Dry conifer forest management has increasingly aimed to mitigate the risk of uncharacteristically severe wildfire by implementing treatments that restore a more historical structure to dense and homogeneous present-day stands. Environmental gradients may have influenced the range of historical structures among stands in the Colorado and Wyoming Front Range, but linkages between historical structure and environment remain poorly understood. To address this knowledge gap, we quantified eight spatial and nonspatial historical forest (ca. 1860) structure metrics using tree-ring data from 172 0.5-ha plots distributed across dry conifer forests in the Front Range. We then predicted historical forest structure with random forest and representative classification and regression tree (CART) analyses that used soils, topography, productivity, and present-day climate predictor variables. Historical structure ranged from areas with no trees, to pure ponderosa pine (Pinus ponderosa) woodlands with a few trees and open conditions, to denser mixed conifer forests with greater clumped tree cover. Four structural attributes had random forest models with reasonable predictive performance (R2 > 0.4), including basal area, the percentage of basal area that was composed of ponderosa pine, clumped tree cover, and open space. The four representative CARTs primarily included very coarse sand, site index, elevation, and latitude, indicating that soil characteristics, site productivity, and broad-scale topography were more predictive of historical forest structure than modern climate and fine-scale topographic indicators like slope and aspect. Our findings suggest that environmental gradients can provide managers with a basis for designing prescriptions that are informed by historical forest conditions.

Wildfires are among the most devastating natural disasters, causing widespread and often destructive effects to ecosystems, human communities, and economies. In the eastern edge of the Tibetan Plateau (TP), with the increasing frequency of extreme heatwave events, wildfires have resulted in significant casualties among firefighters, particularly in March, a period known as the “evil fire season”. Here, we show the meteorological driving factors of wildfires across different time scales based on three large and extremely large wildfires in the eastern edge of the TP and examine the impact of fire control policies. At a monthly scale, high vapor pressure deficit and drought provide weather conditions highly conducive for fires to occur in the evil fire season. At daily and hourly scales, temperature spikes, low relative humidity, and wind shifts are key triggers for extreme wildfires in the evil fire season. Furthermore, long-term factors such as climate warming and fire control policies have led to the accumulation of forest fuels, raising the risk of extreme fire behavior. The study suggests a more balanced fire management strategy to mitigate wildfire risks in the eastern edge of the TP and safeguard the lives of firefighters.

The frequent occurrence of fatalities from wildfires is an ongoing problem in China, even though great improvements have been achieved in overall wildfire management in recent years. We analysed the occurrence patterns and correlative environments of fatalities from forest fires in China from 1951 to 2018. Changes in fire policies affected changes in the numbers of fires, forest area burned and number of fatalities before and after 1987, after the large Great Black Dragon Fire that burned in the Daxing’anling Mountains in northeastern China. Most fatalities occurred in the southern, southwestern and eastern forest regions of the country where population centres are concentrated, while most of the burned area was distributed in forests of northeast China with fewer population centres. Fatalities were correlated with higher values of fire weather indices, coniferous forests, coniferous and broad-leaved mixed forests, moderate–average slopes (5.1–15°), and primarily small fires of less than 100 ha in area. These results should be a first step to help improve awareness of inherent dangers during wildfires and to assist fire managers and policy-makers in strengthening safety procedures for both professional firefighters and the public to reduce wildfire fatalities in the future.

Implementation of wildfire- and climate-adaptation strategies in seasonally dry forests of western North America is impeded by numerous constraints and uncertainties. After more than a century of resource and land use change, some question the need for proactive management, particularly given novel social, ecological, and climatic conditions. To address this question, we first provide a framework for assessing changes in landscape conditions and fire regimes. Using this framework, we then evaluate evidence of change in contemporary conditions relative to those maintained by active fire regimes, i.e., those uninterrupted by a century or more of human-induced fire exclusion. The cumulative results of more than a century of research document a persistent and substantial fire deficit and widespread alterations to ecological structures and functions. These changes are not necessarily apparent at all spatial scales or in all dimensions of fire regimes and forest and nonforest conditions. Nonetheless, loss of the once abundant influence of low- and moderate-severity fires suggests that even the least fire-prone ecosystems may be affected by alteration of the surrounding landscape and, consequently, ecosystem functions. Vegetation spatial patterns in fire-excluded forested landscapes no longer reflect the heterogeneity maintained by interacting fires of active fire regimes. Live and dead vegetation (surface and canopy fuels) is generally more abundant and continuous than before European colonization. As a result, current conditions are more vulnerable to the direct and indirect effects of seasonal and episodic increases in drought and fire, especially under a rapidly warming climate. Long-term fire exclusion and contemporaneous social-ecological influences continue to extensively modify seasonally dry forested landscapes. Management that realigns or adapts fire-excluded conditions to seasonal and episodic increases in drought and fire can moderate ecosystem transitions as forests and human communities adapt to changing climatic and disturbance regimes. As adaptation strategies are developed, evaluated, and implemented, objective scientific evaluation of ongoing research and monitoring can aid differentiation of warranted and unwarranted uncertainties.

