历史变域在森林生态系统管理中的应用现状与展望

历史变域描述了自然干扰下生态系统条件和过程的变化范围,能够使人们认识现代生态系统如何变化,为生态系统的有效管理提供了重要的参照和目标,使管理者能够制定有效措施最终使生态系统达到可持续状态.近年来,历史变域在森林生态系统管理中发挥着越来越重要的作用,已成功用于揭示生态系统变化的原因、保护生物多样性和濒危物种及恢复生态系统功能等多个领域.本文介绍了历史变域的概念并对其在森林生态系统管理中的应用及所面临的挑战(数据缺乏、环境变化和人类影响等)进行了论述.加大数据解译和分析的研究力度、注重自然环境和人类社会变化的研究及加强对公众的宣传力度可以更好地认识研究区的生态环境及其主要干扰机制,有利于提高历史变域在生态系统管理中的应用效率,使森林生态系统最终达到可持续的状态.     

大兴安岭呼中林区虫害与火干扰交互作用的长期模拟

虫害和林火是森林生态系统的两种主要干扰类型,各种干扰在大时空尺度上存在一定的交互作用.本文采用空间直观景观模型LANDIS模拟虫害和林火在300年内的交互作用.结果表明:虫害干扰降低了细可燃物载量,提高了模拟前期(0～100 a)和中期(100～200 a)的粗可燃物载量,降低了模拟前期和中期的林火频率,不同干扰预案模拟后期(200～300 a)火烧频率的结果比较接近;虫害干扰降低了模拟前期和后期的火烧强度,增加了模拟中期的火烧强度,提高了模拟中期的森林火险等级,降低了模拟前期和后期的火险等级.人类灭火可增加虫害的发生面积,因此建议森林管理部门采取适当的防虫措施,不可只注重灭火,可以采取可燃物去除和计划火烧等方式管理林火,促进森林生态系统的可持续发展.     

森林自然度评价研究进展

森林自然度是描述森林状态和确定景观保护价值的重要指标,广泛应用于近自然林业经营和植被恢复与重建。本文在分析森林自然度概念、森林自然度评价类型与方法的基础上,认为森林自然度概念应从森林的自然状况与人类干扰两方面结合起来考虑,森林自然度评价应在潜自然植被参照系研究的基础上采取定性描述与定量表达相结合的方法。林分尺度的自然度评价已形成了较一致的评价方法体系,但应针对不同的植被类型统一制定各植被类型自然度评价的指标选取与赋值标准、权重确定方法和等级划分与命名标准。景观和区域尺度的森林自然度评价对于森林的保护与管理可能更客观和实用,应进一步加强不同组成要素的自然度属性、指标体系及评价方法研究。     

不同干扰因素对森林和湿地温室气体通量影响的研究进展

森林和湿地是CO2、CH4和N2O等温室气体重要的源、汇和转换器,在全球气候变化过程中起着重要作用。森林和湿地温室气体通量受到诸多因子的作用,其中干扰便是一个重要的因素。不同干扰因素对于森林和湿地生态系统温室气体通量的影响,国际上已经开展了相应的研究。基于人为和自然两大类干扰方式,分别从采伐、施肥、垦殖等人为干扰因素和火烧、台风(飓风)等自然干扰因素综述了干扰对于森林和湿地生态系统CO2、CH4和N2O通量的影响。根据目前研究中存在的不足,提出了今后应需加强的领域,以期更好地揭示干扰对于森林和湿地生态系统温室气体通量的影响及作用机制,为今后深入开展相关研究提供一定的参考价值。     

