Subscribe to our newsletter
YouTube logo
Facebook logo
Twitter logo
YouTube logo

The Northwest Fire Science Consortium works to accelerate the awareness, understanding, and adoption of wildland fire science. We connect managers, practitioners, scientists, and local communities and collaboratives working on fire issues on forest and range lands in Washington and Oregon.

Learn more about NWFSC...

JFSP Regions


NWFSC is one of
fifteen regional exchanges
sponsored by the Joint Fire Science Program.

Hot Topics

Risk terminology primer: Basic principles and a glossary for the wildland fire management community

Authored by M.P. Thompson; Published 2016

Risk management is being increasingly promoted as an appropriate method for addressing wildland fire management challenges. However, a lack of a common understanding of risk concepts and terminology is hindering effective application. In response, this General Technical Report provides a set of clear, consistent, understandable, and usable definitions for terms associated with wildland fire risk management. The material presented herein is not brand-new or innovative per se, but rather synthesizes the extant science so that readers can readily make a crosswalk to the professional literature. The broad objectives of this effort are to provide context and information to support application of risk terminology across all levels of risk management, and to facilitate clear exchange of data, information, and ideas among fire management officers, staff, and scientists.

Women in Fire: Prescribed Fire Training Exchange (WTREX)

Key things to know about WTREX:

-This year, WTREX will represent a one-time refocusing of the Nor Cal TREX (working in the same locations with Nor Cal TREX burn hosts); new WTREX locations are anticipated for future years.
-WTREX is an intensive 12-day training exchange that combines practical live-fire training with indoor learning and discussion to advance participants’ qualifications and experience in wildland fire operations.
-WTREX will engage both women and men in building a support network for female fire practitioners working to advance their leadership in wildland fire management.
-WTREX participants will work together to accomplish much-needed prescribed burning in a variety of fire-adapted ecosystems in northwestern California.
-Today’s fire problems are so complex that we need to elevate diversity in intellect, talent, and perspective in order to solve them.
-Managers of federal, tribal, and private lands will serve as hosts, inviting teams of WTREX participants to burn on their lands.

Application: To apply, visit the application website at http://trexregistration.weebly.com/2016-wtrex and submit by the end of the day on July 31, 2016. Be sure to select the WTREX. Email Lenya Quinn-Davidson, Director of the Northern California Prescribed Fire Council, with any questions: nwcapfc@gmail.com. Space is limited to 25 trainees; selection will be made to ensure a diverse group.

Get more information by clicking on the link to the flyer.

Forest fire policy: change conventional thinking of smoke management to prioritize long-term air quality and public health

Authored by D.W. Schweizer; Published 2016

Wildland fire smoke is inevitable. Size and intensity of wildland fires are increasing in the western USA. Smoke-free skies and public exposure to wildland fire smoke have effectively been postponed through suppression. The historic policy of suppression has systematically both instilled a public expectation of a smoke-free environment and deferred emissions through increased forest fuel loads that will lead to an eventual large spontaneous release. High intensity fire smoke is impacting a larger area including high density urban areas. Policy change has largely attempted to provide the avenue for increased use of ecologically beneficial fire but allows for continued reliance on suppression as a primary tool for a smoke averse population. While understanding the essential role of suppression in protection of life and property, we dispute the efficacy of attempting to eliminate smoke exposure through suppression in a fire prone area to protect human health at the population level. Sufficient consideration to future negative health outcomes needs to be considered in fire management decisions. It is likely that long term air quality is inextricably linked to ecosystem health in the Sierra Nevada. We contend that landscape use of ecological fire is essential to forest and human health. Radical change is needed where beneficial wildland fire smoke is treated as natural background and exempted from much of the regulation applied to anthropogenic sources.
Tolerance of the measured release of routine smoke emissions from beneficial fire is needed. Using present air quality standards in the more remote areas will provide an opportunity to increase burning in many forests while protecting public health.

NWFSC Research Brief #8: Cumulative disturbances on the landscape: Lessons from the Pole Creek fire, Oregon

Authored by N.W.Fire Scien Consortium; Published 2016

Previous research has focused on quantifying fuel loadings and using operational fire behavior models to understand changes in fire severity following MPB outbreaks. In this study however, researchers used direct field measurements taken from the 2012 Pole Creek Fire that burned in lodgepole pine forests in central Oregon’s Eastern Cascade Mountains, which had experienced a MPB epidemic 8-15 years prior to the fire. They examined the combined effects of MPB and fire disturbances on stand structure, and investigated the influence of previous MPB severity and fire weather on subsequent fire severity and cumulative disturbance severity.

