Unionid growth patterns in rivers of differing riparian vegetation

1. Growth rates were examined as potential controlling agents of unionid distributions.
2. Analyses of long-term growth in unionid shells revealed two distinct patterns. Species which dominate rivers with forested riparian vegetation (e.g. Elliptio dilatata ) show slow growth throughout life, whereas species which dominate grassy rivers (e.g. Pyganodon grandis ) show rapid growth during early life and achieve a smaller maximum size at a younger age.
3.  Pyganodon grandis , which occurs in both river types but is much more abundant in grassy habitats, demonstrates a single growth pattern in both basin types. In contrast, Lasmigona complanata (Barnes, 1823), which occurs equally in both basin types, demonstrates two growth patterns which differ depending upon which river is inhabited. In forested rivers, L . complanata grow slow and steady, whereas in grassy rivers, these unionids grow faster and achieve maximum size earlier.
4. Short-term transplant studies of P . grandis and E . dilatata confirmed this pattern of growth for specialist species.     

Urban catchment hydrology overwhelms reach scale effects of riparian vegetation on organic matter dynamics

1. Urbanisation severely affects stream hydrology, biotic integrity and water quality, but relatively little is known about effects on organic matter dynamics. Coarse particulate organic matter (CPOM) is a source of energy and nutrients in aquatic systems, and its availability has implications for ecosystem productivity and aquatic communities. In undisturbed environments, allochthonous inputs from riparian zones provide critical energy subsidies, but the extent to which this occurs in urbanised streams is poorly understood. 2. We investigated CPOM inputs, standing stocks, retention rates and retention mechanisms in urban and peri‐urban streams in Melbourne, Australia. Six streams were chosen along a gradient of catchment urbanisation, with the presence of reach scale riparian canopy cover as a second factor. CPOM retention was assessed at baseflow via replicate releases of marked Eucalyptus leaves where the retention distance and mechanism were recorded. CPOM and small wood (>1 cm diameter) storage were measured via cores and direct counts, respectively, while lateral and horizontal CPOM inputs were assessed using riparian litter traps. Stream discharge, velocity, depth and width were also measured. 3. CPOM inputs were not correlated with urbanisation, but were significantly higher in ‘closed’ canopy reaches. Urbanisation and riparian cover altered CPOM retention mechanisms, but not retention distances. Urban streams showed greater retention by rocks; while in less urban streams, retention by small wood was considerably higher. CPOM and small wood storage were significantly lower in more urban streams, but we found only a weak effect of riparian cover. 4. These findings suggest that while riparian vegetation increases CPOM inputs and has modest/weak effects on storage, catchment scale urbanisation decreases organic matter availability. Using an organic matter budget approach, it appears likely that the increased frequency and magnitude of high flows associated with catchment urbanisation exerts an overriding influence on organic matter availability. 5. We conclude that to maintain both organic matter inputs and storage, the restoration and protection of streams in urban or rapidly urbanising environments relies on the management of both riparian vegetation and catchment hydrology.     

Variability in flood disturbance and the impact on riparian tree recruitment in two contrasting river systems

The vegetation within the riparian zone performs animportant ecological function for in-stream processes.In Australia, riparian zones are regarded as the mostdegraded natural resource zone due to disturbancessuch as river regulation and livestock grazing. Thisstudy looks at factors influencing vegetation dynamicsof riparian tree species on two contrasting riversystems in Western Australia. The Blackwood River insouth-western Australia is influenced by aMediterranean type climate with regular seasonalwinter flows. The Ord River in north-western Australiais characterized by low winter base flows andepisodic, extreme flows influenced by monsoon rains inthe summer. For both rivers, reproductive phenology ofstudied overstory species is timed to coincide withseasonal river hydrology and rainfall. An evendistribution of size classes of trees on the BlackwoodRiver indicated recruitment into the population iscontinual and related to the regular predictableseasonal river flows and rainfall. In contrast, on theOrd River tree size class distribution was clustered,indicating episodic recruitment. On both rivers treeestablishment is also influenced by elevation abovethe river, microtopography, moisture status and soiltype. In terms of vegetation dynamics riparianvegetation on the Ord River consists of long periodsof transition with short lived stable states incontrast to the Blackwood river where tree populationstructure is characterized by long periods of stablestates with short transitions.     

