Time filter

Source Type

Boulder City, CO, United States

Bracho R.,University of Florida | Starr G.,University of Alabama | Gholz H.L.,National Science Foundation | Martin T.A.,University of Florida | And 3 more authors.
Ecological Monographs | Year: 2012

Planted pine forests (plantations) in the southeastern United States are an important component of the continent's carbon balance. Forest carbon dynamics are affected by a range of factors including climatic variability. Multiyear droughts have affected the region in the past, and an increase in the frequency of drought events has been predicted. How this increased climatic variability will affect the capacity of the region's pine plantations to sequester carbon is not known. We used eddy covariance and biometric approaches to measure carbon dynamics over nine years in two slash pine plantations (Pinus elliottii var elliottii Englm) in north Florida, consisting of a newly planted and a mid-rotation stand. During this time, the region experienced two multiyear droughts (1999-2002 and 2006-2008), separated by a three-year wet period. Net ecosystem carbon accumulation measured using both approaches showed the same trends and magnitudes during plantation development. The newly planted site released 15.6 Mg C/ha during the first three years after planting, before becoming a carbon sink in year 4. Increases in carbon uptake during the early stages of stand development were driven by the aggrading leaf area index (LAI). After canopy closure, both sites were continuous carbon sinks with net carbon uptake (NEE) fluctuating between 4 and ∼8Mg C·ha -1· -1, depending on environmental conditions. Drought reduced NEE by ∼25% through its negative effects on both LAI and radiation-use efficiency, which resulted in a larger impact on gross ecosystem carbon exchange than on ecosystem respiration. While results indicate that responses to drought involved complex interactions among water availability, LAI, and radiation-use efficiency, these ecosystems remain carbon sinks under current management strategies and climatic variability. Variation within locations is primarily due to major disturbances, such as logging in the current study and, to a much lesser extent, local environmental fluctuations. When data from this study are compared to flux data from a broad range of forests worldwide, these ecosystems fill a data gap in the warm-temperate zone and support a broad maximum NEE (for closed-canopy forests) between 8°C and 20°C mean annual temperature. © 2012 by the Ecological Society of America.

Arredondo T.,San Luis Potosi Institute of Scientific Research and Technology | Garcia-Moya E.,Colegio de Mexico | Huber-Sannwald E.,San Luis Potosi Institute of Scientific Research and Technology | Loescher H.W.,National Ecological Observatory Network NEON | And 3 more authors.
Agricultural and Forest Meteorology | Year: 2016

Future precipitation changes in the semiarid grassland region in Central Mexico are expected to be larger for winter rainfall (-20%) than for summer rain (-10%). Winter rainfall however comprises a small proportion of annual precipitation (5-6%), therefore the potential effects on productivity are expected to be negligible. We are realizing however, that winter rain events are important controls of tiller population and consequently of grassland productivity. To attest its influence we examined rain legacy effects using rainout shelters, by reducing rainfall by 42% (2011) and 20% (2012) relative to unmanipulated rainfall on monodominant Bouteloua gracilis and mixed-species disturbed grasslands. In 2013 rainout shelters were removed to allow all incoming rain into the plots. Plant cover type was a significant predictor of aboveground productivity with monodominant B. gracilis consistently producing 50-80 g/m2 more than mixed stands. Decreased rainfall did not have negative effects on aboveground productivity except in an extreme drought year for the mixed-species grassland. We also observed a significant legacy effect of winter precipitation on summer aboveground productivity in both grassland types, but not to previous-year total precipitation. In spite of the large annual variability of soil ψ, leaf ψ fluctuated between -0.5 and -1.5 MPa most of the year suggesting a geologic source of water. © 2016 Elsevier B.V.

