变化环境下火干扰研究进展

火是地球系统的重要过程,也是一种剧烈的环境干扰因素。火是生态系统变化的驱动力和催化剂,调节着生态系统的结构和功能,同时反馈给气候系统。近年来,世界多个国家相继爆发了历史上罕见的极端火事件,使得火干扰、气候变化和人类活动之间的相互作用关系得到了空前的关注。主要从3个方面回顾了变化环境下火干扰研究的进展,包括(1)火干扰的时空格局;(2)火干扰的驱动机制;(3)火干扰的生态效应。概括起来,遥感技术的发展使得火监测精度不断提高,对火时空格局的刻画由过去侧重火燃烧面积单一因素转向具有多重属性的火干扰体系。气候变化和人类活动共同决定着火干扰的分布格局、频率和强度,考虑气候的季节性能够提高火干扰的预测能力。火干扰调节着生态系统的草木平衡,对于生物多样性和生境的维持非常重要。此外,火干扰通过生物质燃烧释放的大量温室气体影响大气组成和空气质量,同时通过改变地表状况和陆-气相互作用来影响气候系统。正确理解气候-植被-火之间的相互作用和反馈机制有助于未来火干扰体系的预测。随着高温、大风、干旱等极端气候事件增多,未来全球大部分区域火发生的风险增加,但是人类活动可能会使火和气候之间的关系发生解耦。可持续的火管...     

火对森林主要生态系统过程的影响

火及火生态学是当代生态系统生态学研究最为深入的领域之一.理解火生态效应及其基本原理,对降低野火灾害并适当利用火作为一种有效管理手段起着关键的作用.本文介绍了目前火对若干具倾火性的生态系统（尤其是位于北美的寒温带及温带森林生态系统）影响的研究进展,并着重论述了火作为一种主导性的力量在植被动态、养分循环、土壤及水分关系的紧密关联过程中所起的作用.火通过以下主要过程影响生态系统的组成、结构和功能,即选择性地保留和去除物种,释放贮于生物量中的养分且增进其循环,藉改变土壤微生物活动及水分关系等影响土壤性能,并形成异质的时空环境镶嵌格局,而这些变化反过来又进一步影响火行为及其生态效应.火作为一种毁灭性的力量能迅速消耗大量生物量,并导致继后的土壤侵蚀、水土流失和空气污染等负面影响;但火作为一种建设性力量,对维持一些对火有依赖性的生态系统的健康及持续具有极重要的作用.考虑到火在生态系统过程中的独特调节作用,火应被视为生态系统及其管理中有机组分之一.火对生态系统的影响取决于火情势（包括火发生的季节、规模大小、频率及强度等）、植被类型、气候条件、物理环境及评价所用的时空尺度.未来有必要加强有关火对一些特定生态系统的作用研究,尤其是基于长期试验性的监测和模型来研究火对生态系统时空变化的影响.     

黄土高原流域水沙变化研究进展

人类活动和气候变化是影响流域水文过程的两大驱动因素,径流输沙是流域水文过程的总体反映,变化环境下径流输沙的变化规律与成因分析是水文学和全球变化研究的热点问题。黄土高原是我国水土流失最严重的地区。20世纪50年代以来,黄土高原地区开展了大规模的生态环境建设和水土流失综合治理,显著改变了流域土地利用和植被覆盖。下垫面条件改变与气候变化综合作用,使得流域水沙情势发生剧变。围绕黄土高原流域水沙变化的时空尺度特征与驱动机制,总结了径流输沙和水沙关系变化特征的研究结果,归纳了径流输沙变化的归因分析方法与人类活动和气候变化影响的贡献分割结果,探讨了气候变化、植被恢复、水土保持工程措施以及流域景观格局对水沙变化的影响机制。未来应加强流域水沙演变的时空尺度特征特别是水沙关系非线性特征的定量研究,阐明极端事件对水沙动态的影响与贡献;开展水沙变化影响机制的多要素综合解析,发展耦合地表覆被动态特征和气候变化的降雨-径流-输沙模型,揭示生态恢复与水沙演变过程互馈机制;开展未来气候变化、社会经济发展和生态建设工程情景下水沙动态的趋势预测,为黄土高原生态综合治理和水资源管理与黄河水沙调控提供策略建议。     

