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Invasions in urban settings have been understudied in terms of how invasions are impacted by uniquely urban stressors, such as streetlights. Plant physiology and phenology are impacted by artificial light at night (ALAN), but no studies have yet examined if light pollution differentially affects native versus invasive plant species. We tested the hypothesis that ALAN affects plant traits important to plant fitness and susceptibility to herbivory and whether they differ between invasive versus native grass species. We found that aboveground production of invasive cheatgrass was >5 × greater under ALAN than any other species in any treatment, and ALAN also altered plant traits important to herbivory. This suggests that ALAN may influence the outcomes of interspecific interactions. As urbanization increases, its role in invasion biology becomes more important, especially when an urban disturbance such as ALAN benefits the growth of invasive species.

Invasive species are a major cause of biodiversity loss worldwide, but their impact on communities and the mechanisms driving those impacts are varied and not well understood. This study employs functional diversity metrics and guilds—suites of species with similar traits—to assess the influence of an invasive tree (Tamarix spp.) on riparian plant communities in the southwestern United States. We asked: (1) What traits define riparian plant guilds in this system? (2) How do the abundances of guilds vary along gradients of Tamarix cover and abiotic conditions? (3) How does the functional diversity of the plant community respond to the gradients of Tamarix cover and abiotic conditions? We found nine distinct guilds primarily defined by reproductive strategy, as well as growth form, height, seed weight, specific leaf area, drought and anaerobic tolerance. Guild abundance varied along a covarying gradient of local and regional environmental factors and Tamarix cover. Guilds relying on sexual reproduction, in particular, those producing many light seeds over a long period of time were more strongly associated with drier sites and higher Tamarix cover. Tamarix itself appeared to facilitate more shade-tolerant species with higher specific leaf areas than would be expected in resource-poor environments. Additionally, we found a high degree of specialization (low functional diversity) in the wettest, most flood-prone, lowest Tamarix cover sites as well as in the driest, most stable, highest Tamarix cover sites. These guilds can be used to anticipate plant community response to restoration efforts and in selecting appropriate species for revegetation.

Changes in historical disturbance regimes have been shown to facilitate non-native plant invasions, but reinstatement of disturbance can be successful only if native colonizers are able to outcompete colonizing invasives. Reintroduction of flooding in the southwestern United States is being promoted as a means of reestablishing Populus deltoides subsp. wislizenii, but flooding can also promote establishment of an introduced, invasive species, Tamarix ramosissima. We investigated competition between Populus and Tamarix at the seedling stage to aid in characterizing the process by which Tamarix may invade and to determine the potential ability of Populus to establish itself with competitive pressure from Tamarix. We planted seedlings of Tamarix and Populus in five ratios at three densities for a total of 15 treatments. The growth response of each species was measured in terms of height, above-ground biomass, and tissue concentrations of nitrogen and phosphorous. These measurements across treatments were modeled as three-dimensional response surfaces. For both species, Populus density was more important than Tamarix density for determining growth response. Both species were negatively affected by increasing numbers of Populus seedlings. Due to the larger size of the native Populus, we predict that its superior competitive ability can lead to its dominance when conditions allow native establishment. Our results suggest that even in the presence of an invader that positively responds to disturbance, reestablishment of historical flooding regimes and post-flood hydrology can restore this ecosystem by promoting its dominant plant species.Los cambios en los regímenes históricos de perturbaciones han mostrado que facilitan invasiones de plantas no nativas; sin embargo, la reinstauración de la perturbación solo puede ser exitosa si los colonizadores nativos son capaces de competir y desplazar a las especies invasoras. La reintroducción de las inundaciones en el sudoeste de los Estados Unidos está siendo promovida como una forma de restablecer Populus deltoides subespecie wislizenii, pero las inundaciones pueden promover también el establecimiento de una especie invasora, Tamarix ramosissima. Investigamos la competencia entre Populus y Tamarix al estado de plántula para ayudar a caracterizar el proceso por el cual Tamarix puede invadir y para determinar la habilidad potencial de Populus para establecer presión competitiva contra Tamarix. Sembramos plántulas de Tamarix y Populus en 5 diferentes radios y densidades para un total de 15 tratamientos. La respuesta en crecimiento de cada especie fue medida en forma de altura, biomasa sobre el suelo y concentraciones de nitrógeno y fósforo en tejido. Estas mediciones en los tratamientos fueron modeladas en superficies de respuesta tridimensionales. La densidad de Populus fue más importante para la determinación del crecimiento que la densidad de Tamarix. Ambas especies estuvieron negativamente afectadas por el incremento en el número de plántulas de Populus. Debido al mayor tamaño de la nativa Populus, nosotros predecimos que su superior habilidad competitiva puede conducir a su dominación cuando las condiciones permiten el establecimiento nativo. Nuestros resultados sugieren que aún en presencia de una especie invasora que responde positivamente a las perturbaciones, el restablecimiento de los regímenes históricos de inundaciones y de la hidrología post-inundación puede restaurar este ecosistema al promover a sus especies de plantas dominantes.

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Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs., Randomised controlled experiments are the gold standard for scientific inference, but environmental and social scientists often rely on different study designs. Here the authors analyse the use of six common study designs in the fields of biodiversity conservation and social intervention, and quantify the biases in their estimates.

Coupled human and natural systems (CHANS) are frequently represented by large datasets with varied data including continuous, ordinal, and categorical variables. Conventional multivariate analyses cannot handle these mixed data types. In this paper, our goal was to show how a clustering method that has not before been applied to understanding the human dimension of CHANS: a Gower dissimilarity matrix with partitioning around medoids (PAM) can be used to treat mixed-type human datasets. A case study of land managers responsible for invasive plant control projects across rivers of the southwestern U.S. was used to characterize managers’ backgrounds and decisions, and project properties through clustering. Results showed that managers could be classified as “federal multitaskers” or as “educated specialists”. Decisions were characterized by being either “quick and active” or “thorough and careful”. Project goals were either comprehensive with ecological goals or more limited in scope. This study shows that clustering with Gower and PAM can simplify the complex human dimension of this system, demonstrating the utility of this approach for systems frequently composed of mixed-type data such as CHANS. This clustering approach can be used to direct scientific recommendations towards homogeneous groups of managers and project types.

