperature of the flood-water. 3. Both Rumex spp. were less reduced in size during flooding, and better capable of regeneration afterwards, than C. rubrum. 4. Later-raised cohorts of the short-day species C. rubrum started to flower after a shorter time and at an earlier developmental stage than earlier cohorts. Flooding had little effect on probability of flowering and caused only a slight delay in flowering in this species. In both long-day species of Rumex, flowering stems were not initiated until a minimal leaf number was formed. As a result later cohorts remained vegetative, while flooding delayed flowering until later in the season or even until the following year. 5. All flooded plants of C. rubrum and most flooded plants in early cohorts of R. maritimus attempted to reproduce in the first growing season. Seed number was severely reduced in C. rubrum due to both reduction of plant biomass and destruction of flowers during flooding. In flooded plants of R. maritimus, seed output was correlated with plant size at the time of bolting. Seed number was maximized at the expense of seed size in R. maritimus. 6. These results suggest that there is a trade-off between survival of flooding and early reproduction in these species, and that there are complex interrelationships between highly variable environmental factors and developmental factors which determine the survival and reproductive success of short-lived species in river forelands.

Wetlands sometimes serve as nutrient sinks to improve the quality of wastewaters, yet scientists' current understanding of the biogeochemical processes involved is inadequate. Several experiments studied the effects of environmental changes in a seasonally flooded hardwood wetland in the Lower Mississippi Valley on the speciation and solubility of chromium. The wetland studied was shown to act as a chromium sink, but the model is not applicable to other sites. The precipitation, sorption, complexation, redox reactions and diffusion will vary for each wetland and need to be examined separately.

SUMMARY (1) Relationships between vegetation composition and nutrient and major ion concentrations in groundwater and peat were examined in 58 stands of fen vegetation in the Biebrza mire, Poland. The 58 stands included rich fens with a large standing biomass, rich fens with lower standing biomass and poor fens. (2) The highly productive rich fen (i.e. rich fen with large standing biomass) receives moderately eutrophic river water. The rheophilous part of the mire that is not, or only occasionally flooded contains gradients from quite productive rich fens to less productive rich fens and poor fens. In this part of the gradient, occasional river flooding appeared to be an important source of K and was probably responsible for the presence of quite productive rich fen vegetation. (3) Upward seepage of calcium-rich and phosphate-poor groundwater keeps phosphate concentration low in the superficial mire water and the peat from the lower productive rich fen. Phosphate concentration is higher in the mire water and the peat from the poor fen which is fed by downward-flowing rainwater. (4) Nitrogen concentration in mire water and peat is only poorly correlated with species composition and vegetation structure.

1 Plant performance of species in river floodplains is negatively affected by submergence, due to severely hampered gas exchange under water. Several individual traits have been shown to determine flooding tolerance, but the interrelationships among these traits and their effects on plant performance still remain largely unknown. 2 Here, we aim for a more coherent understanding of submergence tolerance, by investigating whether different traits are alternative strategies to enhance survival under water or whether these traits act in concert. 3 Because responses to submergence may be taxon-specific, we chose a multiple-species approach that allowed phylogenetic comparisons. The phenotypic traits investigated in the current study were constitutively different in species originating from frequently flooded habitats than in species from dry habitats: wet species were taller and had a higher specific leaf area (SLA), chlorophyll content, aerenchyma content, and longer longevity of terrestrial and 'aquatic' leaves compared with species from dry habitats. Moreover, the frequently flooded species appeared to be more plastic for these traits in response to submergence. Neither the phylogenetic component nor the light climate under water were important for the expression of the submergence-related traits. 4 Principal component analysis (PCA) showed that these traits were divided in two independent clusters structured either around the petiole (i.e. aerenchyma content and shoot length) or the leaf lamina (i.e. SLA, chlorophyll content and leaf longevity). Shoot length and aerenchyma content of the petiole were also positively correlated, albeit not significantly. A positive correlation between SLA and leaf longevity was observed under water, indicating that thinner leaves may have an increased potential for gas exchange, resulting in increased leaf longevity and plant survival. 5 Path analyses indicated significant positive effects of the two trait clusters on plant performance during full submergence. 6 Our study shows that multiple ecophysiological traits act in concert to fine tune responses to dynamic and unpredictable environments such as river floodplains.

