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Evidence-based responses to climate change by society require operational and sustained information including biophysical indicator systems that provide up-to-date measures of trends and patterns against historical baselines. Two key components linking anthropogenic climate change to impacts on socio-ecological systems are the periodic inter- and intra-annual variations in physical climate systems (seasonality) and in plant and animal life cycles (phenology). We describe a set of national indicators that reflect sub-seasonal to seasonal drivers and responses of terrestrial physical and biological systems to climate change and variability at the national scale. Proposed indicators and metrics include seasonality of surface climate conditions (e.g., frost and freeze dates and durations), seasonality of freeze/thaw in freshwater systems (e.g., timing of stream runoff and durations of lake/river ice), seasonality in ecosystem disturbances (e.g., wildfire season timing and duration), seasonality in vegetated land surfaces (e.g., green-up and brown-down of landscapes), and seasonality of organismal life-history stages (e.g., timings of bird migration). Recommended indicators have strong linkages to variable and changing climates, include abiotic and biotic responses and feedback mechanisms, and are sufficiently simple to facilitate communication to broad audiences and stakeholders interested in understanding and adapting to climate change.

Insect pests cost billions of dollars per year globally, negatively impacting food crops and infrastructure, and contributing to the spread of disease. Timely information regarding developmental stages of pests can facilitate early detection and control, increasing efficiency and effectiveness. In 2018, the U.S. National Phenology Network (USA-NPN) released a suite of ‘Pheno Forecast’ map products relevant to science and management. The Pheno Forecasts include real-time maps and short-term forecasts of insect pest activity at management-relevant spatial and temporal resolutions and are based on accumulated temperature thresholds associated with critical life-cycle stages of economically important pests. Pheno Forecasts indicate, for a specified day, the status of the insect’s target life-cycle stage in real time across the contiguous United States. The maps are available for 12 pest species including the invasive emerald ash borer (Agrilus planipennis Fairmaire [Coleoptera: Buprestidae]), hemlock woolly adelgid (Adelges tsugae Annand), and gypsy moth (Lymantria dispar Linnaeus [Lepidoptera: Erebidae]). Preliminary validation based on in-situ observations for hemlock woolly adelgid egg and nymph stages in 2018 indicated the maps to be ≥93% accurate depending on phenophase. Since their release in early 2018, these maps have been adopted by tree care specialists and foresters across the United States. Using a consultative mode of engagement, USA-NPN staff have continuously sought input and critique of the maps and delivery from end users. Based on feedback received, maps have been expanded and modified to include additional species, improved descriptions of the phenophase event of interest, and e-mail-based notifications to support management decisions.

ContextLandscape science relies on foundational concepts of landscape ecology and seeks to understand the physical, biological, and human components of ecosystems to support land management decision-making. Incorporating landscape science into land management decisions, however, remains challenging. Many lands in the western United States are federally owned and managed for multiple uses, including recreation, conservation, and energy development.ObjectiveWe argue for stronger integration of landscape science into the management of these public lands.MethodsWe open by outlining the relevance of landscape science for public land planning, management, and environmental effects analysis, including pertinent laws and policies. We identify challenges to integrating landscape science into public land management, including the multijurisdictional nature and complicated spatial pattern of public lands, the capacity of agencies to identify and fill landscape science needs, and perceptions about the meaning of landscape approaches to management.ResultsWe provide several recent examples related to landscape monitoring, restoration, reclamation, and conservation in which landscape science products were developed specifically to support decision-making.ConclusionsWe close by highlighting three actions—elevating the importance of science-management partnerships dedicated to coproducing actionable landscape science products, identifying where landscape science could foster efficiencies in the land-use planning process, and developing scenario-based landscape models for shrublands—that could improve landscape science support for public land planners and managers.

• Rising atmospheric CO

Citizen science involves a range of practices involving public participation in scientific knowledge production, but outcomes evaluation is complicated by the diversity of the goals and forms of citizen science. Publications and citations are not adequate metrics to describe citizen-science productivity. We address this gap by contributing a science products inventory (SPI) tool, iteratively developed through an expert panel and case studies, intended to support general-purpose planning and evaluation of citizen-science projects with respect to science productivity. The SPI includes a collection of items for tracking the production of science outputs and data practices, which are described and illustrated with examples. Several opportunities for further development of the initial inventory are highlighted, as well as potential for using the inventory as a tool to guide project management, funding, and research on citizen science.

