Rozprawy doktorskie na temat „Riparian vegetation”

The objective of this study was to increase understanding of the processes structuring and controlling the species richness of riparian plant communities. In particular, I examined the unimodal relationship, found in many rivers, between plant species richness and location along the river corridor. The most important finding was that this pattern is dynamic and varies with time, most likely in response to large-scale flood disturbances. I also found that the sensitivity to flood disturbance varied with the environmental setting of the riparian reaches. Turbulent sections of the river retained high species richness, whereas tranquil reaches had significantly lower species richness in years following high and prolonged flooding, compared to a period without extreme flood events. Riparian soils along turbulent reaches are more resistant to oxygen depletion during floods, a factor which is likely to contribute to the maintenance of species richness.

The finding that the species richness pattern varied with time led me to ask which factors control plant diversity along riparian zones. I addressed this question by formulating three contrasting, although not mutually exclusive, hypotheses: (1) longitudinal patterns in riparian plant species richness are governed by local, river-related processes independent of the regional species richness, (2) riparian plant species richness is controlled by dispersal along the river, i.e., longitudinal control, and (3) the variation in riparian plant species richness mirrors variation in regional richness, i.e., lateral control. I found indications of all three types of control, although local factors seemed to fit most of the criteria. Riparian species richness was not significantly correlated to species richness in the surrounding upland valley. It was however significantly negatively correlated to soil pH, a local habitat factor of the reach. The fact that the species richness pattern varied in time, corresponding to the presence or absence of extreme flood events suggest that it is influenced by local disturbance regimes. The potential for control by longitudinal dispersal was found to be highest in the middle reaches of a river. Here, the similarity between upland and riparian vegetation was lowest, and invasibility (germination ability) was highest. Earlier work has shown that regulated rivers have an inverted species richness pattern compared to free-flowing rivers, with lowest species richness in the middle reaches. One potential mechanism behind this could be varying susceptibility to disturbance along the river. I tested this by experimentally disturbing the vegetation, applying the same level of disturbance along an entire free-flowing river. However, the response to experimental disturbance did not vary with location, likely because of a major flood disturbance preceding the experiment.

Mestrado em Gestão e Conservação de Recursos Naturais - Instituto Superior de Agronomia
The present master's thesis, had as its main objective the application of a dynamic model of riparian habitats in a case study with pronounced mediterranean characteristics. he vegetation model used is based on the existence of water conditions (water height and distance to water) suitable for the development of each type of riparian vegetation in different stages of their development, modeling annually its space-time evolution. The rules underlying the model take into account the height of the flow, the shear stress and duration of flooding. The modeling of vegetation held in ArcGIS environment, bases on three general ohases: initial creation of landscape, simulation of temporal and spatial evolution of vegetation and the presentation of annual results.

Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Riparian vegetation communities that occur along perennial rivers are structured in lateral zones that run parallel to river flow. This dissertation investigated the structure of South African riparian vegetation communities along perennial, single-thread headwater streams. The central assumption was that lateral zones result from differential species’ responses to changing abiotic factors along a lateral gradient up the river bank. It was first necessary to establish the pattern of zones and whether this pattern occurs repetitively and predictably on different rivers in different biomes. Since the flow regime is considered to be the master variable that controls the occurrence of lateral zones, the link between flow as the major abiotic driver and the distribution of plants in zones was determined. Predictions were made with respect to how variable flow may influence phenological traits, particularly with respect to seed dispersal, and physiological tolerances to drying out and were tested. The existence of lateral zones at reference sites in the Western Cape of South Africa was explored and their vegetation characteristics were described. Plant distribution was related to bank slope, as defined by elevation and distance from the wetted channel edge during summer (dry season) low flow, indicating a direct link to river bank hydraulics. Whether or not the same zonation patterns occur in riparian communities in other parts of South Africa was explored next. The four zones described for Fynbos Riparian Vegetation were evident at all of the other rivers tested, despite major differences in geographic location, vegetation community type, climate and patterns of seasonal flow. The four lateral zones could be separated from each other using a combination of flood recurrence and inundation duration. Functional differences were investigated between three tree species that occur in Fynbos Riparian Vegetation. Functional differences were apparent with respect to timing of seed dispersal, growth in branch length versus girth and three physiological measures of tolerance to drying out; specific leaf area (cm2.g-1), wood density (g.cm-3) and levels of carbon isotopes (δ13C). In order to determine the impact of invasive alien plants and to monitor recovery after clearing, the physical rules devised to help delineate zones were used to locate lateral zones that had been obliterated after invasion and subsequent clearing. At the sites invaded by A. mearnsii plants, the zone delineations showed that invasion started in the lower dynamic zone, where adult and sapling A. mearnsii were most abundant. In un-invaded systems, this zone was the least densely vegetated of the four zones, the most varied in terms of inundation duration and the frequency of inter- and intra-annual floods, and was an area of active recruitment comprised mainly of recruiting seedlings and saplings. An understanding of the functional differences between lateral zones was a common thread at each riparian community that was linked to the annual frequency of inundation and the period, when inundated.
AFRIKAANSE OPSOMMING: Oewer plantegroei gemeenskappe wat langs standhoudende riviere voorkom is gestruktureer in laterale sones parallel met die rivier vloei. Hierdie verhandeling ondersoek die struktuur van Suid-Afrikaanse oewer plantegroei gemeenskappe langs standhoudende, enkelloop hoof strome. Die sentrale aanname was dat laterale sones vorm as gevolg van verskillende spesies se reaksie teenoor die verandering van abiotiese faktore teen 'n laterale gradiënt met die rivierbank op. Dit was eers nodig om die patroon van die gebiede vas te stel en uit te vind of hierdie patroon herhaaldelik en voorspelbaar binne verskillende riviere in verskillende biome voorkom. Aangesien die vloeiwyse beskou word as die hoof veranderlike wat die teenwoordigheid van laterale sones beheer, is die skakel tussen die vloei, as die belangrikste abiotiese bestuurder, en die verspreiding van plante in sones bepaal. Voorspellings is gemaak met betrekking tot hoe veranderlike vloei fenologiese eienskappe kan beïnvloed, veral met betrekking tot die saad verspreiding, en fisiologiese toleransie teen uitdroog, en is getoets. Die bestaan van laterale sones binne verwysings studie terreine in die Wes-Kaap van Suid- Afrika is ondersoek en hul plantegroei eienskappe is beskryf. Plant verspreiding was verwant aan bank helling, soos gedefinieer deur hoogte en afstand vanaf die nat kanaal rand gedurende somer (droë seisoen) lae vloei, en dui dus op 'n direkte skakel met die rivier bank hidroulika. Of dieselfde sonering patrone voorkom in oewer gemeenskappe in ander dele van Suid-Afrika is volgende verken. Die vier sones beskryf vir fynbos oewer plantegroei was duidelik by al die ander riviere wat ondersoek is, ten spyte van groot verskille in geografiese ligging, plantegroei gemeenskap tipe, klimaat en patrone van seisoenale vloei. Die vier laterale sones kan onderskei word van mekaar deur middel van 'n kombinasie van vloed herhaling en oorstroomde toestand duur. Funksionele verskille is ondersoek tussen drie boom spesies wat voorkom in Fynbos Oewer Plantegroei. Funksionele verskille was duidelik met betrekking tot tydsberekening van saad verspreiding, groei in tak lengte tenoor omtrek, en drie fisiologiese maatstawwe van verdraagsaamheid teenoor uitdroging; spesifieke blaar area (cm2.g-1), hout digtheid (g.cm-3) en vlakke van koolstof isotope (δ13C). Ten einde die impak van indringerplante te bepaal en die herstel na ontbossing te monitor is die fisiese reëls voorheen vasgestel om sones te help baken gebruik om laterale sones, wat vernietig is na indringing en die daaropvolgende ontbossing, te vind. Op die terreine wat deur A. mearnsii indringerplante binnegeval is, het die indeling van sones getoon dat die indringing begin het in die laer dinamiese sone, waar volwasse en klein A. mearnsii bome die volopste was. In stelsels wat nie binnegeval is deur indringerplante was hierdie sone die minste dig begroei van die vier sones, die mees verskillend in terme van oorstroomde toestand duur en die frekwensie van inter-en intra-jaarlikse vloede, en was 'n gebied van aktiewe werwing hoofsaaklik bestaande uit rekruut saailinge en boompies. 'n Begrip van die funksionele verskille tussen laterale sones was 'n algemene verskynsel by elke oewer gemeenskap wat gekoppel was aan die jaarlikse frekwensie van oorstroming en die oorstroomde toestand duur.

The relationship between photosynthesis and transpiration from riparian vegetation in a semi-arid region is the primary focus of interest in this study. An eddy covariance system was used to measure fluxes of energy, momentum, and carbon over an extended period which included a monsoon season and a subsequent prolonged dry period. The photosynthetic portion of the measured CO2 flux was obtained by subtracting the mean value of nighttime CO2 flux (respiration) from the daytime CO2 flux, and the resulting photosynthesis estimates were then compared with transpiration and other variables. Because the data revealed a somewhat complex relationship between photosynthesis and transpiration on both an hourly and a daily basis, a further analysis was made involving both the calculation of the canopy conductance and a 'stand alone' version of the Simple Biosphere (SiB2) Model. The results showed the assumed relationship between canopy photosynthesis and canopy conductance used in SiB2 is inconsistent with observations, however Monteith's suggestion that the ratio of the CO2 concentration inside leaves to that outside leaves is approximately constant, which leads to a linear relationship between canopy conductance and photosynthesis, is consistent with observations.

