Riparian ecosystems are valued for ecosystem services which have impacts on the well-being of humans and the environment. Anthropogenic disturbances along rivers in arid and semiarid regions have altered historical flow regimes and compromised their integrity. Many rivers are hydroecologically deteriorated, have diminished native riparian forests, and are pressured for their water supplies. My first study is founded on the premise that river restoration has increased exponentially with little documentation on effectiveness. We designed a conference to discuss lessons learned from past restoration activities to benefit future efforts. Participants, including scientists, managers, and practitioners, agreed that creating measureable objectives with subsequent monitoring is essential for quantifying success and employing adaptive management. Attendees stated that current projects are local and have limited funding and time, whereas future efforts must have longer funding cycles, larger timeframes, should contribute to regional goals, and address factors responsible for ecological decline. Bridging gaps among science, management, and policy in the 21st century is a key component to success. My second study focused on the benefits of long-term monitoring of local riparian restoration. Many efforts include revegetation components to re-establish native cottonwood-willow communities, but do not address how high-density establishment impacts vegetation dynamics and sustainability. Over five years, we documented significantly higher growth rates, lower mortality, and higher cover in cottonwood compared to non-native tamarisk. Cottonwood height, diameter at breast height, growth rates, and foliar volumes were reduced at higher densities. Herbaceous species decreased every year but native shrubs volunteered after two years resulting in a reduction of overall plant diversity from 2007-2009 with a slight increase from 2009-2011.My third study focused on improving basin-scale evapotranspiration (ET), a large component of the water budget, to better inform water resource allocation. My research suggests that multiple models are required for basin-scale ET estimates due to vegetation variability across water-limitation gradients. We created two empirical models using remote sensing, a multiplicative riparian ET model (r²=0.92) using MODIS nighttime land surface temperature (LST(n)) and enhanced vegetation index, and an upland ET model (r²=0.77) using multiple linear regression replacing LST(n) with a precipitation input.

Competition over freshwater resources is increasing at local and global scales. Growing urban and suburban centers utilize surface and groundwater resources to meet municipal, industrial, and agricultural demands, often at the expense of riparian ecosystems. Paradoxically, those same urban centers produce a significant volume of treated effluent that can be reused to restore and sustain riparian systems. Use of effluent as a source of water for the environment raises important questions about the benefits and impacts of effluent on riparian functions and ecosystem services, particularly in the context of climate change and drought conditions. This dissertation addresses knowledge gaps surrounding riparian change and resilience along the effluent-dominated Upper Santa Cruz River in southern Arizona. Appendix A investigates whether the Netleaf hackberry (Celtis laevigata var. reticulata) tree can provide accurate information on historic changes in climatic and hydrological conditions. Results indicate that hackberry trees do record climate-related stress in annual ring-width patterns and can therefore provide a historic frame of reference against which to compare current and future changes in riparian conditions. Appendix B documents spatial and temporal patterns of effluent uptake by Fremont cottonwood trees (Populus fremontii) through development of a new application for dendrochronology, specifically dendrochemistry. Results show that annual tree rings contain temporally variable concentrations of a micropollutant found only in effluent and may have the potential to record spatial and temporal patterns of effluent dispersion in riparian ecosystems. Appendix C investigates the complex interactions of ecohydrological conditions that led to a riparian mortality event along the Upper Santa Cruz River in 2005. Effluent is shown to contribute to riparian vegetation expansion, but also, due to its consistent delivery of nutrients and water, homogenize the system and ultimately diminish its resilience to perturbations and stress. Results highlight the paradoxical nature of effluent as both a contributor to riparian growth and a potential impediment to riparian function. This paradox can be resolved through a well-defined effluent impact monitoring and assessment program that incorporates historic information as well as current trends to detect significant changes in ecosystem functions and services.