Phenology is the study of recurring plant and animal life-cycle stages which can be observed across spatial and temporal scales that span orders of magnitude (e.g., organisms to landscapes). The variety of scales at which phenological processes operate is reflected in the range of methods for collecting phenologically relevant data, and the programs focused on these collections. Consideration of the scale at which phenological observations are made, and the platform used for observation, is critical for the interpretation of phenological data and the application of these data to both research questions and land management objectives. However, there is currently little capacity to facilitate access, integration and analysis of cross-scale, multi-platform phenological data. This paper reports on a new suite of software and analysis tools – the “Pheno-Synthesis Software Suite,” or PS3 – to facilitate integration and analysis of phenological and ancillary data, enabling investigation and interpretation of phenological processes at scales ranging from organisms to landscapes and from days to decades. We use PS3 to investigate phenological processes in a semi-aride, mixed shrub-grass ecosystem, and find that the apparent importance of seasonal precipitation to vegetation activity (i.e., “greenness”) is affected by the scale and platform of observation. We end by describing potential applications of PS3 to phenological modeling and forecasting, understanding patterns and drivers of phenological activity in real-world ecosystems, and supporting agricultural and natural resource management and decision-making.

Citizen science is a growing phenomenon. With millions of people involved and billions of in-kind dollars contributed annually, this broad extent, fine grain approach to data collection should be garnering enthusiastic support in the mainstream science and higher education communities. However, many academic researchers demonstrate distinct biases against the use of citizen science as a source of rigorous information. To engage the public in scientific research, and the research community in the practice of citizen science, a mutual understanding is needed of accepted quality standards in science, and the corresponding specifics of project design and implementation when working with a broad public base. We define a science-based typology focused on the degree to which projects deliver the type(s) and quality of data/work needed to produce valid scientific outcomes directly useful in science and natural resource management. Where project intent includes direct contribution to science and the public is actively involved either virtually or hands-on, we examine the measures of quality assurance (methods to increase data quality during the design and implementation phases of a project) and quality control (post hoc methods to increase the quality of scientific outcomes). We suggest that high quality science can be produced with massive, largely one–off, participation if data collection is simple and quality control includes algorithm voting, statistical pruning, and/or computational modeling. Small to mid-scale projects engaging participants in repeated, often complex, sampling can advance quality through expert-led training and well-designed materials, and through independent verification. Both approaches—simplification at scale and complexity with care—generate more robust science outcomes.

Developing Enterprise Tools and Capacities for Large-Scale Natural Resource Monitoring; Fort Collins, Colorado, 12–13 October 2016

Among the many effects of climate change is its influence on the phenology of biota. In marine and coastal ecosystems, phenological shifts have been documented for multiple life forms; however, biological data related to marine species' phenology remain difficult to access and is under-used. We conducted an assessment of potential sources of biological data for marine species and their availability for use in phenological analyses and assessments. Our evaluations showed that data potentially related to understanding marine species' phenology are available through online resources of governmental, academic, and non-governmental organizations, but appropriate datasets are often difficult to discover and access, presenting opportunities for scientific infrastructure improvement. The developing Federal Marine Data Architecture when fully implemented will improve data flow and standardization for marine data within major federal repositories and provide an archival repository for collaborating academic and public data contributors. Another opportunity, largely untapped, is the engagement of citizen scientists in standardized collection of marine phenology data and contribution of these data to established data flows. Use of metadata with marine phenology related keywords could improve discovery and access to appropriate datasets. When data originators choose to self-publish, publication of research datasets with a digital object identifier, linked to metadata, will also improve subsequent discovery and access. Phenological changes in the marine environment will affect human economics, food systems, and recreation. No one source of data will be sufficient to understand these changes. The collective attention of marine data collectors is needed—whether with an agency, an educational institution, or a citizen scientist group—toward adopting the data management processes and standards needed to ensure availability of sufficient and useable marine data to understand marine phenology.

Changes in the timing of plant and animal life cycle events, in response to climate change, are already happening across the globe. The impacts of these changes may affect biodiversity via disruption to mutualisms, trophic mismatches, invasions and population declines. To understand the nature, causes and consequences of changed, varied or static phenologies, new data resources and tools are being developed across the globe. The USA National Phenology Network is developing a long-term, multi-taxa phenological database, together with a customizable infrastructure, to support conservation and management needs. We present current and potential applications of the infrastructure, across scales and user groups. The approaches described here are congruent with recent trends towards multi-agency, large-scale research and action.