次生林概念与生态干扰度

近一个世纪强烈的人为干扰使世界范围内的原始林面积锐减,次生林已成为中国乃至世界森林资源的主体.虽然在文献与现实中"次生林（Secondary forest）"被广泛使用,但次生林的概念在各个国家,甚至同一国家或地区以及各种不同文献中存在相互矛盾的情况,这给次生林研究与经营实践带来诸多不便;而不准确的次生林定义也为与各个层次的决策制定者及公众之间的交流带来了障碍.本文在查阅大量国内外关于次生林概念文献的基础上,结合近年来关于次生林生态与经营研究实践,综合分析了次生林概念的不确定性,同意以往次生林定义中的基本内涵,并认为：次生林是由于人为破坏性干扰或异常自然干扰使原始林固有的林分结构、物种组成或基本功能发生了显著变化,经过天然更新或人工诱导天然更新恢复形成的林分.但该定义中仍存在着很多不确定性, 如:怎样的干扰为"人为破坏性干扰"和"异常自然干扰";"林分结构、物种组成或基本功能"发生了怎样的变化为"显著变化";"人工诱导天然更新"中"人工"参与的成分比例如何等.次生林概念是在20世纪初由植物演替学家提出,当时未考虑干扰的持续性;而实际上,无论是次生林还是原始林,均是森林生态系统演替过程中的某一状态,在现代森林生态系统研究中,应重新规范"次生林"的概念.考虑到"次生林"定义的不确定性或困难性,建议使用"森林自然度"或"森林生态系统成熟度"或"森林干扰度"来表达现实森林所处的状态,但该方面的研究与实践尚需加强.     

呼中林区森林景观的历史变域模拟及评价

在大兴安岭地区呼中区,将物种的年龄和分布信息进行随机化处理后,应用空间直观景观模型LANDIS对森林景观进行长时间(2500a)模拟,取物种演替稳定时间段作为模拟历史变域的数据来源.分别在景观水平和年龄类型水平上利用景观指数空间分析、主成分分析和核密度估计方法分析景观格局历史变域的模拟结果,并在二维空间坐标内,将研究区1990年、2000年森林景观特征与之比较.结果表明,各树种面积比例在模拟900a后都达到稳定状态,可作为无干扰条件下森林景观特征的历史变域;由于长期采伐,研究区1990年景观的斑块面积和破碎化程度都偏离了该历史变域,其中,过熟林偏离最明显,其斑块面积远小于历史变域,破碎化程度非常严重;虽然1990年后的采伐管理方案比之前的更为合理,但2000年的森林景观仍旧继续偏离历史变域.     

乡村景观生物多样性研究进展

乡村景观是一种人文和自然共生的复合生态系统, 为生物多样性的维持提供了支持。目前, 中国传统乡村地区生物多样性的维持正面临着农业集约化、人工林树种单一化、非农业用地急剧扩张及生态传承机制解体等复杂多样的威胁, 亟待展开深入研究。本文在总结乡村景观生物多样性相关概念及特征的基础上, 通过文献分析概括了国际乡村景观生物多样性的热点研究方向, 包括农业集约化下的生物多样性管理、区域尺度乡村景观与生物多样性的协同关系、局地尺度不同乡村景观类型的物种多样性及乡村景观中的生物文化多样性, 进一步梳理了国内在相关研究方向上的主要进展并指出研究不足。在此基础上提出未来研究展望, 包括突出生物文化多样性特征、加强多时空尺度分析、深化动态维持机制研究、推进生物多样性研究在乡村生态景观规划中的全过程应用等建议。     

河岸带生态系统退化机制及其恢复研究进展

恢复和重建自然和人为干扰导致的退化河岸带生态系统是目前恢复生态学、流域生态学等学科研究的重要内容之一．对河岸带生态系统的干扰表现在河流水文特征改变、河岸带直接干扰和流域尺度干扰3个方面,分别具有不同的影响机制．河流水文特征改变通过改变河岸土壤湿度、氧化还原电位、生物生存环境以及沉积物传输规律对河岸带生态系统产生影响;河岸带直接干扰通过人类活动及外来物种入侵而直接影响河岸带植被多样性;流域尺度干扰则主要表现在河道刷深、河道淤积、河岸带地下水位降低和河流冲刷过程改变等．河岸带生态恢复评价对象包括河岸带生态系统各要素,评价指标已从单一的生态指标转向综合性指标．河岸带生态恢复应在景观或者流域尺度上进行考虑,识别对其影响的生物和物理过程以及导致其退化的干扰因子,通过植被重建与水文调控来进行．扩展研究尺度和研究对象及采用多学科的研究方法将是今后相关研究中的重要问题．     