Thesis (MScConEcol)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Soil respiration (Rs) is a major component of CO2 emissions and the global carbon balance. In the context of global change it of interest to understand seasonal patterns of RS in fynbos riparian ecosystems, particularly in invaded-riparian ecotones of these Mediterranean type ecosystems (MTE's) in the Western Cape, South Africa. Riparian ecotones are three dimensional transitional zones that provide multiple ecosystem services and functions and they act as the linkage between terrestrial and aquatic ecosystems where key ecological and geomorphological processes occur. Riparian ecotones are highly prone to disturbance, and because of this reason are also vulnerable to invasion by invasive alien plants (IAPs), notably Acacia species. Invasion by IAPs is considered one of the major threats to global change and biodiversity causing extensive ecological, economical, and social impacts. In south-western Cape, more than two thirds of the riparian environment is invaded to some extent, IAPs replacing the well adapted native species along river systems. In particular, impact of IAPs on soil respiration (Rs) may be relevant, with consequences for ecosystem function and services. Clearing of invaded riparian zones initiated by the Working for Water program has been a successful in eradicating alien plants within riparian areas even though recovery after alien clearing is lagging at many sites, and knowledge on repair of ecosystem function is lacking. Various studies have generated knowledge on carbon cycling and Rs in forests, savanna, grasslands, tundra and Mediterranean shrublands, but little is known about Rs in riparian zones, and even less about soil CO2 efflux in invaded riparian fynbos riparian ecotones. The objective of this study was to contribute to a better understanding and quantifying the effect and impact of IAPs on carbon cycling between and across riparian ecotones with different invasion status: natural, invaded, and cleared. The study areas were located in the south-western Cape and measurements of Rs, soil temperature, soil moisture, root mass, litter mass, and soil properties were carried out in riparian soils of the mountain and transitional stream longitudinal river sections, and uplands fynbos areas of six different perennial river systems. In each site, four to five transects were laid out with one sampling site of each landscape position (wet bank, dry bank, and terrestrial areas) giving a total of 12 to 15 samples per site. Soil respiration measurements were taken over a period of two years, and were done seasonally. Results from this study showed that Rs was different among seasons with highest soil respiration rates in summer. Soil CO2 efflux increased in response to warm and dry conditions during summer, while seasonal soil CO2 efflux declined in autumn and winter in response to wet and cold soil conditions. The large increase in soil CO2 efflux response to warm and dry periods when temperature was 25 to 30 °C over all riparian sites and was highest in invaded sites compared to the natural and cleared sites. A significant difference was found between sites with different statuses with invaded sites leading seasonal Rs rates. Natural and cleared sites did not differ significantly in their CO2 efflux rates, suggesting that clearing of IAPs may put invaded ecosystems on a trajectory of restoration. There were also differences in terms of landscape positions; dry banks zones of the invaded sites had higher rates compared to wet banks and the uplands areas. Our results further suggest that roots are the most important component of overall Rs rates, rather than microbial respiration. When we incubated soils minus roots, little difference was evident, either when viewing the results by invasion status or by landscape position, which suggest that inherent soil differences in terms of microbial respiration were not different. We also use a trenching approach to further investigate this, and though we found Rs to decline significantly, trends later suggest that decomposition of fine and course roots likely obscured the decline in overall Rs due to root respiration. Overall, our results showed that clearing of invaded riparian zones will likely lead to successful restoration of soil functioning in terms of C cycling. Clearing of Acacia-invaded riparian ecotones will likely lead to a decline in root density, and which removes a major component of overall Rs. These results make the investigation of the C balance of invaded riparian ecotones and terrestrial areas critical in order to assess their contribution to regional C cycles. / AFRIKAANSE OPSOMMING: Grondrespirasie (Rs) is 'n belangrike