Questions Woody plant encroachment into former grasslands currently represents a major physiognomic shift globally. Seedling establishment is a critical demographic bottleneck and is considered to be alleviated by increases in water availability and negatively impacted by interactions with grasses, particularly when water stress increases. However, interactions with grasses that are not actively competing for resources (‘passive interactions’ when grasses are dead) has seldom been considered. Could the transition from a live to a dead grass (litter) canopy favour recruitment of woody seedlings in a semi-arid grassland of the American SW? How does the sign and intensity of grass–seedling interactions change across drastically different summer precipitation regimes with and without passive interactions? Location Sonoran Desert shrub savanna at the Santa Rita Experimental Range, near Tucson, AZ, US. Methods Four cohorts of Prosopis velutina seeds were planted annually (2002–2005) under rainout shelters that intercepted all incoming precipitation on a soil with sandy loam texture. Summer precipitation was manipulated to simulate either a 50% increase or decrease in the long-term mean, and cover was manipulated to simulate a grassland dominated by the C4 bunchgrass Heteropogon contortus or left unvegetated. Emergence and survival of P. velutina was monitored and compared across cover types, along with monitoring of soil water content and light interception. Results Strong active competition was observed with live grasses, under both summer drought and also under ample summer water supply. However, the pattern was reversed and strong passive facilitation of P. velutina was observed over time when grass canopies died and remained in place. This passive facilitation under dry summers was so strong that recruitment under dead grass conditions was comparable to that observed when ample water supply removed the effects of competition on unvegetated plots. Conclusions After significant mortality of standing grass canopies, which typically compete for limited soil moisture resources, rates of recruitment by shrubs may increase even with significant seasonal drought. This work extends our understanding of interactions among co-located organisms and their effects on plant community dynamics, and introduces a new hypothesis on how grass litter facilitates woody plant encroachment during seasonal droughts.

The sensitivity of phenology to environmental drivers can vary across geography and species. As such, models developed to predict phenology are typically site- or taxon-specific. Generation of site- and taxon-specific models is limited by the intensive in-situ phenological monitoring effort required to generate sufficient data to parameterize each model. Where in-situ phenological observations exist, the data are often subject to analytical issues due to the limited duration of any individual monitoring program, spotty site- and species- level coverage, lack of standardized methodology, and infrequent or variable census intervals. Together, these characteristics constrain our ability to make phenological inferences outside of select sites and taxa where long-duration, intensive monitoring has occurred. In this study, we leveraged two national, standardized phenology datasets to develop a multi-species and multi-site state-space survival model of the onset of deciduous tree and shrub spring (leaf out) and fall (leaf-color) events across temperate ecoregions of the United States. We used data from two national-scale phenological databases, a 9-year, broadly distributed dataset from the USA National Phenology Network and a 4-year dataset from the National Ecological Observatory Network, to quantify regional and interspecific variation in sensitivity to environmental drivers for both spring and fall leaf phenophases. Spring leaf out was generally promoted by longer days, spring growing degree day accumulation, overwinter chilling, and was suppressed by frost events, whereas fall leaf color was promoted by shorter days and cold accumulation. The sensitivity to most environmental drivers tended to be more variable among species than among the regions as defined here (EPA ecoregions of North America, excluding desert and tropical areas). The results of this study lay the groundwork for incorporating the growing collection of phenological observations into a generalized framework for predicting the transition states for any species, in any location.

Workshop on Phenology at Scales from Individual Plants to Satellite Pixels; Cambridge, Massachusetts, 21–23 June 2016

NPS landscape dynamics monitoring project, NPScape; NASA-NPS Landscape Climate Change Vulnerability Project (NASA Applied Sciences program) [10-BIOCLIM10-0034]; United States Geological Survey [G14AC00405]

© 2016 Elmendorf et al. Phenology is an integrative science that comprises the study of recurring biological activities or events. In an era of rapidly changing climate, the relationship between the timing of those events and environmental cues such as temperature, snowmelt, water availability, or day length are of particular interest. This article provides an overview of the observer-based plant phenology sampling conducted by the U.S. National Ecological Observatory Network (NEON), the resulting data, and the rationale behind the design. Trained technicians will conduct regular in situ observations of plant phenology at all terrestrial NEON sites for the 30-yr life of the observatory. Standardized and coordinated data across the network of sites can be used to quantify the direction and magnitude of the relationships between phenology and environmental forcings, as well as the degree to which these relationships vary among sites, among species, among phenophases, and through time. Vegetation at NEON sites will also be monitored with tower-based cameras, satellite remote sensing, and annual high-resolution airborne remote sensing. Ground-based measurements can be used to calibrate and improve satellite-derived phenometrics. NEON's phenology monitoring design is complementary to existing phenology research efforts and citizen science initiatives throughout the world and will produce interoperable data. By collocating plant phenology observations with a suite of additional meteorological, biophysical, and ecological measurements (e.g., climate, carbon flux, plant productivity, population dynamics of consumers) at 47 terrestrial sites, the NEON design will enable continental-scale inference about the status, trends, causes, and ecological consequences of phenological change.

Continental-scale monitoring is vital for understanding and adapting to temporal changes in seasonal climate and associated phenological responses. The success of monitoring programs will depend on recruiting, retaining, and managing members of the public to routinely collect phenological observations according to standardized protocols. Here, we trace the development of infrastructure for phenological monitoring in the US, culminating in the USA National Phenology Network, a program that engages scientists and volunteers.

