Tree-ring stable isotopes show different ecophysiological strategies in native and invasive woody species of a semi-arid riparian ecosystem in the Great Plains of the United States

Persistent shifts in riparian vegetation associated with the invasion of introduced Elaeagnus angustifolia and native nonriparian Juniperus virginiana have been reported in the U.S. Great Plains, with significant impacts on ecosystem services. In Nebraska, these species have been expanding into the native Populus deltoides riparian forests along the Republican River. Using dendrochronological data and stable isotope ratios, we examined the annual growth and acclimation strategies of these three species to climatic and streamflow variability. We hypothesized that the ability of invasive species to grow under a wide range of environmental conditions favour vegetation shifts at the expense of native species. Streamflow was the strongest predictor for performance. When accompanied with above-average annual precipitation, streamflow resulted in peak tree-ring widths in P. deltoides. J. virginiana showed less sensitivity, and E. angustifolia showed no response. delta O-18 values did not differ among species, which indicates that all species compete for the same water source. delta C-13 ratios and WUEi were higher in J. virginiana than in P. deltoides and E. angustifolia and increased in all species over time. E. angustifolia and P. deltoides exhibit a strong stomatal control and response to relative humidity relative to J. virginiana, which showed anisohydric stomatal behaviour. Our results show that once established, J. virginiana and E. angustifolia thrive in the understory of P. deltoides using different adaptive and acclimation strategies. Based on current water flow management, which prevents high-flood pulses through the riparian zone, these species will continue to establish and spread throughout the Republican River watershed

Mapping and linking supply- and demand-side measures in climate-smart agriculture. A review

Climate change and food security are two of humanity’s greatest challenges and are highly interlinked. On the one hand, climate change puts pressure on food security. On the other hand, farming significantly contributes to anthropogenic greenhouse gas emissions. This calls for climate-smart agriculture—agriculture that helps to mitigate and adapt to climate change. Climate-smart agriculture measures are diverse and include emission reductions, sink enhancements, and fossil fuel offsets for mitigation. Adaptation measures include technological advancements, adaptive farming practices, and financial management. Here, we review the potentials and trade-offs of climate-smart agricultural measures by producers and consumers. Our two main findings are as follows: (1) The benefits of measures are often site-dependent and differ according to agricultural practices (e.g., fertilizer use), environmental conditions (e.g., carbon sequestration potential), or the production and consumption of specific products (e.g., rice and meat). (2) Climate-smart agricultural measures on the supply side are likely to be insufficient or ineffective if not accompanied by changes in consumer behavior, as climate-smart agriculture will affect the supply of agricultural commodities and require changes on the demand side in response. Such linkages between demand and supply require simultaneous policy and market incentives. It, therefore, requires interdisciplinary cooperation to meet the twin challenge of climate change and food security. The link to consumer behavior is often neglected in research but regarded as an essential component of climate-smart agriculture. We argue for not solely focusing research and implementation on one-sided measures but designing good, site-specific combinations of both demand- and supply-side measures to use the potential of agriculture more effectively to mitigate and adapt to climate change

Water and Energy Balance Response of a Riparian Wetland to the Removal of \u3ci\u3ePhragmites australis\u3c/i\u3e

Vegetation and climate both play integral roles in water availability, particularly for arid to semi-arid regions. Changes in these variables can lead to extreme shortages in water for regions that rely on water for crop irrigation (i.e., the Great Plains). The objective of this study is to evaluate the impacts of vegetation on water availability in the Republican River basin in central Nebraska. Decreases in streamflow have been observed in the river basin for many years and, as a result, an invasive riparian plant species (Phragmites australis) is being removed in an effort to reduce evapotranspiration and reclaim surface water. Meteorological variables and energy balance data have been collected at a field site during the 2009 and 2010 growing seasons. Vegetation was sprayed with herbicide in July 2009, killing all P. australis in the wetland. Significant decreases in evapotranspiration were observed during the 2010 growing season due to the limited amount of transpiring vegetation in the wetland. Greenhouse growth experiments were also conducted with both invasive and native varieties of P. australis to determine basic plant physiological parameters. Nitrogen fertilizer was applied to half of the plants in each subset. Gas exchange (e.g., photosynthesis, stomatal conductance, and transpiration rates), and the efficiency of the water and nitrogen use, were assessed under variable light, temperature and CO2 concentrations. As well as providing specific vegetation parameters for modeling purposes, this study was interested in evaluating the differences in physiology and growth characteristics between the two varieties of P. australis present in Nebraska. Lastly, the plant physiological parameters were incorporated into Agro-IBIS, a dynamic vegetation model, and this model was evaluated using observed energy balance data from the wetland field site from 2009. Experiments were also performed for 2010 to assess the ability of the model to capture the response to vegetation removal. Adviser: John Lenter

Rethinking America’s Joint Force: Strength and Credibility in a Constrained Fiscal Environment

