The human dimension of fire regimes on Earth

Humans and their ancestors are unique in being a fire-making species, but 'natural' (i.e. independent of humans) fires have an ancient, geological history on Earth. Natural fires have influenced biological evolution and global biogeochemical cycles, making fire integral to the functioning of some biomes. Globally, debate rages about the impact on ecosystems of prehistoric human-set fires, with views ranging from catastrophic to negligible. Understanding of the diversity of human fire regimes on Earth in the past, present and future remains rudimentary. It remains uncertain how humans have caused a departure from 'natural' background levels that vary with climate change. Available evidence shows that modern humans can increase or decrease background levels of natural fire activity by clearing forests, promoting grazing, dispersing plants, altering ignition patterns and actively suppressing fires, thereby causing substantial ecosystem changes and loss of biodiversity. Some of these contemporary fire regimes cause substantial economic disruptions owing to the destruction of infrastructure, degradation of ecosystem services, loss of life, and smoke-related health effects. These episodic disasters help frame negative public attitudes towards landscape fires, despite the need for burning to sustain some ecosystems. Greenhouse gas-induced warming and changes in the hydrological cycle may increase the occurrence of large, severe fires, with potentially significant feedbacks to the Earth system. Improved understanding of human fire regimes demands: (1) better data on past and current human influences on fire regimes to enable global comparative analyses, (2) a greater understanding of different cultural traditions of landscape burning and their positive and negative social, economic and ecological effects, and (3) more realistic representations of anthropogenic fire in global vegetation and climate change models. We provide an historical framework to promote understanding of the development and diversification of fire regimes, covering the pre-human period, human domestication of fire, and the subsequent transition from subsistence agriculture to industrial economies. All of these phases still occur on Earth, providing opportunities for comparative research.     

A biogeographic model of fire regimes in Australia: current and future implications

Aim Patterns of fire regimes across Australia exhibit biogeographic variation in response to four processes. Variations in area burned and fire frequency result from differences in the rates of ‘switching’ of biomass growth, availability to burn, fire weather and ignition. Therefore differing processes limit fire (i.e. the lowest rate of switching) in differing ecosystems. Current and future trends in fire frequency were explored on this basis. Location Case studies of forests (cool temperate to tropical) and woodlands (temperate to arid) were examined. These represent a broad range of Australian biomes and current fire regimes. Methods Information on the four processes was applied to each case study and the potential minimum length of interfire interval was predicted and compared to current trends. The potential effects of global change on the processes were then assessed and future trends in fire regimes were predicted. Results Variations in fire regimes are primarily related to fluctuations in available moisture and dominance by either woody or herbaceous plant cover. Fire in woodland communities (dry climates) is limited by growth of herbaceous fuels (biomass), whereas in forests (wet climates) limitation is by fuel moisture (availability to burn) and fire weather. Increasing dryness in woodland communities will decrease potential fire frequency, while the opposite applies in forests. In the tropics, both forms of limitation are weak due to the annual wet/dry climate. Future change may therefore be constrained. Main conclusions Increasing dryness may diminish fire activity over much of Australia (dominance of dry woodlands), though increases may occur in temperate forests. Elevated CO₂ effects may confound or reinforce these trends. The prognosis for the future fire regime in Australia is therefore uncertain.     

Global characterization of fire activity: toward defining fire regimes from Earth observation data

There is interest in the global community on how fire regimes are changing as a function of changing demographics and climate. The ground-based data to monitor such trends in fire activity are inadequate at the global scale. Satellite observations provide a basis for such a monitoring system. In this study, a set of metrics were developed from 6 years of MODIS active fire data. The metrics were grouped into eight classes representing three axes of fire activity: density, season duration and interannual variability. These groups were compared with biophysical and human explanatory variables on a global scale. We found that more than 30% of the land surface has a significant fire frequency. The most extensive fire class exhibited high fire density, low duration and high variability and was found in boreal and tropical wet and dry environments. A high association was found between population distribution and fire persistence. Low GDP km⁻² was associated with fire classes with high interannual variability and low seasonal duration. In areas with more economic resources, fires tend to be more regular and last longer. High fire duration and low interannual variability were associated with croplands, but often with low fire density. The study was constrained by the limited length of satellite data record but is a first step toward developing a comprehensive global assessment of fire regimes. However, more attention is needed by the global observing systems to provide the underpinning socio-economic observations to better quantify and analyze the human characteristics of fire regimes.     