Large increases in the density of woody plants in former grasslands have been documented globally over the past two centuries. Prosopis velutina (velvet mesquite) has recently expanded on over 38 million ha in the grasslands of the American southwest. Mesquite establishment and expansion is potentially influenced by competitive interactions with grasses, particle size distribution (texture) of soil and changes in the amount and/or seasonality of precipitation, amongst other factors. To investigate the relative importance of precipitation seasonality, grass competition, and soil texture on mesquite seedling and establishment, we experimentally manipulated seasonality of precipitation across 72 1.5 m × 1.7 m plots that we planted with two grasses from contrasting functional groups (or left unvegetated) across two highly contrasting soil textures within a semi-desert grassland in Arizona, USA, wherein we followed the demography of 8640 planted mesquite seeds between 2002 and 2006. Up to 70% of the variance in seedling emergence was explained by soil water content, and seedling mortality was more dependent on summer than on winter precipitation. Mortality of less drought tolerant grasses after drought in coarse textured soils created conditions most favorable for seedling establishment, whereas lower rates of seedling establishment were observed in finer textured soils or in plots dominated by more drought tolerant grasses. We conclude that mesquite encroachment is episodic, based on discontinuous patterns of seedling establishment, favored on coarse textured soils and associated with unique conditions of high summer water availability when precipitation is not limiting and when competition from grasses is lowered.

Aims In this study, we examined the effects of Solidago altissima (hereafter Solidago) and two species in the genus Verbesina, Verbesina virginica and Verbesina occidentalis (hereafter Verbesina), on the structure of an old-field plant community and establishment by an invasive plant species, Lespedeza cuneata (hereafter Lespedeza). Materials and Methods We removed Solidago, Verbesina and both Solidago and Verbesina from 4-m 2 plots in an intact old-field community during two growing seasons. We then quantified the effects of these removals on richness, evenness, diversity and composition of the subdominant plant community. We also measured the total aboveground biomass and the aboveground biomass of the subdominant community. To assess how these removals affected establishment by Lespedeza ,w e planted 20 seeds in each plot and tracked seedling emergence and survival for one growing season. Important Findings Subdominant community evenness and Shannon diversity were higher in plots from which Solidago and Verbesina were removed relative to control plots. However, there were no effects of dominant species removal on species richness or composition of the subdominant community. Total aboveground biomass was not affected by dominant species removal, suggesting that the community of subdominant species exhibited compensation. In fact, subdominant community biomass was greater when Solidago, but not Verbesina, was removed. Light availability was also greater in plots where Solidago was removed relative to control plots throughout the growing season. In addition, removal of dominant species, in particular Solidago, indirectly reduced the emergence, but not survival, of Lespedeza seedlings by directly promoting subdominant community biomass. Taken together, our results suggest that dominant old-field plant species affect subdominant community structure and indirectly promote establishment by Lespedeza.

Atmospheric and climatic change can alter plant biomass production and plant community composition. However, we know little about how climate change-induced alterations in biomass production affect plant species composition. To better understand how climate change will alter both individual plant species and community biomass, we manipulated atmospheric [CO2], air temperature, and precipitation in a constructed old-field ecosystem. Specifically, we compared the responses of dominant and subdominant species to our climatic treatments, and explored how changes in plant dominance patterns alter community evenness over 2 years. Our study resulted in four major findings: (1) all treatments, elevated [CO2], warming, and increased precipitation increased plant community biomass and the effects were additive rather than interactive, (2) plant species differed in their response to the treatments, resulting in shifts in the proportional biomass of individual species, which altered the plant community composition; however, the plant community response was largely driven by the positive precipitation response of Lespedeza, the most dominant species in the community, (3) precipitation explained most of the variation in plant community composition among treatments, and (4) changes in precipitation caused a shift in the dominant species proportional biomass that resulted in lower community evenness in the wet relative to dry treatments. Interestingly, compositional and evenness responses of the subdominant community to the treatments did not always follow the responses of the whole plant community. Our data suggest that changes in plant dominance patterns and community evenness are an important part of community responses to climatic change, and generally, that such compositional shifts can alter ecosystem biomass production and nutrient inputs.

Research in community invasibiliy has focused on biotic and abiotic factors that influence the establishment of invasive species and whether such factors vary with spatial scale. Here, we investigate the role of both biotic and abiotic factors associated with the initial establishment of Lespedeza cuneata (L. cuneata) and its abundance at three spatial scales: neighborhoods (9-m2 plots), communities (50-m2 transect) and old fields (5,000–70,000 m2). We asked: (1) Do resource availability and community structure affect the establishment of L. cuneata?, and (2) Are resource availability and community structure associated with patterns of L. cuneata abundance from neighborhood scales to old-field scales? To investigate the first question, we manipulated soil nitrogen (N) availability at three levels in an existing old-field community and tracked emergence and persistence of L. cuneata seedlings, as well as total plant biomass of the community, availability of light, and soil moisture content. To address the second question, we performed surveys in which we estimated L. cuneata foliar cover at community scales (50-m2 belt transects) and old-field scales (total area of 28 ha), and assessed the same biotic and abiotic variables as in the field experiment. The experiment revealed that establishment and persistence by L. cuneata seedlings were 15× and 5× lower in N-added plots than in N-reduced plots. Total plant community biomass was 30% greater in N-added plots than in N-reduced plots. Conversely, light and soil moisture were 60 and 20% lower in N-added plots than in N-reduced plots. Surveys of old fields indicated that community biomass was positively associated with L. cuneata cover at old-field scales likely resulting from greater soil N input from nitrogen fixation in fields with greater L. cuneata cover. In sum, these results indicate that biotic factors associated with establishment of a Rank 1 invasive plant species at the community scale are also related to its distribution at the old-field scale, but the direction of such associations changed across scales.

