Evidence for and Mechanisms of Ecosystem Transformation In The Great Basin of The Western United States

Ecosystem transformations are difficult to reverse and often create novel ecosystems. These systems can be maintained by stabilizing feedbacks driven by external or internal mechanisms. Increasing our understanding of these feedback components and how they relate to each other is crucial to know if and when they can be reversed. We studied the sagebrush biome in the western United states. Here, cheatgrass invasion and fire are converting vast areas of shrublands into grasslands, which may be two alternative stable states. We aimed to understand the components of positive feedback mechanisms that maintain these two states, and the impacts that conversion from shrubland to grassland has on ecosystem function. In chapter one the connectivity of fuel influenced the burn severity of fire, which favored fire-tolerant annuals in the seedbank. In chapter two invasion and the loss of shrubs and perennial grasses by fire changed the system from a sink to a source of soil carbon and nitrogen. In chapter three, we constructed a fire history atlas to isolate the effect of time since fire by removing the effect of repeated fires. There was little evidence of recovery towards the pre-fire state, and instead livestock grazing and cheatgrass abundance interacted to maintain the grass-dominated state. In chapter four we created an allometric equation to calculate biomass from cover estimates that can be applied to broad-scale models of cheatgrass abundance. Overall, we document self-reinforcing mechanisms of an alternative stable state, over several decades. We demonstrate how interannual climate variability creates initial or sustaining conditions that can alter longer-term trends and interannual oscillations in ecosystem functions. Finally, there are important management implications of this work, as cheatgrass dominance can present a sustained and novel ecosystem type with few opportunities to restore to native shrubland. Cheatgrass-dominated landscapes in the U.S. Great Basin offer a critical view into how novel alternative stable vegetation states can be initiated through disturbance and sustained through self-reinforcing mechanisms. Global changes such as climate warming, expanding land use, and invasive species present novel disturbance regimes and species assemblages. This study provides key insights into what prompts and sustains ecosystem transformation in drylands.</p

Long-Term Effects of Repeated Fires on the Diversity and Composition of Great Basin Sagebush Plant Communities

Sagebrush in the Great Basin is one of the most imperiled ecosystems in North America. Exotic plant invasions and wildfires have combined to convert these systems into those composed mostly of exotic annual grasses and forbs at a broad scale. While it is well documented that annual grass invasions are increasing wildfires, and that exotic annual grasses thrive after fire, the lasting effects that multiple fires have on plant communities are unclear. Namely, do multiple fires affect biodiversity and community composition in a cumulative fashion, or is one fire enough to initiate a lasting alternate state? We created a fire history atlas from 31 years satellite-derived fire data to design a stratified sampling scheme along a fire frequency gradient. We sampled 28 plots for plant community composition and soil characteristics. We examined fire’s effect on species richness using species accumulation curves, and calculated alpha-diversity and 3 metrics of beta-diversity. We used non-metric multidimensional scaling to examine community clustering, and PERMANOVA models to examine how climate variable around the time of the fire affected community clustering and beta diversity.Community clustering measures suggest that one fire pushes the system into an alternate state. Biodiversity measures indicated cumulative effects. There was no significant difference in alpha diversity per plot by fire frequency, but species accumulation show a clear step-wise progression of diversity decreasing as fire frequency increases. Beta diversity showed a significant decline after 3 fires. Non-metric multidimensional scaling showed most burned plots clustering into the one community type dominated by cheatgrass, except three thrice-burned plots. When examining plots just by exotic and native cover, there was a clear threshold effect after one fire, with native shrubs dominating the unburned plots, and exotic annual grasses dominating the burned plots. While one burn might be enough to change the general community type, successive burns still continue to influence biodiversity

A Synthesis of the Effects of Cheatgrass Invasion on US Great Basin Carbon Storage