Effects of river ice on riparian vegetation

1. Many rivers and streams experience pronounced ice dynamics caused by the formation of anchor and frazil ice, leading to flooding and disturbance of riparian and aquatic communities. However, the effects of dynamic ice conditions on riverine biota are little known. 2. We studied the formation of anchor ice in natural streams over 2 years and assessed the effects of anchor ice on riparian vegetation by comparing sites with frequent or abundant and little or no anchor ice formation. We also studied the direct impact of ice on riparian plants by experimentally creating ice in the riparian zone over three winters and by exposing plants of different life forms to ?18 °C cold ice in the laboratory. 3. Riparian species richness per 1‐m² plot was higher at sites affected by anchor ice than at sites where anchor ice was absent or rare, whereas dominance was lower, suggesting that disturbance by ice enhances species richness. Species composition was more homogenous among plots at anchor ice sites. By experimentally creating riparian ice, we corroborated the comparative results, with species richness increasing in ice‐treated plots compared to controls, irrespective of whether the sites showed natural anchor ice. 4. Because of human alterations of running waters, the natural effects of river ice on stream hydrology, geomorphology and ecology are little known. Global warming in northern streams is expected to lead to more dynamic ice conditions, offering new challenges for aquatic organisms and river management. Our results should stimulate new research, contributing to a better understanding of ecosystem function during winter.     

Effects of physical disturbance and granivory on establishment of native and alien riparian trees in Colorado, U.S.A.

Abstract.  In western North America, the alien Elaeagnus angustifolia L. invades riparian habitats usually dominated by pioneer woody species such as Populus deltoides Marshall ssp. monilifera (Aiton) Eckenwalder . We conducted manipulative field experiments to compare the importance of physical disturbance and granivory for seedling establishment of these two species. We planted seeds of both species in disturbed and undisturbed study plots, and used exclosures, seed dish trials and live-trapping to assess the role of granivory. Seedling establishment of both species was increased by physical disturbance and seeds of both species were subject to granivory. However, the relative importance of these two factors differed between species. For P. deltoides , lack of physical disturbance prevented seedling establishment in uncleared subplots, but granivory did not prevent seedling establishment outside of exclosures. For E. angustifolia , granivory prevented seedling establishment outside of exclosures, but lack of physical disturbance did not prevent establishment in uncleared subplots. The lesser dependence on disturbance may enable E. angustifolia to invade areas characterized by low levels of fluvial disturbance, such as floodplains along regulated rivers, where P. deltoides recruitment does not occur. Populations of granivorous rodents may affect the susceptibility of riparian ecosystems to invasion by E. angustifolia .     

Comparisons of benthic communities adjacent to riparian native eucalypt and introduced willow vegetation

1. Willows, Salix spp., have been widely introduced as a riparian species in temperate Australia and New Zealand. The present study was a broad-scale observational survey to document the differences between reaches of river lined with willows and native vegetation in the community structure of benthic invertebrates and the resources which these plants use.
2. Nine rivers in south-eastern Tasmania were examined on three occasions in autumn, spring and summer. Taxa were identified to family level, with the exception of Oligochaeta and Acarina, and benthic organic matter (CPOM and FPOM) and epilithic biomass were measured for each reach.
3. Taxon diversity and evenness were lower in willowed reaches in autumn, and total macroinvertebrate density and number of taxa were lowest in willowed reaches in summer. No differences in the fauna between willowed and native reaches were observed in spring. Measures of community similarity of the fauna in willowed and native reaches were significantly different in autumn and summer, but not in spring.
4. The taxa responsible for the significant differences seemed to be responding to differences in food availability and habitat quality in reaches of each vegetation type. Organic matter standing stock was higher in willowed reaches in autumn although the influence of these litter inputs on the fauna were not marked. Epilithon biomass was highest in autumn and spring in willowed reaches when shading in these reaches was least.
5.  The most marked differences between willowed and native reaches were during summer low flows, when the instream fauna appeared to be responding to changes to shading, water quality and the quality of the habitat.     