Rising concentrations of atmospheric carbon dioxide ([CO{sub 2}]) may influence forest successional development and species composition of understory plant communities by altering biomass production of plant species of functional groups. Here, we describe how elevated [CO{sub 2}] (eCO{sub 2}) affects aboveground biomass within the understory community of a temperate deciduous forest at the Oak Ridge National Laboratory sweetgum (Liquidambar styraciflua) free-air carbon dioxide enrichment (FACE) facility in eastern Tennessee, USA. We asked if (i) CO{sub 2} enrichment affected total understory biomass and (ii) whether total biomass responses could be explained by changes in understory species composition or changes in relative abundance of functional groups through time. The FACE experiment started in 1998 with three rings receiving ambient [CO{sub 2}] (aCO{sub 2}) and two rings receiving eCO{sub 2}. From 2001 to 2003, we estimated species-specific, woody versus herbaceous and total aboveground biomass by harvesting four 1 x 0.5-m subplots within the established understory plant community in each FACE plot. In 2008, we estimated herbaceous biomass as previously but used allometric relationships to estimate woody biomass across two 5 x 5-m quadrats in each FACE plot. Across years, aboveground biomass of the understory community was on average 25% greater in eCO{sub 2} more » than in aCO{sub 2} plots. We could not detect differences in plant species composition between aCO{sub 2} and eCO{sub 2} treatments. However, we did observe shifts in the relative abundance of plant functional groups, which reflect important structural changes in the understory community. In 2001-03, little of the understory biomass was in woody species; herbaceous species made up 94% of the total understory biomass across [CO{sub 2}] treatments. Through time, woody species increased in importance, mostly in eCO{sub 2}, and in 2008, the contribution of herbaceous species to total understory biomass was 61% in aCO{sub 2} and only 33% in eCO{sub 2} treatments. Our results suggest that rising atmospheric [CO{sub 2}] could accelerate successional development and have longer term impact on forest dynamics. « less

Aims The direct effects of atmospheric and climatic change factors— atmospheric [CO2], air temperature and changes in precipitation— can shape plant community composition and alter ecosystem function. It is essential to understand how these factors interact to make better predictions about how ecosystems may respond to change. We investigated the direct and interactive effects of [CO2], warming and altered soil moisture in open-top chambers (OTCs) enclosing a constructed old-field community to test how these factors shape plant communities. Materials and methods The experimental facility in Oak Ridge, TN, USA, made use of 4-m diameter OTCs and rain shelters to manipulate [CO2] (ambient, ambient + 300 ppm), air temperature (ambient, ambient + 3.5C) and soil moisture (wet, dry). The plant communities within the chambers comprised seven common old-field species, including grasses, forbs and legumes. We tracked foliar cover for each species and calculated community richness, evenness and diversity from 2003 to 2005. Important findings This work resulted in three main findings: (1) warming had speciesspecific effects on foliar cover that varied through time and were altered by soil moisture treatments; (2) [CO2] had little effect on individual species or the community; (3) diversity, evenness and richness were influenced most by soil moisture, primarily reflecting the response of one dominant species. We conclude that individualistic species responses to atmospheric and climatic change can alter community composition and that plant populations and communities should be considered as part of analyses of terrestrial ecosystem response to climate change. However, prediction of plant community responses may be difficult given interactions between factors and changes in response through time.

Summary • The hypothesis that drought intensity constrains the recovery of photosynthesis from drought was tested in the C3 woody legume Prosopis velutina, and the mechanisms underlying this constraint examined. • Hydraulic status and gas exchange were measured the day before a 39 mm precipitation pulse, and up to 7 d afterwards. The experiment was conducted under rainout shelters, established on contrasting soil textures and with different vegetation cover at the Santa Rita Experimental Range in southeastern Arizona, USA. • Rates of photosynthesis and stomatal conductance after re-watering, as well as the number of days necessary for photosynthesis to recover after re-watering, were negatively correlated with predawn water potential, a measure of drought intensity (R2 = 0.83, 0.64 and 0.92, respectively). • Photosynthetic recovery was incomplete when the vascular capacity for water transport had been severely impaired (percentage loss of hydraulic conductance > 80%) during the drought, which largely increased stomatal limitations. However, changes in biochemical capacity or in mesophyll conductance did not explain the observed pattern of photosynthesis recovery. Although the control that hydraulic limitations impose on photosynthesis recovery had been previously inferred, the first empirical test of this concept is reported here.