Non-native, invasive Bromus tectorum (cheatgrass) is pervasive in sagebrush ecosystems in the Great Basin ecoregion of the western United States, competing with native plants and promoting more frequent fires. As a result, cheatgrass invasion likely alters carbon (C) storage in the region. Many studies have measured C pools in one or more common vegetation types: native sagebrush, invaded sagebrush and cheatgrass-dominated (often burned) sites, but these results have yet to be synthesized. We performed a literature review to identify studies assessing the consequences of invasion on C storage in above-ground biomass (AGB), below-ground biomass (BGB), litter, organic soil and total soil. We identified 41 articles containing 386 unique studies and estimated C storage across pools and vegetation types. We used linear mixed models to identify the main predictors of C storage. We found consistent declines in biomass C with invasion: AGB C was 55% lower in cheatgrass (40 ± 4 g C/m2) than native sagebrush (89 ± 27 g C/m2) and BGB C was 62% lower in cheatgrass (90 ± 17 g C/m2) than native sagebrush (238 ± 60 g C/m2). In contrast, litter C was \u3e4× higher in cheatgrass (154 ± 12 g C/m2) than native sagebrush (32 ± 12 g C/m2). Soil organic C (SOC) in the top 10 cm was significantly higher in cheatgrass than in native or invaded sagebrush. SOC below 20 cm was significantly related to the time since most recent fire and losses were observed in deep SOC in cheatgrass \u3e5 years after a fire. There were no significant changes in total soil C across vegetation types. Synthesis and applications. Cheatgrass invasion decreases biodiversity and rangeland productivity and alters fire regimes. Our findings indicate cheatgrass invasion also results in persistent biomass carbon (C) losses that occur with sagebrush replacement. We estimate that conversion from native sagebrush to cheatgrass leads to a net reduction of C storage in biomass and litter of 76 g C/m2, or 16 Tg C across the Great Basin without management practices like native sagebrush restoration or cheatgrass removal

Cover-based allometric estimate of aboveground biomass of a non-native, invasive annual grass (Bromus tectorum L.) in the Great Basin, USA

Cheatgrass (Bromus tectorum L.) presence in the Great Basin is associated with an increase in fire frequency andsize, likely due to increased spatial continuity of fine fuel biomass. Measurements of the extent and cover ofcheatgrass are steadily improving, but the strength of the relationship between cover and aboveground biomass(AGB) is unclear. An allometric equation that can reliably convert cover to AGB of cheatgrass would allow forimproved incorporation of regional estimates of cover into models of fire activity, carbon storage, and net pri&shy;mary productivity, all of which rely on biomass. We measured cover and AGB of cheatgrass at 60 locations in thenorth-central Great Basin and used these measurements to model the relationship. We found a strong, linearrelationship between the percent cover and AGB, which was improved after square root transformation of bothcover and AGB, and after incorporating the number of days after peak NDVI that the biomass and cover weremeasured. These results show that AGB of cheatgrass can be reliably estimated from cover. It is likely thatallometric equations based on cover will be effective for other grass species, but care must be taken to account forphenology (e.g., peak NDVI) in the estimation.</p

FIRED (Fire Events Delineation): An Open, Flexible Algorithm and Database of US Fire Events Derived from the MODIS Burned Area Product (2001-2019)

Harnessing the fire data revolution, i.e., the abundance of information from satellites, government records, social media, and human health sources, now requires complex and challenging data integration approaches. Defining fire events is key to that effort. In order to understand the spatial and temporal characteristics of fire, or the classic fire regime concept, we need to critically define fire events from remote sensing data. Events, fundamentally a geographic concept with delineated spatial and temporal boundaries around a specific phenomenon that is homogenous in some property, are key to understanding fire regimes and more importantly how they are changing. Here, we describe Fire Events Delineation (FIRED), an event-delineation algorithm, that has been used to derive fire events (N = 51,871) from the MODIS MCD64 burned area product for the coterminous US (CONUS) from January 2001 to May 2019. The optimized spatial and temporal parameters to cluster burned area pixels into events were an 11-day window and a 5-pixel (2315 m) distance, when optimized against 13,741 wildfire perimeters in the CONUS from the Monitoring Trends in Burn Severity record. The linear relationship between the size of individual FIRED and Monitoring Trends in Burn Severity (MTBS) events for the CONUS was strong (R2 = 0.92 for all events). Importantly, this algorithm is open-source and flexible, allowing the end user to modify the spatio-temporal threshold or even the underlying algorithm approach as they see fit. We expect the optimized criteria to vary across regions, based on regional distributions of fire event size and rate of spread. We describe the derived metrics provided in a new national database and how they can be used to better understand US fire regimes. The open, flexible FIRED algorithm could be utilized to derive events in any satellite product. We hope that this open science effort will help catalyze a community-driven, data-integration effort (termed OneFire) to build a more complete picture of fire.</p