The article of record as published may be found at https://doi.org/10.1080/10803920.2012.666148In today's constrained fiscal environment, we must "remission" a smaller, more interdependent Joint Force with an emphasis on capability rather than capacity. America's military is primarily intended to defend the nation from attack, prevent and deter war, and when required, to win decisively in operations ranging from low-end irregular warfare through high-end conventional warfare. In this century, our nation's economic strength, values, and credible influence will play as much a role in sustaining our security and prosperity as will military power. Working closely with other departments of the government as well as with partners and allies, the Department of Defense must rely on three key stakeholders— Congress, the service chiefs, and the combatant commanders—to shape a strong and adaptive military. Rather than focusing on traditional ends, ways, and means, this article addresses the "concept, form, and function" our Joint Force should pursue in support of the National Security Strategy

Bertil Vallien\u27s Celestial Journey Boat & the Oseberg Viking Burial Ship

Born in 1938 and raised in a devout religious home in Stockholm Sweden, Bertil Vallien became one of the most well-known Swedish glass-designers in the early 1960s. His Celestial Journey Boat (1995) hangs from the ceiling at the Barry Art Museum in Norfolk, Virginia, creating a dream-like floating effect. That Gabriel Gustafson\u27s discovery and unearthing of the Oseberg Viking Burial Ship (1904) was Vallien’s inspiration for Celestial Journey Boat has been confirmed in a 2012 interview. Vallien conceptualized the specific structural, visual, and site-specific placement of an array of items from the ancient ship\u27s discovery and then re-invented them to embody his personal thoughts. Although the Oseberg Viking Ship is much larger than Vallien’s luminous glass vessel, the later artist\u27s intention was to encapsulate his own personal secular journey inside his glass, leaving interpretation open for others

The Y Article

With preface by Anne-Marie SlaughterThe article of record as published may be found at http://nationalstrategicnarrative.org/This Strategic Narrative is intended to frame our National policy decisions regarding investment, security, economic development, the environment, and engagement well into this century. It is built upon the premise that we must sustain our enduring national interests - prosperity and security - within a strategic ecosystem, at home and abroad that in complexity and uncertainty, there are opportunities and hope, as well as challenges, risk, and threat. The primary approach this Strategic Narrative advocates to achieve sustainable prosperity and security, is through the application of credible influence and strength, the pursuit of fair competition, acknowledgement of interdependencies and converging interests, and adaptation to complex, dynamic systems- all bounded by our national values

Responses of Common Reed (Phragmites australis) to Nitrogen and Temperature Manipulations

Invasion of introduced lineage of common reed (Phragmites australis) into water-saturated communities in the Great Plains has modified habitats and ecosystem services. In several areas it grows alongside and out-competes its native counterpart. We investigated ecophysiological responses of the two lineages to nitrogen (N) fertilization and temperature (19°, 25°, and 32°C). Photosynthesis (Amax) did not differ between lineages at temperatures of 19° and 25°C but was higher in the native lineage at 32°C. Fertilization improved Amax at all temperatures, and was more pronounced in the native than in the introduced lineage. Native P. australis had higher δ13C and water use efficiency (wue) compared to the introduced lineage. Differences in maximum photochemical efficiency of photosystem II (Fv/Fm), carboxylation efficiency (Vcmax), and electron transport (Jmax) were observed between lineages, and generally responded positively to treatments. Our results indicated that the native P. australis may better withstand water fluctuations and warmer temperatures than its introduced counterpart, and could contribute to diverse plant communities under warmer climate scenarios. In contrast, under cool temperatures, the introduced lineage has an advantage that could lead to further displacement of native species in water-saturated communities

Decadal-scale changes in the seasonal surface water balance of the Central United States from 1984 to 2007

Variations in climate have important influences on the hydrologic cycle. Observations over the continental United States in recent decades show substantial changes in hydrologically significant variables, such as decreases in cloud cover and increases in solar radiation (i.e., solar brightening), as well as increases in air temperature, changes in wind speed, and seasonal shifts in precipitation rate and rain/snow ratio. Impacts of these changes on the regional water cycle from 1984 to 2007 are evaluated using a terrestrial ecosystem/land surface hydrologic model (Agro-IBIS). Results show an acceleration of various components of the surface water balance in the Upper Mississippi, Missouri, Ohio, and Great Lakes basins over the 24-yr period, but with significant seasonal and spatial complexity. Evapotranspiration (ET) has increased across most of our study domain and seasons. The largest increase is found in fall, when solar brightening trends are also particularly significant. Changes in runoff are characterized by distinct spatial and seasonal variations, with the impact of precipitation often being muted by changes in ET and soil-water storage rate. In snow-dominated regions, such as the northern Great Lakes basin, spring runoff has declined significantly due to warmer air temperatures and an associated decreasing ratio of snow in total precipitation during the cold season. In the northern Missouri basin, runoff shows large increases in all seasons, primarily due to increases in precipitation. The responses to these changes in the regional hydrologic cycle depend on the underlying land cover type—maize, soybean, and natural vegetation. Comparisons are also made with other hydroclimatic time series to place the decadal-scale variability in a longer-term context