西南生态安全格局形成机制及演变机理

我国西南地区地形地貌复杂,生态系统多样,生物多样性丰富,是研究地表复杂过程与生态系统演变规律的关键区域,也是我国重要的生态屏障区。但是同时该区域环境复杂、生态脆弱、灾害严重,在全球气候变化背景下,人类活动和经济发展导致该区域的生态环境问题比较突出,同时区域的社会经济发展地域分异大。突出表现在区域生态系统服务功能受损,区域生态安全水平降低。如何维护区域生态安全具有重要意义。针对生态安全问题,我国已开展生态区划、生态功能区划和生态红线等工作,但在生态安全格局的形成机制、与生态系统服务耦合关系、人类活动和气候变化对生态安全格局影响及其适应、区域社会经济可持续发展等方面需要加强深入研究,在我国西南地区的开展研究西南生态安全格局形成机制及演变机理具有典型性、代表性与紧迫性。     

青藏高原高寒生态区生态系统脆弱性时空变化及驱动机制分析

全球气候变化和人类活动胁迫下, 青藏高原高寒生态区的脆弱生态系统正在发生深刻变化。研究在充分考虑研究区生态环境本底特征(高寒、冻融侵蚀、盐渍化、水力侵蚀强烈)的基础上, 引入了极端气候事件因子(极端高温、极端低温、极端降水)和人类活动干扰因子构建了青藏高原高寒区生态系统脆弱性评价体系, 进而对研究区近13 年的生态系统脆弱性时空变化格局及其驱动机制进行了分析。研究结果表明: 青藏高原高寒生态区的生态系统脆弱性总体上属于中度脆弱状态, 其空间分布格局自东南向西北呈现递增趋势; 2000-2013 年, 青藏高原高寒生态区总体的生态系统脆弱性表现为先增加后减小的趋势; 生态系统脆弱性时空变化分异格局与地形、气候(气温、降水等)、人口密度存在显著地相关性。相关研究成果可以为青藏高原脆弱生态环境的保护和修复提供决策支持。     

森林流域生态水文过程动力学机制与模拟研究进展

水文过程是联系气候变化和森林生态系统时空变化的关键因素．未来的气候变化和人类大尺度活动将影响森林流域生态系统与水文过程的变化,森林流域生态与水文过程耦合、生态系统水文过程动力学机制研究在认识和调控生态资源及其合理利用、区域生态恢复,以及社会经济可持续方面均具有重要意义．森林流域生态系统中的水文过程可分为降雨截留、蒸散和产汇流过程．森林流域生态与水文耦合过程边界条件的确定,土壤表面特定水文过程的参数化,降雨、土壤水分运动和植被的动态耦合作用,分布式模型的应用以及森林生态水文过程动力学机制与调控等将是今后生态水文动力学过程研究的重点,综述了森林流域生态水文过程动力学机制与调控的研究进展。     

植被变化对气候的反馈机制及调节效应

植被通过光合作用固定大气中的CO₂来减缓温室效应，同时植被也通过改变地表能量收支影响温室效应。在过去的气候-植被研究中，大多关注气候变化对植被的影响，而植被对气候反馈的研究相对较少。植被通过调节地表能量收支、水通量等重要地气过程影响局地、区域乃至全球气候，在气候变化中的作用十分重要。因此，需要厘清植被对气候的反馈效应机制及其结果，并识别其地域差异。从生物地球物理和生物地球化学过程两方面分析植被与气候之间的作用机制，对全球及关键区域内植被变化对局地、区域乃至全球的气候反馈效应进行了系统总结：（1）生物地球物理反馈的区域特征明显，生物地球化学反馈则表现在全球尺度上，二者相互作用但难以统一；（2）植被破坏带来的气候影响在气温效应方面与生态系统的类型及地理分布相关：热带森林破坏带来增温效应，北方森林破坏带来降温效应，温带森林破坏则会通过增加森林反照率抵消丢失的固碳降温效应，气温效应表现不明显；（3）当前研究对关键过程机制考虑不够完善，不同研究方法的结果差异较大，且缺乏高质量观测数据的验证；同时考虑生物地球物理和生物地球化学的净气候反馈研究尚无法支撑植树造林对气候变化单一减缓作用的常规理解。本文可为科学评估植树造林对气候变化作用的方向与强度提供理论依据。     