Land use planning to reduce wildfire risk: Lessons from 5 western cities

Webinar Event from California Fire Science Consortium

Presented by Dr. Kimiko Barrett, Headwaters Economics

In the American West, wildfire risk to life and property is accelerating as a result of development trends favoring the region’s Wildland-Urban Interface (WUI). Moreover, extended droughts, unseasonably warm temperatures, and other climate-induced impacts are influencing the frequency and size of wildfires. In response, a number of cities in the West who have been repeatedly threatened by wildfires, are reducing wildfire risk through unique land use planning strategies. In identifying the most effective land use planning measures, we profiled five urban areas across the region, including Austin (Texas), Boulder (Colorado), Flagstaff (Arizona), San Diego (California), and Santa Fe (New Mexico). Examples of the most compelling land use planning tools will be summarized in this webinar and provide an opportunity for others to learn how urban areas in the West are increasingly becoming wildfire-adapted communities.

To register, click HERE.

Administrative and Judicial Review of NEPA Decisions: Risk Factors and Risk Minimizing Strategies for the Forest Service

Authored by A. Bixler; Published 2016

Changes in land use and management practices throughout the past century–in addition to drought and other stressors exacerbated by climate change–have degraded the nation’s forests and led to overgrowth and accumulation of hazardous fuels (GAO 2015). Because of these fuels, some forests now see high-severity fires that threaten communities as well as important natural and cultural resources. Restoring desired vegetation conditions, which can often be accomplished through mechanical thinning or prescribed burning, are central objectives of restoration and fuel reduction projects carried out by federal land management agencies. However, prior to implementing restoration projects or any other major action that may result in a significant impact on the environment, the National Environmental Policy Act (NEPA) of 1969 requires federal land management agencies to conduct an environmental analysis to consider and fully disclose potential impacts (42 USC § 4332(C)).

Rather than enforcing or prohibiting any specific action on the landscape, NEPA prescribes a general process designed to educate decision-makers, relevant agencies, and the general public about the environmental consequences of actions planned on federally-administered public lands. This decision-making process of receiving, documenting, and evaluating public comment on potential impacts of proposed actions is commonly referred to as the NEPA process. Historically, NEPA compliance has posed numerous hurdles for public land managers.
Since early 2013, administrative challenges to Forest Service land management decisions take the form of a pre-decisional administrative review process involving the filing of written “objections” to proposed agency decisions (Brown 2015). Prior to early 2013, administrative challenges generally took the form of a post-decisional administrative review process. The agency’s resolution of an administrative challenge can in turn be judicially challenged via a lawsuit in U.S. District Court (Jones and Taylor 1995; Keele et al. 2006; Portuese et al. 2009), and district court decisions can be challenged in the appropriate U.S. Court of Appeals (Jones and Taylor 1995; Malmsheimer et al. 2004). The Court of Appeals is usually the final level of review for Forest Service land management decisions because very few Court of Appeals cases are selected for discretionary review by the U.S. Supreme Court. Note that the term “legal challenge,” used throughout this synthesis, is an encompassing term that includes both primary types of legal challenges: administrative (agency-level) and judicial (in the courts).

Toward a more ecologically informed view of severe forest fires

Authored by R.L. Hutto; Published 2016

We use the historical presence of high-severity fire patches in mixed-conifer forests of the western United States to make several points that we hope will encourage development of a more ecologically informed view of severe wildland fire effects. First, many plant and animal species use, and have sometimes evolved to depend on, severely burned forest conditions for their persistence. Second, evidence from fire history studies also suggests that a complex mosaic of severely burned conifer patches was common historically in the West. Third, to maintain ecological integrity in forests born of mixed-severity fire, land managers will have to accept some severe fire and maintain the integrity of its aftermath. Lastly, public education messages surrounding fire could be modified so that people better understand and support management designed to maintain ecologically appropriate sizes and distributions of severe fire and the complex early-seral forest conditions it creates.