Context This survey relates to COST (European Cooperation in Science and Technology) Action CA17122 - Alien CSI - Increasing understanding of alien species through citizen science (see https://alien-csi.eu/). The main aim of this survey was to collect information on Citizen Science projects/initiatives involving alien species in European Member States and some neighbouring countries. The survey was performed using a google forms. Survey respondents/contributors are mentioned in this dataset as data collectors. Definitions We defined Citizen Science projects as project which actively involved citizens in scientific enquiry generating new knowledge or understanding on alien species. Citizens may act as contributors, collaborators, or as project leader and have a meaningful role in the project. 'Alien Species' are defined as any live specimen of a species, subspecies or lower taxon of animals, plants, fungi or micro-organisms introduced outside its natural range; it includes any part, gametes, seeds, eggs or propagules of such species, as well as any hybrids, varieties or breeds that might survive and subsequently reproduce. Alien Species thus includes both species that are invasive and species that are alien but not invasive. An 'Invasive Alien Species' is defined as an alien species whose introduction or spread has been found to threaten or adversely impact upon biodiversity and/or related ecosystem services. Survey methodology The survey was made available on Google Forms and disseminated online, collecting responses from June 27, 2019 to April 6, 2020. It was shared with all COST Action CA17122 participants and in each country one person coordinated contacts with existing citizen science projects involving alien and/or invasive species and requested that they complete the survey. Thus, all projects were active in EU member states and neighbouring countries, though some may also be active outside of Europe. To increase reach, the survey was also disseminated through the European Citizen Science Association (ECSA) newsletter and mailing list and respondents were asked to share it with colleagues and local networks via snowball sampling. Questions and attribute values Survey questions and attribute values were developed using JRC metadata standards for CS projects (Bio Innovation Service 2018) and the project metadata model of PPSR Core, a set of global, transdisciplinary data and metadata standards for Public Participation in Scientific Research (https://core.citizenscience.org/). The survey included 62 questions in nine sections: Contact information of the respondent; General characterization of the project, including a brief summary, geographical scope, time scale, hosting entities, funding, etc.; Information on project scope, including target audience, taxonomic and environmental scope, project aims, type of data collected, etc.; Policy-related information, namely if the project has policy relevance and inclusion of species listed in the EU IAS Regulation; Information on engagement, such as type of involvement of citizens in the design of the project, engagement methods and social media used, skills needed to participate and frequency of contributions; Information on feedback and support provided to participants by the project, e.g., if projects provide materials for species identification, guidelines, training activities, information on how data from the project are used, feedback mechanisms and support; Data quality and data management, namely validation mechanism for records, registration type, methods of recording, whether data are open and accessible to citizen scientists, data form used to store data, data standards and data licence used, whether a public data management plan was drafted for the project, and the vocabulary used with respect to biological invasions (origin, occurrence status, degree of establishment and pathway of introduction); Performance indicators of projects, namely, usage of apps, number of participants and number of records, whether learning is assessed, number and type of publications using data from the project; Notes and remarks. Files raw_data.xlsx: includes the non-processed survey responses, supplemented with a project_ID. All GDPR sensitive data such as email addresses were omitted. Each row represents one project. projects_excluded.csv: includes all projects that were omitted from the analysis and the specific criteria for this exclusion. processed_data.csv: includes the cleaned, processed survey responses, used for analysis. The R code used for the analysis is available on this github repository. survey.pdf: a pdf extract from the original Google Forms, including all questions and their specifications. analysis.Rmd: Rmarkdown script for statistical analysis. Also available on this github repository.