Emergent freeze and fire disturbance dynamics in temperate rainforests

The coastal temperate rainforests of South and North America are part of the most biomass dense forest biome on the planet. They are also subject to rapid climatic shifts and, subsequently, new disturbance processes – snow loss‐driven mortality and the emergence of fire in historically non‐fire‐exposed areas. Here, we compare and contrast Southern and Northern Hemisphere coastal temperate rainforests of the Americas, two of the largest examples of the biome, via synthesis of current literature, future climate expectations and new downscaling of a global fire model. In terms of snow loss, a rapid decline in winter snow is leading to mass mortality of certain conifer species in the Northern Hemisphere rainforests. High‐elevation Southern Hemisphere forests, which are beginning to see similar declines in snow, may be vulnerable in the future, especially bogs and high‐water content soils. Southern Hemisphere forests are seeing the invasion of fire as an ecological force at mid‐to‐high latitudes, a shift not yet observed in the north but which may become more prominent with ongoing climate change. We suggest that research should focus on the flammability of seral vegetation and bogs under future climate scenarios in both regions. By comparing these two drivers of change across similar gradients in the Northern and Southern Hemispheres, this work points to the potential for emerging change in unexpected places in both regions. There is a clear benefit to conceptualising the coastal temperate rainforests of the Americas as two examples of the biome which can inform the other, as change is proceeding in similar directions but at different rates in each region.     

Moving from autonomous to planned adaptation in the montane forests of southeastern Australia under changing fire regimes

Forest ecosystems and their associated natural, cultural and economic values are highly vulnerable to climate driven changes in fire regimes. A detailed knowledge of forest ecosystem responses to altered fire regimes is a necessary underpinning to inform options for adaptive responses under climate change, as well as for providing a basis for understanding how patterns of distribution of vegetation communities that comprise montane forest ecosystems may change in the future. Unplanned consequential adaptation of both natural and human systems, i.e. autonomous adaptation, will occur without planned intervention, with potentially negative impacts on ecosystem services. The persistence of forest stands under changing fire regimes and the maintenance of the ecosystem services that they provide pivot upon underlying response traits, such as the ability to resprout, that determine the degree to which composition, structure and function are likely to change. The integration of ecosystem dynamics into conceptual models and their use in exploring adaptation pathways provides options for policy makers and managers to move from autonomous to planned adaptation responses. Understanding where autonomous adaptation provides a benefit and where it proves potentially undesirable is essential to inform adaptation choices. Plausible scenarios of ecological change can be developed to improve an understanding of the nature and timing of interventions and their consequences, well before natural and human systems autonomously adapt in ways that may be detrimental to the long‐term provision of ecosystem services. We explore the utility of this approach using examples from temperate montane forest ecosystems of southeastern Australia.     

Simulating climate change impacts on fire frequency and vegetation dynamics in a Mediterranean-type ecosystem

The impacts of climate change on Mediterranean‐type ecosystems may result from complex interactions between direct effects on water stress and subsequent modifications in flammability and fire regime leading to changes in standing biomass and plant species composition. We analysed these interrelations through a simulation approach combining scenarios of climate change developed from GCM results and a multispecies functional model for vegetation dynamics, SIERRA. A fire risk procedure based on weekly estimates of vegetation water stress has been implemented. Using climate data from 1960 to 1997, simulations of a typical maquis woodland community have been performed as baseline and compared with two climate scenarios: a change in the rainfall regime alone, and changes in both rainfall and air temperature. Climate changes are defined by an increase in temperature, particularly in summer, and a change in the rainfall pattern leading to a decrease in low rainfall events, and an increase in intense rainfall events. The results illustrate the lack of drastic changes in the succession process, but highlight modifications in the water budget and in the length of the drought periods. Water stress lower than expected regarding statistics on the current climate is simulated, emphasizing a long‐term new equilibrium of vegetation to summer drought but with a higher sensibility to rare events. Regarding fire frequency, climate changes tend to decrease the time interval between two successive fires from 20 to 16 years for the maquis shrubland and from 72 to 62 years in the forested stages. This increase in fire frequency leads to shrub‐dominated landscapes, which accentuates the yield of water by additional deep drainage and runoff.     