A 350-million-year legacy of fire adaptation among conifers

Authored by T. He; Published 2016

Current phylogenetic evidence shows that fire began shaping the evolution of land plants 125 Ma, although the fossil charcoal record indicates that fire has a much longer history (>350 Ma). Serotiny (on-plant seed storage) is generally accepted as an adaptation to fire among woody plants. We developed a conceptual model of the requirements for the evolution of serotiny, and propose that serotiny is only expressed in the presence of a woody rachis as supporting structure, compact scales covering seeds as protective structure, seed wing as dispersal structure, and crown fire as the agent of selection and mechanism for seed release. This model is strongly supported by empirical data for modern ecosystems. We reconstructed the evolutionary history of intrinsic structural states required for the expression of serotiny in conifers, and show that these were diagnostic for early ('transitional') conifers from 332 Ma (late-Carboniferous). We assessed the likely flammable characteristics of early conifers and found that scale-leaved conifers burn rapidly and with high intensity, supporting the idea that crown fire regimes may have dominated early conifer ecosystems. Synthesis. Coupled with strong evidence for frequent fire throughout the Permian-Carboniferous and fossil evidence for other fire-related traits, we conclude that many early conifers were serotinous in response to intense crown fires, indicating that fire may have had a major impact on the evolution of plant traits as far back as 350 Ma.

Production possibility frontiers and socioecological tradeoffs for restoration of fire adapted forests

Authored by A.A. Ager; Published 2016

We used spatial optimization to analyze alternative restoration scenarios and quantify tradeoffs for a large, multifaceted restoration program to restore resiliency to forest landscapes in the western US. We
specifically examined tradeoffs between provisional ecosystem services, fire protection, and the amelioration of key ecological stressors. The results revealed that attainment of multiple restoration objectives was constrained due to the joint spatial patterns of ecological conditions and socioeconomic values.We also found that current restoration projects are substantially suboptimal, perhaps the result of compromises in the collaborative planning process used by federal planners, or operational constraints on forest management activities. The juxtaposition of ecological settings with human values generated sharp tradeoffs, especially with respect to community wildfire protection versus generating revenue to support restoration and fire protection activities. The analysis and methods can be leveraged by ongoing restoration programs in many ways including: 1) integrated prioritization of restoration activities at multiple scales on public and adjoining private lands, 2) identification and mapping of conflicts between ecological restoration and socioeconomic objectives, 3) measuring the efficiency of ongoing restoration projects compared to the optimal production possibility frontier, 4) consideration of fire transmission among public and private land parcels as a prioritization metric, and 5) finding socially optimal regions along the production frontier as part of collaborative restoration planning.

Opportunities to utilize traditional phenological knowledge to support adaptive management of social-ecological systems vulnerable to changes in climate and fire regimes

Authored by C.A. Armatas; Published 2016

The field of adaptive management has been embraced by researchers and managers in the United States as an approach to improve natural resource stewardship in the face of uncertainty and complex environmental problems. Integrating multiple knowledge sources and feedback mechanisms is an important step in this approach. Our objective is to contribute to the limited literature that describes the benefits of better integrating indigenous knowledge (IK) with other sources of knowledge in making adaptive-management decisions. Specifically, we advocate the integration of traditional phenological knowledge (TPK), a subset of IK, and highlight opportunities for this knowledge to support policy and practice of adaptive management with reference to policy and practice of adapting to uncharacteristic fire regimes and climate change in the western United States.

Klamath River Prescribed Fire Training Exchange (TREX)

Description: The training is organized as an incident, using a Type 3 Incident Management Team. Participants will serve in qualified and trainee firefighting positions on a burn team and will assist with preparing, scouting, briefing, igniting, holding, mop-up, and patrol on numerous controlled burns in the area. We will also complete pre- and post-fire monitoring, train with equipment, practice fireline leadership skills, and learn about local fire ecology and fire management. There will be field trips to past TREX burns, areas burned in recent wildfires and presentations from local tribal members and other community members, scientists, land managers, and practitioners.

To Apply: Complete the Klamath River TREX Application (http://trexregistration.weebly.com/2016-klamath-river-trex.html) no later than Aug 15, 2016. If you don’t have internet access, contact David Medford (530) 643-1699. Thank you!

To get all the information, click on the link to the flyer.