1 We have studied the reproductive performance, early establishment and insect herbivory in two Tabebuia species found in contrasting distant habitats. Tabebuia ochracea and T. aurea are sympatric in the cerrado (Brazilian savanna), whereas T. aurea also colonizes floodplains in the wetlands of the 'Pantanal Matogrossense' as large monodominant stands, but is sparsely distributed in the cerrado. 2 We test the hypothesis that T. aurea has a more vigorous genotype in the Pantanal than in the cerrado, which may be due to a lower negative selection caused by insect herbivory, positive selection for better soil conditions and an increased growth in the face of stochastic flooding. In addition, we predict that T. ochracea is better adapted to withstand higher herbivory rates than T. aurea, and is thus more successful in the cerrado. 3 KruskaluWallis analysis and Wilcoxon paired-sample tests were used to compare adult tree reproductive traits. A reciprocal transplant experiment, combined with a glasshouse experiment, was used to investigate herbivory on half-sib seed families found in each habitat. 4 Over a 2-year period, T. ochracea had the higher investment in flower and seed production, which compensated for lower germination rates. However, in the Pantanal, T. aurea had the greatest conversion of flowers to fruit. 5 Fewer seeds of T. aurea survived and germinated in the cerrado than in the Pantanal, but seedlings from the Pantanal grew faster than those from the cerrado. The growth rate of T. ochracea was approximately four times lower than that of T. aurea. 6 Herbivory on seedlings was lower in the Pantanal than in the cerrado. Although seedlings of T. aurea from the Pantanal suffered the highest rates of herbivory in the cerrado, they survived equally to seedling genotypes from the cerrado. Tabebuia aurea had a higher mortality in both the cerrado and under controlled environmental conditions. 7 Faster growth rates may evolve when favourable abiotic conditions prevail. Although herbivores may promote habitat specialization by restricting colonization of poor soil environments by fast-growing species, herbivory pressure may select for tree genotypes with conservative growth rates in newly colonized habitats with poor soil conditions and intense herbivory.

1 We studied seedling emergence in four familial pairs of floodplain herbs in response to the experimental manipulation of soil moisture and litter cover to analyse (i) whether the effect of litter changes from negative under humid to positive under dry conditions, and (ii) whether the response to changing water and light conditions with increasing litter cover varies among species and plant families. 2 We carried out a controlled pot experiment using four levels of litter cover (0 g, 2 g, 4 g and 8 g litter per pot, corresponding to 0 kg m2, 0.2 kg m2, 0.4 kg m2 and 0.8 kg m2) and two levels of water-addition, leading to constantly humid substrate or intermittently dry topsoil. 3 Across water-additions, percentage emergence reached a peak at low levels of litter cover (0.2 kg m2 and 0.4 kg m2). There was a significant litter water-addition interaction in six species, with positive effects of litter under intermittently dry conditions and negative or neutral effects under constantly humid conditions. Litter lowered maximum temperature as well as amplitude, and alleviated soil humidity under low water supply, while imposing increasingly shaded conditions. Analysis of species- and family-specific responses suggested that germination under a litter cover of 0.8 kg m2 was significantly reduced in smaller-seeded species (i.e. those that tend to have higher light demands for germination). 4 Our results suggest that transfer of seed-containing plant litter can aid restoration projects if applied at 0.20.4 kg m2. Below these levels, establishment of most species may be inhibited by drought, while higher amounts will increasingly suppress seedling emergence, especially of small-seeded species. 5 In addition to facilitation effects observed between living plants, dead plant remains may also exert positive effects on establishment. The sign of the litter effect on seedling emergence depends on soil humidity, with negative effects seen above a threshold amount, which is species- and family-specific and is closely related to seed size. Whether positive litter effects in grasslands are a consequence of coevolution remains to be examined.