Tracking wood formation in semiarid regions during the seasonal march of precipitation extremes has two important applications. It can provide (i) insight into the adaptive capacities of trees to drought and (ii) a basis for a richer interpretation of tree-ring data, assisting in a deeper understanding of past and current climate. In the southwestern USA, the anatomical signature of seasonally bimodal precipitation is the 'false ring'-a band of latewood-like cells in the earlywood. These occur when a particularly deep drought during the early growing season ends abruptly with timely, mid-growing season monsoonal rains. Such conditions presented in southern Arizona in 2014, enabling us to explore false-ring formation in ponderosa pine (Pinus ponderosa Lawson and C. Lawson) and Douglas-fir (Pseudotsuga menziesii Mirb. Franco) in mixed-conifer forest at 2573 m above sea level. We ask: what were the cell-by-cell timings and durations in the phases of wood cell development in 2014? How do these seasonal patterns relate to strongly fluctuating environmental conditions during the growing season? We took weekly microcores from March through November from six ponderosa pine and seven Douglas-fir trees at a well-instrumented flux tower site. Thin sections were prepared, and we counted cells in cambial, expansion, cell wall thickening and mature phases. For ponderosa pine trees forming a false ring, the first impact of intensifying seasonal drought was seen in the enlarging phase and then, almost a month later, in cambial activity. In this species, recovery from drought was associated with recovery first in cambial activity, followed by cell enlargement. This timing raised the possibility that cell division may be affected by atmospheric moisture increases before soil recharge. In both species, the last false-ring cells matured during the summer rainy season. Bimodal cambial activity coincident with moisture availability was observed in both species, whether or not they formed a false ring. This deeper knowledge of the precise timing of both developmental and environmental events should help define mechanistic connections among these factors in creating bimodal growth patterns.

Fire is a critical ecosystem process that has played a key role in shaping forests throughout the Beartooth Mountains in northwestern Wyoming. The highly variable topography of the area provides ideal conditions to compare fire regimes across contiguous forest types, yet pyro-dendrochronological research in this area is limited. We reconstructed fire frequency, tree age structure, and post-fire tree growth response in the Clarks Fork Ranger District of the Shoshone National Forest to infer variations in historical fire behavior and stand effects. We collected fire-scarred trees and plot-based tree ages on plots ranging 0.5-5 km(2) in size across two forest types separated by 2 km: a lower-elevation forest of mixed Douglas-fir and lodgepole pine and a higher elevation treeline forest dominated by whitebark pine. Fires occurred in the lower-elevation forest in 1664, 1706, 1785, 1804, 1846, and 1900 with a mean fire return interval of 47 years. The fires in 1804 and 1900 were also recorded in the higher elevation forest, with significant tree mortality at high elevation in the 1900 fire. Both forests were multi-aged with little evidence of tree cohorts in response to severe, stand-replacing events. On average, tree growth increased after fires, with mean ringwidths after fire 39% wider in Douglas-fir and 40% wider in lodgepole pine than pre-fire averages, suggesting that some tree mortality likely occurred in association with lowe-relevation forest fires. Burns were more frequent in the lower-elevation forest and were occasionally able to spread into the upper-elevation whitebark stand. Although we suspect the transition of fires from low-to high-elevation occurred during drier years, we did not find any relationship between fire years and available climatic reconstructions via superposed epoch analysis. Regeneration during the 20th Century in the whitebark forest documents recovery of this forest after the 1900 moderate-severity fire event. Finally, especially in the lower-elevation Douglas-fir forest, the period since the last recorded fire (1900) appears to be longer than any fire-free period in the historical record, suggesting that fire exclusion may be creating changes in landscape and patch-scale stand structures, which will likely impact future fire behavior, especially the extent of crown-replacing fire, in these forests.

Old trees (defined here as >= 150 years old) can be rare in many forests because of past timber harvest, uncharacteristically severe wildfires, and-increasingly-climate change. Old trees provide unique structural, ecological, scientific, and aesthetic values missing in forests containing only younger trees. Here we compile crossdated ages from over 10,000 living and dead trees sampled in montane forests of the central Rocky Mountains in Colorado and southern Wyoming, USA, to examine changes in age structure of the oldest trees since Euro-American settlement and to provide guidelines to aid in identification of old trees for retention during ecological restoration treatments. Eroded stumps (containing only heartwood) were found in over 93% of 179 randomly sampled plots. Number of stumps found in each plot was proportional to reconstructed historical (1860 C. E.) stand basal area. The regional median date of maximum plot tree recruitment was over 150 years older when including stumps versus only living trees, suggesting that if all those harvested trees had survived to the present, the ages of oldest trees would be substantially greater than it is today. However, the regional median age of oldest trees in 1860 before harvesting was not different from the median age of oldest living trees in the current forest (246 vs. 248 years), which alternatively suggests that the regional population of oldest trees has recovered to near historical levels in the time since early Euro-American harvests. Each living tree at the time of sampling was assigned to one of three potential age classes based on a subjective assessment of tree morphology: old (likely >= 150 years old), young (likely <150 years old), or transitional (containing a mixture of young and old tree characteristics). Trees assigned to the old and young morphology categories were classified correctly 88% to 96% of the time depending on species as confirmed by their crossdated ages. Regression tree analysis revealed that tree diameter at breast height was not as reliable a predictor of tree age as were morphological characteristics. A measure of site productivity was a significant variable to use to separate transitional morphology trees into old and young age classes, but classification accuracy was not high because of large variability in ages of these trees. Our results suggest that residual live old trees in the current forest, although perhaps not rare compared to historical age distributions, should be retained during restoration treatments, and that using simple morphological and environmental criteria to identify old trees is more reliable than tree size alone.