Kulacki K.J.,University of Notre Dame | Chaloner D.T.,University of Notre Dame | Larson J.H.,U.S. Geological Survey | Costello D.M.,University of Michigan | And 6 more authors.
Current Organic Chemistry | Year: 2011

Aquatic environments are being contaminated with a myriad of anthropogenic chemicals, a problem likely to continue due to both unintentional and intentional releases. To protect valuable natural resources, novel chemicals should be shown to be environmentally safe prior to use and potential release into the environment. Such proactive assessment is currently being applied to room-temperature ionic liquids (ILs). Because most ILs are water-soluble, their effects are likely to manifest in aquatic ecosystems. Information on the impacts of ILs on numerous aquatic organisms, focused primarily on acute LC50 and EC50 endpoints, is now available, and trends in toxicity are emerging. Cation structure tends to influence IL toxicity more so than anion structure, and within a cation class, the length of alkyl chain substituents is positively correlated with toxicity. While the effects of ILs on several aquatic organisms have been studied, the challenge for aquatic toxicology is now to predict the effects of ILs in complex natural environments that often include diverse mixtures of organisms, abiotic conditions, and additional stressors. To make robust predictions about ILs will require coupling of ecologically realistic laboratory and field experiments with standard toxicity bioassays and models. Such assessments would likely discourage the development of especially toxic ILs while shifting focus to those that are more environmentally benign. Understanding the broader ecological effects of emerging chemicals, incorporating that information into predictive models, and conveying the conclusions to those who develop, regulate, and use those chemicals, should help avoid future environmental degradation. © 2011 Bentham Science Publishers Ltd.

Serrano-Ortiz P.,University of Granada | Sanchez-Canete E.P.,University of Granada | Sanchez-Canete E.P.,University of Arizona | Olmo F.J.,University of Granada | And 5 more authors.
Boundary-Layer Meteorology | Year: 2016

The consistency of eddy-covariance measurements is often evaluated in terms of the degree of energy balance closure. Even over sloping terrain, instrumentation for measuring energy balance components is commonly installed horizontally, i.e. perpendicular to the geo-potential gradient. Subsequently, turbulent fluxes of sensible and latent heat are rotated perpendicular to the mean streamlines using tilt-correction algorithms. However, net radiation (Formula presented.) and soil heat fluxes (G) are treated differently, and typically only (Formula presented.) is corrected to account for slope. With an applied case study, we show and argue several advantages of installing sensors surface-parallel to measure surface-normal (Formula presented.) and G. For a 17 % south-west-facing slope, our results show that horizontal installation results in hysteresis in the energy balance closure and errors of up to 25 %. Finally, we propose an approximation to estimate the surface-normal (Formula presented.) , when only vertical (Formula presented.) measurements are available. © 2015, Springer Science+Business Media Dordrecht.

Schmeller D.S.,Helmholtz Center for Environmental Research | Schmeller D.S.,CNRS Functional Ecology & Environment Laboratory | Schmeller D.S.,Ecolab | Julliard R.,University Pierre and Marie Curie | And 20 more authors.
Journal for Nature Conservation | Year: 2015

The Convention on Biological Diversity's strategic plan lays out five goals: "(A) address the underlying causes of biodiversity loss by mainstreaming biodiversity across government and society; (B) reduce the direct pressures on biodiversity and promote sustainable use; (C) improve the status of biodiversity by safeguarding ecosystems, species and genetic diversity; (D) enhance the benefits to all from biodiversity and ecosystem services; (E) enhance implementation through participatory planning, knowledge management and capacity building." To meet and inform on the progress towards these goals, a globally coordinated approach is needed for biodiversity monitoring that is linked to environmental data and covers all biogeographic regions. During a series of workshops and expert discussions, we identified nine requirements that we believe are necessary for developing and implementing such a global terrestrial species monitoring program. The program needs to design and implement an integrated information chain from monitoring to policy reporting, to create and implement minimal data standards and common monitoring protocols to be able to inform Essential Biodiversity Variables (EBVs), and to develop and optimize semantics and ontologies for data interoperability and modelling. In order to achieve this, the program needs to coordinate diverse but complementary local nodes and partnerships. In addition, capacities need to be built for technical tasks, and new monitoring technologies need to be integrated. Finally, a global monitoring program needs to facilitate and secure funding for the collection of long-term data and to detect and fill gaps in under-observed regions and taxa. The accomplishment of these nine requirements is essential in order to ensure data is comprehensive, to develop robust models, and to monitor biodiversity trends over large scales. A global terrestrial species monitoring program will enable researchers and policymakers to better understand the status and trends of biodiversity. © 2015 Elsevier GmbH.

Discover hidden collaborations