Climate change predictions for the desert southwestern U.S. are for shifts in precipitation patterns. The impacts of climate change may be significant, because desert soil processes are strongly controlled by precipitation inputs (“pulses”) via their effect on soil water availability. This study examined the response of soil respiration—an important biological process that affects soil carbon (C) storage—to variation in pulses representative of climate change scenarios for the Sonoran Desert. Because deserts are mosaics of different plant cover types and soil textures—which create patchiness in soil respiration—we examined how these landscape characteristics interact to affect the response of soil respiration to pulses. Pulses were applied to experimental plots of bare and vegetated soil on contrasting soil textures typical of Sonoran Desert grasslands. The data were analyzed within a Bayesian framework to: (1) determine pulse size and antecedent moisture (soil moisture prior to the pulse) effects on soil respiration, (2) quantify soil texture (coarse vs. fine) and cover type (bare vs. vegetated) effects on the response of soil respiration and its components (plant vs. microbial) to pulses, and (3) explore the relationship between long-term variation in pulse regimes and seasonal soil respiration. Regarding objective (1), larger pulses resulted in higher respiration rates, particularly from vegetated fine-textured soil, and dry antecedent conditions amplified respiration responses to pulses (wet antecedent conditions dampened the pulse response). Regarding (2), autotrophic (plant) activity was a significant source (∼60%) of respiration and was more sensitive to pulses on coarse- versus fine-textured soils. The sensitivity of heterotrophic (microbial) respiration to pulses was highly dependent on antecedent soil water. Regarding (3), seasonal soil respiration was predicted to increase with both growing season precipitation and mean pulse size (but only for pulses between 7 and 25 mm). Thus, the heterogeneity of the desert landscape and the timing or the number of medium-sized pulses is expected to significantly impact desert soil C loss with climate change.

Summary 1. A major research focus in population and community ecology is to establish a mechanistic understanding of plant interactions and demographic responses. The first step towards this mechanistic approach relies on understanding the differences in stress caused by different environmental conditions. Leaf-level photosynthetic rate ( A ) within and among plant populations provides important insight into population and community processes, but is difficult to acquire with sufficient replication under field conditions. Instead, chlorophyll fluorescence ( F v / F m ) and predawn water potential ( Ψ pd ) are often used in arid and semi-arid ecosystems. 2. F v / F m reflects the photoactivation status of photosystem II (PSII), whereas Ψ pd indicates water availability in the rhizosphere. Here we compare these indices with A in two perennial C 4 grasses (native Heteropogon contortus and invasive Eragrostis lehmanniana ) and in seedlings of the C 3 shrub Prosopis velutina growing on highly contrasting sandy loam and loamy clay soils in experimental plots. Measurements were made the day prior to and up to 7 days following a 39-mm rainfall pulse after 2 months of drought. 3. A was more sensitive across a broad range of environmental conditions, whereas F v / F m and Ψ pd only responded to periods of protracted drought. The use of these measures was further complicated because their values varied daily and we observed different time-lags in their response to precipitation pulses. 4. We suggest sampling schemes and a priori measurements to capture the value that is representative for the question of interest, and that match the pulsed biological activity in these ecosystems. Finally, we suggest the use of these measures in combination with measurements providing integration over longer time periods, such as δ 13 C, δ 18 O and N concentration in bulk leaf tissue.

The world passed the halfway point of oil supply in 2005. World demand for oil likely will severely outstrip supply in 2008, leading to increasingly higher oil prices. Consequences are likely to include increasing gasoline prices, rapidly increasing inflation, and subsequently a series of increasingly severe recessions followed by a worldwide economic depression. Consequences may include, particularly in industrialized countries such as the United States, massive unemployment, economic collapse, and chaos.

Soil moisture content and leaf area index (LAI) are properties that will be particularly important in mediating whole system responses to the combined effects of elevated atmospheric [CO2], warming and altered precipitation. Warming and drying will likely reduce soil moisture, and this effect may be exacerbated when these factors are combined. However, elevated [CO2] may increase soil moisture contents and when combined with warming and drying may partially compensate for their effects. The response of LAI to elevated [CO2] and warming will be closely tied to soil moisture status and may mitigate or exacerbate the effects of global change on soil moisture. Using open-top chambers (4-m diameter), the interactive effects of elevated [CO2], warming, and differential irrigation on soil moisture availability were examined in the OCCAM (Old-Field Community Climate and Atmospheric Manipulation) experiment at Oak Ridge National Laboratory in eastern Tennessee. Warming consistently reduced soil moisture contents and this effect was exacerbated by reduced irrigation. However, elevated [CO2] mitigated the effects of warming and drying on soil moisture. LAI was determined using an AccuPAR ceptometer and both the leaf area duration (LAD) and canopy size were increased by irrigation and elevated [CO2]. Changes in LAI were closely linked to soil moisture status. The climate of the southeastern United States is predicted to be warmer and drier in the future, and this research suggests that although elevated [CO2] will ameliorate the effects of warming and drying, losses of soil moisture will cause declines in the LAI of old field ecosystems in the future.