Plant community resilience in frequent-fire forests of western North America has been compromised by over a century of fire exclusion. However, there are several western National Parks where fires have been reintroduced over the past several decades, including Zion National Park in southwest Utah. Here we reconstruct historical components of fire regimes in ponderosa pine dominated forests at Zion and compare these to recent fire frequency, current plant community and fuels structure, and potential fire behavior. Historical fires burned every 9-10 years on average up until 1879, when fires ceased contemporaneous with introduction of Euro-American livestock grazing and timber harvest in upland forests. Abundant tree regeneration occurred after fire exclusion, with tree density averaging 45 trees ha(-1) in reconstructed 1880 forests versus 106 trees ha(-1) today. Intervals between recent (since 1988) wildfires and prescribed fires in these same stands ranged from 7 to 13 years, similar to historical fire timing. Depending on whether plots had burned from zero to three times in recent fires, we found significant differences in canopy base heights (increased), duff and litter depths (decreased), and percent cover of grass and forbs (increased), but not tree density, tree basal area, shrub height, shrub cover, or woody fuels. Combined effects of recent fires on overstory and understory structure resulted in a significant difference in likelihood of crown fire occurrence, declining from a mean of 58% in plots with no fire since 1879 to 13% in plots with three fires since 1988. Significant effects were generally seen after two or three fires, suggesting it is the reintroduction of the fire regime and not just individual fire events that restore resiliency. Overall, effects of recent fires are building on the latent resiliency of ponderosa pine forests at Zion National Park, although questions remain about extent and future dynamics of oak and manzanita shrubfields that occupy similar environmental settings, along with a general lack of ponderosa pine regeneration across all plots.

A key challenge to maintaining resilient landscapes is adapting to and maintaining dynamic ecological processes. In fire-dependent ecosystems, this includes identifying and defining mechanisms through which fire influences forest structure and functionality. Interpretations of tree patterns via land survey records in the Lake States have often highlighted the importance of infrequent moderate to extreme disturbance events. However, historical survey methods are limited to observing higher severity disturbances and over large landscapes, thus it is not clear if the origin, structure, and forcing factors for either patterns or processes are adequately quantified by these methods. We used dendrochronological methods to determine how fire history and stand structure, including cohort structure, tree density, and spatial patterning, are linked within Lake States mixed conifer forests in Wisconsin. We found relatively short mean fire return intervals (MFRIs) ranging from 6 to 13 yr with little variation in fire frequency among sites. Current densities of red-pine-dominated forests are 4-37 times historical (ca. 1860) densities (mean 12×) and almost entirely spatially random, whereas historically forests were spatially aggregated at stand scales. Stands also contained multiple and/or loosely defined cohort structures suggesting very different controls operating historically than currently. Heterogeneity that helped maintain ecosystem resilience in these ecosystems historically came from frequent fire disturbance processes that affected stand-scale forest resistance. This was likely the historical dynamic across fire-adapted transitional pine forests of the Lake States.

In response to large, severe wildfires in historically fire-adapted forests in the western US, policy initiatives, such as the USDA Forest Service's Collaborative Forest Landscape Restoration Program (CFLRP), seek to increase the pace and scale of ecological restoration. One required component of this program is collaborative adaptive management, in which monitoring data are used to iteratively evaluate and improve future management actions. Here, we assess the success of seven CFLRP treatments, implemented on 2,300 ha during the first three years of the Colorado Front Range Landscape Restoration Initiative (LAI) at achieving desired forest structure by comparing pre- and post-treatment conditions. We also compare post-treatment conditions with reconstructions of historical (ca. 1860) forest conditions to contextualize the magnitude of treatment effects. Restoration projects moved stands toward desired conditions by reducing basal area, tree density, and canopy cover and increasing average tree diameter, large gap cover, and abundance of small- to medium-sized tree groups. Post-treatment stands were similar to historical stands with respect to basal area of ponderosa pine; however, they had higher total tree density and fewer gaps than historical reference conditions, suggesting that restoration prescriptions may be improved with increased flexibility for density reduction of Douglas-fir and increased gap creation. This examination of early CFLRP treatment outcomes as they relate to desired conditions informs potential areas of adjustments to future treatments and provides baseline data to evaluate the evolution of treatments over the program's lifespan. We also identify and discuss several scientific, social, and logistical constraints to large-scale restoration success and make several recommendations to improve restoration outcomes.