Six central questions about biological invasions to which NEON data science is poised to contribute

Biological invasions are a leading cause of rapid ecological change and often present a signifi-cant financial burden. As a vibrant discipline, invasion biology has made important strides in identifying,mapping, and beginning to manage invasions, but questions remain surrounding the mechanisms bywhich invasive species spread and the impacts they bring about. Frequent, multiscalar ecological monitor-ing such as that provided through the National Ecological Observatory Network (NEON) can be an impor-tant tool for addressing some of these questions. We articulate a set of major outstanding questions ininvasion biology, consider how NEON data science is positioned to contribute to addressing these ques-tions, and provide suggestions to help equip a growing contingent of NEON data users in solving invasionbiology problems. We demonstrate these ideas through four case studies examining the mechanisms ofplant invasions in the U.S. Intermountain West. In Case Study I, we evaluate the relationships betweennative species richness, non-native species richness, and probability of invasion across scales. In Case Stud-ies II and III, we explore the relationship between environmental factors and non-native species presenceto understand invasion mechanisms. Case Study IV outlines a method for improving the ability to distin-guish invasive plants from native vegetation in remotely sensed data by leveraging temporal patterns ofphenology. There are many novel elements in the NEON sampling design that make it uniquely poised toshed light on the mechanisms that can help us understand invasibility, prediction, and progression, as wellas on the variability, longevity, and interactions of multiple invasive species&rsquo; impacts. Thus, knowledgegained through analysis of NEON data is expected to inform sound decision-making in unique ways formanagers of systems experiencing biological invasions.</p

Ten simple rules for working with high resolution remote sensing data

Researchers in Earth and environmental science can extract incredible value from high- resolution (sub-meter, sub-hourly or hyper-spectral) remote sensing data, but these data can be difficult to use. Correct, appropriate and competent use of such data requires skills from remote sensing and the data sciences that are rarely taught together. In practice, many researchers teach themselves how to use high-resolution remote sensing data with ad hoc trial and error processes, often resulting in wasted effort and resources. In order to implement a consistent strategy, we outline ten rules with examples from Earth and environmental science to help academic researchers and professionals in industry work more effectively and competently with high-resolution data

Fractionation of Li, Be, Ga, Nb, Ta, In, Sn, Sb, W and Bi in the peraluminous Early Permian Variscan granites of the Cornubian Batholith: precursor processes to magmatic-hydrothermal mineralisation

The Early Permian Variscan Cornubian Batholith is a peraluminous, composite pluton intruded into Devonian and Carboniferous metamorphosed sedimentary and volcanic rocks. Within the batholith there are: G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz) granites. G1-G2 and G3-G4 are derived from greywacke sources and linked through fractionation of assemblages dominated by feldspars and biotite, with minor mantle involvement in G3. G5 formed though flux-induced biotite-dominate melting in the lower crust during granulite facies metamorphism. Fractionation enriched G2 granites in Li (average 315 ppm), Be (12 ppm), Ta (4.4 ppm), In (74 ppb), Sn (18 ppm) and W (12 ppm) relative to crustal abundances and G1 granites. Gallium (24 ppm), Nb (16 ppm) and Bi (0.46 ppm) are not significantly enriched during fractionation, implying they are more compatible in the fractionating assemblage. Sb (0.16 ppm) is depleted in G1-G2 relative to the average upper and lower continental crust. Muscovite, a late-stage magmatic/subsolidus mineral, is the major host of Li, Nb, In, Sn and W in G2 granites. G2 granites are spatially associated with W-Sn greisen mineralisation. Fractionation within the younger G3-G4 granite system enriched Li (average 364 ppm), Ga (28 ppm), In (80 ppb), Sn (14 ppm), Nb (27 ppm), Ta (4.6 ppm), W (6.3 ppm) and Bi (0.61 ppm) in the G4 granites with retention of Be in G3 granites due to partitioning of Be into cordierite during fractionation. The distribution of Nb and Ta is controlled by accessory phases such as rutile within the G4 granites, facilitated by high F and lowering the melt temperature, leading to disseminated Nb and Ta mineralisation. Lithium, In, Sn and W are hosted in biotite micas which may prove favourable for breakdown on ingress of hydrothermal fluids. Higher degrees of scattering on trace element plots may be attributable to fluid–rock interactions or variability within the magma chamber. The G3-G4 system is more boron-rich, evidenced by a higher modal abundance of tourmaline. In this system, there is a stronger increase of Sn compared to G1-G2 granites, implying Sn in tourmaline-dominated mineral lodes may represent exsolution from G4 granites. G1-G4 granite abundances can be accounted for by 20–30% partial melting and 10–40% fractionation of a greywacke source. G5 granites are analogues of Rare Metal Granites described in France and Germany. These granites are enriched in Li (average 1363 ppm), Ga (38 ppm), Sn (21 ppm), W (24 ppm), Nb (52 ppm) and Ta (15 ppm). Within G5 granites, the metals partition into accessory minerals such as rutile, columbite-tantalite and cassiterite, forming disseminated magmatic mineralisation. High observed concentrations of Li, In, Sn, W, Nb and Ta in G4 and G5 granites are likely facilitated by high F, Li and P, which lower melt temperature and promote retention of these elements in the melt, prior to crystallisation of disseminated magmatic mineralisation