Growth, production and bioenergetics of brown trout in upland streams with contrasting riparian vegetation

1. A series of laboratory-based equations on trout growth and bioenergetics developed by J.M. Elliott were applied to data collected for brown trout ( Salmo trutta L.) under field conditions in Co. Mayo, Western Ireland. Fish were collected by electrofishing eight upland streams with contrasting riparian vegetation; grassland, open canopy and closed canopy deciduous.
2. Stream temperatures, one of the main influencing factors on fish growth and energetics, did not differ significantly between riparian types.
3. Observed growth rates were lower than the predicted maximum growth rates and were not influenced by riparian vegetation type. Growth ranged between 0.66% day⁻¹ for 0 + trout to 0.08% day⁻¹ for 2 + trout.
4. Production estimates showed no clear difference between riparian vegetation types over the growing season.
5. Fish densities and biomass tended to be greater in closed canopy streams particularly in summer.
6. Actual ration sizes calculated for trout were similar to the ration required for maintenance metabolism and were only 45–63% of the maximum potential rations. Although there was an ontogenetic increase in ration size with increasing fish age, the proportion of ration available for growth (i.e. the difference between actual and maintenance rations) did not differ between age classes but was greatest in summer. 1+ and 2+ trout show greatest ration available for growth in grassland streams.
7. Trout growth did not differ between riparian vegetation types but did vary seasonally with greatest attainment in summer. Growth was limited in the present study possibly due to combined effects of reduced prey available to fish and low stream temperatures reducing metabolic requirements. In such food limited systems, terrestrial invertebrate energy subsidies could have significant benefits to brown trout growth, production and bioenergetics.     

Landscape scenario modelling of vegetation condition

Summary   Landscape scenario modelling is a useful aid to planning for biodiversity conservation. Vegetation condition modelling is increasingly being integrated into such analysis. Model complexity and model uncertainty are critical factors that must be addressed when tailoring vegetation condition modelling to individual applications. We describe three approaches that we have used to compare the effects of different landscape scenarios on vegetation condition. The first is a simple land-use–condition approach where vegetation condition is determined solely by land use. The second is a land-use–regeneration approach that introduces transition functions to model vegetation condition dynamics associated with land use change. The third is a threat–regeneration approach, which models vegetation condition dynamics based on the interaction between regeneration and a range of mapped threats. The three approaches represent a progression towards increased refinement and realism, but also increased complexity and data requirements. We examine the relative usefulness of the three approaches and conclude that there is no single 'silver bullet' solution but recommend judicious matching of approaches to applications within a collaborative and adaptive setting.     

旅游干扰对云丘山景区内植被的影响

选择云丘山景区为研究区域,以该区域的主要植被为研究对象,采用样方法对旅游干扰对云丘山景区内植被的影响进行了研究,共设置了40个乔木样方,并利用TWINSPAN聚类分析以及旅游干扰程度（TDD）对所取样方进行分析。结果表明：TWINSPAN聚类分类将景区内的植物群落划分为5个群系,其中、群系Ⅱ中伴人植物的优势度明显高于其它。干扰程度分析表明,在景区的40个乔木样方中,只有4个样方基本没有受到干扰,有3个样方受到中度干扰,其余的33个样方均为轻度干扰。TWINSPAN聚类分析科学合理地对旅游活动作用下植被景观的类型特征进行了分析。旅游干扰程度（TDD）直观地反映出各个样方所在地植被被干扰的程度,该研究结果可为旅游管理者提供一定的理论依据。     

Litter input from riparian vegetation to streams: a case study of the Njoro River,Kenya