We investigated the relative role of manager traits and decisions for explaining the impact of riparian restoration. To do this, we used the difference in vegetation between post-restoration and controls for 243 pairs of sites to create a success index. We then determined how much variability in success could be explained by physical variables that directly impact vegetation (environment and weed removal) versus human variables (characteristics of the people who managed those sites and their management decisions). More than 60% of the variability in vegetation change could be explained, with human variables increasing adjusted R-square values of physical-only models by an average of 47%. Restoration “success” was positively associated with an increase in the number of collaborators, the number of information sources used, and the relative priority of plant-related goals. Worse outcomes were associated with an increase in the number of roles the manager held, monitoring frequency, and with higher manager education level. These results point to the indirect impacts of the human element, and specifically supports recommendations to include multiple partners and set specific goals. To our knowledge, this is the first time the importance of human characteristics as drivers of restoration outcomes has been quantified.

Invasive species removal is a common focus in restoration ecology, but the ultimate goal of native plant species recovery and habitat recovery is often elusive. Control of invasive Tamarix spp. shrubs in the American Southwest has only sometimes led to increased native species cover; this is of particular concern for the protection of the endangered Southwestern willow flycatcher (Empidonax extimus trailii, abbr. SWFL) that nests readily in Tamarix when native Salix canopy is absent. If we can identify the conditions that lead to more native trees as well as habitat protection for the SWFL, we can prioritize restoration efforts more effectively and reduce conflict between conservation goals. To determine whether reduction in the invasive Tamarix led to more Salix cover (and thus no net loss in SWFL habitat), we compiled data on vegetation, soils, and geographic conditions in 260 sites where Tamarix had been subject to control efforts and 132 positive and negative reference sites. We found that (1) reduction in Tamarix only increased Salix cover in wetter sites, and was greater when a particular, low-disturbance removal method was used; however the increase did not typically compensate for the overall losses in canopy cover, and (2) Salix cover was generally highest in locations with low drought stress, as reflected by soil properties, distance to water, and climate. These results suggest that the presence and recovery of Salix is dependent on its relatively narrow environmental niche, in contrast with Tamarix’s broader one. Thus, although abundance of Salix and Tamarix was negatively correlated, this is likely because of Salix’s different niche, as much as or more than direct interspecific competition. Our findings demonstrate that removal of an invasive species does not necessarily lead to reestablishment of the native species they appeared to displace. We suggest that in the case of promoting habitat for SWFL and other birds, outcomes of restoration activity can be improved by focusing Tamarix removal efforts on sites more likely to promote Salix growth based on environmental characteristics.

The science‐practice gap is often cited as a limitation to successful restoration outcomes; however, the existence of such a gap in information exchange is rarely measured. Here, we quantify the gap by focusing on common recommendations from both scientists (i.e. researchers) and managers (i.e. practitioners, land managers) on what is needed for successful restoration. We surveyed 45 managers associated with 244 invasive species (Tamarix spp.) removal projects across the southwestern U.S. to determine the degree to which they have utilized four strategies advocated by scientists: (1) collaborate widely, (2) monitor beyond cursory visual methods, (3) use a variety of information sources, and (4) consider project goals beyond invasive species removal. Half of these managers were also interviewed to assess managers' perceptions of the role of science in restoration. Twenty‐three scientists specializing in Tamarix‐related research in this region were also surveyed to assess how much they understood and/or shared the concerns of land managers. We found that managers were following scientists' recommendations and that managers' perceptions of the role of science in land management did not have any bearing on the management actions taken. Scientists reported being influenced by managers, and the concerns of scientists and managers were more overlapping than expected. Boundary organizations and river‐wide partnerships were often cited as important in facilitating effective communication between land managers and scientists. A lack of funding for monitoring and for longer‐term projects was cited by both groups as a limitation to incorporating scientists' recommendations into restoration.

Spatial modeling has proven to be useful in understanding the drivers of plant populations in the field of ecology, but has yet to be applied to understanding variation in biocontrol impact. In this study, we employ multi-scale analysis (Moran’s Eigenvector Maps) to better understand the variation in tree canopy exposed to defoliation by a biocontrol beetle (Diorhabda spp.). The control of the exotic tree Tamarix in riparian areas has long been a priority for land managers and ecologists in the American southwest. Diorhabda spp. was introduced as a bio-control agent beginning in 2001 and has since become an inseparable part of Tamarix-dominated river systems in the southwest. Between 2013 and 2016 tamarisk dieback was assessed at 79 sites across Grand County, Utah, arguably the epicenter of Diorhabda impact in the U.S. Canopy cover of Tamarix was between 73 and 81% at these sites, with the percent that was live cover fluctuating by year with a minimum of 42%. Using a traditional general linear model, we found that readily and commonly measured environmental factors could explain only up to 26% of the variation in Tamarix live canopy each year. The number of defoliations was correlated with an increase rather than a decrease in percent live canopy, suggesting compensatory growth. Spatial structure alone explained 22–40% of variation. We found fine scale spatial structure at less than 10 km and broad scale spatial structure from 10 to 30 km. Combining both traditional and novel spatial statistical methods we increased that percentage to 43–63%, depending on year. These results suggest that scientists and land managers must look beyond commonly measured environmental variables to explain non-random biocontrol impact in this system. In particular, this study points to the potential for biotic interactions and variation in flood cycles for further exploration of the identified spatial structure.