Effects of plant traits on ecosystem and regional processes: a conceptual framework for predicting the consequences of global change

Human activities are causing widespread changes in the species composition of natural and managed ecosystems, but the consequences of these changes are poorly understood. This paper presents a conceptual framework for predicting the ecosystem and regional consequences of changes in plant species composition. Changes in species composition have greatest ecological effects when they modify the ecological factors that directly control (and respond to) ecosystem processes. These interactive controls include: functional types of organisms present in the ecosystem; soil resources used by organisms to grow and reproduce; modulators such as microclimate that influence the activity of organisms; disturbance regime; and human activities. Plant traits related to size and growth rate are particularly important because they determine the productive capacity of vegetation and the rates of decomposition and nitrogen mineralization. Because the same plant traits affect most key processes in the cycling of carbon and nutrients, changes in plant traits tend to affect most biogeochemical cycling processes in parallel. Plant traits also have landscape and regional effects through their effects on water and energy exchange and disturbance regime.     

Potentials and limitations for human control over historic fire regimes in the boreal forest

Fire, being both a natural and cultural phenomenon, presents problems in disentangling the historical effect of humans from that of climate change. Here, we investigate the potential impact of humans on boreal fire regimes from a perspective of fuels, ignitions and culture. Two ways for a low technology culture to impact the fire regime are as follows: (i) by altering the number of ignitions and their spatial distribution and timing and (ii) by hindering fire spread. Different cultures should be expected to have quite different impacts on the fire regimes. In northern Fennoscandia, there is evidence for fire regime changes associated with the following: a reindeer herding culture associated with few ignitions above the natural; an era of cattle husbandry with dramatically increased ignitions and somewhat higher fire frequency; and a timber exploitation era with decreasing fire sizes and diminishing fire frequency. In other regions of the boreal zone, such schemes can look quite different, but we suggest that a close look at the resource extraction and land use of different cultures should be part of any analysis of past fire regimes.     

A conceptual framework for understanding thermal constraints on ectotherm activity with implications for predicting responses to global change

Activity budgets influence the expression of life history traits as well as population dynamics. For ectotherms, a major constraint on activity is environmental temperature. Nonetheless, we currently lack a comprehensive conceptual framework for understanding thermal constraints on activity, which hinders our ability to rigorously apply activity data to answer ecological and evolutionary questions. Here, we integrate multiple aspects of temperature‐dependent activity into a single unified framework that has general applicability. We also provide examples of the implementation of this framework to address fundamental questions in ecology relating to climate change vulnerability and species’ distributions using empirical data from a tropical lizard.     

Convergence of bark investment according to fire and climate structures ecosystem vulnerability to future change

Fire regimes in savannas and forests are changing over much of the world. Anticipating the impact of these changes requires understanding how plants are adapted to fire. In this study, we test whether fire imposes a broad selective force on a key fire‐tolerance trait, bark thickness, across 572 tree species distributed worldwide. We show that investment in thick bark is a pervasive adaptation in frequently burned areas across savannas and forests in both temperate and tropical regions where surface fires occur. Geographic variability in bark thickness is largely explained by annual burned area and precipitation seasonality. Combining environmental and species distribution data allowed us to assess vulnerability to future climate and fire conditions: tropical rainforests are especially vulnerable, whereas seasonal forests and savannas are more robust. The strong link between fire and bark thickness provides an avenue for assessing the vulnerability of tree communities to fire and demands inclusion in global models.     