Land use practices over the last 200 years have dramatically altered the distribution and amount of riparian vegetation throughout many catchments in Australia. This has lead to a number of negative impacts including a decrease in water quality, an increase in sediment transport and a decrease in the quality of terrestrial and aquatic habitats. The task of restoring the functions of riparian zones is an enormous one and requires spatial and temporal prioritisation. An analysis of the existing and historical functions of riparian zones and their spatial distribution is a major aid to this process and will enable efficient use of remediation resources. The approach developed in this thesis combines remote sensing, field measurement and terrain analysis to describe the distribution of five riparian zone functions: sediment trapping, bank stabilization, denitrification, stream shading and large woody debris production throughout a large semi-arid catchment in central Queensland.

Increasingly, the importance of vegetation in influencing the structure and function of riparian zones has been recognised (e.g. Bendix and Hupp, 2000; Tabacchi et al., 2000). This thesis explores vegetation dispersal and establishment in the riparian zones of two contrasting river systems, with a focus upon Salicaceae. Dispersal, hydrochorous transport, deposition and establishment of vegetation along the River Frome (UK), was investigated over one year. The study demonstrated the importance of hydrochory for dispersing propagules to new environments and for promoting diversity within the riparian zone. The role of hydrochory changed seasonally and with the hydrological regime, highlighting the importance of high flows for structuring and creating diversity in riverbank vegetation.

Models of climate change predict that temperature will increase during the 21th century and the largest warming will take place at high northern latitudes. In addition to warming, predictions for northern Europe include increased annual precipitation and a higher proportion of the precipitation during winter falling as rain instead of snow. These changes will substantially alter the hydrology of rivers and streams and change the conditions for riverine communities. The warming is also expected to result in species adjusting their geographic ranges to stay within their climatic tolerances. Riparian zones and wetlands are areas where excess water determines the community composition. It is therefore likely that these systems will be highly responsive to alterations in precipitation and temperature patterns. In this thesis we have tested the predicted responses of riparian vegetation to climate-driven hydrologic change with a six year long transplant experiment (I). Turfs of vegetation were moved to a new elevation with shorter or longer flood durations. The results demonstrate that riparian species will respond to hydrologic changes, and that without rare events such as unusually large floods or droughts, full adjustment to the new hydrological regime may take at least 10 years. Moreover, we quantified potential effects of a changed hydrology on riparian plant species richness (II) and individual species responses (III) under different climate scenarios along the Vindel River in northern Sweden. Despite relatively small changes in hydrology, the results imply that many species will become less frequent than today, with stochastic extinctions along some reaches. Climate change may threaten riparian vegetation along some of the last pristine or near-natural river ecosystems in Europe. More extensive loss of species than predicted for the Vindel River is expected along rivers in the southern boreal zone, where snow-melt fed hydrographs are expected to be largely replaced by rain-fed ones. With a seed sowing experiment, we tested the differences in invasibility between open wetlands, forested wetlands and riparian zones (IV). All six species introduced were able to germinate and survive in all habitats and disturbance levels, indicating that the tested wetlands are generally invisible. Germination was highest in open wetlands and riparian zones. Increasing seed sowing density increased invasion success, but the disturbance treatments had little effect. The fact that seeds germinated and survived for 2 to 3 years in all wetland habitats indicates that wetland species with sufficiently high dispersal capacity and propagule pressure would be able to germinate and establish here in their respective wetland type. Our results clearly demonstrate that a changed climate will result in substantial changes to functioning, structure and diversity of boreal wetland and riparian ecosystems. To preserve species rich habitats still unaffected by dams and other human stressors, additional protection and management actions may have to be considered.

The riparian forests are hotspots of biodiversity and serve important roles in maintainingthe water quality. The study and understanding of this ecosystem is basic to know how theriparian zones respond to the threat and the changes produced by the urbanization. Theobjective of this pilot study was to know the species richness and check the status of theriparian vegetation along two different rivers in Halmstad, Nissan and Fylleån. The studywas focus on the status of trees at both rivers to see if the proximity of the city has anyimpact on the biodiversity. In total 9 different species were found, nevertheless only 3 ofthese species were founded on both localizations: Quercus robur, Betula pendula and Pinussylvestris. The Shannon Index showed a higher biodiversity on Nissan riparian zones, whichis the river that present the urban component. The urban area is the one that presentshigher level of biodiversity, tree species and number of individuals but there are notenough to be in a good standard. The result just show that the urban area is in a bettercondition that the natural one. The institutional efforts should be focusing on preserveboth environments with special attention to the natural environment.

As public awareness of river degradation has grown in recent years, the number of stream restoration activities has increased dramatically. Anthropogenic influences at a range of spatial scales from watershed landuse to riparian vegetation management to local channel morphology can have hierarchical relationships to local (meso- and macro-) in-stream habitat characteristics. This research examined these influences first by examining the influence of complex channel morphology on meso-scale brook trout (Salvelinus fontinalis) habitat in Shenandoah National Park, VA, and then by examining the combined influence of watershed urbanization and riparian vegetation (100-200 m reaches) on stream temperature. Moving beyond one-dimensional (1D) averaged representations of fish habitat, this research explored the distribution of two-dimensional (2D) flow complexity metrics at the meso-habitat scale as explanatory variables for brook trout habitat preferences and as potential metrics to evaluate habitat restoration design. Spatial hydraulic complexity metrics, including area-weighted circulation and kinetic energy gradients, were calculated based on 2D depth averaged modeled velocity distributions in two 100-m reaches on the Staunton River. While there were no statistically significant correlations between kinetic energy gradients or area-weighted circulation and fish density, fish density was positively correlated to the percent of the channel dominated by protruding boulders. The structural complexity of areas with protruding boulders create complex flow patterns suggesting that flow complexity plays an important role in available brook trout habitat preferences at the local scale, although the 2D depth averaged model may not have adequately represented this complexity. The 2D distribution of flow characteristics was then investigated further to quantify areas of flow refugia (low velocity shelters) and the relationship between these areas, traditional measures of habitat quality, and fish biomass. Flow complexity in the vicinity of flow obstructions (in this case, boulders) was investigated further using patch classification and landscape ecology metrics. The relative influence of riparian vegetation on stream temperature (another important habitat characteristic) in urban and nonurban watersheds was investigated in 27 paired forested and nonforested reaches in PA, MD, and DE. Riparian vegetation and watershed-scale urbanization both influence stream temperature, which can have profound impacts on in-stream ecosystems. Generally, increased urbanization and removal of riparian forest influenced maximum stream temperatures resulting in higher maximum summer stream temperatures (up to 1.8°C); however, the influence of riparian forests (at at 100-200 m reach scale) decreased with increasing urbanization. Extreme maximum summer temperatures, which are a concern for aquatic biota, increased in both frequency and duration in urban nonforested reaches relative to forested reaches indicating that the addition of a forested 100-200 m long buffer partially mitigated these temperature extremes even in urban watersheds. Overall, changes to channel morphology and riparian vegetation had measurable local effects on stream habitat (temperature and hydraulic complexity) yet the implications of restoration efforts at the local scale on ecosystem services at a larger (km +) scale requires further study.
Ph. D.

In the riparian corridor of the San Pedro River in southeastern Arizona, the fluxes of water and energy over three riparian vegetation groupings were monitored and modeled in order to determine their annual water use and water sources. In situ micrometeorological and soil moisture measurements were made from 1996-1998 at a floodplain grassland site composed mainly of the perennial floodplain grass, Sporobolus wrightii (sacaton), and a tree/shrub grouping dominated by Prosopis velutina (mesquite). The results indicate that the grassland obtained water only from the near-surface (recent precipitation), while the mesquite accessed moisture from deeper in the vadose zone and/or from the water table. Both of these sites exhibited little interaction with the underlying groundwater, suggesting that the majority of the groundwater use from riparian vegetation is limited to the areas of dense mesquite and the forest gallery adjacent to the river. Measurements of the forest gallery water use composed mainly of Populus fremontii (cottonwood) and Salix gooddingii (willow) were available for some shorter term periods in 1997. These measurements were used to calibrate the Penman-Monteith model for evaporation in order to determine the water use from the forest gallery for the entire growing season. The total seasonal water use from the forest was considerably less than potential evaporation estimates. Observations of soil moisture under two rangeland sites in the San Pedro Basin were examined in order to determine the magnitude and the depth of root zone recharge characteristics in this semiarid region. Intermittent TDR observations made from 1990 to 1998 show that deeper root zone recharge occurred primarily during the wintertime, when the plants were senescent and evaporation demand was diminished. A physically-based variably-saturated flow model was used to determine the wintertime recharge. Using an automatic calibration algorithm, the model proved capable of reproducing the observations with small error. Simulated wintertime infiltration amounts indicated that substantial, deeper root zone recharge did occur during wet winters, but that the large year-to-year variability of this recharge implies that deeper-rooted plants would still need access to moisture in shallow root zone.