komponent van CO2 uitstroming en die globale koolstofbalans. Binne die konteks van globale verandering is dit van groot belang om die seisoenale patrone van Rs in fynbos oewer ekosisteme, veral in indringer-oewer ekotone, in die Meditereense tipe ekosisteme (MTE's) in die Wes- Kaap, Suid- Afrika te verstaan. Oewerekotone is drie-dimensioneel oorgangssones wat veelvuldige ekosisteem dienste en funksies verskaf. Hulle dien as die verbinding tussen terrestriële en water-ekosisteme waar kern ekologiese en geomorfologiese prosesse plaasvind. Oewerekotone is hoogs vatbaar vir versteuringe, en as gevolg van hierdie rede, is hul ook kwesbaar vir indringing deur indringer plante (IAPs), veral Acacia spesies. Indringing deur IAPs word beskou as een van die groot bedreigings tot en met globale verandering en biodiversiteit, wat ekstensiewe ekologiese, ekonomiese, en sosiale impakte veroorsaak. In die suid- westelike Kaap word meer as twee derdes van die oeweromgewing tot 'n mate binnegedring. IAPs vervang die goed aangepaste inheemse spesies langs riviersisteme. Die impak van IAPs, spesifiek op grondrespirasie mag substansieël wees, met gevolge vir ekosisteem funksies en dienste. Opruiming van hierdie spesifieke oewer sones, geinisieer deur die Working for Water program, was suksesvol in die uitroeing van indringer plante binne oewer areas. Alhoewel herstel na indringer opruiming op baie terreine agter is, is kennis oor die herstel van ekosisteemfunksies gebrekkig. Verskeie studies het kennis ontwikkel oor koolstofsiklisering en Rs in woude, savanna, graslande, tundra en Meditereense struiklande, maar daar is minimale informasie oor oewersones,en nog minder oor grond CO2 uitstroming in indringer oewer fynbos en oewer ekotone. Die doel van hierdie studie is om 'n bydrae te lewer koolstofsiklisering beter te verstaan, en die impak van IAPs op koolstofsiklisering te kwantifiseer tussen en oor oewerekotone met verkillende indringer statusse: natuurlik, binnegedring en skoongemaak. Die studie areas was geleë in die suid- westelike Kaap, en maatstawe van Rs, grond temperature, grondvogtigheid, wortelmassa, plantafvalmassa, en grondeienskappe is uitgevoer in oewergrond van die berg en transisionele stroom longitudinale rivier seksies, asook terrestriële fynbos areas van ses verskillende standhoudende riviersisteme. In elke area is vier tot vyf transekte uitgelê met een monsternemingsarea van elke landskapsposisie (nat bank, droë bank en terrestriële areas) met 'n totaal van 12 tot 15 monsters per area. Grondrespirasie maatstawe is geneem oor 'n periode van twee jaar, en is seisoenaal uitgevoer. Resultate van die studie het getoon dat Rs verkil het tussen seisoene, met die hoogste grondrespirasietempo in die somer. Grond CO2 uitstroming het toegeneem in reaksie op warm en droë kondisies gedurende somer, terwyl seisoenale grond CO2 uitstroming afgeneem het in herfs en winter in reaksie op nat en koue grond kondisies. Die grootste toename in grond CO2 uitstroming was in reaksie op warm en droë periodes wanneer temperature gewissel het tussen 25 tot 30˚C oor alle oewersones, en was die hoogste in binnegedringde sones, vergeleke met die natuurlike en skoongemaakte terreine. 'n Beduidende verskil is gevind tussen terreine met verskillende statusse in CO2 uitstromingskoerse‚ 'n aanduiding dat opruiming van IAPs binnegedringde ekosisteme op 'n trajek van restorasie plaas. Daar was ook verskille in terme van landskapsposisies; droë bank sones van die binnegedringde terreine het hoër tempos gehad, vergeleke met die nat bank en die hoogland areas. Ons resultate dui verder aan dat wortels, eerder as mikrobiologiese respirasie, die mees belangrike komponente van Rs koerse uitmaak. Toe ons grond minus wortels inkubeer, is min verskille opgemerk, as gekyk word na die resultate deur indringer status of landskapsposisie, wat toon dit dat inherente grondveskille in terme van mikrobiologiese respirasie nie verskillend is nie. Ons het verder ook 'n sloot-benadering gebruik om verdere ondersoek hierop in te stel, en alhoewel ons bevind dat Rs aansienlik afgeneem het, dui neigings later aan dat afbraak van fyn en growwe wortels die afname in gehele Rs as gevolg van wortel respirasie waarskynlik verdoesel. Ons resultate dui daarop dat opruiming van binngedringde oewers klaarblyklik sal lei tot suksesvolle restorasie van grondfunksionering in terme van C siklisering. Opruiming van Acacia- binnegedringde oewer ekotone sal vermoedelik lei tot 'n afname in worteldigtheid, en wat 'n belangrike komponent van die gehele Rs kan verwyder. Hierdie resultate maak die ondersoek van die C balans van binngedringde oewer ekotone en terrestriële areas krities, om sodoende hulle bydrae tot streeksgewyse C siklusse te asseseer.

