Recent Fires and Failed Strategies

Forest fires can change forest structure and composition, and low-density Airborne Laser Scanning (ALS) can be a valuable tool for evaluating post-fire vegetation response. The aim of this study is to analyze the structural diversity differences in Mediterranean Pinus halepensis Mill. forests affected by wildfires on different dates from 1986 to 2009. Several types of ALS metrics, such as the Light Detection and Ranging (LiDAR) Height Diversity Index (LHDI), the LiDAR Height Evenness Index (LHEI), and vertical and horizontal continuity of vegetation, as well as topographic metrics, were obtained in raster format from low point density data. In order to map burned and unburned areas, differentiate fire occurrence dates, and distinguish between old and more recent fires, a sample of pixels was previously selected to assess the existence of differences in forest structure using the Kruskal–Wallis test. Then, k-nearest neighbors algorithm (k-NN), support vector machine (SVM) and random forest (RF) classifiers were compared to select the most accurate technique. The results showed that, in more recent fires, around 70% of the laser returns came from grass and shrub layers, yielding low LHDI and LHEI values (0.37–0.65 and 0.28–0.46, respectively). In contrast, the areas burned more than 20 years ago had higher LHDI and LHEI values due to the growth of the shrub and tree strata. The classification of burned and unburned areas yielded an overall accuracy of 89.64% using the RF method. SVM was the best classifier for identifying the structural differences between fires occurring on different dates, with an overall accuracy of 68.79%. Furthermore, SVM yielded an overall accuracy of 75.49% for the classification between old and more recent fires.

Chapter 12 - Statistical Inference for Historical Fire Frequency Using the Spatial Mosaic

Empirical models for predicting volumes of sediment deposited by debris flows and sediment-laden floods in the transverse ranges of southern California

Questions: Did fire regimes in old-growth Pinus ponderosa forest change with Euro-American settlement compared to the pre-settlement period? Do tree age structures exhibit a pattern of continuous regeneration or is regeneration episodic and related to fire disturbance or fire-free periods? Are the forests compositionally stable? Do trees have a clumped spatial pattern and are clumps even- or mixed-age? How might information from this old-growth forest inform current restoration and management practices? Location: A 235-ha old-growth forest in the Ishi Wilderness, southern Cascade Mountains, California. Methods: Age, size, and spatial pattern of trees were quantified in seven stands. Fire history was reconstructed using fire scar dendrochronology. The influence of fire on stand structure was assessed by comparing fire history with age, size, and spatial structure of trees and identifying and measuring trees killed by two recent fires. Results: Species composition in plots was similar but density and basal area of tree populations varied. Age structure for P. ponderosa and Quercus kelloggii showed periods of episodic recruitment that varied among plots. Fire disturbance was frequent before 1905, with a median period between fires of 12 years. Fire frequency declined after 1905 but two recent fires (1990, 1994) killed 36% and 41% of mostly smaller diameter P. ponderosa and Q. kelloggii. Clusters of similar age trees occurred at scales of 28-1018 m2 but patches were not even-aged. Interactions between tree regeneration and fire promoted development of uneven age groups of trees. Conclusions: Fire disturbance strongly influenced density, basal area, and spatial structure of tree populations. Fire exclusion over the last 100 years has caused compositional and structural changes. Two recent fires, however, thinned stands and created gaps favorable for Q. kelloggii and P. ponderosa regeneration. The effects of infrequent 20th century fire indicate that a low fire frequency can restore and sustain structural characteristics resembling those of the pre-fire suppression period forest.

FireWatch: Creative Responses to Bushfire Catastrophes

Fire disturbances are becoming more common, more intense, and further-reaching across the globe, with consequences for ecosystem functioning. Importantly, fire can have strong effects on the soil microbiome, including community and functional changes after fire, but surprisingly little is known regarding the role of soil fire legacy in shaping responses to recent fire. To address this gap, we conducted a manipulative field experiment administering fire across 32 soils with varying fire legacies, including combinations of 1-7 historic fires and 1-33 years since most recent fire. We analyzed soil metatranscriptomes, determining for the first time how fire and fire legacy interactively affect metabolically-active soil taxa, the microbial regulation of important carbon (C), nitrogen (N) and phosphorus (P) cycling, expression of carbohydrate-cycling enzyme pathways, and functional gene co-expression networks. Experimental fire strongly downregulated fungal activity while upregulating many bacterial and archaeal phyla. Further, fire decreased soil capacity for microbial C and N cycling and P transport, and drastically rewired functional gene co-expression. Perhaps most importantly, we highlight a novel role of soil fire legacy in regulation of microbial C, N, and P responses to recent fire. We observed a greater number of functional genes responsive to the interactive effects of fire and fire legacy than those affected solely by recent fire, indicating that many functional genes respond to fire only under certain fire legacy contexts. Therefore, without incorporating fire legacy of soils, studies will miss important ways that fire shapes microbial roles in ecosystem functioning. Finally, we showed that fire caused significant downregulation of carbon metabolism and nutrient cycling genes in microbiomes under abnormal soil fire histories, producing a novel warning for the future: human manipulation of fire legacies, either indirectly through global change-induced fire intensification or directly through fire suppression, can negatively impact soil microbiome functional responses to new fires.