Water quality in streams around the world continues to be degraded by a series of human activities that feed pollutants into the vulnerable stream ecosystem via surface and subsurface runoff. This continues to accelerate global biodiversity and habitat losses within the stream environments and across entire watersheds with net adverse effects on public health and the ability of communities and ecosystems to adapt or become resilient to the prevalent impacts of climate change. One commonly used approach for protecting stream water from pollution is the use of vegetated riparian buffer zones to mitigate pollutants in surface and subsurface runoff prior to runoff entry into the stream channel. The optimal success of this approach requires land and water resource managers to understand the mechanisms by which riparian buffer zones function and the full range of factors that influence the effectiveness of riparian buffer vegetation in abating stream water pollution. Despite this need, resource managers in different geographical locations around the world still struggle to understand the linkages between riparian vegetation and stream chemical quality. This literature review therefore sought to synthesize findings from various scientific articles on the ways in which the major attributes of riparian vegetation [type, age, width, restoration and shading effect] influence the effectiveness of riparian vegetation in protecting the chemical quality of water in streams. This was aimed at generating conclusions and perspectives that could improve academic knowledge and natural resource managers’ understanding of the intricate linkage between riparian vegetation and changes in water chemistry. The study finds that the factors of riparian vegetation type, age, width, restoration and shading effects require due consideration in the development of riparian buffer zone and stream water chemical quality management interventions. I find that these factors require a high degree of integration, triangulation and context-specificity to achieve the objectives of riparian management intervention. I further find that stream water quality decision-making processes need to combine riparian vegetation-based approaches with other measures for mitigating and containing the spillage of pollutants at the source.

Presentation was conducted via Skype

In recent years, global warming awareness has resulted in an increased demand for clean sources of energy such as hydropower. As a consequence, its impact on riparian vegetation must be studied. In this research, I aimed to assess how different functional riparian groups from northern Sweden respond to hydropeaking (i.e. short-term flow regime changes due to differences in the daily energy requirements). I selected seedlings of eight species natural from Swedish riparian ecosystems which can be grouped in three different guilds (forbs, graminoids and woody) according to their habitat and morphological traits.  A seven week greenhouse experiment in which the seedlings were subjected to two watering treatments that simulated prolonged and deep submergence and frequent and short shallow submergence conditions was developed. I measured the root, stem and leaf biomass, followed leaf changes and stem growth over the weeks and evaluated the health status. The study showed how some species and guilds responded differently to the treatments although survival rates were similar. Forbs was the most resilient group unlike the woody guild.  Graminoids grew longer and thinner roots in frequent submergence situations. Small seedlings appeared to be more sensitive to prolonged submergence. No significant differences were found for leaf variables. Collectively, these results suggest that hydropeaking could significantly modify the riparian vegetation. More and longer studies are needed in order to understand the capacity that hydropower has to modify the riparian vegetation and therefore the riverine ecosystems.

The objects of my research were two. To describe ungrazed vegetation of thirty sites well dispersed along the 500 mile length of the Yellowstone River. And to measure the effects of gazing on this vegetation by describing/comparing vegetation of these ungrazed control sites with the vegetation of nearby grazed sites. Vegetation of the Yellowstone consists of three lateral bands on open shore (gravel or sandbar), willow thicket, and cottonwood forest. Their appearance on successively older deposits suggests control both by decreasing water availability (greater depth to water on inland sites with overdeposits) and increasing age (overtopping, first by willow and then by cottonwood, and accumulation of shrubs). The primary longitudinal (downstream) change between foothill and plains sites, probably driven by decreasing rainfall, was the change of forest dominant from P. angustifolia to P. deltoides. The apparent failure of P. deltoides reproduction could eventually eliminate the forest zone. Grazing affects all of the five communities identified. With grazing, overall cover decreased in every vegetation type, with the greatest losses in sandbars, willow thickets and P angustifolia forests. Cottonwood seedlings were grazed on bars and in willow thickets. Cover of hydric (Salix spp., Cornus, Ribes spp.) and mesic (Symphoricarpos) native shrubs was significantly reduced. Rosa spp. lost cover with trampling. Invasive shrubs Russian olive and tamarisk, downstream, are apparently unaffected by grazing, except indirectly as grazing reduces their competition. Forb cover was most affected in Populus forests, with natives declining and non-natives increasing with grazing. Non-native grasses, the dominant herbs in cottonwoods, become more dominant with grazing. Observation of the exotics present emphasized the equal or greater impact of their invasion. Cover of exotics rises laterally from shore (50% with equal grass/forb composition) through willow thicket (70%, mostly exotic grass) to cottonwood forest (76-78%). The diversity of exotic herbs increases (laterally and downstream.). In the shrub layer Russian olive and tamarisk, pests in the American Southwest, increased greatly in the Plains in the 1980-2000 period and have a potential to dominate the forest and willow zones respectively. The ecosystem impacts of exotic increase will likely modify aesthetics, wildlife, and ranching drastically.

The Little Bow River Project was implemented in 2003 and includes Alberta’s newest dam. The Project involves tripling the diversion of water from the Highwood River to the Little Bow River and subsequently storing the water in the Twin Valley Reservoir. This MSc Thesis provided part of the environmental monitoring for that Project and particularly investigated the impacts of augmented flows on the river channel and riparian vegetation along the upper reach of the Little Bow River. An initial component of the long-term study was to determine the existing associations between fluvial geomorphic characteristics and riparian plant communities. Poplar (Populus balsamifera L.), willow (Salix bebbiana Sargent and S. exigua Nutt.) and wolf-willow (Elaeagnus commutata Bernh.) communities were located along the upper section of the river, where the channel had a steeper gradient and was narrower and more sinuous. Cattail (Typha latifolia L.) and grass (grasses and sedges) communities were generally located along the lower section of the river that was shallower in gradient, wider and straighter. Plant community distribution also reflected impacts from cattle grazing. Initial channel and vegetation responses in the first two years following the increase in flow augmentation were slight and included bank slumping, sediment scour and inundation of flooded zones. The initial responses are consistent with the primary prediction of channel widening and this will probably be associated with some changes in the adjacent riparian plant communities.
xiv, 139 leaves : ill. (some col.) ; 29 cm.

Overall, the results of this study show that there are evident trends among the three ecoregions and delta of the White River. The forest stands of the Pine Ridge/Pierre Shale Ecoregion are the oldest along the river, as evidenced by aerial mapping going back into the 1930s and by the larger average trunk diameters of the trees. Historic aerial photographs for this ecoregion shows a relative static system from the 1930s-2010, with little destruction of existing or creation of new forests within the floodplain. Along with the older age of the forests, the stands in this ecoregion have the lowest floral diversity. The Pine Ridge/Pierre Shale forests are also unique along the river in that they are largely dominated by Acer negundo (box elder), a late-successional species that is largely absent from the forests of the other ecoregions. As the river continues downstream and enters the Badlands Ecoregion it gains size and volume, while its riparian forests decrease in patch size and tree density. Although the forests become smaller, the variety of communities and diversity of species increase. Unlike the Pine Ridge/Pierre Shale Ecoregion, the Badlands’ land cover was dynamic from the 1930s-2010, with increases in forest and declines in river channel area (-29%). Farther downstream and with a larger river channel, the River Breaks has even larger and more diverse riparian forests and the highest plant species richness and diversity among the ecoregions. The rate of land cover change was the greatest in the River Breaks, as the larger river has greater power for eroding existing communities and depositing sediment for recruitment. The area of riparian woody vegetation increased sharply from the 1930s-2010 (58%), while the area of channel declined (-20%). This ecoregion had the most perennial streamflow, with fewer zero flow days than in the upstream ecoregions. The Delta is unique as the only portion of the river where flows are affected by the Fort Randall Dam on the Missouri River. The impact of the reservoir on the area is evident, as it has the largest proportional area of forest along the river, as well as having the flora with the highest wetland affinity.