Riparian ecosystems of the southwestern United States are highly valuable to both the ecological and human communities which surround them. Over the past century, they have been subject to shifting management practices to maximize human use, control, ecosystem service, and conservation. This creates a complex relationship between water policy, management, and the natural ecosystem necessitating research on spatial and temporal dynamics of riparian vegetation. The San Acacia Reach of the Middle Rio Grande, a 60 mile stretch from the San Acacia Diversion Dam to San Marcial, has experienced multiple management and river flow fluctuations over the past 80 years, resulting in threats to riparian and aquatic ecosystems. This research was completed through the use and analysis of multi-source remote sensing data, GIS, and a review of the on-the-ground management decisions to better understand how the location and composition of the riparian vegetation has been affected by these shifting practices. This research focused on four phases, each highlighting different management practices and river flow patterns during the last 80-years. Each of these periods provides a unique opportunity to observe a direct relationship between river management and riparian land cover response and change. Overall, management practices reduced surface river flows and limited overbank flooding and resulted in changes in the composition, density, and spatial patterns of the vegetation, including increased non-native vegetation growth. Restoration efforts over the past few decades have begun to reduce the presence of non-native species. Despite these changes, this ecosystem was shown to be extremely resilient in maintaining its function/service throughout the entire study time frame.

abstract: Over the past century in the southwestern United States human actions have altered hydrological processes that shape riparian ecosystems. One change, release of treated wastewater into waterways, has created perennial base flows and increased nutrient availability in ephemeral or intermittent channels. While there are benefits to utilizing treated wastewater for environmental flows, there are numerous unresolved ecohydrological issues regarding the efficacy of effluent to sustain groundwater-dependent riparian ecosystems. This research examined how nutrient-rich effluent, released into waterways with varying depths to groundwater, influences riparian plant community development. Statewide analysis of spatial and temporal patterns of effluent generation and release revealed that hydrogeomorphic setting significantly influences downstream riparian response. Approximately 70% of effluent released is into deep groundwater systems, which produced the lowest riparian development. A greenhouse study assessed how varying concentrations of nitrogen and phosphorus, emulating levels in effluent, influenced plant community response. With increasing nitrogen concentrations, vegetation emerging from riparian seed banks had greater biomass, reduced species richness, and greater abundance of nitrophilic species. The effluent-dominated Santa Cruz River in southern Arizona, with a shallow groundwater upper reach and deep groundwater lower reach, served as a study river while the San Pedro River provided a control. Analysis revealed that woody species richness and composition were similar between the two systems. Hydric pioneers (Populus fremontii, Salix gooddingii) were dominant at perennial sites on both rivers. Nitrophilic species (Conium maculatum, Polygonum lapathifolium) dominated herbaceous plant communities and plant heights were greatest in effluent-dominated reaches. Riparian vegetation declined with increasing downstream distance in the upper Santa Cruz, while patterns in the lower Santa Cruz were confounded by additional downstream agricultural input and a channelized floodplain. There were distinct longitudinal and lateral shifts toward more xeric species with increasing downstream distance and increasing lateral distance from the low-flow channel. Patterns in the upper and lower Santa Cruz reaches indicate that water availability drives riparian vegetation outcomes below treatment facilities. Ultimately, this research informs decision processes and increases adaptive capacity for water resources policy and management through the integration of ecological data in decision frameworks regarding the release of effluent for environmental flows. / Dissertation/Thesis / Ph.D. Plant Biology 2011