Wildfire risk as a socioecological pathology

Authored by P. Fischer; Published 2016

Wildfire risk in temperate forests has become a nearly intractable problem that can be characterized as a socioecological “pathology”: that is, a set of complex and problematic interactions among social and ecological systems across multiple spatial and temporal scales. Assessments of wildfire risk could benefit from recognizing and accounting for these interactions in terms of socioecological systems, also known as coupled natural and human systems (CNHS). We characterize the primary social and ecological dimensions of the wildfire risk pathology, paying particular attention to the governance system around wildfire risk, and suggest strategies to mitigate the pathology through innovative planning approaches, analytical tools, and policies. We caution that even with a clear understanding of the problem and possible solutions, the system by which human actors govern fire-prone forests may evolve incrementally in imperfect ways and can be expected to resist change even as we learn better ways to manage CNHS.

Living on a flammable planet: interdisciplinary, cross-scalar and varied cultural lessons, prospects and challenges

Authored by C.I. Roos; Published 2016

Living with fire is a challenge for human communities because they are influenced by socio-economic, political, ecological and climatic processes at various spatial and temporal scales. Over the course of 2 days, the authors discussed how communities could live with fire challenges at local, national and transnational scales. Exploiting our diverse, international and interdisciplinary expertise, we outline generalizable properties of fire-adaptive communities in varied settings where cultural knowledge of fire is rich and diverse. At the national scale, we discussed policy and management challenges for countries that have diminishing fire knowledge, but for whom global climate change will bring new fire problems. Finally, we assessed major fire challenges that transcend national political boundaries, including the health burden of smoke plumes and the climate consequences of wildfires. It is clear that to best address the broad range of fire problems, a holistic wildfire scholarship must develop common agreement in working terms and build across disciplines. We must also communicate our understanding of fire and its importance to the media, politicians and the general public.

Building a path to resiliency

Conference Event from ANREP and NACDEP
For more information and to register for this conference, http://www.nacdep.net/2016-anrep-nacdep-conference


Wildfire risk associated with different vegetation types within and outside wildland-urban interfaces

Authored by M. Calviño-Cancela; Published 2016

Wildland-urban interfaces (WUIs) are areas where urban settlements and wildland vegetation intermingle, making the interaction between human activities and wildlife especially intense. Their relevance is increasing worldwide as they are expanding and are associated with fire risk. The WUI may affect the fire risk associated with the type of vegetation (land cover/land use; LULC), a well-known risk factor, due to differences in the type and intensity of human activities in different LULCs within and outside WUIs. No previous studies analyse this interaction between the effects of the WUI and the LULC, despite its importance for understanding the patterns of fire risk, an essential prerequisite to undertake management decisions that can influence fire regimes.

The aim of this study is to assess the effect of the WUI on fire ignition risk and the area burned, and the interaction between its effect and that of the LULC. We used a database of 26,838 wildfires recorded in 2006–2011 in NW Spain and compared fire patterns in relation to WUI and LULC with a random model, using a Montecarlo approach.

There was a clear effect of the WUI on the risk of both fire ignition and spread (higher ignition risk but lower risk of spread in WUIs). The risk of fire was also affected by LULC and, interestingly, the pattern among LULCs differed between WUI and non-WUI areas. This interaction WUI × LULC was particularly important for forestry plantations, which showed the highest increase in ignition risk in WUI compared to non-WUI areas. Native forests and agricultural areas had the lowest ignition risk. Agricultural areas showed the smallest difference in fire size between WUI and non-WUI areas, while shrublands showed much larger fires outside WUIs. Deliberate fires were larger in general than those with other causes, especially outside the WUI.

The differences found between LULCs in fire risk, both in WUI and non-WUI areas, have interesting implications for fire management. Promotion of land covers with low fire risk should be considered as a low cost alternative to the usual fire prevention measures based on fuel load reduction, which require the continuous clearing of vegetation. In this regard, the low fire risk in native forests should be taken into account. Native forests naturally colonize many areas in the study region and require low or no management, in contrast with agricultural areas, also with low fire risk but requiring continuous management in order to avoid colonization by natural vegetation.