Thesis (M.S.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Marine, Estuarine, Environmental Sciences Graduate Program . Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The health of natural vegetation communities is of concern due to observed changes in the climatic-hydrological regime and land cover changes particularly in arid and semiarid regions. Monitoring vegetation at multi temporal and spatial scales can be the most informative approach for detecting change and inferring causal agents of change and remediation strategies. Riparian communities are tightly linked to annual stream hydrology, ground water elevations and sediment transport. These processes are subject to varying magnitudes of disturbance overtime and are candidates for multi-scale monitoring. My first research objective focused on the response of vegetation in the Upper San Pedro River, Arizona, to reduced base flows and climate change. I addressed the correlation between riparian vegetation and hydro-climate variables during the last three decades in one of the remaining undammed rivers in the southwestern U.S. Its riparian forest is threatened by the diminishing base flows, attributed by different studies either to increases in evapotranspiration (ET) due to conversion of grasslands to mesquite shrublands in the adjacent uplands, or to increased regional groundwater pumping to serve growing populations in surrounding urban areas and or to some interactions of those causes. Landsat 5 imagery was acquired for pre- monsoon period, when riparian trees had leafed out but before the arrival of summer monsoon rains in July. The result has showed Normalized Difference Vegetation Index (NDVI) values from both Landsat and Moderate Resolution Imaging Spectrometer (MODIS) had significant decreases which positively correlated to river flows, which decreased over the study period, and negatively correlated with air temperatures, which have increased by about 1.4°C from 1904 to the present. The predictions from other studies that decreased river flows could negatively impact the riparian forest were supported by this study. The pre-monsoon Normalized Different Vegetation Index (NDVI) average values in the adjacent uplands also decreased over thirty years and were correlated with the previous year's annual precipitation. Hence an increase in ET in the uplands did not appear to be responsible for the decrease in river flows in this study, leaving increased regional groundwater pumping as a feasible alternative explanation for decreased flows and deterioration of the riparian forest. The second research objective was to develop a new method of classification using very high-resolution aerial photo to map riparian vegetation at the species level in the Colorado River Ecosystem, Grand Canyon area, Arizona. Ground surveys have showed an obvious trend in which non-native saltcedar (Tamarix spp.) has replaced native vegetation over time. Our goal was to develop a quantitative mapping procedure to detect changes in vegetation as the ecosystem continues to respond to hydrological and climate changes. Vegetation mapping for the Colorado River Ecosystem needed an updated database map of the area covered by riparian vegetation and an indicator of species composition in the river corridor. The objective of this research was to generate a new riparian vegetation map at species level using a supervised image classification technique for the purpose of patch and landscape change detection. A new classification approach using multispectral images allowed us to successfully identify and map riparian species coverage the over whole Colorado River Ecosystem, Grand Canyon area. The new map was an improvement over the initial 2002 map since it reduced fragmentation from mixed riparian vegetation areas. The most dominant tree species in the study areas is saltcedar (Tamarix spp.). The overall accuracy is 93.48% and the kappa coefficient is 0.88. The reference initial inventory map was created using 2002 images to compare and detect changes through 2009. The third objective of my research focused on using multiplatform of remote sensing and ground calibration to estimate the effects of vegetation, land use patterns and water cycles. Climate change, hydrological and human uses are also leading to riparian, upland, grassland and crop vegetation changes at a variety of temporal and spatial scales, particularly in the arid and semi-arid ecosystems, which are more sensitive to changes in water availability than humid ecosystems. The objectives of these studies from the last three articles were to evaluate the effect of water balance on vegetation indices in different plant communities based on relevant spatial and temporal scales. The new methodology of estimating water requirements using remote sensing data and ground calibration with flux tower data has been successfully tested at a variety sites, a sparse desert shrub environment as well as mixed riparian and cropland systems and upland vegetation in the arid and semi-arid regions. The main finding form these studies is that vegetation-index methods have to be calibrated with ground data for each new ecosystem but once calibrated they can accurately scale ET over wide areas and long time spans.

In urban riparian areas, vegetation composition may be affected by urban land use changes at both the stream reach and the watershed scale. Moreover, the mechanisms by which seeds disperse may be affected both by reduction in seed sources due to vegetation removal and by the urban stream syndrome that produces flashier hydrographs and incised channels. I hypothesized that vegetation communities with high cover of native and hydrophilic species would be found in watersheds with high forest cover, while more limited cover of these species would be found in highly developed watersheds. Additionally, to examine the dispersal mechanisms contributing to these patterns, I hypothesized that 1) more seeds would be deposited in riparian areas by water than by wind; 2) the number of seeds deposited by streams would decrease as watershed urbanization increased; and 3) seeds deposited in the most urbanized sites would be primarily from species with traits favoring deposition by water, including large seed size and presence of a dispersal appendage. To investigate relationships between urban land cover types and riparian vegetation, I surveyed 30 randomly-selected riparian forests in the Portland-Vancouver metro area and related vegetation assemblages to watershed land cover. Vegetation was mapped to the nearest 1cm along three transects in each site. Land cover was characterized both within a 500m buffer around each site, and within the entire watershed. Relationships between land cover and vegetation assemblages were investigated using nonmetric multidimensional scaling and classification trees. To investigate the effect of watershed urbanization intensity on riparian seed deposition, I collected seeds deposited in nine riparian sites along a gradient of watershed total impervious area (TIA). I used a stratified-random approach to select sites. In each site, wind-deposited seeds were collected in funnel traps three times, and water-deposited seeds were collected in turf traps four times, over a 15-month period, spanning both wet and dry seasons. Consistent with my first hypothesis, communities dominated by native understory species were found exclusively in watersheds that were at least 15% forested by evergreen canopy. These findings suggest that native understory communities can persist in urban areas if adequate surrounding forest cover is maintained. Regarding my second major hypothesis, significantly more seeds were deposited by water than by wind (p < 0.05; mean of 155 seeds per turf trap; mean of 30 seeds per funnel trap). For shrubs, for species primarily dispersed by animals, and for species under 15m tall, hydrochory significantly increased delivery to riparian areas over the background seed delivery rate measured in funnel traps. There was a significant reduction in the number of seeds deposited by streams as TIA increased (adjusted R² = 0.74; p < 0.01). Deposition of shade-tolerant seeds decreased significantly, while deposition of non-native seeds increased significantly (p < 0.05) with watershed TIA and with development within 500m from the site, likely due to alterations of seed source pools of these species. Findings indicate that in an urban setting, small streams have the capacity to act as dispersal vectors, connecting fragmented populations that may otherwise be seedlimited. Riparian forests with diverse understory assemblages maintained by ongoing seed deposition may persist in urban areas with sufficient watershed forest, as well as with low development cover, in both the whole watershed and the near-stream area. Total seed deposition by streams, as well as deposition of shade-tolerant species, can be expected to decrease with increased watershed development. Results suggest that passive approaches to restoration of riparian forest understories in urban watersheds will only likely be successful with sufficiently high forest cover and with restricted development.

>Magister Scientiae - MSc
Riparian vegetation occurs in two distinct zones, the wet bank and the dry bank. Knowledge on how the flow regime influences the zonal structure of riparian vegetation is required to mitigate the adverse effects of water resource utilization on riparian vegetation. The first objective of this study was to determine whether flow exerts a physical influence on zonal structure pre- or post-recruitment. An examination of the survival of seedlings and saplings was conducted along Western Cape rivers to investigate seedling persistence and survival on lateral zones. A comparison of the ratios of seedlings, saplings and adults in different riparian zones for the years, 2004, 2011 and 2013, was carried out. The results suggest that in general seeds are deposited randomly on the banks, where they germinate and become seedlings. Seedlings that become established at locations unsuitable for their persistence into adulthood are removed either by high flows or perish during dry conditions. Thus, lateral zonation eventually develops due to species differences in tolerance to conditions at different positions on the banks. The second objective was to explore the effects of the reduction in dry season low flows on the recruitment success of riparian species at sites upstream and downstream of abstraction points. At most sites plants were arranged into different lateral zones and the numbers of species between upstream and downstream sites were not significantly different. There were significant differences in the abundances between up- and downstream sites, with the loss of herbaceous plants and sedges at downstream sites, both of which favour moist conditions. Also, in the absence of dry season flows, the seedlings of dry bank tree species recruited closer to the channel than those at the sites with summer flows. The shifting of the dry bank into the channel narrows the channel, which may affect the hydraulic pressures exerted during floods. The spatial arrangement in the riparian zone has as much to do with flow conditions post recruitment as it does with conditions during recruitment. This shows that the structure of riparian plants is determined not only by whether or not the minimum flows are met, this points to the need to reinstate the naturally variable flow and adopting a holistic approach for the understanding and management of aquatic systems.

Numerous studies have addressed the role of stream geomorphology on vegetation distribution. These studies have shown that channel morphology, including depositional and erosional processes, influence vegetation colonization. However, few studies have addressed the impact of vegetation on the geomorphic processes of streams. Vegetation has the ability to stabilize channel banks and alter stream hydrology and stream power. Little research has addressed the impact of invasive vegetation and its ability to change river channel processes. My research addresses the impact of the highly invasive Phalaris arundinacea and quantifies its influence on the stream channel form of the Sprague River, Oregon. I conducted field research that included root density and root strength surveys to determine the below ground influences of vegetation in terms of added bank cohesion provided by the invasive and two similar native species: Eleocharis palustris and Carex vesicaria. To ascertain differences between the species above ground characteristics and influences, I measured stem density and elasticity to calculate their roughness (Manning's n) and determine their potential impact on stream velocity. Finally, I used these vegetation characteristics to model stream velocity, water depth, and bed shear stress within the 2-D model MD-SWMS. Differences in root size were significant with C. vesicaria having the largest root diameters, largest root area ratio, and largest bank cohesion provided by roots. This was followed by the invasive and then E. palustris. E. palustris had the highest stem density, followed by C. vesicaria and P. arundinacea. The invasive had the highest stem stiffness. E. palustris was associated with the highest roughness value, closely followed by the invasive and C. vesicaria. Using modeling I found the presence of the invasive increased velocity compared to E. palustris and increased bed shear stress compared to C. vesicaria. Therefore, changes in species composition, such as a shift from either of the natives to the invasive, could affect channel morphology over time. By comparing the impact of this invasive to that of native grasses and sedges, this research provides insight into how further spread of the invasive may affect the Sprague River and other riparian ecotones.
2015-10-03