The Changing Landscape for Stroke\ua0Prevention in AF: Findings From the GLORIA-AF Registry Phase 2

Background GLORIA-AF (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients with Atrial Fibrillation) is a prospective, global registry program describing antithrombotic treatment patterns in patients with newly diagnosed nonvalvular atrial fibrillation at risk of stroke. Phase 2 began when dabigatran, the first non\u2013vitamin K antagonist oral anticoagulant (NOAC), became available. Objectives This study sought to describe phase 2 baseline data and compare these with the pre-NOAC era collected during phase&nbsp;1. Methods During phase 2, 15,641 consenting patients were enrolled (November 2011 to December 2014); 15,092 were eligible. This pre-specified cross-sectional analysis describes eligible patients\u2019 baseline characteristics. Atrial fibrillation&nbsp;disease characteristics, medical outcomes, and concomitant diseases and medications were collected. Data were analyzed using descriptive statistics. Results Of the total patients, 45.5% were female; median age was 71 (interquartile range: 64, 78) years. Patients were from Europe (47.1%), North America (22.5%), Asia (20.3%), Latin America (6.0%), and the Middle East/Africa (4.0%). Most had high stroke risk (CHA2DS2-VASc [Congestive heart failure, Hypertension, Age&nbsp; 6575 years, Diabetes mellitus, previous Stroke, Vascular disease, Age 65 to 74 years, Sex category] score&nbsp; 652; 86.1%); 13.9% had moderate risk (CHA2DS2-VASc&nbsp;= 1). Overall, 79.9% received oral anticoagulants, of whom 47.6% received NOAC and 32.3% vitamin K antagonists (VKA); 12.1% received antiplatelet agents; 7.8% received no antithrombotic treatment. For comparison, the proportion of phase 1 patients (of N&nbsp;= 1,063 all eligible) prescribed VKA was 32.8%, acetylsalicylic acid 41.7%, and no therapy 20.2%. In Europe in phase 2, treatment with NOAC was more common than VKA (52.3% and 37.8%, respectively); 6.0% of patients received antiplatelet treatment; and 3.8% received no antithrombotic treatment. In North America, 52.1%, 26.2%, and 14.0% of patients received NOAC, VKA, and antiplatelet drugs, respectively; 7.5% received no antithrombotic treatment. NOAC use was less common in Asia (27.7%), where 27.5% of patients received VKA, 25.0% antiplatelet drugs, and 19.8% no antithrombotic treatment. Conclusions The baseline data from GLORIA-AF phase 2 demonstrate that in newly diagnosed nonvalvular atrial fibrillation patients, NOAC have been highly adopted into practice, becoming more frequently prescribed than VKA in&nbsp;Europe and North America. Worldwide, however, a large proportion of patients remain undertreated, particularly in&nbsp;Asia&nbsp;and North America. (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients With Atrial Fibrillation [GLORIA-AF]; NCT01468701