Riparian ecosystems are valuable to the ecological and human communities that depend on them. Over the past century, they have been subject to shifting management practices to maximize human use and ecosystem services, creating a complex relationship between water policy, management, and the natural ecosystem. This has necessitated research on the spatial and temporal dynamics of riparian vegetation change. The San Acacia Reach of the Middle Rio Grande has experienced multiple management and river flow fluctuations, resulting in threats to its riparian and aquatic ecosystems. This research uses remote sensing data, GIS, a review of management decisions, and an assessment of climate to both quantify how riparian vegetation has been altered over time and provide interpretations of the relationships between riparian change and shifting climate and management objectives. This research focused on four management phases from 1935 to 2014, each highlighting different management practices and climate-driven river patterns, providing unique opportunities to observe a direct relationship between river management, climate, and riparian response. Overall, we believe that management practices coupled with reduced surface river-flows with limited overbank flooding influenced the compositional and spatial patterns of vegetation, including possibly increasing non-native vegetation coverage. However, recent restoration efforts have begun to reduce non-native vegetation coverage.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Riparian ecosystems of the Mediterranean south-western Cape region are projected to experience significant decreases in streamflow due to climate change and increased demands for water associated with human demographic trends and increasing living standards. Aggravating this problem are woody invasive alien plants, such as Acacia mearnsii, whose impacts, including those on catchment water yields, have justified extensive eradication programmes such as Working for Water (WfW). WfW has been highly successful in managing invasive alien species in some areas, while at the same time enhancing the quality of life of poor South Africans. Unfortunately, the managers of these eradication initiatives often experience a lack of information on the species- and site-specific ecological properties that may aid in prioritising sites more prone to invasion, essentially inhibiting accurate management output. Knowledge, such as that associated with the possible future distribution of invasive species in a changing environment, may help to optimise eradication initiatives. I therefore determined whether woody plants portray different physiological (vulnerability to cavitation) and wood anatomical traits (wood density, vessel resistance to implosion, vessel lumen and wall diameters) across three prominent riparian zones in the south-western Cape that each differ in streamflow quantity – to gain a mechanistic understanding of how woody species, especially invasive species, adapt their hydraulic strategy across this proxy for water availability. Using factorial ANOVA’s, to distinguish any differences in plant physiological and wood anatomical responses to water availability within and between species, showed Acacia mearnsii having consistently higher drought-tolerance (lower P50 values and denser wood) compared to native species under reduced water availability. These results supported the significant variation in drought-tolerance strategies that exist within and between taxonomically different species across different environments. Water availability thus has a strong selective effect on functional traits of species; however, minimum water potentials were more useful in describing in situ hydrological conditions than streamflow. Additionally, a non-causal relationship between wood anatomical traits and drought-induced cavitation was observed. Therefore, using only wood anatomical measurements to assess drought-tolerance of species might not be accurate across all species. This mechanistic approach to