气候变化背景下定量解析生态工程对植被动态的影响研究方法概述

植被动态变化受气候和人类活动双重作用力的驱动。在气候变化的背景下,如何定量剖析人类活动在植被动态变化中的作用力,对增加植被生态系统碳储量和缓解气候变化具有重要意义。随着生态文明建设和环境保护意识的加强,就植被生态系统而言,生态工程作为一项巨大的人类活动,对植被影响的广度和深度日益加强。系统分析气候变化背景下生态工程对植被的生态效应影响,对后期生态恢复措施的制定和实施具有十分重要的理论指导意义。虽已有一些生态工程对植被影响的定量化研究方法,但不同方法之间的结果难以进行比较研究。比较探讨各定量研究方法的优缺点有利于推动植被驱动机制的研究,有助于恢复生态学和人类生态学的应用和发展。系统梳理了定量研究生态工程对植被动态的影响主要研究方法:回归分析、残差趋势分析、基于生物物理过程模型方法和阈值分割方法。对比发现,基于生物物理过程模型方法具有较高的应用潜力,趋势分析方法和阈值分割方法仍需进一步完善。目前,定量剖析生态工程对植被变化的影响研究主要侧重于模型模拟,野外实证研究和模型验证较为缺乏,是恢复生态学未来研究的重点和难点之一。     

涡度相关技术及其在陆地生态系统通量研究中的应用

通量观测是定量描述土壤-植被-大气间物质循环和能量交换过程的基础。涡度相关技术作为直接测量植被冠层与大气间能量与物质交换通量的技术手段, 已经逐步发展成为国际通用的通量观测标准方法。随着涡度相关技术在全球碳水循环研究中的广泛应用, 长期连续的通量观测正在为准确评价生态系统碳固持能力、水分和能量平衡状况、生态系统对全球气候变化的反馈作用、区域和全球尺度模型的优化与验证、极端事件对生态系统结构与功能影响等方面的研究提供重要数据支撑和机制理解途径。通过站点尺度通量长期动态观测, 明确了不同气候区和植被类型生态系统碳水通量强度基线及其季节与年际变异特征。通过多站点联网观测, 在区域和全球尺度研究生态系统碳通量空间变异特征, 揭示了区域尺度上温度和降水对生态系统碳通量空间格局的生物地理学控制机制。该文概括地介绍了涡度相关技术的基本原理、假设与系统构成, 总结了涡度通量长期联网观测在陆地生态系统碳水通量研究中的主要应用, 并对通量研究发展前景进行了展望。     

可持续生态学

可持续生态学系用生态学原理和方法解决自然与社会经济协调发展问题,或者说生态学不断将人类及其社会经济活动纳入研究范畴而形成的自然科学与社会科学的交叉学科。40年来,我国在可持续生态学研究和实践领域取得了丰硕的成果,一是提出了"社会-经济-自然"复合生态系统理论;二是构建了适应中国国情的可持续发展评价指标体系;三是推进实施了国家可持续发展战略,并在不同时空尺度进行了试点示范;四是将可持续发展的区域生态安全格局和生态风险管理理论与方法应用于城市与区域发展规划中,并利用生态补偿机制推进跨域的生态安全格局建设;五是为国家生态文明建设规划纲要的出台提供了重要的科学支撑,有力地推进了生态文明建设战略的实施;六是系统地研究了全球气候变化对中国生态系统的影响,科学评估了气候变化的现状、趋势及其影响,提出了气候变化的生态适应对策;七是不断推进国家和地方层面的生态省、生态市、生态县建设,创建了不同层次和规模的可持续发展实验区、国家可持续发展议程创新示范区、生态农业试点示范县、生态工业示范园区等。本文从宏观生态学与可持续发展、生态城市与可持续发展、生态产业与可持续发展三个方面评述可持续性生态学的研究进展。可持续生态学的重点研究内容随着时代发展而不断更新,生态文明建设、生态安全格局构建、落实联合国2030可持续发展目标、应对全球环境变化、新型城市化和工业化对生态系统的影响等是当前和未来一段时间的研究热点。     