Allochthonous coarse particulate organic matter (CPOM) input into the Njoro River was measured between January and June 1998 at two contrasting sites: open-canopy and closed-canopy sites. Bank runoff and aerial drift traps were used for collecting CPOM inputs over periods of two weeks. Collected litter was sorted into four categories: leaves, fruits, wood and plant fragments. Monthly input ranged from 77 to 228 g ash free dry weight m^–1 for bank runoff input and from 64 to 129 g ash free dry weight m^–2 for aerial input. The highest input of 228 g ash free dry weight m^–1 was recorded in May at the closed-canopy site. Wood, fruits and plant fragments of particle size >100 m contributed a mean ± SE of 60±9% of the total inputs with the rest from leaf litter. The closed-canopy site had higher inputs (P<0.05) of bank and aerial input than the open canopy site. There was no relationship between total bank runoff input and rainfall (r _s = 0.08), however, total aerial input increased with decrease in rainfall (r _s = – 0.59). There were differences between inputs from different plant species (P<0.05) that ranked in the following order: Syzygium cordatum > Rhus natalensis > Pittosporum viridiflorum > Vangueria madagascariensis. Removal of riparian vegetation from the banks of the Njoro River would alter the quantity and quality of the litter and reduce CPOM inputs to the river and to a downstream lake with attendant consequences to the energy budget of biocoenoses in the two ecosystems.     

Importance of low-flow and high-flow characteristics to restoration of riparian vegetation along rivers in arid south-western United States

1. Riparian vegetation in dry regions is influenced by low‐flow and high‐flow components of the surface and groundwater flow regimes. The duration of no‐flow periods in the surface stream controls vegetation structure along the low‐flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow‐regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low‐flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees (Populus, Salix) to more drought‐tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient‐holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood‐dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on flood‐suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport. 6. Determining the causes of vegetation change is critical for determining riparian restoration strategies. Of the many riparian restoration efforts underway in south‐western United States, some focus on re‐establishing hydrogeomorphic processes by restoring appropriate flows of surface water, groundwater and sediment, while many others focus on manipulating vegetation structure by planting trees (e.g. Populus) or removing trees (e.g. Tamarix). The latter approaches, in and of themselves, may not yield desired restoration outcomes if the tree species are indicators, rather than prime causes, of underlying changes in the physical environment.     

Seasonal dynamics of macroinvertebrate assemblages in the benthos and associated with detritus packs in two low-order streams with different riparian vegetation

• 1 The seasonal dynamics of the benthic macroinvertebrate assemblage, and the subset of this assemblage colonising naturally formed detritus accumulations, was investigated in two streams in south‐west Ireland, one draining a conifer plantation (Streamhill West) and the other with deciduous riparian vegetation (Glenfinish). The streams differed in the quantity, quality and diversity of allochthonous detritus and in hydrochemistry, the conifer stream being more acid at high discharge. We expected the macroinvertebrate assemblage colonising detritus to differ in the two streams, due to differences in the diversity and quantity of detrital inputs.
• 2 Benthic density and taxon richness did not differ between the two streams, but the density of shredders was greater in the conifer stream, where there was a greater mass of benthic detritus. There was a significant positive correlation between shredder density and detritus biomass in both streams over the study period.
• 3 Detritus packs in the deciduous stream were colonised by a greater number of macroinvertebrates and taxa than in the conifer stream, but packs in both streams had a similar abundance of shredders. The relative abundance of taxa colonising detritus packs was almost always significantly different to that found in the source pool of the benthos.
• 4 Correspondence analysis illustrated that there were distinct faunal differences between the two streams overall and seasonally within each stream. Differences between the streams were related to species tolerances to acid episodes in the conifer stream. Canonical correspondence analysis demonstrated a distinct seasonal pattern in the detrital composition of the packs and a corresponding seasonal pattern in the structure of the detritus pack macroinvertebrate assemblage.
• 5 Within‐stream seasonal variation both in benthic and detritus pack assemblages and in detrital inputs was of similar magnitude to the between‐stream variation. The conifer stream received less and poorer quality detritus than the deciduous stream, yet it retained more detritus and had more shredders in the benthos. This apparent contradiction may be explained by the influence of hydrochemistry (during spate events) on the shredder assemblage, by differences in riparian vegetation between the two streams, and possibly by the ability of some taxa to exhibit more generalist feeding habits and thus supplement their diets in the absence of high quality detritus.