1 Competition is widely thought to be responsible for constraining species limits at the favourable ends of freshwater flooding gradients. However, field studies testing this idea rarely consider the role of competition beyond a species' field distribution limits. 2 To test whether species distributions are, instead, constrained by physiological limits, and only narrowed by biotic interactions, we measured the effect of competition on survival and fecundity of Rumex crispus and Rumex palustris within and above their distribution range along an elevation gradient in a river floodplain. 3 Flooding reduced the fitness of both species at the lowest elevations. A decline in fitness was also noticed at the two highest elevations in control as well as in removal plots, although standing crop measurements indicated that conditions here were the most favourable. 4 Both leaf herbivore damage and likeliness of drought increased with elevation. Because herbivore damage only reinforced prevailing abiotic influences, drought appeared to be the strongest constraint at higher positions. 5 Competition merely narrowed both species' physiological ranges by displacing them downwards from their optimum and maximum elevation. The displacement was strongest for the weak competitor Rumex palustris. 6 Our study provides experimental field evidence for earlier suggestions that both ends of a species niche can be defined in hydrological terms. It thus indicates that spatial variability in water availability may segregate species niches and thereby promote species richness in plant communities.

Lake Albacutya is a well-known intermittent lake in north-western Victoria. The lake is near the termination of the Wimmera River. From time-to-time the lake fills and flow passes down Outlet Creek into Wyperfeld National Park. The wetlands associated with the lake have a high biodiversity value and are named in international treaties. This paper examines the hydrologic factors associated with lake filling and flow into Wyperfeld. The lake has filled approximately six times since 1880 and has partially filled on other occasions. Examination of rainfall data from 1875 at Horsham gave no indication of long term rainfall decline, and showed that rainfall at Horsham can be viewed as representative of rainfall in the Wimmera River catchment. However a double-mass analysis showed that the relationship between the Wimmera River flow and rainfall has varied from 1890 to the present. Examination of data associated with six fillings of Lake Albacutya suggested that filling is a two-year event requiring at least 550 GL of flow passing Horsham over the two years immediately associated with the flood. A simple model based on rainfall and this threshold reproduced observed characteristics of the data reasonably well. This suggested that the flooding frequency of Lake Albacutya has dropped from about one in 25 years in the natural state to a substantially lower frequency under current river conditions. The results also suggested that because of changes in the Wimmera River the last filling and flood into Wyperfeld in 1976 was far smaller than it would otherwise have been. This is consistent with field mapping of the flood in relation to River Red Gum (Eucalyptus camaldulensis Dehnh.) stands. Analysis of the health of these stands showed major dieback with the severity of this being roughly proportional to the distance from the 1976 flood boundaries. An examination of values associated with the lake and adjoining Wyperfeld National Park suggested that biodiversity and economic values are and will be compromised by the reduction in flooding. In particular, an internationally-known provenance of Red Gum is at risk, and bird-breeding opportunities have diminished.

1 Restored floodplains and backwaters lacking a viable propagule bank, may need flood pulses to facilitate inward dispersal of diaspores. Temporal patterns of hydrochorous plant dispersal are, however, not well known. 2 Diversity and abundance of diaspores dispersed in a water body over 12 months were quantified using a 200 [micro]m net in order to: (i) test for a relationship between discharge and the number of species and diaspores dispersed; (ii) examine the effect of seed buoyancy and seed release period on the length of the dispersal period; and (iii) test whether diaspores of species that disperse during a similar period of the year are characterized by similar dispersal and dormancy traits. 3 A total 359 188 individuals of 174 vascular species developed from 144 samples, with most (90%) from vegetative diaspores and only 10% from seeds. Mean number of species and diaspores varied between months in parallel with discharge levels. Stepwise multiple regression analysis showed that both seed buoyancy and seed release influenced dispersal periods. 4 In general, species that dispersed most diaspores in spring and summer had non-dormant seeds, a shorter seed release period and a shorter seed dispersal period than species whose dormant seeds dispersed in autumn and winter. Vegetative diaspores were dispersed on average over 8 months, indicating their importance to long-distance dispersal. Several species dispersed both generative and vegetative diaspores, often in different seasons. 5 Our results may assist the planning of regenerative processes in riverine wetlands at landscape scales, as dispersal phenology, and discharge rates must be taken into consideration. Vegetative diaspores may be more important than seeds, although the latter may extend the species dispersal period into other seasons. Temporal heterogeneity in diaspore dispersal influences the identity of diaspores reaching restored habitats.