Fire as a fundamental ecological process: Research advances and frontiers

© 2020 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire-dependent ecosystems. As an ecological process, fire integrates complex feedbacks among biological, social and geophysical processes, requiring coordination across several fields and scales of study. Here, we describe the diversity of ways in which fire operates as a fundamental ecological and evolutionary process on Earth. We explore research priorities in six categories of fire ecology: (a) characteristics of fire regimes, (b) changing fire regimes, (c) fire effects on above-ground ecology, (d) fire effects on below-ground ecology, (e) fire behaviour and (f) fire ecology modelling. We identify three emergent themes: the need to study fire across temporal scales, to assess the mechanisms underlying a variety of ecological feedbacks involving fire and to improve representation of fire in a range of modelling contexts. Synthesis: As fire regimes and our relationships with fire continue to change, prioritizing these research areas will facilitate understanding of the ecological causes and consequences of future fires and rethinking fire management alternatives

Fire as a fundamental ecological process: Research advances and frontiers

© 2020 The Authors.Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire‐dependent ecosystems. As an ecological process, fire integrates complex feedbacks among biological, social and geophysical processes, requiring coordination across several fields and scales of study. Here, we describe the diversity of ways in which fire operates as a fundamental ecological and evolutionary process on Earth. We explore research priorities in six categories of fire ecology: (a) characteristics of fire regimes, (b) changing fire regimes, (c) fire effects on above‐ground ecology, (d) fire effects on below‐ground ecology, (e) fire behaviour and (f) fire ecology modelling. We identify three emergent themes: the need to study fire across temporal scales, to assess the mechanisms underlying a variety of ecological feedbacks involving fire and to improve representation of fire in a range of modelling contexts. Synthesis: As fire regimes and our relationships with fire continue to change, prioritizing these research areas will facilitate understanding of the ecological causes and consequences of future fires and rethinking fire management alternatives.Support was provided by NSF‐DEB‐1743681 to K.K.M. and A.J.T. We thank Shalin Hai‐Jew for helpful discussion of the survey and qualitative methods.Peer reviewe

Overview of the history of ozone exposure and the experimental designs.

<p>Starting from a four-year exposure of a weed community under three ozone selection treatments (0, 90 and 120 ppb) [8]; the subsequent sowing of the soil seed bank samples, coming from each ozone selection treatment replication, in nine plots; the <i>Germination </i><i>experiments</i> (Seed germination and Seed dormancy experiments) carried out with <i>S. arvensis</i> seeds harvested from the plots; and the <i>Soil </i><i>seed </i><i>bank </i><i>experiment</i> developed with seeds harvested from plants exposed to ambient and added ozone (control and added ozone treatment respectively; maternal ozone treatments).</p

Germination (%) of <i>Spergula</i><i>arvensis</i> seeds for each ozone selection treatment

<p><b>, storage condition and incubation temperature</b>. White, grey and black bars represent germination of seeds (n = 3, ± SE) for 0, 90 and 120 ppb ozone selection treatment, respectively, after being exposed for 22 days to storage conditions combining two temperatures (panels A, B and C: 5 °C, and panels D, E and F: 25 °C) and three relative humidity regimes (panels A and D: 5% RH; panels B and E: 75% RH; panels C and F: 11 days at 75% and 11 days at 5% RH) and incubation temperatures (10, 15 and 15/25 °C). Above each plot, <i>P-values</i> indicate the effects of Incubation Temperature (Temp.), Ozone selection treatment (Ozone) and the interaction (Temp. xOzone) within each storage condition.</p

Germination (%) of <i>Spergula</i><i>arvensis</i> seeds for each ozone selection treatment, pre-treatment and incubation temperature.

<p>White, grey and black bars represent germination of seeds (n = 3, ± SE) for 0, 90 and 120 ppb ozone selection treatment, respectively, after 22 days of exposure to pre-treatments: storage at 10 °C and dry condition (control) (A), storage at 5 °C and 75% RH followed by scarification (B), and storage at 25 °C and 75% followed by scarification (C); and then incubated at 10, 15 and 15/25 °C. Above each plot, <i>P-values</i> indicate the effects of Incubation Temperature (Temp.), Ozone selection treatment (Ozone) and the interaction (Temp. xOzone) within each Pre-treatment.</p

Legacy of historic ozone exposure on plant community and food web structure.