Dissertation (PhD)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: Riparian vegetation has received a lot of attention in South Africa recently, mainly because of its importance in bank stabilization and its influence on flood regimes and water conservation. The upper reaches have thus far received the least of this attention because of their inaccessibility. This study mainly focuses on these reaches where riparian vegetation is still mostly in a pristine state. The study area chosen for this purpose is the Hottentots Holland Mountains in the Southwestern Cape, the area with the highest rainfall in the Cape Floristic Region, which is very rich in species. Five rivers originate in this area and the vegetation described around them covers a large range of habitats, from high to low altitude, with different geological substrates and different rainfall regimes. All of these rivers are heavily disturbed in their lower reaches but are still relatively pristine in their upper reaches. All of them are dammed in at least one place, except for the Lourens River. An Interbasin Transfer Scheme connects the Eerste-, Berg- and Riviersonderend Rivers. The water of this scheme is stored mainly in Theewaterskloof Dam. Another big dam for water storage, Skuifraam Dam, will be built on the Berg River near Franschhoek in the nearby future. In order to study the vegetation around a river, a zonation pattern on the river bank is described and several physical habitats are recognized. A primary distinction is made between a Wet Bank (flooding at least once a year) and a Dry Bank (flooding less than once a year). The Dry Bank is further subdivided into a Lower Dynamic, a Shrub/Tree and a Back Dynamic Zone. In the lower reaches these zones are very distinct, but in the upper reaches of a river they tend to blend into each other and some zones can be absent or very narrow. Vegetation has been sampled in transects across the riverbed, following the Braun-Blanquet method. Additional vegetation samples have been recorded in the bogs and mires at the sources of the rivers. Vegetation structure and physical habitat has been described to contribute to the description of the vegetation types. In order to understand the environmental processes that determine the vegetation, environmental parameters were recorded in every vegetation sample, such as, slope, aspect, rockiness and soil variables. The classification of the vegetation samples resulted in the identification and subsequent description of 26 riverine and 11 mire communities. The riverinecommunities have been subdivided into ten Community Groups, including a group of Aquatic communities and three groups of Wet Bank communities. The main distinction within the Wet Bank Zone is the importance of erosion or deposition as a driving force of the ecosystem. Three groups of Fynbos communities are identified in the Back Dynamic Zone, with Asteraceous Fynbos occurring on shales and granites, Ericaceous Fynbos occurring on Table Mountain Group sandstones and Transitional Fynbos on a variety of substrates. One community group is characterized by the dominance of Cliffortia odorata, which shows affinity with some renosterveld communities known from literature. The two final groups contain the Afromontane Forests and Riparian Scrub communities, respectively. Discharges are calculated from data recorded at existing gauging weirs. The recurrence intervals, inundation levels and stream power of several flood events are derived from these data and are extrapolated to upstream sites. It appears that most vegetation types in the zonation pattern on the riverbank can be explained by these flood events, except for the Afromontane Forests, which are dependent on other sitespecific factors including protection from fire. Constrained and unconstrained ordinations are used to relate vegetation patterns to the environment. The vegetation is determined by three environmental gradients, operating at different scales. The lateral gradient across the riverbed is mainly determined by inundation frequency and stream power, which are difficult to measure in rocky mountain situations, although variables like distance from the water’s edge, elevation above the water level and rockiness are correlated to them. The longitudinal gradient is the gradient along the length of the river, from high to low altitude. This gradient has the least influence on the riparian vegetation. The geographical gradient reflects the large-scale climatic processes across the mountain range. This gradient accounts for the biggest part of the total explained variation. Important variables are especially the ratio between the summer and winter rainfall and the geological substrate. In the Fynbos Biome, where gamma diversity is extremely high, large-scale environmental processes are important in azonal vegetation as well. The most species-rich vegetation associated with the rivers is found furthest from the water’s edge at intermediate altitudes. Knowledge about the vegetation types and environmental processes in Western Cape rivers is essential for monitoring and maintaining these special ecosystems. Specific threats are related to possible abstraction of water from theTable Mountain Group aquifer and from climate change, which might result in an overall drying of the ecosystem.
AFRIKAANSE OPSOMMING: Riviere se oewerplantegroei kry die laaste tyd baie aandag in Suid-Afrika, hoofsaaklik vanweë die belang vir die beheer van vloede, stabilisasie van die oewers en die bewaring van drinkwater. Die hoë-liggende dele van die riviere het tot dusver die minste aandag geniet omdat hulle tot ’n groot mate ontoeganklik is weens die onherbergsame terrein waarin hulle geleë is. In hierdie studie is daar veral na bergstrome gekyk waar die plantegroei nog taamlik natuurlik en onversteur is. Die studiegebied wat vir hierdie doel gekies is, is die Hottentots-Holland berge in die Wes-Kaap. Die gebied het die hoogste reënval in die Kaapse Floristiese Ryk en is ook baie ryk aan spesies. Vyf riviere het in hierdie gebied hulle oorsprong. Die plantegroei wat hier voorkom sluit ‘n wye reeks habitatte in: van hoog tot laag in hoogte bo seespieël, verskeie geologiese substrate asook verskillende reënval patrone. Al die vyf riviere wat ondersoek is, is baie versteur in hul onderlope, maar is nog grotendeels natuurlik in hul hoë-liggende dele. Almal is reeds opgedam deur een of meer damme, behalwe die Lourensrivier. ’n Tussenopvanggebied-oordragskema verbind tans die Eerste-, Berg- en Riviersonderendriviere met mekaar. Die water uit hierdie riviere word tans hoofsaaklik in die Theewaterskloofdam opgegaar. ’n Verdere groot opgaardam, die sogenaamde Skuifraamdam, word binnekort in die Bergrivier te Franschhoek gebou. Al die riviere se onderlope is tot ’n mindere of meerdere mate vervuil met landbou- en rioolafvoerprodukte. Uitheemse indringerplante, wat die natuurlike oewerplantegroei verdring, skep veral probleme stroomaf van plantasies en dorpe. Om die plantegroei van die rivieroewers na te vors, te klassifiseer en te beskryf, is variasies in die fisiese omgewing bepaal en korrelasies gesoek om die verspreiding van die plantegroei te verklaar. Die belangrikste verdeling in die oewerplantegroei wat gevind is, is tussen die Nat-oewersone (dit word meer as een keer per jaar oorstroom) en die Droë-oewersone (dit word minder as een keer per jaar oorstroom). Die Droë-oewersone word verder onderverdeel in die Laerdinamiesesone, die Boom/Struiksone en die Agter-dinamiesesone. In die laer dele van die rivier is hierdie soneringspatrone baie duidelik, maar in die boonste dele van die rivier kan die onderverdelings dikwels nie van mekaar onderskei word nie omdat hulle gemeng is, of kan die sones baie smal wees of selfs heeltemal afwesig wees.Die plantegroei is gemonster in transekte wat dwarsoor die rivierloop uitgelê is. Die Braun-Blanquet monstertegniek is gevolg. Bykomende monsterpersele is opgemeet in die moerasse in die boonste dele van die berg-opvanggebiede. Om die omgewingsprosesse wat die plantegroei bepaal te verstaan, is ’n aantal omgewingsfaktore in elke monsterperseel aangeteken, wat, onder andere, helling, aspek en bedekking van rotse ingesluit het, terwyl die variasie in samestelling van die bodem ook aangeteken is. Die klassifikasie van die plantegroei het tot die beskrywing van 26 plantgemeenskappe in die riviere en 11 gemeenskappe in die moerasse gelei. Die struktuur van die plantegroei asook kenmerke van die fisiese habitat is in die beskrywing van die plantegroei-eenhede ingesluit. Die gemeenskappe in die riviere is onderverdeel in tien gemeenskapsgroepe. Daar is een gemeenskapsgroep wat die akwatiese gemeenskappe en drie wat die Nat-oewersone gemeenskappe insluit. Die belangrikste verskille tussen die verskillende Nat-oewersone gemeenskappe word bepaal deur die mate waartoe erosie of deposisie voorkom. Daar is ook drie gemeenskapsgroepe van Fynbos onderskei wat in die Agter-dinamiesesone voorkom. Dit sluit in die Aster-fynbos op die skalies en graniete, die Erica-fynbos op die sandstene en die Oorgangs-fynbos op gemengde substrate. Een gemeenskapsgroep is deur die dominansie van Cliffortia odorata gekenmerk. Dit toon verwantskap met renosterveld gemeenskappe wat reeds in die literatuur beskryf is. Die laaste twee groepe sluit die Afromontane woude en Oewerstruikbosse in. Die waterafloop is bereken deur middel van data verkry vanaf bestaande keerwal meetstasies. Die herhalings-intervalle, oorstromingsdiepte en vloei-sterkte van verskillende vloedtipes word vanaf hierdie data afgelei en stroomop geekstrapoleer. Die meeste plantegroeivariasie op die oewers kan deur die vloede verklaar word, behalwe in die geval van die Afromontane woude, wat deur ander omgewingsfaktore bepaal is. Beperkte en onbeperkte ordinasie is gebruik om die verband tussen die plantegroeipatrone en die omgewing te bepaal. Die plantegroei se verspreiding is bepaal deur drie omgewingsgradiënte, wat op verskillende skale ‘n uitwerking het. Die laterale gradiënt oor die rivierbedding is hoofsaaklik bepaal deur oorstromingsfrekwensie en stroomvloeisterkte. Hierdie veranderlikes is moeilik bepaalbaar, alhoewel ander soos, afstand vanaf die rivier, hoogte bo watervlak en bedekking van rotse, wat hieraan gekorreleer is, wel meetbaar is. Die lengte gradiënt,dit is die gradiënt wat van oorsprong na einde langs die lengte van die rivier teenwoordig is, het die minste invloed op die plantegroei. Die geografiese gradiënt weerspieel die grootskaalse klimaatsveranderinge oor die bergreeks. Deur hierdie gradiënt word die grootste deel van die totale variasie tussen die monsters verklaar. Die belangrikste veranderlikes is die verhouding van somer- teenoor winter-reënval en die geologiese substraat. Soortgelyk aan die fynbos in die Fynbosbioom, waar gammadiversiteit buitegewoon hoog is, is die grootskaalse omgewingsprosesse, ook vir asonale oewerplantegroei, baie belangrik. Die spesierykste plantegroei rondom die rivier word die verste van die oewer op gemiddelde hoogtes bo seespieël gevind. Kennis oor die plantegroei en die omgewingsprosesse in die riviere in die Wes-Kaap is belangrik vir die monitering en effektiewe beheer van hierdie besondere ekosisteem. Spesifieke bedreigings is gekoppel aan die potensiële ontginning van water uit die akwifer in die Tafelberggroep-sedimente asook deur grootskaalse klimaatsveranderinge waartydens die hoeveelheid water, volgens voorspellings, waarskynlik sal afneem in hierdie ekosisteem.