     

The influence of riparian vegetation on macroinvertebrate community structure and functional organization in six new Guinea streams

Information on the ecology of New Guinea streams is meagre, and data are needed on the trophic basis of aquatic production in rivers such as the Sepik in Papua New Guinea which have low fish yields. This study investigates the relationship between riparian shading (from savanna grassland to primary rainforest), algal and detrital food, and macroinvertebrate abundance and community structure in 6 Sepik River tributary streams. A particular aim was to elucidate macroinvertebrate community responses to changes in riparian conditions. All streams supported diverse benthic communities, but morphospecies richness (overall total 64) was less than in streams on the tropical Asian mainland; population densities of benthic invertebrates, by contrast, were similar to those recorded elsewhere. Low diversity could reflect limited taxonomic penetration, but may result from the absence of major groups (Plecoptera, Heptageniidae, Ephemerellidae, Psephenidae, Megaloptera, etc.) which occur on the Asian mainland. Population densities of all 19 of the most abundant macroinvertebrate taxa varied significantly among the 6 study streams, but community composition in each was broadly similar with dominance by Baetidae and (in order of decreasing importance), Leptophlebiidae, Orthocladiinae, Elmidae and Hydropsychidae. Principal components analysis (PCA) undertaken on counts of abundant macroinvertebrate taxa clearly separated samples taken in two streams from the rest. Both streams contained high detrital standing stocks and one was completely shaded by rainforest. Stepwise multiple-regression analysis indicated that population densities of the majority of abundant taxa (11 out of 19) across streams (10 samples per stream; n = 60) were influenced by algae and/or detritus, although standing stocks of these variables were not clearly related to riparian conditions. When regression analysis was repeated on mean counts of taxa per stream (dependent variables) versus features of each stream as a whole (thus n = 6), % shading and detritus were the independent variables yielding significant regression models most frequently, but pH, total-nitrogen loads and algae were also significant predictors of faunal abundance. Further regression analysis, undertaken separately on samples (n = 10) from each stream, confirmed the ability of algae and detritus to account for significant portions of the variance in macroinvertebrate abundance, but the significance of these variables varied among streams with the consequence that responses of individual taxa to algae or detritus was site-specific.Community functional organization — revealed by investigation of macroinvertebrate functional feeding groups (FFGs) — was rather conservative, and streams were codominated by collector-gatherers (mean across 6 streams = 43%) and grazers (36%), followed by filter-feeders (15%) and predators (7%). The shredder FFG was species-poor and comprised only 0.4% of total macroinvertebrate populations; shredders did not exceed 2% of benthic populations in any stream. PCA of FFG abundance data was characterized by poor separation among streams, although there was some evidence of clustering of samples from unshaded sites. The first 2 PCA axes accounted for 84% of the variation in the data suggesting that the poor separation resulted from the general similarity of FFG representation among streams. Although stepwise multiple-regression analysis indicated that algae and detritus accounted for significant proportions of the variations in population density and relative abundance of some FFGs, the response of community functional organization to changes in riparian conditions and algal and detrital food base was weak — unlike the deterministic responses that may be typical of north-temperate streams.     

Development, maintenance and role of riparian vegetation in the river landscape

1. Riparian structure and function were considered from a longitudinal perspective in order to identify multiscale couplings with adjacent ecosystems and to identify research needs. 2. We characterized functional zones (with respect to vegetation development in association with various biogeochemical processes) within geomorphological settings using a delineation based upon erosional, transitional and depositional properties. 3. Vegetation dynamics within the riparian corridor are clearly influenced substantially by hydrological disturbance regimes. In turn, we suggest that vegetation productivity and diversity may widely influence riverine biogeochemical processes, especially as related to the consequences of changing redox conditions occurring from upstream to downstream. 4. However, surface and groundwater linkages are the predominant controls of landscape connectivity within riparian systems. 5. The importance of riparian zones as sources and sinks of matter and energy was examined in context of structural and functional attributes, such as sequestering or cycling of nutrients in sediments, retention of water in vegetation, and retention, diffusion or dispersal of biota. 6. The consequences of interactions between different communities (e.g. animals and plants, micro-organisms and plants) on biogeochemical processes are notably in need of research, especially with respect to control of landscape features. Multiscale approaches, coupling regional and local factors in all three spatial dimensions, are needed in order to understand more synthetically and to model biogeochemical and community processes within the river-riparian-upland landscape of catchments.     