Information on whole community responses is needed to predict direction and magnitude of changes in plant and animal abundance under global changes. This study quantifies the effect of past ozone exposure on a weed community structure and arthropod colonization. We used the soil seed bank resulting from a long-term ozone exposure to reestablish the plant community under a new low-pollution environment. Two separate experiments using the same original soil seed bank were conducted. Plant and arthropod richness and species abundance was assessed during two years. We predicted that exposure to episodic high concentrations of ozone during a series of growing cycles would result in plant assemblies with lower diversity (lower species richness and higher dominance), due to an increase in dominance of the stress tolerant species and the elimination of the ozone-sensitive species. As a consequence, arthropod-plant interactions would also be changed. Species richness of the recruited plant communities from different exposure histories was similar (≈ 15). However, the relative abundance of the dominant species varied according to history of exposure, with two annual species dominating ozone enriched plots (90 ppb: Spergula arvensis, and 120 ppb: Calandrinia ciliata). Being consistent both years, the proportion of carnivore species was significantly higher in plots with history of higher ozone concentration (≈3.4 and ≈7.7 fold higher in 90 ppb and 120 ppb plots, respectively). Our study provides evidence that, past history of pollution might be as relevant as management practices in structuring agroecosystems, since we show that an increase in tropospheric ozone may influence biotic communities even years after the exposure

Pine Plantations and Invasion Alter Fuel Structure and Potential Fire Behavior in a Patagonian Forest-Steppe Ecotone

Planted and invading non-native plant species can alter fire regimes through changes in fuel loads and in the structure and continuity of fuels, potentially modifying the flammability of native plant communities. Such changes are not easily predicted and deserve system-specific studies. In several regions of the southern hemisphere, exotic pines have been extensively planted in native treeless areas for forestry purposes and have subsequently invaded the native environments. However, studies evaluating alterations in flammability caused by pines in Patagonia are scarce. In the forest-steppe ecotone of northwestern Patagonia, we evaluated fine fuels structure and simulated fire behavior in the native shrubby steppe, pine plantations, pine invasions, and mechanically removed invasions to establish the relative ecological vulnerability of these forestry and invasion scenarios to fire. We found that pine plantations and their subsequent invasion in the Patagonian shrubby steppe produced sharp changes in fine fuel amount and its vertical and horizontal continuity. These changes in fuel properties have the potential to affect fire behavior, increasing fire intensity by almost 30 times. Pruning of basal branches in plantations may substantially reduce fire hazard by lowering the probability of fire crowning, and mechanical removal of invasion seems effective in restoring original fuel structure in the native community. The current expansion of pine plantations and subsequent invasions acting synergistically with climate warming and increased human ignitions warrant a highly vulnerable landscape in the near future for northwestern Patagonia if no management actions are undertaken

Community structure of the experimental plots during ozone exposure at 0, 90 and 120 ppb and after transplanting under common ecological conditions.

<p>Community structure of the experimental plots during ozone exposure at 0, 90 and 120 ppb and after transplanting under common ecological conditions.</p

Relative abundance of <i>Spergula arvensis</i>, <i>Calandrinia ciliata</i> and other species in plant communities selected under different episodic concentrations of tropospheric ozone.

<p>Ozone concentrations in the open top chambers during long-term exposure were 0 ppb (white bars), 90 ppb (grey bars) and 120 ppb (dark bars). Data represents species abundances during the first (a) and second (b) year of experiment after original soil seed bank was transplanted to a common natural field environment. Relative abundance for each plant species was calculated as the summed abundances of each plant species for a particular year/total number of seedlings recorded in the plot (n = 3). Error bars represent standard error. Year a ANOVA <i>P</i> _species < 0.01, <i>P</i>_ozone 0.016, <i>P</i>_{species x ozone} 0.034; year b ANOVA <i>P</i> _species < 0.01, <i>P</i>_ozone 0.024, <i>P</i>_{species x ozone} 0.042</p

Means and statistics from analysis of variance of species richness (<i>S</i>), species diversity (Shannon-Weaver index, H´) and species evenness (<i>H</i>´/log_e (<i>S</i>)) for arthropod communities established from different historic exposure regimens.

<p>Means and statistics from analysis of variance of species richness (<i>S</i>), species diversity (Shannon-Weaver index, H´) and species evenness (<i>H</i>´/log_e (<i>S</i>)) for arthropod communities established from different historic exposure regimens.</p