Degraded rangelands and riparian woodlands in eastern North Dakota are increasing in frequency. Two studies were conducted to address reduced forage quantity and quality and reduced regeneration of riparian tree and shrub species. Research objectives were to (1) analyze multiple pre-seeding treatments to determine impacts on rangeland production of interseeded native species; and (2) determine if fencing, weed-barrier fabric, mowing, or herbicide treatments can increase survivability of riparian tree and shrub seedling plantings. Pre-seeding treatments with herbicide showed significantly higher production of native species than the control. High-fencing/mowing treatment and high-fencing/weed-barrier fabric/herbicide treatment in riparian tree and shrub plantings resulted in significantly higher survival than the control. These findings will be used to develop future research and management strategies.
Robert H. Levis II Cross Ranch Fellowship
Gladys Allen Trust of St. Louis
Red River Regional Council
North Dakota Department of Health
Environmental Protection Agency (EPA)

Woody vegetation encroachment has become a major threat to tallgrass prairie streams mainly because of fire suppression. This process converts prairie streams from open to closed canopy systems. The effects of these riparian changes are poorly understood, but the relative importance of basal resources presumably shifts from primarily autochthonous to allochthonous with increasing canopy cover, potentially altering macroinvertebrate functional structure and production. To assess the effects of woody vegetation encroachment on stream ecosystem structure and function, riparian trees were removed from two headwater stream reaches on the Konza Prairie Biological Station (KPBS) in eastern Kansas. Experimental stream reaches were compared to streams with naturally open and closed canopies before and after the manipulation. Benthic organic matter and macroinvertebrates were collected monthly from each reach for one year before and one year after woody vegetation removal. Total community production in canopy removal reaches ranged from 8.9-10.2 g AFDM m-2 y-1 before riparian removal, and this increased significantly to 13.4-14.5 g AFDM m-2 y-1 after riparian removal. Scraper production in canopy removal reaches was 2.8-3.9 g AFDM m-2 y-1 before riparian removal, and increased significantly to 6.0-8.7 g AFDM m-2 y-1 after riparian removal, presumably due to enhanced food availability. Total community production in naturally open reaches ranged from 7.6-12.6 g AFDM m-2 y-1 before riparian removal and decreased to 6.5-9.8 g AFDM m-2 y-1 after riparian removal. Riparian forest removal altered macroinvertebrate production and functional structure, but higher macroinvertebrate production in canopy removal reaches compared to naturally open reaches suggested natural conditions were not restored one year after riparian removal. However, macroinvertebrate communities in naturally open and canopy removal reaches became more similar after riparian removal. Functional structure, based on production, in naturally open and canopy removal reaches after riparian removal was dominated by scrapers (45-60% of total production), with similar proportions of collector-gatherers (12-26%) and predators (15-25%). Collector-filterers and shredders contributed < 9% of total production in naturally open and canopy removal reaches after riparian removal. Results demonstrate that woody vegetation encroachment and riparian forest removal significantly influence tallgrass prairie stream structure and function. Information from this study can help inform and guide management, restoration, and conservation of remaining tallgrass prairie streams.

The dissertation presented in this manuscript contributes to river science by providing a detailed overview on the state of the art on the interaction between riparian vegetation and hydrogeomorphological processes, by devising a novel model encompassing most of such processes and by proposing a field methodology aimed at providing means for improving the modelling of such interactions. The state of the art is summarized in an extensive review describing riparian vegetation and hydrogeomorphological processes mutual feedbacks. Such review did not simply seek to describe these feedbacks but, compiling from a large array of results from field, laboratory and modelling studies, provides a set of physical thresholds that trigger system changes. Therefore, processes are not only described terms but also explained with a quantitative approach. Processes description provided the conceptual foundation for the development of the novel simulation model while model parameterization was based on the quantitative information collected in the review. Such novel model, encompasses the main relationships entwining riparian woody vegetation and hydrogeomorphological processes and is able of replicating long term riparian landscape dynamics considering disturbance events, environmental stressor and riparian woody vegetation establishment from seeds and large wood. The manuscript presents the model structure and its conceptual validation by means of hydrological scenarios aimed at testing the coherence of the simulation results with expected system behaviour. Examples of such coherences are vegetation growth rate in response to hydrological regime, entrainment and establishment of large wood in an unconfined river system and vegetation effect on erosion and deposition patterns. Analysis of sedimentation patterns from the modelled results suggested that vegetation flow resistance should be modelled with greater detail. These conclusions pointed the dissertation research towards the testing of a novel class of vegetation flow resistance equations, proposed by different authors, able of describing woody vegetation flow resistance on a physical basis. These equations have the advantage of considering flow stage, plants foliation level and species-specific flexibility. However, the use of such equations is limited by the difficulty of measuring the vegetation properties required as equation-inputs. In order to test if these equations could effectively improve sediment dynamics predictions, a field method was formulated and tested. The field method allows to sample vegetation properties that can be used with these novel class of flow resistance equations. In the manuscript, such method is applied and the resulting vegetation properties used in several modelling scenarios. Such scenario proved that hydraulic variables modelled with these novel flow resistance approaches are more realistic and thus that the model developed during the dissertation could benefit from inclusion of such flow resistance equations in its source code.

Riparian areas connect terrestrial and aquatic environments. The objectives of this research were to compare the vegetation community composition and structure eight years after harvesting and to explore successional trends among buffer widths at year eight after disturbance and in a chronosequence. A series of small clearcuts were harvested in 1998 in a 70 year old second growth stand at the Malcolm Knapp Research Forest and 0m, 10m and 30m reserve zones were established adjacent to the streams. Each treatment was replicated 3 times and 3 unharvested streams were identified as controls. Overstory and understory vegetation was measured annually from the year of harvest. Canopy density was measured using a densiometer. For comparative purposes, four vegetation plots were added in riparian areas within an 1868 and an old-growth stand during the summer of 2006. Eight years after harvesting, understory vegetation development is affected by buffer width due to higher light levels, and species richness in the 10m and 0m buffers is higher than in the 30m buffer and control. Shrubs and deciduous trees dominate the 0m and 10m buffer treatments. Proximity to the stream does not affect the composition and abundance of species with the exception of herbs and mosses. In the 10m and 30m buffer treatments, up to 15% overstory trees were windthrown in the first 2 years after harvest producing large canopy gaps. Consequently, the understory development in the 10m and 30m buffers is more like that in the 1868 and old-growth stands than in the controls, but these treatments still lack the very large trees and microsite heterogeneity of the older stands. In the unharvested controls, self-thinning continues and there has been 30% mortality of mostly smaller trees over the past 8 years. However, overstory density remains high. The 0m buffer was quickly colonized by shrubs and ferns and within the last 2 years has become dominated by juvenile deciduous trees. Overall, the 10m buffer balances timber production with the maintenance of overstory and understory structure dynamics. The combined effect of light from the edge and partial windthrow is accelerating succession towards a more mature or ‘old-growth’ condition.

Thesis (M.S.) University of Missouri-Columbia, 2004.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (June 30, 2006) Vita. Includes bibliographical references.