Removal of invasive species is often an important, if not central, component of many riparian restoration projects, however little is known about the response of plant communities following this practice. In particular, active control of the exotic, dominant tree Tamarix spp is often a focus of riparian restoration, much of which occurring against a backdrop of biological control by a folivore beetle. Our research employed controls in both time and space to investigate the impact of active Tamarix removal methods in sites subjected to biological control in 40 sites sampled three times over a period of five years. We found that reduction in Tamarix cover was much greater over time with active means of removal, however the native understory increased both with and without active removal. Importantly, change in the relative cover of understory native species was significantly negatively correlated with change in Tamarix cover, with those sites that received a combination of low-disturbance-mechanical, chemical and bio-control showing greater increases in native understory dominance than those sites with biological control alone or high-disturbance mechanical control. Sites with only bio­control still contained 10% live Tamarix cover >7 yr since the beetle was released there. Taken together, these results suggest that the reduction of this exotic tree, even by biological control that leaves some canopy intact, can facilitate recovery of the native plant community. As such, this study supports the Field of Dreams hypothesis that states that once niches are restored, native plants should be able to recolonize.

The human aspect of conservation and restoration is implicit and widely considered in the literature. However, human traits are rarely if ever incorporated into models to explain actual quantitative measures of success or failure. A paper by Sher et al. recently published in a special issue of Wetlands filled this gap by exploring the impact of the characteristics of managers and managing organizations on restoration success among 243 sites where an invasive tree had been removed. Among the 15 human variables considered were how many agencies were involved in the project, the relative priority of particular goals, how intensive monitoring was, and what type of degree the manager had. Given that Sher et al. found that as much as 63% of the variability in restoration outcomes could be explained by such human factors alone, we argue that future studies seeking to understand conservation and restoration outcomes would do well to incorporate such variables in a more explicit way. Quantitative inclusion of the human element can expand our understanding of the processes at work and test theories regarding the importance of goal-setting and other often proposed recommendations about process and project organization. Given that to do so requires an interdisciplinary approach, we also make a case that greater integration between the social and natural sciences will improve our understanding of these systems and lead to better results.

Control of invasive species within ecosystems may induce secondary invasions of non-target invaders replacing the first alien. We used four plant species listed as noxious by local authorities in riparian systems to discern whether 1) the severity of these secondary invasions was related to the control method applied to the first alien; and 2) which species that were secondary invaders persisted over time. In a collaborative study by 16 research institutions, we monitored plant species composition following control of non-native Tamarix trees along southwestern U.S. rivers using defoliation by an introduced biocontrol beetle, and three physical removal methods: mechanical using saws, heavy machinery, and burning in 244 treated and 79 untreated sites across six U.S. states. Physical removal favored secondary invasions immediately after Tamarix removal (0–3 yrs.), while in the biocontrol treatment, secondary invasions manifested later (> 5 yrs.). Within this general trend, the response of weeds to control was idiosyncratic; dependent on treatment type and invader. Two annual tumbleweeds that only reproduce by seed ( Bassia scoparia and Salsola tragus ) peaked immediately after physical Tamarix removal and persisted over time, even after herbicide application. Acroptilon repens , a perennial forb that vigorously reproduces by rhizomes, and Bromus tectorum , a very frequent annual grass before removal that only reproduces by seed, were most successful at biocontrol sites, and progressively spread as the canopy layer opened. These results demonstrate that strategies to control Tamarix affect secondary invasions differently among species and that time since disturbance is an important, generally overlooked, factor affecting response.

Most studies assessing vegetation response following control of invasive Tamarix trees along southwestern U.S. rivers have been small in scale (e.g., river reach), or at a regional scale but with poor spatial-temporal replication, and most have not included testing the effects of a now widely used biological control. We monitored plant composition following Tamarix control along hydrologic, soil, and climatic gradients in 244 treated and 172 reference sites across six U.S. states. This represents the largest comprehensive assessment to date on the vegetation response to the four most common Tamarix control treatments. Biocontrol by a defoliating beetle (treatment 1) reduced the abundance of Tamarix less than active removal by mechanically using hand and chain-saws (2), heavy machinery (3) or burning (4). Tamarix abundance also decreased with lower temperatures, higher precipitation, and follow-up treatments for Tamarix resprouting. Native cover generally increased over time in active Tamarix removal sites, however, the increases observed were small and was not consistently increased by active revegetation. Overall, native cover was correlated to permanent stream flow, lower grazing pressure, lower soil salinity and temperatures, and higher precipitation. Species diversity also increased where Tamarix was removed. However, Tamarix treatments, especially those generating the highest disturbance (burning and heavy machinery), also often promoted secondary invasions of exotic forbs. The abundance of hydrophytic species was much lower in treated than in reference sites, suggesting that management of southwestern U.S. rivers has focused too much on weed control, overlooking restoration of fluvial processes that provide habitat for hydrophytic and floodplain vegetation. These results can help inform future management of Tamarix-infested rivers to restore hydrogeomorphic processes, increase native biodiversity and reduce abundance of noxious species.

Premise of research. Despite a lack of experimental support, enhanced drought tolerance is one of the recurring hypotheses suggested to explain trace element hyperaccumulation. Trace elements may have osmolytic and/or antioxidative properties that help hyperaccumulating plants reduce water loss or its resultant damage. Selenium in particular seems like a promising candidate because of its known antioxidative and drought protectant properties in nonaccumulators, but it has not been tested in hyperaccumulators.Methodology. Here we investigate the drought tolerance hypothesis in a controlled greenhouse setting using a full-factorial design with seedlings of a selenium hyperaccumulator in the genus Astragalus and a nonaccumulating congener.Pivotal results. While selenium increased plant survivorship and longevity and drought reduced them, we found no evidence that selenium improved the drought tolerance of either species.Conclusions. Drought tolerance appears to not be a mechanism that would explain the evolu...

Riparian zones are the interface between aquatic and terrestrial systems along inland watercourses. They have a disproportionate ecological role in the landscape considering their narrow extent, wh ...

