Experiments can provide insight on whether invasive plant dominance is caused by superior competitive ability (driver) or by environmental changes that facilitate plant invasion (passenger). Reed canarygrass (Phalaris arundinacea, hereafter RCG) displaces native plants and forms near-monocultures in North American wetlands. In the Upper Mississippi River (UMR) system, floodplain forests are negatively impacted by RCG invasion. We tested two RCG control techniques on a reforestation project at four sites in SE Minnesota. Treatments consisted of (1) applying glyphosate (Rodeo) herbicide and (2) mulching followed by applying sulfometuron methyl (Oust XP) herbicide. Treatments were applied in Fall 2016. We monitored herbaceous plant response and RCG performance over the 2017 and 2018 growing seasons. We also calculated the number of days flooded in each plot for the 2017 growing season using linear interpolation of river gauge data. Both treatment methods significantly reduced RCG performance relative to controls during the 2017 growing season; however, RCG performance in treatment plots was similar to control plots during the 2018 growing season. Herbaceous plants increased in species richness and cover relative to control plots, although volunteer plant diversity varied among sites. These results indicate that follow-up herbicide applications are necessary to control RCG to facilitate tree establishment. Further, flooding and lack of native propagules may be factors in RCG invasions. Our results indicate that RCG may behave as a driver in some parts of the UMR and as a passenger in parts of the UMR that are more affected by hydrologic alteration.
Floodplain forest loss in the Upper Mississippi Valley is concerning because of the habitat these forests provide, especially for birds. Native floodplain forest systems are increasingly susceptible to reed canarygrass (Phalaris arundinaceae; RCG) establishment and spread. Once invaded by RCG, ecological restoration of floodplain requires integrated treatments that reduce the existing RCG population, along with additional long-term control measures. A common secondary measure is tree or shrub plantings to provide shade and reduce the competitive ability of this shade-intolerant invader.
Floodplain forests provide ecosystem services such as nutrient storage and rapid biogeochemical cycling which may reduce transport of nitrogen (N) downstream. Invasion by nuisance plant species, however, may modify a floodplain's ability to capture N by altering soil properties, litter decomposition rates, N availability, and rates of N cycling. I examined the effect of flooding on soil properties and N cycling at a floodplain site in Pool 8 of the Upper Mississippi River with two different plant communities: mature native forest (Acer saccarinum) and patches of an invasive grass (Phalaris arundinacea). Plots were established within each vegetation type along an elevation gradient and sampled throughout the summers of 2013 and 2014. Spatial trends in flooding resulted in better conditions for microbial activity in low elevations. Nutrient processes and NH4 and NO3− availability, however, were best explained by vegetation type and time after flooding. Phalaris plots maintained higher rates of nitrification and higher concentrations of available NH4+ and NO3−. These results suggest that invasion by Phalaris may make nitrogen more readily available and could help to reinforce this species' persistence in floodplain wetlands. They also raise the possibility that Phalaris may decrease floodplain N storage capacity.
Reed canarygrass (Phalaris arundinacea L.) is a desirable pasture grass on wet areas in the Northern United States and Southern Canada, but it is a serious and troublesome ditchbank weed in the Pacific Northwest and Rocky Mountain States. The purpose of this study was to learn more about the development, growth habits, and control of reed canarygrass on irrigation ditchbanks. Ninety-seven percent or more of the seed of this species germinated ediately after harvest under favorable conditions. Seeds stored in damp sand at constant temperatures of 1 and 23C for periods of time up to one year did not germinate until they were subjected to alternating temperatures of 20 and 30C. The first rhizome development on reed canarygrass seedlings grown in the greenhouse was observed 26 days after emergence. Within 16 weeks after emergence, the plants were in bloom and had 48 short rhizomes (6.5 cm maximum) per plant. In the field, 88 percent or more of the emergent: shoots on established plants originated from rhizome or tiller buds located in the upper 5 cm of soil. Some shoots developed from buds located at depths up to 20 cm, but none arose from a greater depth. Several vegetative characteristics of reed canarygrass plants collected from six irrigation projects in four states differed widely when grown in a garden at Prosser, Washington. The plant height, seed weights, panicle length, leaf length, leaf width, number of stems per plant, stem diameter, and the rate of spread by rhizomes were statistically different at the 5% level of probability. Large differences in the color and posture of the leaves were also observed. Plants collected near Huntley, Montana, were the most vigorous. Total available carbohydrates in the roots and rhizomes of established reed canarygrass were not affected by single applications of 2,2,dichloropropionic acid (dalapon) at 22 kg/ha, 3-amino-s-triazoleammonium thiocyanate (amitrole-T) at 4.5 kg/ha, or 1,1i-dimethy1-4,4'- bipyridinium ion (paraquat) at 1.1 kg/ha until 2 months after treatments were applied in May. By October, single applications of dalapon and amitrole-T and five repeated applications of paraquat reduced the carbohydrates 24, 28, and 50 percent, respectively. Two additional treatments of dalapon or amitrole-T or five additional treatments of paraquat in the second year of the study did not reduce the carbohydrate levels below those present during the first year. Dalapon and trichloroacetic acid (TCA), applied to the soil or to the senescent foliage in November at rates from 22 to 88 kg/ha, provided good to excellent temporary control of reed canarygrass without denuding ditchbanks. Redtop (Avostis alba L.) and reed canarygrass seedlings developed on the treated areas the following summer and reed canarygrass retained the dominant position unless the seedlings and plants that escaped the fall treatment were controlled with post-emergence applications of dalapon or amitrole-T. When the latter plants were controlled, redtop developed from natural or artificial seeding of the ditchbank and became the dominant species. Maximum residue levels of TCA in irrigation water ranged from 104 to 225 ppb following fall applications of TCA at 82 kg/ha to both banks of three irrigation laterals that ranged from 4 to 14.5 kilometers long. Average residue levels at the downstream ends of the laterals during the first four hours that water flowed through them in the spring ranged from 34 to 47 ppb. Eight hours after the initial flow of water through laterals 4, 8.4, and 14.5 kilometers long, residue levels were less than 1 ppb in the two shortest laterals and only 2.7 ppb in the longest lateral. No residues were detectable in the water from any of the laterals after 48 hours.