森林干扰度评价

干扰普遍存在于森林生态系统,是森林群落演替的驱动力之一。干扰对森林生态系统的影响程度,决定于干扰的频率、强度、空间范围等,过度频繁或不合理的干扰,可能导致森林生态系统的毁灭。森林对干扰的响应表现在多方面,其内在联系十分复杂,因此,很难用森林中某个现象或某几个现象反映森林生态系统对干扰的响应。为了准确、科学地评价现有森林生态系统对干扰的响应程度,本文提出应用森林干扰度（REFD）评价现有森林受干扰的程度。森林干扰度是由于干扰的存在造成森林生态系统结构与功能的改变程度,仅反映干扰后现有森林与目标森林（地带性顶极植被或原有森林等）的距离程度（差距）,不反映干扰的种类、强度、性质等因素;在对森林干扰度内涵进行详细分析的基础上,确定了评价森林干扰度的原则及不同尺度条件下森林干扰度的评价指标。     

边缘效应及其对森林生态系统影响的研究进展

边缘效应是生态学和生物保护的重要概念之一,它在研究生态系统尺度和景观生态系统尺度的能量流和物质流等生态过程中具有重要作用.本文对边缘效应的内涵、特征、定量评价(包括定量分析基础、强度、影响区、模型等)、应用研究等方面进行阐述,分析了边缘效应研究中存在的不足,总结了边缘效应对森林生态系统的影响及其研究方向,以期为森林经营、保护区管理等生产实践提供借鉴.     

Climate change, human land use and future fires in the Amazon

There is increasing consensus that the global climate will continue to warm over the next century. The biodiversity-rich Amazon forest is a region of growing concern because many global climate model (GCM) scenarios of climate change forecast reduced precipitation and, in some cases, coupled vegetation models predict dieback of the forest. To date, fires have generally been spatially co-located with road networks and associated human land use because almost all fires in this region are anthropogenic in origin. Climate change, if severe enough, could alter this situation, potentially changing the fire regime to one of increased fire frequency and severity for vast portions of the Amazon forest. High moisture contents and dense canopies have historically made Amazonian forests extremely resistant to fire spread. Climate will affect the fire situation in the Amazon directly, through changes in temperature and precipitation, and indirectly, through climate-forced changes in vegetation composition and structure. The frequency of drought will be a prime determinant of both how often forest fires occur and how extensive they become. Fire risk management needs to take into account landscape configuration, land cover types and forest disturbance history as well as climate and weather. Maintaining large blocks of unsettled forest is critical for managing landscape level fire in the Amazon. The Amazon has resisted previous climate changes and should adapt to future climates as well if landscapes can be managed to maintain natural fire regimes in the majority of forest remnants.     

森林植被的自然火干扰

森林植被的自然火干扰邱扬（山西大学黄土高原研究所,太原０３０００６）ＮａｔｕｒａｌＦｉｒｅＤｉｓｔｕｒｂａｎｃｅｏｆＦｏｒｅｓｔＶｅｇｅｔａｔｉｏｎ．ＱｉｕＹａｎｇ（ＩｎｓｔｉｔｕｔｅｏｆＬｏｅｓＰｌａｔｅａｕ,ＳｈａｎｘｉＵｎｉｖｅｒｓｉｔｙ,...     

The interacting effects of land use change,climate change and suppression of natural disturbances on landscape forest structure in the Swiss Alps

Ecosystems are being modified by a multiplicity of interacting natural and anthropogenic factors. The most important of these factors include changes in land use, changes in climate, and alterations of disturbance regimes. Many studies have considered these factors separately; however, these factors do not act in isolation, but rather interact to affect ecosystem structure and function. In the present study, we analyzed the interacting effects of abandonment of agricultural practices, increases in temperature, and anthropogenic suppression of the avalanche regime on landscape forest structure (percent canopy cover) in the Davos region of the Swiss Alps over the past 45 years. Compared to 1954, the Davos region is now characterized by greater forest cover and lower landscape heterogeneity. The greatest increases in forest structural stage occurred in areas in which land use changed from agricultural to non‐agricultural, that were the closest to formerly active avalanche tracks, and in which the percentage change in number of growing degree days (GDD) was high. Change in land use was the most important variable contributing to changes in landscape forest structure, followed by changes in the disturbance regime, then changes in GDD. There also exist clear interactions among these variables, which indicate, for example, that the effects of the suppression of disturbances and changes in climate are contingent on the more immediate effects of changes in land use. Understanding the relative importance of, and interactions among, changes in land use, climate, and disturbances can contribute to an improved understanding of ecosystem dynamics and to better management decisions.     