We characterized the relationship between soil and leaf concentrations of selenium in a hyperaccumulator and a non-accumulator to test the hypothesis that hyperaccumulators take up selenium while non-accumulators exclude it. We examined plant performance metrics and the ability of selenium to protect against herbivory by spider mites. Known hyperaccumulator and non-accumulator species within the genus Astragalus were grown under a range of selenium concentrations and measured for tissue selenium, extent of herbivory, and vigor. Both hyperaccumulators and non-accumulators either failed to meet even the lenient threshold or exceeded even the strict threshold for hyperaccumulation depending on soil concentration. Both had decreased herbivory with increasing leaf selenium, and both grew larger at higher levels of selenium regardless of herbivory, despite a negative impact of higher relative uptake. The relationships between selenium dosage and tissue concentrations matched only some model predictions. Under these conditions, the bioconcentration factor was a better delimiter between species than the absolute tissue concentration. We provide evidence that despite the apparent cost of uptake, selenium can enhance the growth of hyperaccumulators even when herbivory is not a significant factor. We propose the term “elemental stimulation” for this phenomenon.

[EN] Human activities on floodplains have severely disrupted the regeneration of foundation riparian shrub and tree species of the Salicaceae family (Populus and Salix spp.) throughout the Northern Hemisphere. Restoration ecologists initially tackled this problem from a terrestrial perspective that emphasized planting. More recently, floodplain restoration activities have embraced an aquatic perspective, inspired by the expanding practice of managing river flows to improve river health (environmental flows). However, riparian Salicaceae species occupy floodplain and riparian areas, which lie at the interface of both terrestrial and aquatic ecosystems along watercourses. Thus, their regeneration depends on a complex interaction of hydrologic and geomorphic processes that have shaped key life-cycle requirements for seedling establishment. Ultimately, restoration needs to integrate these concepts to succeed. However, while regeneration of Salicaceae is now reasonably well-understood, the literature reporting restoration actions on Salicaceae regeneration is sparse, and a specific theoretical framework is still missing. Here, we have reviewed 105 peer-reviewed published experiences in restoration of Salicaceae forests, including 91 projects in 10 world regions, to construct a decision tree to inform restoration planning through explicit links between the well-studied biophysical requirements of Salicaceae regeneration and 17 specific restoration actions, the most popular being planting (in 55% of the projects), land contouring (30%), removal of competing vegetation (30%), site selection (26%), and irrigation (24%). We also identified research gaps related to Salicaceae forest restoration and discuss alternative, innovative and feasible approaches that incorporate the human component., EG's participation in this work was partially supported by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (ESFFORES project grant number 299044). VMF was supported by a pre-doctoral program from the Ministerio de Educacion, Cultura y Deporte, Spain, FPU 2013. PBS and EG were partially supported by the U.S. Geological Survey, Invasive Species Program. We thank M. Grabau and three anonymous reviewers for helpful comments on earlier drafts of the manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Riparian Salicaceae are prolific producers of short-lived seeds that require very restrictive hydro-geomorphic conditions for establishment. It is generally assumed that if floods are able to create nursery sites timed with seed dispersal, recruitment will occur. Other spatial and temporal seed dispersal patterns besides the dispersal period have historically received little attention. However, seed dispersal patterns can be highly variable between regions, species and over the years. In this paper, we report the seed dispersal patterns of three dominant riparian Salicaceae trees in Europe: Populus alba, P. nigra and Salix alba to suggest possible trade-offs between seed dispersal patterns, germinability, longevity and establishment. Seed rain of the three species was monitored in 33 glue-coated traps for three months yearly from 2006 to 2008 in an 8-km stretch of the Middle Ebro River (N Spain), which has a pluvio-nival regime. P. alba dispersed seeds earlier during a shorter time period and with a fewer number of seed release pulses compared with P. nigra, and especially with S. alba. With overlapping seed dispersal periods, the two latter species occupy similar landform units but rarely compete with P. alba, usually at higher elevations, as shown in a previous study in the same study area. The three species had very high germinability immediately after release (>90%), but longevity in S. alba was eight times shorter than that of its two Populus counterparts. We suggest that S. alba has compensated its lower seed quality with a more spaced seed release in several pulses of similar magnitude. With similar seed dispersal patterns and germinability but a higher longevity, P. nigra had a much higher density of individuals than S. alba in the recruitment zones of the study area. We hope that our results may inform river managers about how to optimize river flows to promote sexual regeneration of these species. Copyright © 2015 John Wiley & Sons, Ltd.

Questions Have species expanded their ranges upward in elevation? Have α- and β-diversity changed over time? Have species richness changes along the gradient shown distributional patterns? Have community compositions changed over time, and if so, which plant families are responsible for variation? Do herbaceous changes correspond to increased warming, overstorey shifts and disturbance events at each site? Location Long-term Ecological Research (LTER) sites near Niwot Ridge, CO, US. Methods We surveyed four herbaceous plant communities along an elevational gradient for species composition, diversity and frequency. Our results were compared to those found in 1981 and 1996 in the same plots to determine long-term community change at each site and along the elevational gradient. We evaluated changes in elevational species range expansion, community diversity, and composition. We related herbaceous change to tree data and site-specific literature on climate and disturbance to analyze change patterns and drivers. Results Our investigation showed the upward range expansion of eight species. Alpha-diversity changes were site-specific, while species richness changes along the gradient did not exhibit distinctive patterns. Each community changed significantly (P

A detailed simulation of Fourier transformed large amplitude square-wave voltammetry is presented in the frequency domain for the process Red ⇌ Ox + e-. The simulation takes into account the influence of the electrode kinetics (Butler-Volmer model), uncompensated resistance (R u) and double layer capacitance (Cdl). Of particular significance is the prediction that the even harmonic responses are only detected in the presence of quasi-reversibility or uncompensated resistance, and also are essentially devoid of charging current. In contrast, the DC and odd harmonic AC components exhibit much larger faradaic currents and also contain charging current. Conveniently, detailed analysis of the simulated DC and AC harmonic components reveals the presence of readily recognised patterns of behaviour with unique levels of sensitivity to electrode kinetics, Ru and Cdl, that facilitate quantitative analysis of these terms. These electrochemical parameters are generally calculated by small amplitude impedance spectroscopy and utilisation of linear analysis of equivalent circuits. Experimental studies on the one electron oxidation of ferrocene in dichloromethane (0.1 M Bu4NPF6) and the one electron reduction of [Fe(CN)6]3- in aqueous 0.5 M KCl electrolyte analysed via heuristic forms of data analysis based on recognition of patterns of behaviour, are presented as examples of a reversible process with significant uncompensated resistance and a quasi-reversible process with minimal ohmic drop, respectively. Results demonstrate the advantages of a more intuitively implemented form of data analysis than presently available with conventional forms of impedance spectroscopy. © 2005 Wiley-VCH Verlag GmbH and Co. KGaA.