Trajectories of change: riparian vegetation and soil conditions following livestock removal and replanting

Riparian zones provide critically important ecological functions, including the interception of nutrients and sediments before they enter waterways. Consequently, riparian zones, and the vegetation they support, are often considered as an important ‘final buffer’ between waterways and adjacent land. In agricultural ecosystems, riparian zones are therefore increasingly recognized as an important component of strategies aimed at minimizing the flow of nutrients and sediments into waterways. Accordingly, riparian zones are increasingly afforded protection and are targeted for restoration. Here we present results of a study in which we aimed to identify patterns of change in soil and vegetation properties in riparian zones, under different management regimes, adjacent to tributary streams in one of south‐eastern Australia's main agricultural regions. We compared riparia that were heavily impacted by agricultural activities, were in remnant condition or had undergone some restoration activities and were thus in a transitional state. There was an increase in plant cover and soil C concentration between impacted through to remnant sites, with transitional sites intermediate, suggesting that improvements in soil conditions were becoming evident following restoration activities. In our assessment of soil physicochemical properties we investigated the relationships between riparian condition and soil properties, taking into account the influence of adjacent land use on these relationships. Importantly, the concentrations of NO₃^‐ and plant available P in riparian surface soils were more or less influenced by concentrations in the adjacent land depending upon riparian condition. This will, in turn, have consequences for nutrient inputs into streams. This study emphasizes that riparian zones need to be managed within their wider landscape context. Furthermore, the results of this study will inform efforts seeking to minimize impacts of agricultural activities on waterways, through the conservation and/or restoration of riparian ecosystems.     

Effects of removal of riparian vegetation on algae and heterotrophs in a Mediterranean stream

The effect of removal of a riparian strip on aquaticautotrophic (algae) and heterotrophic (bacteria,macroinvertebrates) organisms was monitored in aMediterranean stream during the canopy growing period.Community composition, biomass and metabolicactivities were compared with those recorded during apre-riparian removal period and in a forested stretchdownstream. Higher irradiance was associated with Cladophora increase in the logged section. Algalbiomass increased up to ten times, and productivitywas up to four times higher than in the pre-removalperiod and the forested section. Bacterialcommunities showed higher ectoenzymatic activities(-glucosidase, -xylosidase) in thelogged section than in forested conditions. Moreoverthe coincidence between the maxima of-glucosidase and chlorophyll-a suggeststhat bacterial activity was enhanced by the higheravailability of high-quality algal material. Themacroinvertebrate community had higher density andbiomass in the logged section than in the forestedsection and in the pre-removal period. Scrapers andfilterers become dominant after riparian removal,while shredders, predators and collectors did not showsignificant changes either between sites or periods.Responses of environmental variables and bioticcommunities indicate that the changes occurring in thestream due to riparian removal could be consideredbottom-up controlled, as increased illumination wasthe main mechanism responsible.     

Flood disturbance and riparian species diversity on the Colorado River Delta

We investigated the influence of channel migration and expansion on riparian plant species diversity along the lower Colorado River near the United States–Mexico border. Using repeat aerial photography in a GIS we identified and classed areas of low, moderate, and high disturbance frequency caused by channel expansion and migration. Replicate vegetation plots (12m×12m) were sampled in each of the three disturbance classes. One-way ANOVA was used to test for differences in species richness, species diversity (using the Shannon–Weiner Index) and overall percent ground cover of plants between the three disturbance classes. Regardless of disturbance class, plots were dominated by trees or shrubs, especially the non-native Tamarix ramosissima, as well as Pluchea sericea, Baccharis salicifolia and Salix goodingii. Clearly woody species constitute the great bulk of overall species richness, percent ground cover, and species diversity (H) in each disturbance group. No overall statistically significant differences were revealed among the disturbance groups for values of species richness, percent ground cover, or the Shannon–Wiener Index, though paired contrasts of means revealed that total percent ground cover on low disturbance plots was significantly higher than on moderately disturbed plots. Spatial and temporal variability in riparian diversity in the study area appears to hinge on factors other than disturbance frequency such as salt or drought stress. Alternately, our results could be interpreted as suggesting that in the presence of intensive flow regulation, disturbance plays a secondary role to ecological stresses, similar to that demonstrated by others. Intentional flood pulses are advocated as a restorative management strategy for improving plant productivity, management of exotic species (particularly T. ramosissima), and restoration of overall biodiversity.