气候变化、林火和营林措施对寒温带典型森林生态弹性的影响

生态弹性是森林生态系统在遭受外在扰动后恢复到稳定状态的能力,是森林资源可持续发展的重要目标之一,且森林生态弹性对诸如气候变化、林火和营林措施等外部因子的影响较为敏感.探究这些外部因子对森林生态弹性的影响在未来森林生态系统管理方面有重要意义.本研究首先从森林组成、结构和功能等方面选取指标因子并估算了森林生态弹性值,然后运用LANDIS PRO模型,模拟气候变化、林火干扰和营林措施等对寒温带典型森林生态弹性的影响,并探讨了当前抚育采伐方案在未来气候下的可持续性.结果表明: 模型初始化的2000年林分密度和胸高断面积与2000年真实景观较为吻合,模拟的2010年森林景观与野外调查数据无明显差异,基于当前林火干扰状况的模拟结果与火烧迹地调查数据基本匹配,说明林火模块能很好地模拟当前研究区林火发生状况.林火干扰增加30%将会使该区模拟期内景观水平上森林生态弹性提高15.7%～40.8%,而林火干扰增加200%则会降低该区4.4%～24.6%的森林生态弹性.短期和中期林火干扰增加对森林生态弹性的影响大于气候变化的影响.与当前预案相比,B1气候(林火增加30%预案)和A2气候(林火增加200%预案)对整个模拟阶段景观尺度森林生态弹性的影响分别处于-15.9%～38.9%和-60.4%～34.8%范围内.与无采伐预案相比,B1和A2气候下在整个模拟时期内若继续实施当前抚育采伐方案,将不利于景观水平森林生态弹性的提高.在B1气候(林火增加30%预案)下,在各模拟时期内无需实施任何营林措施;而在A2气候(林火增加200%预案)下,建议实施中、高强度种植的营林措施以提升景观水平森林生态弹性.     

气候变化和林火干扰对大兴安岭林区地上生物量影响的动态模拟

预测森林地上生物量对气候变化和林火干扰的响应是陆地生态系统碳循环研究的重要内容,气温、降水等因素的改变和气候变暖导致林火干扰强度的变化将会影响森林生态系统的碳库动态.东北森林作为我国森林的重要组成部分,对气候变化和林火干扰的响应逐渐显现.本文运用LANDIS PRO模型,模拟气候变化对大兴安岭森林地上生物量的影响,并比较分析了气候变暖对森林地上生物量的直接影响与通过林火干扰强度改变所产生的影响.结果表明: 未来气候变暖和火干扰增强情景下,森林地上生物量增加;当前气候条件和火干扰下,研究区森林地上生物量为(97.14±5.78) t·hm^-2;在B1F2预案下,森林地上生物量均值为(97.93±5.83) t·hm^-2;在A2F3预案下,景观水平第100～150和150～200年模拟时期内的森林地上生物量均值较高,分别为(100.02±3.76)和(110.56±4.08) t·hm^-2.与当前火干扰相比,CF2预案(当前火干扰增加30%)在一定时期使景观水平地上生物量增加(0.56±1.45) t·hm^-2,CF3预案(当前火干扰增加230%)在整个模拟阶段使地上生物量减少(7.39±1.79) t·hm^-2.针叶、阔叶树种对气候变暖的响应存在差异,兴安落叶松和白桦生物量随气候变暖表现为降低趋势,而樟子松、云杉和山杨的地上生物量则随气候变暖表现出不同程度的增加;气候变暖对针阔树种的直接影响具有时滞性,针叶树种响应时间比阔叶树种迟25～50年.研究区森林对高CO₂排放情景下气候变暖和高强度火干扰的共同作用较为敏感,未来将明显改变研究区森林生态系统的树种组成和结构.     