Understanding physiological mechanisms underlying the activity of the heart is of great medical importance. Mathematical modeling and numerical simulation have become a widely accepted method of unraveling the underlying mechanism of the heart. Calcium (Ca2∈+∈) dynamics regulate the excitation-contraction coupling in heart muscle cells and hence are among the key players in maintaining normal activity of the heart. Many existing ventricular single cell models lack the biophysically detailed description of the Ca2∈+∈ dynamics. In this paper we examine how we can improve existing ventricular cell models by replacing their description of Ca2∈+∈ dynamics with the local Ca2∈+∈ control models. When replacing the existing Ca2∈+∈ dynamics in a given cell model with a different Ca2∈+∈ description, the parameters of the Ca2∈+∈ subsystem need to be re-fitted. Moreover, the search through the plausible parameter space is computationally very intensive. Thus, the Grid enabled Nimrod/O software tools are used for optimizing the cell parameters. Nimrod/O provides a convenient, user-friendly framework for this as exemplified by the incorporation of local Ca2∈+∈ dynamics into the ventricular single cell Noble 1998 model. © 2008 Springer-Verlag Berlin Heidelberg.

Computational cardiac models provide important insights into the underlying mechanisms of heart function. Parameter estimation in these models is an ongoing challenge with many existing models being overparameterised. Sensitivity analysis presents a key tool for exploring the parameter identifiability. While existing methods provide insight into the significance of the parameters, they are unable to identify redundant parameters in an efficient manner. We present a new singular value decomposition based algorithm for determining parameter identifiability in cardiac models. Using this local sensitivity approach, we investigate the Mahajan 2008 rabbit ventricular myocyte L-type calcium current model. We identify non-significant and redundant parameters and improve the Ical model by reducing it to a minimum one that is validated to have only identifiable parameters. The newly proposed approach provides a new method for model validation and evaluation of the predictive power of cardiac models.

Co-localization of Na + /Ca 2+ exchangers (NCX) with ryanodine receptors (RyRs) is debated. We incorporate local NCX current in a biophysically detailed model of L-type Ca 2+ channels (LCCs) and RyRs and study the effect of NCX on the regulation of Ca 2+ -induced Ca 2+ release and the shape of the action potential. In canine ventricular cells, under pathological conditions, e.g., impaired LCCs, local NCXs become an enhancer of sarcoplasmic reticulum release. Under such conditions incorporation of local NCXs is critical to accurately capture mechanisms of excitation-contraction coupling.

The underlying mechanisms of irregular cardiac rhythms are still poorly understood. Many experimental and modeling studies are aimed at identifying factors which cause cardiac arrhythmias. However, a lack of understanding of heart rhythm dynamical properties makes it difficult to uncover precise mechanisms of electrical instabilities, and hence to predict the onset of heart rhythm disorders. We review and compare the existing methods of studying cardiac dynamics, including restitution protocol (S1-S2), dynamic restitution protocol and multistability test protocol (S1-CI-S2). We focus on cardiac cell dynamics to elucidate regularities of heart rhythm. We demonstrate the advantages of our newly proposed systematic approach of analysis of cardiac cell dynamics using mammalian Luo Rudy 1991 and human ventricular Ten Tusscher 2006 single cell models under healthy and diseased conditions such as altered K(+) or Ca(2+) related currents. We investigate the role of ionic properties and the shape of an action potential on the nonlinear dynamics of electrical processes in periodically stimulated cardiac cells. We show the existence of multistability property for human ventricular cells. Moreover, the multistability is proposed to be an intrinsic property of cardiac cells, and is also suggested to be one of the mechanisms which could underlie the sudden triggering of life-threatening ventricular arrhythmias in the human heart.

Elevated soil salinity is often associated with Tamarix invasion; however, it's unclear whether soils are more saline because of Tamarix or other environmental factors. Surface soil salinity was investigated along a flow-regulated, arid river with dense Tamarix of varying age to determine which factors best explain soil salinity. Flooding was the most important predictor, reducing salinity by nearly 70%. Soils under Tamarix had lower salinity than adjacent areas without woody cover in non-flooded areas suggesting that evaporation in arid environments may contribute more surface salts than Tamarix or may exacerbate plant inputs. Under most conditions, higher salinities were found under Tamarix than natives. An exception to this pattern was that soils under the smallest trees were more saline for natives. Relationships between soil salinity and stem size suggest that salts increase over time under Tamarix unless they are removed by flooding. However, the most mature stands had lower salinity than expected, reflecting some additional mechanism. Soil texture and distance from the river were important, but interacted strongly with other factors. The observed relationships between surface soil salinity and Tamarix stem size, a predictor of aboveground age, suggest Tamarix plays an active role in floodplain salinization within the sampled area.