Predicting large wildfires across western North America by modeling seasonal variation in soil water balance

Authored by R.H. Waring; Published 2016

A lengthening of the fire season, coupled with higher temperatures, increases the probability of fires throughout much of western North America. Although regional variation in the frequency of fires is well established, attempts to predict the occurrence of fire at a spatial resolution <10 km2 have generally been unsuccessful. We hypothesized that predictions of fires might be improved if depletion of soil water reserves were coupled more directly to maximum leaf area index (LAImax) and stomatal behavior. In an earlier publication, we used LAImax and a process-based forest growth model to derive and map the maximum available soil water storage capacity (ASWmax) of forested lands in western North America at l km resolution. To map large fires, we used data products acquired from NASA’s Moderate Resolution Imaging Spectroradiometers (MODIS) over the period 2000–2009. To establish general relationships that incorporate the major biophysical processes that control evaporation and transpiration as well as the flammability of live and dead trees, we constructed a decision tree model (DT). We analyzed seasonal variation in the relative availability of soil water (fASW) for the years 2001, 2004, and 2007, representing respectively, low, moderate, and high rankings of areas burned. For these selected years, the DT predicted where forest fires >1 km occurred and did not occur at ~100,000 randomly located pixels with an average accuracy of 69 %. Extended over the decade, the area predicted burnt varied by as much as 50 %. The DT identified four seasonal combinations, most of which included exhaustion of ASW during the summer as critical; two combinations involving antecedent conditions the previous spring or fall accounted for 86 % of the predicted fires. The approach introduced in this paper can help identify forested areas where management efforts to reduce fire hazards might prove most beneficial.

Global trends in wildfire and its impacts: perceptions versus realities in a changing world

Authored by S.H. Doerr; Published 2016

Wildfire has been an important process affecting the Earth's surface and atmosphere for over 350 million years and human societies have coexisted with fire since their emergence. Yet many consider wildfire as an accelerating problem, with widely held perceptions both in the media and scientific papers of increasing fire occurrence, severity and resulting losses. However, important exceptions aside, the quantitative evidence available does not support these perceived overall trends. Instead, global area burned appears to have overall declined over past decades, and there is increasing evidence that there is less fire in the global landscape today than centuries ago. Regarding fire severity, limited data are available. For the western USA, they indicate little change overall, and also that area burned at high severity has overall declined compared to pre-European settlement. Direct fatalities from fire and economic losses also show no clear trends over the past three decades. Trends in indirect impacts, such as health problems from smoke or disruption to social functioning, remain insufficiently quantified to be examined. Global predictions for increased fire under a warming climate highlight the already urgent need for a more sustainable coexistence with fire. The data evaluation presented here aims to contribute to this by reducing misconceptions and facilitating a more informed understanding of the realities of global fire.

Tamm Review: Are fuel treatments effective at achieving ecological and social objectives? A systematic review

Authored by E.L. Kalies; Published 2016

The prevailing paradigm in the western U.S. is that the increase in stand-replacing wildfires in historically frequent-fire dry forests is due to unnatural fuel loads that have resulted from management activities including fire suppression, logging, and grazing, combined with more severe drought conditions and increasing temperatures. To counteract unnaturally high fuel loads, fuel reduction treatments which are designed to reduce fire hazard and improve overall ecosystem functioning have been increasing over the last decade. However, until recently much of what we knew about treatment effectiveness was based on modeling and predictive studies. Now, there are many examples of wildfires burning through both treated and untreated areas, and the effectiveness of treatments versus no action can be evaluated empirically. We carried out a systematic review to address the question: Are fuel treatments effective at achieving ecological and social (saving human lives and property) objectives? We found 56 studies addressing fuel treatment effectiveness in 8 states in the western US. There was general agreement that thin + burn treatments had positive effects in terms of reducing fire severity, tree mortality, and crown scorch. In contrast, burning or thinning alone had either less of an effect or none at all, compared to untreated sites. Most studies focused on carbon storage agreed that treatments do not necessarily store more carbon after wildfire, but result in less post-wildfire emissions and less carbon loss in a wildfire due to tree mortality. Understory responses are mixed across all treatments, and the response of other ecological attributes (e.g., soil, wildlife, water, insects) to treatment post-wildfire represents an important data gap; we provide a detailed agenda for future research. Overall, evidence is strong that thin + burn treatments meet the goal of reducing fire severity, and more research is needed to augment the few studies that indicate treatments protect human lives and property.