Wildfire refugia in forests: Severe fire weather and drought mute the influence of topography and fuel age

Wildfire refugia (unburnt patches within large wildfires) are important for the persistence of fire‐sensitive species across forested landscapes globally. A key challenge is to identify the factors that determine the distribution of fire refugia across space and time. In particular, determining the relative influence of climatic and landscape factors is important in order to understand likely changes in the distribution of wildfire refugia under future climates. Here, we examine the relative effect of weather (i.e. fire weather, drought severity) and landscape features (i.e. topography, fuel age, vegetation type) on the occurrence of fire refugia across 26 large wildfires in south‐eastern Australia. Fire weather and drought severity were the primary drivers of the occurrence of fire refugia, moderating the effect of landscape attributes. Unburnt patches rarely occurred under ‘severe’ fire weather, irrespective of drought severity, topography, fuels or vegetation community. The influence of drought severity and landscape factors played out most strongly under ‘moderate’ fire weather. In mesic forests, fire refugia were linked to variables that affect fuel moisture, whereby the occurrence of unburnt patches decreased with increasing drought conditions and were associated with more mesic topographic locations (i.e. gullies, pole‐facing aspects) and vegetation communities (i.e. closed‐forest). In dry forest, the occurrence of refugia was responsive to fuel age, being associated with recently burnt areas (<5 years since fire). Overall, these results show that increased severity of fire weather and increased drought conditions, both predicted under future climate scenarios, are likely to lead to a reduction of wildfire refugia across forests of southern Australia. Protection of topographic areas able to provide long‐term fire refugia will be an important step towards maintaining the ecological integrity of forests under future climate change.     

Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring

Prior work shows western US forest wildfire activity increased abruptly in the mid-1980s. Large forest wildfires and areas burned in them have continued to increase over recent decades, with most of the increase in lightning-ignited fires. Northern US Rockies forests dominated early increases in wildfire activity, and still contributed 50% of the increase in large fires over the last decade. However, the percentage growth in wildfire activity in Pacific northwestern and southwestern US forests has rapidly increased over the last two decades. Wildfire numbers and burned area are also increasing in non-forest vegetation types. Wildfire activity appears strongly associated with warming and earlier spring snowmelt. Analysis of the drivers of forest wildfire sensitivity to changes in the timing of spring demonstrates that forests at elevations where the historical mean snow-free season ranged between two and four months, with relatively high cumulative warm-season actual evapotranspiration, have been most affected. Increases in large wildfires associated with earlier spring snowmelt scale exponentially with changes in moisture deficit, and moisture deficit changes can explain most of the spatial variability in forest wildfire regime response to the timing of spring.This article is part of the themed issue ‘The interaction of fire and mankind’.     

Housing arrangement and location determine the likelihood of housing loss due to wildfire