Devastating wildfires have occurred around the world in recent years. While fire has always been part of the landscape, the trend toward increasingly widespread and severe wildfires is a key sentinel of the rapidly intensifying risks caused by global warming and climate change. Using atmospheric observations and climate model simulations, Zhuang et al. (1) quantify the relative contributions of natural climate variability and anthropogenic climate forcing to the increasing area burned in the western United States. They find that atmospheric variability can explain at most approximately one-third of the historical trend in atmospheric aridity that is conducive to wildfire. By contrast, global warming has contributed at least two-thirds of the rising trend in atmospheric aridity. Understanding the causes of increasing wildfire risk is a critical scientific and societal challenge. First and foremost, the rapidly increasing size and intensity of wildfires is having severe impacts. In California, the eight largest wildfires in recorded history have occurred in the past 5 y, and 9 of the 17 largest have occurred in the past 2 y (including the two largest and six of the top seven). Recent fires have had widespread impacts on people and ecosystems. Just in California alone these impacts include dozens of lives lost and tens of thousands of homes destroyed, leading to extended displacement of individuals, families, and communities. In addition, the massive plumes of smoke that have blanketed much of the western United States have impacted millions of people and have accounted for up to half of fine particulate matter pollution in some areas of the region (2). Recent fires have also exceeded the intensity to which fire-adapted vegetation is accustomed, posing risks to ecosystems and individual species such as California’s giant sequoias (e.g., ref. 3). While California’s fires have received much public attention, similar challenges are playing … [↵][1]1To whom correspondence may be addressed. Email: diffenbaugh{at}stanford.edu. [1]: #xref-corresp-1-1

Taiwan’s government has ordered Formosa Plastics Group to shut down much of its Mailiao petrochemical complex in phases and to conduct thorough safety inspections. The order follows the latest of seven fires that have plagued the facility over the past year. Taking responsibility for all the accidents, three senior executives of Formosa Petrochemical, including its chairman and its president, have resigned. A core company in the Formosa group, Formosa Petrochemical is the largest operator of facilities at the giant Mailiao site. Worth more than $10 billion, Mailiao came on-line in 1998 after Formosa fought the government and nearby residents for 13 years over environmental concerns. Relations between the Formosa group and residents living near its facilities have historically been poor. After the most recent fire, local residents of Yunlin County, where Mailiao is located, demanded a complete halt to operations at the complex. Formosa says it does not know what caused the most recent fire, ...

BackgroundDysregulated microRNA (miRNA) expression could provide a mechanism linking firefighter exposure to increased cancer risk.ObjectiveTo determine if changes in longitudinal miRNA expression in firefighters are associated with occupational exposures.MethodsWhole blood MiRNA was evaluated in 52 new recruits prior to live-fire training and 20–37 months later. Linear mixed effects models adjusted for age, ethnicity, BMI, and batch effects were used to determine associations separately for all fires and structure fires only between employment duration, cumulative fire-hours and fire-runs, and time since most recent fire with (1) nine a priori and (2) the full array of 799 miRNAs.ResultsFor multivariable models including all fires, two a priori miRNAs were associated with employment duration and four with time since most recent fire. For multivariable models restricted to structure fires, three a priori miRNAs were associated with employment duration and one with fire-runs. Additional miRNAs from the full array were associated with employment duration for all fires and/or structure fires. In general, tumor suppressive miRNAs decreased and oncogenic miRNAs increased with exposure.SignificanceChanges in miRNAs may serve as biomarkers of exposure effects and a mechanism for increased cancer risk in firefighters.