Climatic influences on fire regimes in the northern Sierra Nevada mountains, Lake Tahoe Basin, Nevada, USA

Aim The goal of this study was to understand better the role of interannual and interdecadal climatic variation on local pre‐EuroAmerican settlement fire regimes in fire‐prone Jeffrey pine (Pinus jeffreyi Grev. & Balf.) dominated forests in the northern Sierra Nevada Mountains. Location Our study was conducted in a 6000‐ha area of contiguous mixed Jeffrey pine‐white fir (Abies concolor Gordon & Glend.) forest on the western slope of the Carson Range on the eastern shore of Lake Tahoe, Nevada. Methods Pre‐EuroAmerican settlement fire regimes (i.e. frequency, return interval, extent, season) were reconstructed in eight contiguous watersheds for a 200‐year period (1650–1850) from fire scars preserved in the annual growth rings of nineteenth century cut stumps and recently dead pre‐settlement Jeffrey pine trees. Superposed epoch analysis (SEA) and correlation analysis were used to examine relationships between tree ring‐based reconstructions of the Palmer Drought Severity Index (PDSI), Southern Oscillation Index (SOI), Pacific Decadal Oscillation (PDO) and pre‐EuroAmerican fire regimes in order to assess the influence of drought and equatorial and north Pacific teleconnections on fire occurrence and fire extent. Results For the entire period of record (1650–1850), wet conditions were characteristic of years without fires. In contrast, fire years were associated with drought. Drought intensity also influenced fire extent and the most widespread fires occurred in the driest years. Years with widespread fires were also preceded by wet conditions 3 years before the fire. Widespread fires were also associated with phase changes of the PDO, with the most widespread burns occurring when the phase changed from warm (positive) to cold (negative) conditions. Annual SOI and fire frequency or extent were not associated in our study. At decadal time scales, burning was more widespread during decades that were dryer and characterized by La Niña and negative PDO conditions. Interannual and interdecadal fire–climate relationships were not stable over time. From 1700 to 1775 there was no interannual relationship between drought, PDO, and fire frequency or extent. However, from 1775 to 1850, widespread fires were associated with dry years preceded by wet years. This period also had the strongest association between fire extent and the PDO. In contrast, fire–climate associations at interdecadal time scales were stronger in the earlier period than in the later period. The change from strong interdecadal to strong interannual climate influence was associated with a breakdown in decadal scale constructive relationships between PDO and SOI. Main conclusions Climate strongly influenced pre‐settlement pine forest fire regimes in northern Sierra Nevada. Both interannual and interdecadal climatic variation regulated conditions conducive to fire activity, and longer term changes in fire frequency and extent correspond with climate‐mediated changes observed in both the northern and southern hemispheres. The sensitivity of fire regimes to shifts in modes of climatic variability suggests that climate was a key regulator of pine forest ecosystem structure and dynamics before EuroAmerican settlement. An understanding of pre‐EuroAmerican fire–climate relationships may provide useful insights into how fire activity in contemporary forests may respond to future climatic variation.     

Restoring ecosystem health and integrity during a human population increase to ten billion

Human population growth and the improving condition of human populations in developing countries affect ecological health and integrity. Agricultural development co-opts increasing amounts of global primary production, degrading lands, and reducing species richness. The development of human populations and associated increasing demands for energy assures disposal for increasing amounts of waste, further damaging local ecosystems. Global climate change resulting from diffuse pollutants will affect even the most pristine ecosystems. The human challenge is to maintain ecological integrity and restore ecosystems in the face of accelerating development. The present level of ecosystem protection in not sufficient. Only integrated means of assessing recovery potential and acting to restore ecological productivity can assure continued availability of ecosystem services ranging from free production of food and fiber by plants and animals to final waste assimilation. Restoring ecosystems presumes that species sources are available and that adequate management is in place to monitor and manage recovery. Today, even in the most advanced societies, management is fragmented by non-integrative thinking and the failure to realize that the human scale of political decision-making and management is inappropriate to assure ecosystem restoration. Only by adopting radically new ideas integrating management and ecosystem science can ecological integrity be maintained.     

A conceptual framework for ecosystem management based on tradeoff analysis

Three dimensions (natural, social and economic factors) in tradeoff analysis have not been focused in ecology. It is necessary to consider the multi-dimensions through a tradeoff analysis of disturbances to find their positive and negative effects (referred to as two-sidedness). We proposed an 11-step approach to integrate the concepts, methods and examples to understand ecological two-sidedness. We recommend that: (1) ecological complexity and large-scale systematic perspectives need to be integrated; (2) disparate disciplines should be integrated to classify the two-sidedness indicators; (3) models should be adopted to define the characteristic metrics of disturbed ecosystems; (4) researchers need to reconsider evaluation standards and for each indicator with marginal changes; and (5) initial decision-making should refer to the two-sidedness value and that final decision-making should be subject to debate. This approach has great significance for ecosystem management because decision-makers can obtain the superiority and inferiority of disturbance strategies and select optimal strategy.     