Average Stand Age from Forest Inventory Plots Does Not Describe Historical Fire Regimes in Ponderosa Pine and Mixed-Conifer Forests of Western North America

Authored by J.T. Stevens; Published 2016

Quantifying historical fire regimes provides important information for managing contemporary forests. Historical fire frequency and severity can be estimated using several methods; each method has strengths and weaknesses and presents challenges for interpretation and verification. Recent efforts to quantify the timing of historical high-severity fire events in forests of western North America have assumed that the “stand age” variable from the US Forest Service Forest Inventory and Analysis (FIA) program reflects the timing of historical high-severity (i.e. stand-replacing) fire in ponderosa pine and mixed-conifer forests. To test this assumption, we re-analyze the dataset used in a previous analysis, and compare information from fire history records with information from co-located FIA plots. We demonstrate that 1) the FIA stand age variable does not reflect the large range of individual tree ages in the FIA plots: older trees comprised more than 10% of pre-stand age basal area in 58% of plots analyzed and more than 30% of pre-stand age basal area in 32% of plots, and 2) recruitment events are not necessarily related to high-severity fire occurrence. Because the FIA stand age variable is estimated from a sample of tree ages within the tree size class containing a plurality of canopy trees in the plot, it does not necessarily include the oldest trees, especially in uneven-aged stands. Thus, the FIA stand age variable does not indicate whether the trees in the predominant size class established in response to severe fire, or established during the absence of fire. FIA stand age was not designed to measure the time since a stand-replacing disturbance. Quantification of historical “mixed-severity” fire regimes must be explicit about the spatial scale of high-severity fire effects, which is not possible using FIA stand age data.

NWFSC Research Brief #9: Wildfire impacts on spring Chinook Salmon: Habitat quality in the Wenatchee River sub-basin

Authored by N.W.Fire Scien Consortium; Published 2016

In this study, researchers developed models of freshwater habitat for spring Chinook Salmon in pre- and post-fire scenarios in the Wenatchee River sub-basin of central Washington, where a large number of wildfires have occurred in the past 30 years. They predicted changes in in-stream wood, sediment, and water temperature as a result of wildfires and modeled their influence on habitat quality for three life stages (egg/fry, juvenile, and adult) of spring Chinook Salmon. They also compared their model results with the current and historic distribution of spring Chinook Salmon to better understand if decreasing populations are distributed in ways that correlate with fire impacts on habitats.

Drivers of Wildfire Suppression Costs: A Review

Authored by A. Ellison; Published 2016

As federal spending on wildland fire suppression has increased dramatically in recent decades, significant policymaking has been designed, at least in part, to address and temper rising costs. Effective strategies for controlling public spending and leveraging limited wildfire management resources depend on a comprehensive understanding of the drivers of suppression costs. Problematically, frequently noted drivers often do not explain variability between similar wildfires or comparable wildfire seasons. As speculation and scrutiny around rising costs have increased, so too have scholarly investigations into a variety of influences on suppression costs. This review gathered and synthesized recent literature that examines how different variables affect wildfire suppression costs in order to present a more complete
understanding of what is known and not known about what drives suppression costs.

Areas of Agreement and Disagreement Regarding Ponderosa Pine and Mixed Conifer Forest Fire Regimes: A Dialogue with Stevens et al.

Authored by D.C. Odion; Published 2016

In a recent PLOS ONE paper, we conducted an evidence-based analysis of current versus historical fire regimes and concluded that traditionally defined reference conditions of low-severity fire regimes for ponderosa pine (Pinus ponderosa) and mixed-conifer forests were incomplete, missing considerable variability in forest structure and fire regimes. Stevens et al. (this issue) agree that high-severity fire was a component of these forests, but disagree that one of the several sources of evidence, stand age from a large number of forest inventory and analysis (FIA) plots across the western USA, support our findings that severe fire played more than a minor role ecologically in these forests. Here we highlight areas of agreement and disagreement about past fire, and analyze the methods Stevens et al. used to assess the FIA stand-age data. We found a major problem with a calculation they used to conclude that the FIA data were not useful for evaluating fire regimes. Their calculation, as well as a narrowing of the definition of high-severity fire from the one we used, leads to a large underestimate of conditions consistent with historical high-severity fire. The FIA stand age data do have limitations but they are consistent with other landscape-inference data sources in supporting a broader paradigm about historical variability of fire in ponderosa and mixed-conifer forests than had been traditionally recognized, as described in our previous PLOS paper.