Historical and current fire regimes in ponderosa pine forests at Zion National Park, Utah: Restoration of pattern and process after a century of fire exclusion

Fire frequency is the number of fires experienced by a particular community within a given time period. This concept can potentially be resolved into a number of interacting variables, including: time since the most recent fire, the length of the inter‐fire intervals, and the variability of the length of the inter‐fire intervals. We estimated the effects of these three variables on the floristic composition of 65 samples from dry sclerophyll vegetation with different fire histories in Brisbane Water, Ku‐ring‐gai Chase and Royal National Parks near Sydney.Our analyses suggest that fire frequency may account for about 60% of the floristic variation among our samples. They confirm the hypothesis that the recent (<30 years) fire frequency produces effects on floristic composition of fire‐prone communities that can recognizably be attributed both to the time since the most recent fire and to the length of the intervals between fires. These effects are equal in magnitude but are different in the nature of the floristic variation they are associated with. Increasing time‐since‐fire is associated with a decline in the evenness of fire‐tolerant species, indicating that fewer of these species come to dominate the community in the prolonged absence of fire. Herbs and small shrubs decrease in abundance, while larger shrubs increase in abundance. Inter‐fire intervals of decreasing length are associated with a decrease in the evenness of the fire‐sensitive species, particularly those large Proteaceae shrubs that often dominate the community biomass in dry sclerophyll shrublands of southeastern Australia.Furthermore, the variation associated with inter‐fire intervals is not necessarily solely related to the shortest inter‐fire interval, but is related to combinations of inter‐fire intervals through time. Thus, increasing variability of the length of the inter‐fire intervals is associated with an increase in the species richness of both fire‐sensitive and fire‐tolerant species, implying that it may be variation of the inter‐fire intervals through time that is primarily responsible for maintaining the presence of a wide variety of plant species in a particular community. Our results also suggest that the floristic variation associated with different inter‐fire intervals decreases with increasing time‐since‐fire.

Fire severity, size, and climate associations diverge from historical precedent along an ecological gradient in the Pinaleño Mountains, Arizona, USA

Several Melaleuca (Myrtaceae) species are invasive globally. Recently an increase in invasive species from this genus have been reported in South Africa. Here we document the first detailed assessment of the distribution and invasive potential of Melaleuca rugulosa in South Africa. We assess population structure, determine the current and potential future distribution in South Africa using climatic variables, conduct a risk analysis, provide recommendations for management, and consider the feasibility of eradication. We found one naturalising population of ∼665 individuals covering more than 1.2 hectares. It was first recorded in 1961 invading the native fynbos vegetation in the Table Mountain National Park (TMNP). Two recent fires – in 2009 and 2016 – likely enhanced spread, this spread happened despite undocumented clearing attempts in the last decade. The south-western Cape is the most climatically suitable for M. rugulosa, with most other wetter areas of the country being only partly suitable regions. The risk analysis indicated a medium risk, and we suggest listing M. rugulosa as category 1a (eradication target) under the South African National Environmental Management: Biodiversity Act (10/ 2004). Given the small area occupied, ease of access and the lack of a soil seed bank, the population can be extirpated from Devil's Peak within the TMNP. We highlight that serotinous alien species, particular from the Myrtaceae, should receive more attention as potential invasive species in fire-driven ecosystems and that their lack of invasiveness in areas where fire is suppressed, should not be misinterpreted as being a low-risk species.

Savannas are among the most unknown biomes concerning the plant below-ground system. Root biomass might be influenced by the availability of limiting resources and by the type and intensity of disturbances, mediated by the plant functional attributes related to environmental conditions. Fine and coarse roots should be affected differently: the former should be more responsive to resource supplies, whilst the latter should be related to changes in disturbance frequency. We studied the roles of soil fertility, topography of the plots indicating water availability, fire frequency and plant resistance to fire in affecting fine and coarse root biomass. We sampled the root biomass, environmental variables and functional attributes of all individuals present in 100 plots in savanna physiognomies of cerrado, in central Brazil. We used structural equation modelling to test our hypothesis and found that shallow root biomass, from 0 to 20 cm deep, was not caused by resource availability, by disturbances, as fire or drought, or by functional attributes. Biotic interactions were not considered in our study, but they may have a central role in affecting the shallow root biomass. In the deep layer, from 20 to 100 cm deep, we identified soil fertility and recent fires as the main factors causing changes in fine and coarse root biomass in the cerrado, respectively. Low nutrient availability in the soil caused higher fine root biomass, increasing the uptake of resources, whereas recent fires led to less coarse root biomass below 20 cm deep, probably due to the higher dominance of the herbaceous layer in the plots, with less coarse root biomass. According to our expectation, fine roots were mostly affected by nutrient availability in the soil, whereas coarse roots were more related to disturbance, in our case, recent fires.

A bird’s eye view of ecosystem conversion: Examining the resilience of piñon-juniper woodlands and their avian communities in the face of fire regime change