assess the invasive potential of species under projected drier conditions has great practical value. It can be used to improve species selection for restoration initiatives, and is of great value for future use in prioritizing eradication programmes. / AFRIKAANSE OPSOMMING: Rivieroewer ekosisteme in die Mediterreense Suidwes-Kaap streek kan groot afnames in stroomvloei verwag, wat meestal toegeskryf kan word aan klimaatsverandering en die verhoogde aanvraag na water geassosieerd met stygende populasiegrootte. Uitheemse indringerplante soos Acacia mearnsii vererger hierdie probleem. Laasgenoemde spesies plaas groot druk op opvanggebiede se water opbrengs, en vorm grootliks die rede waarom uitroeiing programme soos Werk vir Water (WfW) gestig is. WfW het al groot suksesse behaal in die bestuur van uitheemse indringerplante, en terselfdertyd die lewenskwaliteit van arm Suid-Afrikaners verhoog. Ongelukkig sukkel hierdie indringer uitroeiing inisiatiewe telkens met ongenoegsame bewyse wat kan help om leiding te verskaf by die prioritisering van areas meer geneig tot indringing. Die gevolg is dat onvoldoende bestuurs besluite gemaak kan word. Gevolglik sal kennis geassosieerd met die moontlike toekomstige verspreiding van hierdie indringerplant in ʼn veranderlike omgewing help om uitroeiing programme meer akkuraat te stel en gevolglik waardevol wees t.o.v. prioritisering van kwesbare areas. Die doel van hierdie studie was om die kwesbaarheid van sleutel inheemse houtagtige rivier spesies en veral die dreigende indringerplant Acacia mearnsii, te bestudeer in terme van verlaagde stroomvloei soos voorspel vir die Wes-Kaap fynbos ekosisteem. Deur te bepaal of houtagtige plante verskillende fisiologiese (kwesbaarheid teen xileem blokkasie) en anatomiese (hout digtheid, vat weerstandbiedendheid teen inmekaarkolking, vat holte en wand deursnee) hidrologiese eienskappe tentoonstel gemeet tussen drie prominente rivieroewer sones in die suidwes Kaap wat variëer in stroomvloei kwantiteit, verskaf ʼn meganistiese begrip van hoe spesies, veral die indringerplante, hul hidrologiese strategieë ten opsigte van droogtes kan aanpas. Faktoriële ANOVAS’s tussen spesies en liggings het getoon dat beide plant fisiologiese en hout anatomiese data beduidend variëer tussen taksonomies verskillende spesies. Veral Acacia mearnsii het deurgaans laer P50 waardes asook hoër houtdigtheid getoon, ‘n teken van hierdie spesies se verhoogde droogte toleransie in vergelyking met die inheemse spesies. Wat beduidend is is dat spesies-spesifieke lewensstrategieë ten opsigte van droogte toleransie in hierdie rivieroewer sones voorkom. Resultate het bevestig dat water beskikbaarheid ʼn groot rol speel in die seleksie van funksionele karaktereienskappe in plante, maar, dat minimum water potensiaal meer akkuraat was om in situ hidrologiese toestande te beskryf as wat stroomvloei kon. Die verhouding tussen plant fisiologiese en hout anatomiese karaktereienskappe was indirek as gevolg van spesies-spesifieke lewensstrategieë. Gevolglik sal die allenige gebruik van hout anatomiese eienskappe om droogte toleransie in plante te assesseer onakkuraat wees omdat daar ʼn swak verhouding tussen hout anatomie en droogte-geïnduseerde xileem blokkasie bestaan. ʼn Meganistiese benadering om die indringing potensiaal van spesies onder voorspelde droër kondisies te assesseer, asook om spesies seleksie vir restourasie doeleindes op te skerp, is prakties uitvoerbaar, en van groot waarde vir toekomstige gebruik in uitroeiing en restourasie inisiatiewe.

Ecological research involving habitat studies was conducted on the Elm Fork of the Trinity River in Denton County, Texas, from spring 1985 to spring 1986. Habitat Evaluation Procedures and Habitat Suitability Index Models developed by the United States Fish and Wildlife Service were applied to a 1419 hectares study area to determine the quality of habitat for four species: beaver, Castor canadensis, wood duck, Aix sponsa, pileated woodpecker, Dryocopus pileatus, and white crappie, Poxomis annularis. Population estimates were generated. A wildlife management plan was developed for the study area. Habitat Suitability Index Models were found to be overly conservative, underestimating the quality of habitat in areas of ecological transition.