Surging wildfires across the globe are contributing to escalating residential losses and have major social, economic, and ecological consequences. The highest losses in the U.S. occur in southern California, where nearly 1000 homes per year have been destroyed by wildfires since 2000. Wildfire risk reduction efforts focus primarily on fuel reduction and, to a lesser degree, on house characteristics and homeowner responsibility. However, the extent to which land use planning could alleviate wildfire risk has been largely missing from the debate despite large numbers of homes being placed in the most hazardous parts of the landscape. Our goal was to examine how housing location and arrangement affects the likelihood that a home will be lost when a wildfire occurs. We developed an extensive geographic dataset of structure locations, including more than 5500 structures that were destroyed or damaged by wildfire since 2001, and identified the main contributors to property loss in two extensive, fire-prone regions in southern California. The arrangement and location of structures strongly affected their susceptibility to wildfire, with property loss most likely at low to intermediate structure densities and in areas with a history of frequent fire. Rates of structure loss were higher when structures were surrounded by wildland vegetation, but were generally higher in herbaceous fuel types than in higher fuel-volume woody types. Empirically based maps developed using housing pattern and location performed better in distinguishing hazardous from non-hazardous areas than maps based on fuel distribution. The strong importance of housing arrangement and location indicate that land use planning may be a critical tool for reducing fire risk, but it will require reliable delineations of the most hazardous locations.     

The effect of wildfire on scattered trees, ‘keystone structures’, in agricultural landscapes

Scattered trees are considered ‘keystone structures’ in many agricultural landscapes worldwide because of the disproportionate effect they have on ecosystem function and biodiversity. Populations of these trees are in decline in many regions. Understanding the processes driving these declines is crucial for better management. Here, we examine the impact of wildfire on populations of this keystone resource. We examined 62 observation plots affected by wildfire and matched with 62 control observation plots where fire was absent. Counts of scattered trees were conducted pre‐fire in 2005 and repeated post‐fire in 2011. Changes in populations were compared between the control and fire‐affected observation plots. Our results show wildfire had a significant local impact, with an average decline of 19.9% in scattered tree populations on burned plots. In contrast, scattered trees increased on average by 5.3% in the control observation plots. The impact of wildfire was amplified (as revealed by greater percentage tree losses) by larger wildfires. Wildfire effects on scattered tree populations are of concern, given a background of other (usually) chronic stressors (often associated with agriculture) and that the frequency and intensity of wildfire are predicted to increase in many landscapes.     

Quantitative Evidence for Increasing Forest Fire Severity in the Sierra Nevada and Southern Cascade Mountains, California and Nevada, USA

Recent research has concluded that forest wildfires in the western United States are becoming larger and more frequent. A more significant question may be whether the ecosystem impacts of wildfire are also increasing. We show that a large area (approximately 120000 km²) of California and western Nevada experienced a notable increase in the extent of forest stand-replacing (“high severity”) fire between 1984 and 2006. High severity forest fire is closely linked to forest fragmentation, wildlife habitat availability, erosion rates and sedimentation, post-fire seedling recruitment, carbon sequestration, and various other ecosystem properties and processes. Mean and maximum fire size, and the area burned annually have also all risen substantially since the beginning of the 1980s, and are now at or above values from the decades preceding the 1940s, when fire suppression became national policy. These trends are occurring in concert with a regional rise in temperature and a long-term increase in annual precipitation. A close examination of the climate–fire relationship and other evidence suggests that forest fuels are no longer limiting fire occurrence and behavior across much of the study region. We conclude that current trends in forest fire severity necessitate a re-examination of the implications of all-out fire suppression and its ecological impacts. Author Contributions: Jay Miller designed the study, performed research, analyzed data, and wrote the article. Hugh Safford performed research, analyzed data, and wrote the article. Michael Crimmins performed research and analyzed data. Andi Thode designed the study and performed research.     

Human disturbance and environmental factors as drivers of long‐term post‐fire regeneration patterns in Mediterranean forests

Question: What are the main forces driving natural regeneration in burned mature Mediterranean forests in the medium‐long term and what are the likely successional trajectories of unmanaged vegetation? Location: Valencia Region, eastern Spain. Methods: A wildfire burned 33 000 ha of Pinus halepensis and P. pinaster forest in 1979, and subsequent smaller wildfires took place between 1984 and 1996. The study was designed to sample the range of environmental and disturbance (fire recurrence and land use) conditions. The territory was classified into 17 different geomorphological and fire‐recurrence units. Vegetation cover and floristic composition were measured on a total of 113 plots (1000 m² each) randomly selected within these units. Results: The results show that 23 years after the fire the regenerated vegetation consists of successional shrublands, and that forest ecosystem resilience can be very low. The vegetation presents a strong correlation with most of the environmental variables, but fire (one or two fires), soil type and land use (in that order) are the main drivers of vegetation composition. Quercus coccifera shrublands persist on limestone soils while diverse types of other shrublands (dominated by seeder species) are found on marl soils. Conclusions: The results of this study indicate that disturbance factors strongly coupled to human activities, such as land use and fire, play a critical role in the current state of vegetation. Fire creates vegetation patches in different successional states while land use and soil type define the different types of shrubland in terms of their specific composition.     