面向生态监管的多等级生态功能网格概念与框架

科学有效的生态监管是落实我国生态文明建设、保障区域生态安全、实现城市可持续发展的必要途径和重要抓手。生态系统的监管涉及到社会、经济、自然等多个维度,水、土、气、生等多类要素,国家到局地等多个尺度。目前,已有生态监管常存在生态系统、生态要素、行政单元的割裂。如何整体考虑以上特征,开展科学的、系统的、空间显性的生态监管亟需理论技术的创新。通过整合等级斑块动态范式、复合生态系统理论、多功能景观理论,构建了多等级生态功能网格框架,以期为生态监管提供一个综合的概念与技术框架。等级斑块动态范式从等级作用的角度构建了多等级网格骨架,复合生态系统理论从多个维度丰富了多等级网格内涵,多功能景观理论明确了网格的功能。通过耦合多等级生态功能网格的划分、评价和监管,可实现系统、整体、差异化的生态监管,为生态文明建设提供有力支撑。     

气候变化影响与风险研究的理论范式和方法体系

以全球变暖为主的气候变化将会在本世纪持续,针对气候变化影响与风险而采取适应和减缓措施,得到了国际社会的广泛认同。然而,气候变化影响与风险研究领域理论和方法并不规范,研究结果缺乏可比性。基于科学哲学家库恩提出的理论范式和构造范式概念,梳理、集成气候变化影响与风险研究的"脆弱性-要素分离-不确定性-风险"理论框架,总结相应的方法体系包括实地观测与科学实验、数值模型和统计方法、风险定量化评估框架等。气候变化影响与风险研究应遵循理论范式"四要素"的逻辑关系,综合运用多种分析方法,力求相关研究的整体性和系统化,以利增强气候变化影响与风险研究的科学性及其成果的应用指导意义。     

Endemic species and ecosystem sensitivity to climate change in Namibia

We present a first assessment of the potential impacts of anthropogenic climate change on the endemic flora of Namibia, and on its vegetation structure and function, for a projected climate in ～2050 and ～2080. We used both niche‐based models (NBM) to evaluate the sensitivity of 159 endemic species to climate change (of an original 1020 plant species modeled) and a dynamic global vegetation model (DGVM) to assess the impacts of climate change on vegetation structure and ecosystem functioning. Endemic species modeled by NBM are moderately sensitive to projected climate change. Fewer than 5% are predicted to experience complete range loss by 2080, although more than 47% of the species are expected to be vulnerable (range reduction >30%) by 2080 if they are assumed unable to migrate. Disaggregation of results by life‐form showed distinct patterns. Endemic species of perennial herb, geophyte and tree life‐formsare predicted to be negatively impacted in Namibia, whereas annual herb and succulent endemic species remain relatively stable by 2050 and 2080. Endemic annual herb species are even predicted to extend their range north‐eastward into the tree and shrub savanna with migration, and tolerance of novel substrates. The current protected area network is predicted to meet its mandate by protecting most of the current endemicity in Namibia into the future. Vegetation simulated by DGVM is projected to experience a reduction in cover, net primary productivity and leaf area index throughout much of the country by 2050, with important implications for the faunal component of Namibia's ecosystems, and the agricultural sector. The plant functional type (PFT) composition of the major biomes may be substantially affected by climate change and rising atmospheric CO₂– currently widespread deciduous broad leaved trees and C₄ PFTs decline, with the C₄ PFT particularly negatively affected by rising atmospheric CO₂ impacts by ～2080 and deciduous broad leaved trees more likely directly impacted by drying and warming. The C₃ PFT may increase in prominence in the northwestern quadrant of the country by ～2080 as CO₂ concentrations increase. These results suggest that substantial changes in species diversity, vegetation structure and ecosystem functioning can be expected in Namibia with anticipated climate change, although endemic plant richness may persist in the topographically diverse central escarpment region.