AIMS: The level of inhibition of the human Ether-à-go-go-related gene (hERG) channel is one of the earliest preclinical markers used to predict the risk of a compound causing Torsade-de-Pointes (TdP) arrhythmias. While avoiding the use of drugs with maximum therapeutic concentrations within 30-fold of their hERG inhibitory concentration 50% (IC(50)) values has been suggested, there are drugs that are exceptions to this rule: hERG inhibitors that do not cause TdP, and drugs that can cause TdP but are not strong hERG inhibitors. In this study, we investigate whether a simulated evaluation of multi-channel effects could be used to improve this early prediction of TdP risk. METHODS AND RESULTS: We collected multiple ion channel data (hERG, Na, L-type Ca) on 31 drugs associated with varied risks of TdP. To integrate the information on multi-channel block, we have performed simulations with a variety of mathematical models of cardiac cells (for rabbit, dog, and human ventricular myocyte models). Drug action is modelled using IC(50) values, and therapeutic drug concentrations to calculate the proportion of blocked channels and the channel conductances are modified accordingly. Various pacing protocols are simulated, and classification analysis is performed to evaluate the predictive power of the models for TdP risk. We find that simulation of action potential duration prolongation, at therapeutic concentrations, provides improved prediction of the TdP risk associated with a compound, above that provided by existing markers. CONCLUSION: The suggested calculations improve the reliability of early cardiac safety assessments, beyond those based solely on a hERG block effect.

Cardiac electrophysiology is a mature discipline, with the first model of a cardiac cell action potential having been developed in 1962. Current models range from single ion channels, through very complex models of individual cardiac cells, to geometrically and anatomically detailed models of the electrical activity in whole ventricles. A critical issue for model developers is how to choose parameters that allow the model to faithfully reproduce observed physiological effects without over-fitting. In this paper, we discuss the use of a parametric modelling toolkit, called N imrod , that makes it possible both to explore model behaviour as parameters are changed and also to tune parameters by optimizing model output. Importantly, N imrod leverages computers on the Grid, accelerating experiments by using available high-performance platforms. We illustrate the use of N imrod with two case studies, one at the cardiac tissue level and one at the cellular level.

We investigated the spatial distribution of the three Acacia and two Tamarix tree species and related the spatial distribution of these two genera to their 18O value, i.e. their 18O/16O isotopic ratio in the Negev desert, Israel. At the regional spatial scale, there was a significant difference in the overall distributions of these two genera, although there was considerable overlap. At the 1 km2 scale, there was no deviation from homogeneity. At a finer scale, no deviation from a random distribution was found in three ephemeral rivers between the two largest trees in these two genera, Acacia raddiana and Tamarix nilotica. We found that Tamarix used deep water from aquifers while Acacia trees used an alternate source, most likely surface water. Spatial segregation of Tamarix and Acacia occurs at the large spatial scale but not at the small scale, perhaps because of the high tolerance of Tamarix species for salinity and the low tolerance of Acacia species for saline conditions. It appears that the trees are not spatially segregated on the small scale because they use different water sources.

Current invasion ecology theory predicts that disturbance will stimulate invasion by exotic plant species. Cheatgrass or Downy brome (Bromus tectorum) was surveyed in three sites near Florence, Colorado, U.S.A., immediately following Tamarisk or Saltcedar (Tamarix spp.) control and restoration activities that caused disturbance. Despite predictions to the contrary, neither mowing with heavy machinery nor tilling for seedbed preparation stimulated invasion, with a trend for the opposite pattern such that highest percent cover of B. tectorum was observed in the least disturbed transects. Aerial application of imazapyr for Tamarix spp. control caused mortality of nearly all B. tectorum and other understory plant species in all sites. Mechanical control of Tamarix spp. will not necessarily result in increased abundance of invasive species already present, possibly due to the effects of mulch usually left on-site. Imazapyr will control B. tectorum and other herbaceous understory species when applied aerially for Tamarix spp. control. These results are encouraging for managers of riparian systems who may fear that control of woody invasives will stimulate herbaceous invasions.

Throughout the world, the condition of many riparian ecosystems has declined due to numerous factors, including encroachment of non-native species. In the western United States, millions of dollars are spent annually to control invasions of Tamarix spp., introduced small trees or shrubs from Eurasia that have colonized bottomland ecosystems along many rivers. Resource managers seek to control Tamarix in attempts to meet various objectives, such as increasing water yield and improving wildlife habitat. Often, riparian restoration is an implicit goal, but there has been little emphasis on a process or principles to effectively plan restoration activities, and many Tamarix removal projects are unsuccessful at restoring native vegetation. We propose and summarize the key steps in a planning process aimed at developing effective restoration projects in Tamarix-dominated areas. We discuss in greater detail the biotic and abiotic factors central to the evaluation of potential restoration sites and summarize information about plant communities likely to replace Tamarix under various conditions. Although many projects begin with implementation, which includes the actual removal of Tamarix, we stress the importance of pre-project planning that includes: (1) clearly identifying project goals; (2) developing realistic project objectives based on a detailed evaluation of site conditions; (3) prioritizing and selecting Tamarix control sites with the best chance of ecological recovery; and (4) developing a detailed tactical plan before Tamarix is removed. After removal, monitoring and maintenance as part of an adaptive management approach are crucial for evaluating project success and determining the most effective methods for restoring these challenging sites.

Invasion by the non-native tree Tamarix has led to implementation of restoration projects aimed at maintaining the ecological integrity of many riparian communities in the southwestern United States. These restoration efforts may include Tamarix removal, manipulation of hydrologic regimes, and active revegetation of native species. The goal of this study was to determine which site characteristics are correlated with restoration success, defined in terms of reductions of undesirable species such as Tamarix and establishment of desirable, native species. To accomplish this, vegetative and environmental data were collected at 28 sites in the southwestern United States where active revegetation was completed after Tamarix removal. These data were incorporated into regression tree models with predictor variables that included number of years since removal (1‐18 years) and multiple management, climate, soils, and hydrological variables to determine success of Tamarix control, revegetation success, and general plant community responses. Our results suggest that there are easily measurable site characteristics that are associated with greater native cover and richness, planting success, and Tamarix control. Close proximity to perennial water, sufficient precipitation, recent flooding, and good drainage as well as coarser soil texture, and lower soil pH all 4 favored native species. Overall, those site characteristics associated with native species success were the same as those related to lower Tamarix cover. These quantitative models are intended to assist researchers and land mangers to design more effective riparian restoration efforts in this critical arid lands ecosystem type.