Severe wildfires promoted by climate change negatively impact forest amphibian metacommunities

Aim

Changes to the extent and severity of wildfires driven by anthropogenic climate change are predicted to have compounding negative consequences for ecological communities. While there is evidence that severe weather events like drought impact amphibian communities, the effects of wildfire on such communities are not well understood. The impact of wildfire on amphibian communities and species is likely to vary, owing to the diversity of their life-history traits. However, no previous research has identified commonalities among the amphibians at most risk from wildfire, limiting conservation initiatives in the aftermath of severe wildfire. We aimed to investigate the impacts of the unprecedented 2019–2020 black summer bushfires on Australian forest amphibian communities.

Location

Eastern coast of New South Wales, Australia.

Methods

We conducted visual encounter surveys and passive acoustic monitoring across 411 sites within two regions, one in northeast and one in southeast New South Wales. We used fire severity and extent mapping in two multispecies occupancy models to assess the impacts of fire on 35 forest amphibian species.

Results

We demonstrate a negative influence of severe fire extent on metacommunity occupancy and species richness in the south with weaker effects in the north—reflective of the less severe fires that occurred in this region. Both threatened and common species were impacted by severe wildfire extent. Occupancy of burrowing species and rain forest specialists had mostly negative relationships with severe wildfire extent, while arboreal amphibians had neutral relationships.

Main Conclusion

Metacommunity monitoring and adaptive conservation strategies are needed to account for common species after severe climatic events. Ecological, morphological and life-history variation drives the susceptibility of amphibians to wildfires. We document the first evidence of climate change-driven wildfires impacting temperate forest amphibian communities across a broad geographic area, which raises serious concern for the persistence of amphibians under an increasingly fire-prone climate.     

Wildfire risk for main vegetation units in a biodiversity hotspot: modeling approach in New Caledonia,South Pacific

Wildfire has been recognized as one of the most ubiquitous disturbance agents to impact on natural environments. In this study, our main objective was to propose a modeling approach to investigate the potential impact of wildfire on biodiversity. The method is illustrated with an application example in New Caledonia where conservation and sustainable biodiversity management represent an important challenge. Firstly, a biodiversity loss index, including the diversity and the vulnerability indexes, was calculated for every vegetation unit in New Caledonia and mapped according to its distribution over the New Caledonian mainland. Then, based on spatially explicit fire behavior simulations (using the FLAMMAP software) and fire ignition probabilities, two original fire risk assessment approaches were proposed: a one‐off event model and a multi‐event burn probability model. The spatial distribution of fire risk across New Caledonia was similar for both indices with very small localized spots having high risk. The patterns relating to highest risk are all located around the remaining sclerophyll forest fragments and are representing 0.012% of the mainland surface. A small part of maquis and areas adjacent to dense humid forest on ultramafic substrates should also be monitored. Vegetation interfaces between secondary and primary units displayed high risk and should represent priority zones for fire effects mitigation. Low fire ignition probability in anthropogenic‐free areas decreases drastically the risk. A one‐off event associated risk allowed localizing of the most likely ignition areas with potential for extensive damage. Emergency actions could aim limiting specific fire spread known to have high impact or consist of on targeting high risk areas to limit one‐off fire ignitions. Spatially explicit information on burning probability is necessary for setting strategic fire and fuel management planning. Both risk indices provide clues to preserve New Caledonia hot spot of biodiversity facing wildfires.