Responses of soil respiration to atmospheric and climatic change will have profound impacts on ecosystem and global C cycling in the future. This study was conducted to examine effects on soil respiration of the concurrent driving factors of elevated atmospheric CO2 concentration, rising temperature, and changing precipitation in a constructed old-field grassland in eastern Tennessee, USA. Model ecosystems of seven old-field species in 12 open-top chambers (4 m in diameter) were treated with two CO2 (ambient and ambient plus 300 ppm) and two temperature (ambient and ambient plus 3 C) levels. Two split plots with each chamber were assigned with high and low soil moisture levels. During the 19-month experimental period from June 2003 to December 2004, higher CO2 concentration and soil water availability significantly increased mean soil respiration by 35.8% and 15.7%, respectively. The effects of air warming on soil respiration varied seasonally from small reductions to significant increases to no response, and there was no significant main effect. In the wet side of elevated CO2 chambers, air warming consistently caused increases in soil respiration, whereas in other three combinations of CO2 and water treatments, warming tended to decrease soil respiration over the growing season but increase it overmore » the winter. There were no interactive effects on soil respiration among any two or three treatment factors irrespective of testing time period. Temperature sensitivity of soil respiration was reduced by air warming, lower in the wet than the dry side, and not affected by CO2 treatment. Variations of soil respiration responses with soil temperature and soil moisture ranges could be primarily attributable to the seasonal dynamics of plant growth and its responses to the three treatments. Using a conceptual model to interpret the significant relationships of treatment-induced changes in soil respiration with changes in soil temperature and moisture observed in this study, we conclude that elevated CO2, air warming, and changing soil water availability had both direct and indirect effects on soil respiration via changes in the three controlling factors: soil temperature, soil moisture, and C substrate. Our results demonstrate that the response of soil respiration to climatic warming should not be represented in models as a simple temperature response function. A more mechanistic understanding of the direct and indirect impacts of concurrent global change drivers on soil respiration is needed to facilitate the interpretation and projection of ecosystem and global C cycling in response to atmospheric and climate change.« less

Invasive species are a global threat to biodiversity and the functioning of natural ecosystems. Here, we report on a two-year experiment aimed at elucidating the combined and relative effects of three key controls on plant invasions: propagule supply, soil nitrogen (N) availability, and herbivory by native insects. We focus on the exotic species Lespedeza cuneata, a Rank 1 invasive species. Propagule supply and soil N-availability interacted to control the density and foliar cover of L. cuneata. In low N plots, density and foliar cover of L. cuneata were higher in the propagule addition plots than in the plots to which propagules were not added. Surprisingly, this interaction was significant only when the abundance of herbivores was experimentally reduced. This experiment provides evidence that native insect herbivores mediate the interactive effects of propagule supply and resources on invasion by a widespread invasive plant species.

Plant communities are often structured by interactions among species, such as competition or facilitation. If competition is an important factor that controls the presence and absence of species within intact communities, then a competitive hierarchy, a ranked order from competitive dominant to competitive subordinate, should predict the composition of intact communities. We tested whether a competitive hierarchy derived from pairwise comparisons accurately predicts species abundances within a constructed polyculture community consisting of seven species common to old-field plant communities. We first conducted a pot experiment in field conditions wherein we grew the species in all possible combinations, then created a competitive hierarchy derived from both competitive effect and competitive response for each species. Concurrently, at the same site in native field soil, we constructed polycultures consisting of the same seven species and calculated an abundance hierarchy based on foliar cover, biomass, and an index of species performance. The competitive hierarchy was not concordant with the abundance hierarchy, indicating that simple pairwise comparisons may not account for other factors that influence the abundance of species within relatively complex communities.

Competitive hierarchy for four common old-field plant species depends on resource identity and availability. J. Torrey Bot. Soc. 134: 166–176. 2007.—Competition is an important factor structuring plant communities. Competitive hierarchies may facilitate prediction of the outcome of interactions among multi-species mixtures, but their utility depends upon invariance along environmental gradients. We examined interactions among four common old-field herbaceous dicots (Dactylis glomerata, Festuca elatior, Trifolium pratense, Plantago lanceolata) with pairwise monoculture and polyculture competition experiments at two levels each of light and water. We constructed competitive hierarchies for unique treatment combinations based on competitive effect and response scores. Biomass production and relative yield were affected by presence and identity of neighbor species and inter- and intraspecific competition were typically not distinguishable. Competitive effect and response scores were inversely correla...