There is no sign of saturation in accumulation of alien species (AS) introductions worldwide, additionally the rate of spread for some species has also been shown to be increasing. However, the challenges of gathering information on AS are recognized. Recent developments in citizen science (CS) provide an opportunity to improve data flow and knowledge on AS while ensuring effective and high quality societal engagement with the issue of IAS (Invasive Alien Species). Advances in technology, particularly on-line recording and smartphone apps, along with the development of social media, have revolutionized CS and increased connectivity while new and innovative analysis techniques are emerging to ensure appropriate management, visualization, interpretation and use and sharing of the data. In early July 2018 we launched a European CO-operation in Science and Technology (COST) Action to address multidisciplinary research questions in relation to developing and implementing CS, advancing scientific understanding of AS dynamics while informing decision-making specifically implementation of technical requirements of relevant legislation such as the EU Regulation 1143/2014 on IAS. It will also support the EU biodiversity goals and embedding science within society. The Action will explore and document approaches to establishing a European-wide CS AS network. It will embrace relevant innovations for data gathering and reporting to support the implementation of monitoring and surveillance measures, while ensuring benefits for society and citizens, through an AS CS European network. The Action will, therefore, increase levels of participation and quality of engagement with current CS initiatives, ensuring and evaluating educational value, and improve the value outcomes for potential users including citizens, scientists, alien species managers, policy-makers, local authorities, industry and other stakeholders.

Management practices since the late 19th century, including fire exclusion and harvesting, have altered the structure of ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) dominated forests across the western United States. These structural changes have the potential to contribute to uncharacteristic wildfire behavior and effects. Locally-relevant information on historical forest structure can improve efforts to restore more fire adapted conditions. We used a dendrochronological approach to reconstruct pre-settlement era (ca. 1860) structure for 170, 0.5-ha plots in montane ponderosa pine-dominated forests of the Colorado and Wyoming Front Range. Historical reconstructions were quantitatively compared with current conditions to highlight key departures. In lower montane forests, historical basal area averaged 6.3 m(2) ha(-1), density averaged 97 trees ha(-1), and quadratic mean diameter (QMD) averaged 26.5 cm, while current basal area averaged 17.6 m(2) ha(-1), density averaged 438 trees ha(-1), and QMD averaged 24.3 cm. Similar trends were observed in upper montane forests, where historical basal area averaged 9.5 m(2) ha(-1), historical density averaged 163 trees ha(-1), and historical QMD averaged 29.4 cm, while current basal area averaged 17.2 m(2) ha(-1), current density averaged 389 trees ha(-1), and current QMD averaged 25.2 cm. Most differences between historical and current conditions were significant. Across the montane zone, ponderosa pine dominated historical (88% and 83% of basal area in the lower and upper montane, respectively) and current forests (80% and 74% of basal area, respectively), but pine dominance decreased primarily due to infilling of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Much of this establishment occurred around the period of settlement (1861-1920) and continued throughout the 20th century. Results from this study help inform ecological restoration efforts that seek to integrate elements of historical forest structure and aim to increase the resilience of Front Range ponderosa pine forests to future wildfires and a warmer climate.

Dendroecology is the science that dates tree rings to their exact calendar year of formation to study processes that influence forest ecology (e.g., Speer 2010 [1], Amoroso et al., 2017 [2]) [...]

Wildfires have become larger and more severe over the past several decades on Colorado's Front Range, catalyzing greater investments in forest management intended to mitigate wildfire risks. The complex ecological, social, and political context of the Front Range, however, makes forest management challenging, especially where multiple management goals including forest restoration exist. In this report, we present a science-based framework for managers to develop place-based approaches to forest restoration of Front Range ponderosa pine and dry mixed-conifer forests. We first present ecological information describing how Front Range forest structure and composition are shaped at multiple scales by interactions among topography, natural disturbances such as fire, and forest developmental processes. This information serves as a foundation for identifying priority areas for treatment and designing restoration projects across scales. Treatment guidelines generally reduce forest densities and surface and crown fuels, enhance spatial heterogeneity across scales, and retain drought- and fire-tolerant species, old trees, and structures important for wildlife. Implementation of these guidelines is expected to enhance forest resilience to disturbance and climate change, as well as sustain important ecosystem services. Finally, this report emphasizes the importance of adaptive management and learning through monitoring and experimentation to address uncertainties inherent in the restoration process.