Pacific salmon employ a semelparous reproductive strategy where sexual maturation is followed by rapid senescence and death. Cortisol overproduction has been implicated as the central physiologic event responsible for the post-spawning demise of these fish. Cortisol homeostasis is regulated through the action of hormones of the hypothalamus-pituitary-interrenal (HPI) axis. These include corticotropin-releasing factor (CRF) and urotensin-I (UI). In the present study, masu salmon (Oncorhynchus masou) were assayed for changes in the levels CRF-I and UI mRNA transcripts by quantitative real-time PCR (qRT-PCR). These results were compared to plasma cortisol levels in juvenile, adult, and spawning masu salmon to identify specific regulatory factors that appear to be functionally associated with changes in cortisol levels. Intramuscular implantation of GnRH analog (GnRHa) capsules was also used to determine whether GnRH influences stress hormone levels. In both male and female masu salmon, spawning fish experienced a 5- to 7-fold increase in plasma cortisol levels relative to juvenile non-spawning salmon. Changes in CRF-I mRNA levels were characterized by 1-2 distinctive short-term surges in adult masu salmon. Conversely, seasonal changes in UI mRNA levels displayed broad and sustained increases during the pre-spawning and spawning periods. The increases in UI mRNA levels were positively correlated (R(2)=0.21 male and 0.26 female, p0.0001) with levels of plasma cortisol in the pre-spawning and spawning periods. Despite the importance of GnRH in sexual maturation and reproduction, the administration of GnRHa to test animals failed to produce broad changes in CRF-I, UI or plasma cortisol levels. These findings suggest a more direct role for UI than for CRF-I in the regulation of cortisol levels in spawning Pacific salmon.

Arundo donax L. is a perennial reed and is an invasive weed of riparian systems in North America. A structural model (L-DONAX) of the species was constructed using L-system modelling in order to assist in understanding and demonstrating the complexities of the plant's development and structure. The model produces a realistic number of plant components from a single rhizome segment over the course of the first year of growth, using empirical relationships derived from outdoor experiments. Biomass production is also simulated, through the use of relationships found between aerial plant portion sizes and masses. L-DONAX demonstrates that control of A. donax clumps is likely to require more than annual biomass removal, due to the bulk of biomass being present underground, and the ability of remaining rhizome or stem segments to produce large clumps quickly. The model extrapolates to years of growth beyond the first, but is found to require some re-parameterisation to improve accuracy.

The ever increasing demand for native plants and seed for use in restoration and revegetation has created a sizable industry. The large-scale production and planting of native plants have given rise to a suite of ecological concerns including collection impacts, genetic diversity, and provenance. This study examines the practices and beliefs of 12 restoration plant production companies in Colorado with regard to arising ecological issues and identifies where further research is needed. We found that native seed collection in Colorado was largely unregulated and unmonitored and impacts were unknown. Maintaining genetic diversity in restoration materials is costly and does not have universal support. The use of provenance material (or local ecotypes) was hotly contested with strong and sound arguments on both sides of the issue. Procurement of pure ecotypes was difficult because of the variety of institutions involved in production and complications such as artificial selection and cross-pollination.

Leaf carbon (C) content, leaf nitrogen (N) content, and C:N ratio are especially useful for understanding plant-herbivore interactions and may be important in developing control methods for the invasive riparian plant Arundo donax L. We measured C content, N content, C:N ratio, and chlorophyll index (SPAD 502 reading) for 768 leaves from A. donax collected over a five year period at several locations in California, Nevada, and Texas. Leaf N was more variable than leaf C, and thus we developed a linear regression equation for estimating A. donax leaf N from the leaf chlorophyll index (SPAD reading). When applied to two independent data sets, the equation (leaf N content % = -0.63 + 0.08 x SPAD) produced realistic estimates that matched seasonal and spatial trends reported from a natural A. donax population. Used in conjunction with the handheld SPAD 502 meter, the equation provides a rapid, non-destructive method for estimating A. donax leaf quality.

UNLABELLED • PREMISE OF THE STUDY Mountainous regions support high plant productivity, diversity, and endemism, yet are highly vulnerable to climate change. Historical records and model predictions show increasing temperatures across high elevation regions including the Southern Rocky Mountains, which can have a strong influence on the performance and distribution of montane plant species. Rare plant species can be particularly vulnerable to climate change because of their limited abundance and distribution.• METHODS We tracked the phenology of rare and endemic species, which are identified as imperiled, across three different habitat types with herbarium records to determine if flowering time has changed over the last century, and if phenological change was related to shifts in climate.• KEY RESULTS We found that the flowering date of rare species has accelerated 3.1 d every decade (42 d total) since the late 1800s, with plants in sagebrush interbasins showing the strongest accelerations in phenology. High winter temperatures were associated with the acceleration of phenology in low elevation sagebrush and barren river habitats, whereas high spring temperatures explained accelerated phenology in the high elevation alpine habitat. In contrast, high spring temperatures delayed the phenology of plant species in the two low-elevation habitats and precipitation had mixed effects depending on the season.• CONCLUSIONS These results provide evidence for large shifts in the phenology of rare Rocky Mountain plants related to climate, which can have strong effects on plant fitness, the abundance of associated wildlife, and the future of plant conservation in mountainous regions.