Arid and semi-arid ecosystems of the southwestern US are undergoing changes in vegetation composition and are predicted to experience shifts in climate. To understand implications of these current and predicted changes, we conducted a precipitation manipulation experiment on the Santa Rita Experimental Range in southeastern Arizona. The objectives of our study were to determine how soil surface and seasonal timing of rainfall events mediate the dynamics of leaf-level photosynthesis and plant water status of a native and non-native grass species in response to precipitation pulse events. We followed a simulated precipitation event (pulse) that occurred prior to the onset of the North American monsoon (in June) and at the peak of the monsoon (in August) for 2002 and 2003. We measured responses of pre-dawn water potential, photosynthetic rate, and stomatal conductance of native (Heteropogon contortus) and non-native (Eragrostis lehmanniana) C(4) bunchgrasses on sandy and clay-rich soil surfaces. Soil surface did not always amplify differences in plant response to a pulse event. A June pulse event lead to an increase in plant water status and photosynthesis. Whereas the August pulse did not lead to an increase in plant water status and photosynthesis, due to favorable soil moisture conditions facilitating high plant performance during this period. E. lehmanniana did not demonstrate heightened photosynthetic performance over the native species in response to pulses across both soil surfaces. Overall accumulated leaf-level CO(2) response to a pulse event was dependent on antecedent soil moisture during the August pulse event, but not during the June pulse event. This work highlights the need to understand how desert species respond to pulse events across contrasting soil surfaces in water-limited systems that are predicted to experience changes in climate.

Quality and quantity of publications are among the most important measures determining the success of ecologists. The past 50 years have seen a steady rise in the number of researchers and collaborative manuscripts, and a corresponding increase in multi-authored articles. Despite these increases, there remains a shortage of useful and definitive guidelines to aid ecologists in addressing authorship issues, leading to a lack of consistency in what the term “author” really means. Deciding where to draw the line between those who have earned authorship and those who are more appropriately credited in the acknowledgments may be one of the more challenging aspects of authorship. Here, we borrow ideas from other scientific disciplines and propose a simple solution to help ecologists who are making such decisions. We recommend improving communication between co-authors throughout the research process, and propose that authors publish their contributions to a manuscript in a separate byline.

• The influences of prior monsoon-season drought (PMSD) and the seasonal timing of episodic rainfall ('pulses') on carbon and water exchange in water-limited ecosystems are poorly quantified. • In the present study, we estimated net ecosystem exchange of CO₂ (NEE) and evapotranspiration (ET) before, and for 15 d following, experimental irrigation in a semi-arid grassland during June and August 2003. Rainout shelters near Tucson, Arizona, USA, were positioned on contrasting soils (clay and sand) and planted with native (Heteropogon contortus) or non-native invasive (Eragrostis lehmanniana) C4 bunchgrasses. Plots received increased ('wet') or decreased ('dry’) monsoon-season (July–September) rainfall during 2002 and 2003. • Following a June 2003 39-mm pulse, species treatments had similar NEE and ET dynamics including 15-d integrated NEE (NEEpulse). Contrary to predictions, PMSD increased net C uptake during June in plots of both species. Greater flux rates after an August 2003 39-mm pulse reflected biotic activity associated with the North American Monsoon. Furthermore, August NEEpulse and ecosystem pulse-use efficiency (PUE(e) = NEE(pulse)/ET(pulse)) was greatest in Heteropogon plots. • PMSD and rainfall seasonal timing may interact with bunchgrass invasions to alter NEE and ET dynamics with consequences for PUE(e) in water-limited ecosystems.

Summary 1 In water-limited ecosystems, discrete precipitation events trigger brief but important episodes of biological activity. Differential responses of above- and below-ground biota to precipitation may constrain biogeochemical transformations at the ecosystem scale. 2 We quantified short-term dynamics of whole ecosystem response to 39 mm irrigation events (precipitation pulses) during June 2002 and 2003 using plant physiological and ecosystem gas-exchange measurements as state variables in a principal components analysis (PCA). Experimental plots consisted of either native ( Heteropogon contortus L.) or non-native ( Eragrostis lehmanniana Nees) bunchgrasses planted in monoculture on two distinct geomorphic surfaces in a semi-arid grassland. 3 For 15 days, treatments followed similar, non-linear trajectories through state variable space with measurement periods forming distinct clusters; PCA axes 1 and 2 combined to explain 80.7% of the variation during both 2002 and 2003. 4 During both years, bunchgrass species interacted with soil type such that there was a reduction in ecosystem functional resistance in plots planted with the non-native bunchgrass species on the fine-textured clay geomorphic surface. 5 System-level hysteresis, emerging as a result of independent responses of photosynthesis, respiration and evapotranspiration to precipitation, indicated the potential for alternative functional states. 6 Quantifying the frequency and duration of ecosystem alternative functional states in response to individual precipitation events within a season will provide insights into the controls of species, soils and climate on ecosystem carbon and water cycles.