River environments are complex and dynamic ecosystems, and provide valuable ecosystem services such as clean water. The species rich riparian vegetation performs many important ecosystem functions such as reducing erosion and filter inputs from upland areas. Regulated flow regimes have decreased riparian plant species richness, cover and plant performance. To restore the integrity of riparian ecosystems, mitigation measures such as re-regulation of water-level regimes toward more natural seasonal fluctuations may be needed. The aim of this study was to assess potential responses of riparian plants to changes in water-level regulation in run-of-river impoundments to better match natural flow regimes. The elevational extent of plant species on riverbanks of two run-of-river impoundments in the Ume River were surveyed and their probability of occurrence along the gradient of inundation duration was modelled and compared to their distribution in the free-flowing Vindel River. Most species showed similar tolerance to flooding in the Ume and Vindel Rivers. Changes in elevational extent in response to three simulated environmental flow regimes were predicted by using the relationship between plant occurrence and inundation duration. A simulated spring flood and low water levels during the latter part of the growing season is predicted to result in the largest increase in elevational extent, with increases of 70-80% for several riparian species. However, only 47% of the riverbanks along run-of-river impoundments in the Ume River is deemed to be suitable for plant establishment, since many riverbanks are steep and devoid of fine-grained substrate as a result of erosion.
Älvmiljöer utgör komplexa och dynamiska ekosystem som tillhandahåller värdefulla ekosystemtjänster så som rent vatten. Den artrika strandvegetation bidrar till många viktiga ekosystemsfunktioner som närings- och giftupptag och till minskad erosion. Vattenregleringen med förändrade flödesregimer har minskat artrikedom, täckningsgrad och tillväxt av strandväxter. För restaurering av strandekosystemen kan omreglering till mer naturliga säsongsvariationer i vattenståndet vara nödvändigt. Den här studien syftade till att förutsäga hur utbredningen av strandväxter längs stränder i vattenkraftsmagasin potentiellt skulle förändras vid användande av miljöanpassade flöden för att mer likna naturliga flödesregimer i outbyggda älvar. Jag undersökte växternas utbredning i höjdled på stranden längs två magasin i Umeälven och beräknade sannolikheten för varje arts förekomst längs strandens översvämningsgradient. Av de arter som förekom i både Umeälven och den närliggande, outbyggda Vindelälven jämfördes växternas utbredningsgränser i respektive älv. De flesta arterna uppvisade liknande översvämningstolerans i Umeälven och Vindelälven. För att förutsäga förändringar i utbredning som respons på tre olika simulerade miljöanpassade vattenståndsregimer, jämfördes arternas översvämningstolerans vid nuvarade vattenstånd med simulerade vattenståndsregimer. En simulerad vårflod och lågt vattenstånd under sensommaren förväntas ge de största responserna i artutbredning med ökningar på 70-80% för ett flertal strandväxter. Endast 47% av älvstränderna i magasinen i Umeälven bedöms vara lämpliga för växtetablering eftersom stora delar av strandsträckorna är branta och saknar finkornigt substrat till följd av erosion.

What drives species diversity across landscapes is one of the most fundamental questions in ecology. Further, understanding the mechanisms underlying species diversity patterns is important not only for forming and challenging ecological theories but also essential for appropriate landscape management and effective nature conservation. This thesis focuses on patterns of vascular plant, moss and liverwort species richness and composition in relation to water flow in boreal-forest catchments, focusing mostly on riparian zones (RZs), that is terrestrial areas bordering streams and rivers. I addressed some of the most essential questions related to the ecology of riparian vegetation including the role of stream network position, groundwater (GW) flow paths, substrate availability, upland perturbations, and stream restoration. I also investigated how riparian soil processes and habitat properties relate to these factors in order to provide a holistic understanding of riparian dynamics. The results showed that the species richness and composition of riparian vascular plants, mosses and liverworts are strongly influenced by position along the stream network, GW discharge, presence of variable substrates in RZs, and by stream restoration. Generally, more species were found downstream in the network, at sites with inputs of upland GW, sites with high diversity of substrates (e.g., open mineral soil, rocks, stones, wood and bark), and along streams restored after channelization. This thesis also describes how riparian habitat properties responded to position in the landscape and human impacts, thus providing mechanistic links between plant species diversity and riparian processes across spatial scales. These ecological insights are further implemented into numerous recommendations for freshwater and upland management in boreal Sweden. Given that streams and rivers connect landscape elements both longitudinally and laterally I argue that management plans should be designed for entire catchments instead of individual river segments. Ignoring the connectivity of streams as well as the high connectivity of riparian areas to uplands via GW flows may result in failure of restoration, mitigation and/or protection actions. Further, during forestry operations more emphasis should be placed on GW discharge areas along streams and rivers, because they represent important ecological and biogeochemical hotspots in the landscape. The riparian buffers left along streams in boreal catchments affected by forestry are presently insufficiently wide and often uniform in width. This threatens the assemblages of species in GW discharge hotspots and the ecosystem services they provide. Overall, this thesis describes a holistic picture of riparian diversity patterns and riparian processes in boreal landscapes, acknowledges and elaborates on current ecological theories, presenting new patterns in biodiversity, and offers management guidelines.

Dans les écosystèmes, tels que les rivières, les marais salés, les mangroves, les dunes côtières, qui sont exposés à des flux hydrogéomorphologiques fréquents et réguliers (c’est-à-dire à des perturbations physiques), des rétroactions se mettent en place entre la géomorphologie (eau, sédiments et formes fluviales) et les plantes (par exemple Populus nigra L., Salix alba L., Salix purpurea L. dans les rivières). L’établissement de la végétation est contrôlé par des processus hydrogéomorphologiques qui, en retour, sont modulés par la végétation. De telles rétroactions contrôlent la dynamique des écosystèmes riverains. Dans cette thèse, nous avons abordé deux questions principales afin de mieux comprendre les rétroactions entre la végétation riveraine et les processus hydrogéomorphologiques : (i) comment la végétation riveraine répond-elle aux contraintes hydrogéomorphologiques ? (ii) comment et dans quelle mesure les plantes ingénieures, une fois établies, affectent-elles la géomorphologie fluviale ? Nous avons étudié ces questions sur la rivière Allier (France) à travers une approche emboîtée multi-échelles allant de l’échelle du patron paysager au trait de plante. Nous avons testé l’applicabilité de la méthode de photogrammétrie pour quantifier la réponse et l’effet de la végétation riveraine et des rétroactions biogéomorphologiques à différentes échelles spatio-temporelles (corridor, banc alluvial et individu). À l’échelle du corridor, nous avons recherché la signature topographique de la végétation riveraine dans le paysage, en utilisant des données photogrammétriques et LiDAR. À l’échelle intermédiaire du banc alluvial, nous avons étudié l’aptitude des trois espèces pionnières dominantes riveraines de Salicaceae (P. nigra, S. purpurea, S. alba) à s’établir et à agir comme ingénieurs d’écosystème en piégeant les sédiments fins. À l’échelle la plus fine du trait de plante, nous avons quantifié la relation existante entre les attributs de trait de réponse des jeunes plantes de P. nigra et leur exposition à trois niveaux différents de stress mécanique (tête de banc fortement exposée, queue de banc moins exposée, chute alluviale). Nous avons identifié les difficultés et les erreurs à ne pas commettre pour appliquer correctement la photogrammétrie dans les études des rétroactions biogéomorphologiques. En tout état de cause, la photogrammétrie s’est avérée être un outil performant pour quantifier un ensemble de paramètres pertinents pour répondre à des questions de recherche fondamentale aux trois échelles spatiales considérées. À l’échelle la plus large, la signature topographique de la végétation est particulièrement difficile à identifier en raison de la dynamique complexe des formes fluviales de la rivière Allier. Cependant, en concentrant les observations sur des zones de taille réduite et fortement connectées (bancs alluviaux bordant le chenal), la signature de la végétation a pu être identifiée par cette méthode. Elle semble augmenter avec la croissance de la hauteur végétale (progression temporelle de la succession biogéomorphologique), ce qui est en accord avec le modèle de succession biogéomorphologique fluviale (SBF). À l’échelle intermédiaire du banc alluvial, les rétroactions biogéomorphologiques pouvaient être bien identifiées. La capacité des plantes riveraines à s’établir et à agir comme ingénieurs d’écosystème dépend à la fois des espèces et de leur physionomie, de leur âge et de leur position respective sur les bancs alluviaux. À l’échelle la plus fine de l’individu, nous avons capturé la réponse morphologique et biomécanique contrastée de P. nigra à l’exposition aux différents niveaux de contrainte mécanique d’un point de vue de trait. Dans tous les niveaux hiérarchiques, des rétroactions biogéomorphologiques liées aux échelles ont été détectées et synthétisées dans un modèle conceptuel. [...]
N ecosystems, such as rivers, salt marshes, mangroves, coastal dunes which are exposed to frequent and regular hydrogeomorphic fluxes (i.e. physical disturbances), feedbacks between geomorphology (water, sediment and landforms) and plants (e.g. Populus nigra L., Salix alba L., Salix purpurea L. in rivers) can occur. Vegetation esta¬blishment is controlled by hydrogeomorphic processes which in turn are modulated by vegetation. Such feedbacks control riparian ecosystem dynamics. In this thesis, we addressed two main questions in an effort to better understand feedbacks between riparian vegetation and hydrogeomorphic processes: (i) How does riparian vegetation respond to hydrogeomorphic constraints? (ii) How, and to what extent, do established engineer plants affect fluvial geomorphology? We studied these questions through a nested multi-scale approach from landscape pattern to plant trait scales on the dynamic wandering Allier River (France). We tested the applicability of the method of photogrammetry to quantify the response and the effect of riparian vegetation and biogeomorphic feedbacks at different spatio-temporal scales (i.e. corridor, alluvial bar and individual). At the corridor scale, we searched for the topographic signature of riparian vegetation in the landscape, using photogrammetric and LiDAR data. At the intermediate alluvial bar scale, we investigated the aptitude of three dominant pioneer riparian Salicaceae species (P. nigra, S. purpurea and S. alba) to establish and to act as ecosystem engineers by trap¬ping fine sediment. At the finest, plant trait scale, we quantified the relation between response trait attributes of young P. nigra plants and their exposure to three different levels of mechanical stress (a highly exposed bar-head, a less exposed bar-tail, a chute channel). We identified some difficulties or failures to properly apply photogrammetry in biogeomorphic feedback studies. However, photogrammetry appeared as a useful tool to quantify a set of relevant parameters to respond to fundamental research questions concerning biogeomorphic feedbacks at the three nested spatial scales. At the broadest, the topographic signature of vegetation was not easy to capture because of the complex shifting mosaic of landforms of the Allier River. However, by focusing on more connec¬ted, restricted areas (i.e. alluvial bars), the signature of vegetation could be captured. It seems to increase with increasing vegetation height corresponding to the evolutionary phases of the fluvial biogeomorphic succession (FBS) model. At the intermediate, alluvial bar scale, biogeomorphic feedbacks could be well identified. The capacity of riparian plants to establish and act as ecosystem engineers depended both on species and their physiognomy, their age and their location on alluvial bars. At the finest, individual plant scale, we captured the contrasting morphological and biomechanical response of P. nigra to variable mechanical stress exposure from a trait perspective. In all hierarchical levels, scale-related biogeomorphic feedbacks were detected and described in a conceptual model. The three scales were considered as cycles composed of four different phases, which can have a variable temporality. The broadest spatio-temporal scale represents the evolution over several decades of the landscape mosaic resulting from the balance between constructive (vegetation establishment, growth and succession) and destruc¬tive (floods) forces. [...]