Flooding dynamics are expected to drive compositional patterns of woody overstory species in bottomland ecosystems, yet there is some evidence that flood variability may differentially constrain assemblage composition. Numerous studies have related distributions of plant species to floodplain landforms and geomorphic processes, documenting shifts in community composition along hydrologic and hydraulic gradients. Despite clear associations between species composition and local physical conditions, models predicting composition over broad areas are underdeveloped due to imprecise or implicit characterizations of environmental gradients, difficulty of reconciling fine-scale environmental heterogeneity with broader physical constraints, and overcoming cross-site differences in species' pools. My dissertation examines the relationships between environmental gradients and species' abiotic tolerances as characterized by functional traits in order to understand: 1) what processes constrain or support functional diversity of floodplain forests, and 2) at what scales these processes operate. First, in Chapter 2 I use a regional approach to characterize broad-scale patterns in hydrologic and functional trait diversity of floodplain forest ecosystems from Michigan's Lower Peninsula and Maryland. The analysis tests the hypothesis that if flooding dynamics impose a strong environmental filtering effect as demonstrated in the literature, regional differences in flood frequency, duration and intensity should result in different regional trait pools. I find that regional shifts in hydrologic regime are not matched by similar shifts in functional trait pools, suggesting that functional diversity is maintained through processes operating at finer scales. In Chapter 3 I evaluate the relative strength of environmental filtering, a community assembly process, at the river-valley segment scale by analyzing distributions of functional traits across implicit, regional gradients of inundation dynamics found throughout Michigan's Lower Peninsula. I find evidence of important biotic interactions in certain hydrogeomorphic settings that would indicate a highly variable role of inundation dynamics in shaping floodplain forest assemblages. In Chapter 4 I then build on the findings of the previous chapter to describe how patterns of environmental heterogeneity and flood regime interact across scales affect functional diversity. The results demonstrate the importance of hydrogeomorphic context in shaping patterns of functional composition across floodplain landforms. The final two chapters investigate how ecological strategies of woody overstory species shift under multi-scalar physical constraints within the Maryland Piedmont. In Chapter 5 I characterize flood regime of four Piedmont river-valley segments of contrasting size and morphologies using a validated 2D hydrodynamic model. I demonstrate the novel application of a 3D array of temperature sensors for validating spatially-explicit flood models, and summarize model results to show that patterns of inundation dynamics observed both within and among the four study sites are consistent with river-valley morphologic characteristics. Finally, I relate spatially-explicit flood regime quantifications to systematic surveys of floodplain forest composition to understand how functional attributes of assemblages shift along gradients of hydroperiod at and across multiple spatial scales. The results of Chapter 6 underscore the complexity of biophysical interactions in floodplain ecosystems as evidenced by shifts in functional trait distributions along gradients of aggregate flood regime at both the within- and among-site levels. Overall, my dissertation research has contributed to the advancement of floodplain forest ecology by describing trait-environment linkages at and across multiple spatial scales, demonstrated several novel methodological approaches, and offered new conceptual models of flooding and flood constraint on functional responses in bottomland ecosystems.
As scientific understanding about ecological processes has grown, the idea that ecosystem dynamics are complex, nonlinear, and often unpredictable has gained prominence. Of particular importance is the idea that rather than following an inevitable progression toward an ultimate endpoint, some ecosystems may occur in a number of states depending on past and present ecological conditions. The emerging idea of “restoration thresholds” also enables scientists to recognize when ecological systems are likely to recover on their own and when active restoration efforts are needed. Conceptual models based on alternative stable states and restoration thresholds can help inform restoration efforts. New Models for Ecosystem Dynamics and Restoration brings together leading experts from around the world to explore how conceptual models of ecosystem dynamics can be applied to the recovery of degraded systems and how recent advances in our understanding of ecosystem and landscape dynamics can be translated into conceptual and practical frameworks for restoration. In the first part of the book, background chapters present and discuss the basic concepts and models and explore the implications of new scientific research on restoration practice. The second part considers the dynamics and restoration of different ecosystems, ranging from arid lands to grasslands, woodlands, and savannahs, to forests and wetlands, to production landscapes. A summary chapter by the editors discusses the implications of theory and practice of the ideas described in preceding chapters. New Models for Ecosystem Dynamics and Restoration aims to widen the scope and increase the application of threshold models by critiquing their application in a wide range of ecosystem types. It will also help scientists and restorationists correctly diagnose ecosystem damage, identify restoration thresholds, and develop corrective methodologies that can overcome such thresholds.
The Clean Water Act (CWA) requires that wetlands be protected from degradation because of their important ecological functions including maintenance of high water quality and provision of fish and wildlife habitat. However, this protection generally does not encompass riparian areasâ€"the lands bordering rivers and lakesâ€"even though they often provide the same functions as wetlands. Growing recognition of the similarities in wetland and riparian area functioning and the differences in their legal protection led the NRC in 1999 to undertake a study of riparian areas, which has culminated in Riparian Areas: Functioning and Strategies for Management. The report is intended to heighten awareness of riparian areas commensurate with their ecological and societal values. The primary conclusion is that, because riparian areas perform a disproportionate number of biological and physical functions on a unit area basis, restoration of riparian functions along America's waterbodies should be a national goal.