We examined how restoration of riparian vegetation has been implemented and evaluated in the scientific literature during the past 25 years. A total of 169 papers were read systematically to extract information about the following: 1) restoration strategies applied, 2) scale of monitoring and use of reference sites, 3) metrics used for evaluation, and 4) drivers of success. Hydro-geomorphic approaches (e.g., dam operations, controlled floods, landform reconfiguration) were the most frequent, followed by active plant introduction, exotic species control, natural floodplain conversion and grazing and herbivory control. Our review revealed noteworthy limitations in the spatio-temporal approaches chosen for evaluation. Evaluations were mostly from one single project and frequently ignored the multi-dimensional nature of rivers: landscape spatial patterns were rarely assessed, and most projects were assessed locally (i.e., ≤meander scale). Monitoring rarely lasted for more than six years and the projects evaluated were usually not more than six years old. The impact of the restoration was most often (43%) assessed by tracking change over time rather than by comparing restored sites to unrestored and reference sites (12%), and few projects (30%) did both. Among the ways which restoration success was evaluated, vegetation structure (e.g., abundance, density, etc.) was assessed more often (152 papers) than vegetation processes (e.g., biomass accumulation, survival, etc.) (112 papers) and vegetation diversity (78 papers). Success was attributed to hydro-geomorphic factors in 63% of the projects. Future evaluations would benefit from incorporating emerging concepts in ecology such as functional traits to assess recovery of functionality, more rigorous experimental designs, enhanced comparisons among projects, longer term monitoring and reporting failure. © 2015 Elsevier Ltd., This research was supported by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme.

The Rio Grande watershed ecosystem has been increasingly threatened since the construction of dams and severe channelization in the past century. Rio Grande cottonwood (Populus deltoides var. wislizenii (S. Wats.) Eckenw.) has been suffering stress and high mortality rates with decreased water availability and increased salinity levels. Ge- netic variation in salt tolerance has been documented in adult cottonwoods, and we hypothesized that these traits might be heritable. This potential heritable genetic variation in seedling offspring might be advantageous in reforestation ef- forts along the Rio Grande. We screened four New Mexican Rio Grande populations for seedling genotypes that might be salt tolerant and correlated seedling performance under both high- and low-salt treatments with the physiological performance of their open-pollinated family. For all populations, we found significant stunting effects of high salinity on mean leaf size, plant height, total plant mass, root mass, and shoot mass, with no effects on chlorophyll content (as measured by a Minolta SPAD-502 meter) or root/shoot ratio. Although there were no significant differences between the four populations, there were highly significant differences between open-pollinated families within each site. In ad- dition, at one site (San Antonio), genetically based open-pollinated family physiology, as measured in a common gar- den, was significantly correlated with seedling performance, especially under low-salt conditions. This indicates these traits are heritable, and adult salt tolerance may convey an advantage in offspring establishment under high-salt condi- tions. Resume : L'ecosysteme du bassin versant du Rio Grande est de plus en plus menace par la construction de barrages et la canalisation intense survenues au cours du siecle dernier. Le peuplier deltoide du Rio Grande (Populus deltoides var. wislizenii (S. Wats.) Eckenw.) montre des signes de stress et connait un taux eleve de mortalite du a la diminution de la disponibilite en eau et a l'augmentation du degre de salinite. La variabilite genetique de la tolerance au sel a ete etudiee chez les peupliers adultes et nous avons fait l'hypothese que ces traits pourraient etre hereditaires. Cette varia- bilite genetique pourrait presenter un avantage pour le reboisement avec des semis le long du Rio Grande si elle est transmissible. Nous avons crible quatre populations du Rio Grande au Nouveau-Mexique pour trouver des semis avec des genotypes potentiellement tolerants au sel et nous avons correle la performance des semis soumis a des traitements de faible et forte salinite avec la performance physiologique de leur famille issue de pollinisation libre. Nous avons ob- serve un rabougrissement significatif chez toutes les populations du a une salinite elevee qui affectait la dimension moyenne des feuilles, la hauteur des plants, la masse totale des plants, la masse des racines et la masse des pousses sans qu'il y ait d'effets sur le contenu en chlorophylle (mesure avec l'appareil Minolta SPAD-502) ou sur le rapport racine:tige. Alors qu'il n'y avait pas de difference significative entre les quatre populations, il y avait des differences tres significatives entre les familles issues de pollinisation libre a chaque endroit. De plus, a un endroit (San Antonio), la physiologie genetiquement determinee des familles issues de pollinisation libre, telle qu'elle fut mesuree dans un test de provenance, etait significativement correlee avec la performance des semis, particulierement dans des conditions de faible salinite. Ces resultats indiquent que ces traits sont hereditaires et que la tolerance au sel des arbres adultes peut representer un avantage pour l'etablissement de leurs descendants dans des conditions de salinite elevee.

Resource availability is often characterized by mean annual amounts, while ignoring the spatial variation within habitats and the temporal variation within a year. Yet, temporal and spatial variation may be especially important for identifying the source of stress in low productivity environments such as deserts where resources are often pulsed and resource renewal events are separated by long periods of low resource availability. Therefore, the degree of stress will be determined in part by the length of time between recharge events. Here, we investigated the effect of timing and total amount of water application on two congeneric pairs, each with a population from a low (desert) and a high (Mediterranean) productivity habitat. As expected, highest survival and greatest growth were found at low or intermediate recharge intervals, and the magnitude of response to increases in total seasonal amounts was greater for Mediterranean species than desert species. The species that had greater survival switched in the hierarchy under high total water depending on interval length. These results demonstrate that temporal variation in resource availability can be as important as annual total amounts for plant performance and that response to temporal dynamics can vary between species. This has implications for community-level processes, as competitive hierarchies may switch based on resource dynamics rather than only total availability.

Populus deltoides subsp. wislizinii (Salicaceae), a cottonwood native to the Middle Rio Grande of New Mexico, must potentially compete against exotic Tamarix ramosissima (Tamaricaceae) during establishment after flooding. We investigated competitive interactions between seedlings of Tamarix and Populus in two substrates representing field textures and declining (i.e., draw-down) or stagnant water tables. The experiment was performed using a full-additive series design and interpreted with response surface models for each species. As reflected in both aboveground mass and height, Populus suppressed aboveground growth of Tamarix across all treatments, whereas competitive effects of Tamarix against Populus could only be seen at low Populus densities. Clay substrates with draw-down stimulated the greatest growth and created the most intense competitive environment for both species. Tamarix was competitively suppressed in every substrate tested, with the weakest response in sand with no draw-down, where growth of Populus was poorest. These results suggest that stream flow management that promotes Populus establishment could also aid in controlling Tamarix invasion across a range of substrates.