Flow regime, the magnitude, duration and timing of streamflow, controls the development of floodplain landforms on which riparian vegetation communities assemble. Streamflow scours and deposits sediment, structures floodplain soil moisture dynamics, and transports propagules. Flow regime interacts with environmental gradients like climate, land-use, and biomass-removing disturbance to shape riparian plant distributions across landscapes. These gradients select for groups of riparian plant species with traits that allow them to establish, grow, and reproduce on floodplains – riparian vegetation guilds. Here I ask, what governs the distributions of groups of similar riparian plant species across landscapes? To answer this question, I identify relationships between riparian vegetation guilds and communities and environmental gradients across the American West. In Chapter One, I discuss guild-based classification in the context of community ecology and streams. In Chapter Two, I identified five woody riparian vegetation guilds across the interior Columbia and upper Missouri River Basins, USA, based on species’ traits and morphological attributes. I modeled guild occurrence across environmental gradients, including climate, disturbance, channel form attributes that reflect hydrology, and relationships between guilds. I found guilds’ distributions were related to hydrology, disturbance, and competitive or complementary interactions (niche partitioning) between co-occurring guilds. In Chapter Three, I examine floodplain riparian vegetation across the American West, identifying how hydrology, climate, and floodplain alteration shape riparian vegetation communities and their guilds. I identified eight distinct plant communities ranging from high elevation mixed conifer forests to gallery cottonwood forests to Tamarisk-dominated novel shrublands. I aggregated woody species into four guilds based on their traits and morphological attributes: an evergreen tree guild, a mesoriparian shrub guild, a mesoriparian tree guild, and a drought and hydrologic disturbance tolerant shrub guild. Communities and guilds’ distributions were governed by climate directly, and indirectly as mediated through streamflow. In Chapter Four, I discuss the utility of guild-based assessments of riparian vegetation, current limitations to these approaches, and potential future applications of the riparian vegetation guild concept to floodplain conservation and management. The classification of vegetation into functional trait-based guilds provides a flexible, framework from which to understand riparian biogeography, complementing other models frameworks for riparian vegetation.

Modeling of surface energy fluxes and evapotranspiration (ET) requires the understanding of the interaction between land and atmosphere as well as the appropriate representation of the associated spatial and temporal variability and heterogeneity. This dissertation provides new methodology showing how to rationally and properly incorporate surface features characteristics/properties, including the leaf area index, fraction of cover, vegetation height, and temperature, using different representations as well as identify the related effects on energy balance flux estimates including ET. The main research objectives were addressed in Chapters 2 through 4 with each presented in a separate paper format with Chapter 1 presenting an introduction and Chapter 5 providing summary and recommendations. Chapter 2 discusses a new approach of incorporating temporal and spatial variability of surface features. We coupled a remote sensing-based energy balance model with a traditional water balance method to provide improved estimates of ET. This approach was tested over rainfed agricultural fields ~ 10 km by 30 km in Ames, Iowa. Before coupling, we modified the water balance method by incorporating a remote sensing-based estimate for one of its parameters to ameliorate its performance on a spatial basis. Promising results were obtained with indications of improved estimates of ET and soil moisture in the root zone. The effects of surface features heterogeneity on measurements of turbulence were investigated in Chapter 3. Scintillometer-based measurements/estimates of sensible heat flux (H) were obtained over the riparian zone of the Cibola National Wildlife Refuge (CNWR), California. Surface roughness including canopy height (hc), roughness length, and zero-plane displacement height were incorporated in different ways, to improve estimates of H. High resolution, 1-m maps of ground surface digital elevation model and canopy height, hc, were derived from airborne LiDAR sensor data to support the analysis. The effects of using different pixel resolutions to account for surface feature variability on modeling energy fluxes, e.g., net radiation, soil, sensible, and latent heat, were studied in Chapter 4. Two different modeling approaches were applied to estimate energy fluxes and ET using high and low pixel resolution datasets obtained from airborne and Landsat sensors, respectively, provided over the riparian zone of the CNWR, California. Enhanced LiDAR-based hc maps were also used to support the modeling process. The related effects were described relative to leaf area index, fraction of cover, hc, soil moisture status at root zone, groundwater table level, and vegetation stress conditions.

With the ever increasing reliance on hydropower in the world, it is important that its effects on riparian vegetation is well understood. This study aimed to explore the effects of different forms of hydropeaking, which results from the rapid and frequent opening and closure of hydroturbines, on different species groups of riparian species native to northern Sweden. Thirteen riparian species belonging to three different species groups, forbs, graminoids and woody species, were subjected to three different watering treatments simulating water stress, rapid fluctuation and prolonged flooding, which often correspond to different hydropeaking conditions. A fourth treatment maintained individuals under controlled conditions and simulated a non-regulated stream. The treatments were carried out over seven weeks. The results showed that the treatments affect the three tested species groups differently. Woody species responded to all treatments with lower germination, higher mortality and lower root elongation, while forbs and graminoids responded to flooding and fluctuation with increased germination but higher mortality and lower root elongation. Fluctuation and flooding had in general positive effects on germination and short term growth but also increased mortality, particularly fluctuation. There were no significant results regarding change in number of leaves for any treatment or species group. As this study only covered seven weeks it can only account for short-term trends, but it still provides interesting information about general expected trends for a wide variety of species native to northern Sweden and belonging to the main three species groups. Such information is key for river management.

This study investigates whether the flood regime in a catchment is sensitive to the condition of riparian vegetation along the river network. The research is based on a comprehensive assessment and synthesis of field and laboratory measurements of vegetation flow resistance. A new numerical model is developed to estimate the roughness characteristics of multi-species riparian assemblages at a cross-section. Reach-scale and catchment-scale flood routing models are then applied to estimate the impact of vegetation on flood characteristics at successively larger scales. The investigation reveals that when riparian vegetation is removed at catchment-scale, peak stage declines as channel capacity increases but is also increased as the upstream catchment responds more rapidly to rain. In fact, the two competing impacts tend to cancel out leaving flood peak stage relatively insensitive to riparian condition. However, the overbank duration of a flood and flow speeds (including wave celerity) were both found to be sensitive to vegetation condition; respectively increasing and decreasing with density of vegetation. The first stage of this research examines the magnitude of the vegetation contribution to overall channel roughness, and established a means to predict it. The features of the flow resistance generated by six plant types (mature trees; grasses; aquatic plants; flexible saplings; and large woody debris) were distilled from a comprehensive review of over 160 existing publications (Chapter 2).

The Kentucky Division of Water indicates that agriculture is responsible for 55% of the Commonwealth’s assessed streams not supporting their designated uses. Riparian buffers reduce nonpoint source pollution in agroecosystems by storing and cycling nutrients, stabilizing streambanks, increasing infiltration, and storing water. Specific information regarding riparian buffer management is needed for land managers to maximize buffer effectiveness at reducing agricultural contaminants impairing water quality. Baseline soil properties (texture, pH, C and nutrients) of the riparian buffer surrounding a tributary of Cane Run Creek in Fayette County, KY were characterized prior to imposing three mowing regimes (intense, moderate, and no mow treatments) and one native grass regime. Measurements were made along parallel transects located 2-m and 8-m distances from the stream. Root biomass, aggregate distribution, and saturated hydraulic conductivity were measured along the 2-m transect in two consecutive years following treatment establishment. The 2-m transect soils had the highest C, pH, Ca, Zn, and sand content. The 8-m transect had the highest P, K, Mg, and clay content. Semivariogram analysis of C content indicated slight to moderate spatial dependency along the 2m transect and moderate to strong spatial dependency along the 8m transect. Root biomass increased with decreased mowing frequency at the surface depth after one year; the native grass treatment had significantly less root biomass in both years compared to mowing treatments. There was no significant treatment effect on aggregate size distribution at the surface depth in either year. Mean weight diameter and large macroaggregates decreased from 2011 to 2012. Vegetation treatment had no statistically significant effect on water stable aggregates or saturated hydraulic conductivity. Experimental semivariograms provided evidence of spatial structure at multiple scales in root biomass, aggregates, and soil C. Spatial variability occurred over a shorter lag distance in 2012 than 2011, suggesting an effect of imposed treatments slowly developing over time. This study provides important insights on riparian buffer soil properties, soil sampling strategies to detect spatial variability in riparian buffers, and length of time needed to assess effects of vegetation management regimes on riparian root biomass, soil aggregates, and hydraulic conductivity.