Late‐Holocene fire history in a forest‐grassland mosaic in southern Brasil: Implications for conservation

Question: Is the diverse mosaic of forest/grassland (Campos) vegetation on the hills in the Porto Alegre region natural or of anthropogenic origin? What are the best approaches to management and conservation of forest/grassland mosaics in southern Brazil? Location: 280 m a.s.l., Rio Grande do Sul State (30°04′32″S; 51°06′05″W, southern Brazil. Methods: A 50-cm long radiocarbon dated sediment core from a swamp on Morro Santana was analysed for pollen and charcoal, and multivariate data analysis was used to reconstruct past vegetation and fire dynamics. Results: The formation of swamp deposits is related to a change to wetter climatic conditions since 1230 cal yr BP. The diverse forest/grassland mosaic existed already at that time and can be seen as natural in origin as it has been also shown from other studies in southern Brazil. Since 580 cal yr BP, forests expanded continuously. The marked higher occurrence of the pioneer Myrsine during the last 70 years, indicates a change in the disturbance regime. In the past, vegetation has been influenced by mostly anthropogenic fire, set first by Amerindians and later by European settlers. Conclusions: Management for conservation of forest/grassland mosaics should take into account, first, that grasslands are remnants of earlier drier Holocene periods and not a result of deforestation and, second, the history of disturbance by grazing and fire. Suppression of grazing and burning has likely resulted in a trend towards more woody vegetation under modern wet climatic conditions. If management for conservation excludes fire, the present grassland patches will tend to disappear due to forest expansion under the modern humid climate. Maintaining or reintroducing cattle grazing in conservation areas could be an alternative to fire.     

呼中林区火烧点格局分析及影响因素

林火是森林生态系统景观格局、动态和生态过程的重要自然驱动力,理解林火发生空间格局与影响因素对于林火安全管理具有重要的作用。采用点格局分析方法,以黑龙江大兴安岭呼中林区1990-2005年火烧数据为研究案例,分析了火烧点空间格局及其影响因素。结果表明,火烧点在空间上的分布是不均匀的,呈现聚集分布,存在一些火烧高发区和低发区。呼中林区火烧概率是0.004-0.012次/(km² · a),平均火烧概率为0.0077次/(km² · a)。人类活动因子、地形因子和植被因子对林火的发生均具有重要作用。应用空间点格局分析方法表明,距离居民点和道路的距离、高程、坡度和林型是影响林火发生的显著因子。因此在进行森林防火管理时,仅仅通过控制人类活动对于降低林火火险的效果是有限的,地形和林型也是林火防控时重点要考虑的因素。     

A Bayesian Approach to Landscape Ecological Risk Assessment Applied to the Upper Grande Ronde Watershed,Oregon

We present a Bayesian network model based on the ecological risk assessment framework to evaluate potential impacts to habitats and resources resulting from wildfire, grazing, forest management activities, and insect outbreaks in a forested landscape in northeastern Oregon. The Bayesian network structure consisted of three tiers of nodes: landscape disturbances, habitats, and the ecological resources or endpoints of interest to land managers. Nodes at each tier were linked to lower nodes if ecological and spatial relationships existed between them. All parameters had four potential discrete states: zero, low, medium, and high. Our model reliably predicted probable risk to habitats and endpoints from natural and anthropogenic disturbances. The disturbances most likely to transform habitats and effect ecological resources were forest management and wildfire. Of the six habitats, moist forest (characterized by Douglas fir and grand fir) was found to be at greatest risk of ecological impacts. The management endpoint with the highest likelihood of impact was historical range of variability (HRV) for salmon habitat, followed by recreation (hunting native ungulates) and HRV wildfire. We found that the Bayesian approach to ecological risk assessment was a useful method to assess potential impacts to ecological resources resulting from forest management and natural disturbances.     

Impacts of climate variability on tree demography in second growth tropical forests: the importance of regional context for predicting successional trajectories

Naturally regenerating and restored second growth forests account for over 70% of tropical forest cover and provide key ecosystem services. Understanding climate change impacts on successional trajectories of these ecosystems is critical for developing effective large‐scale forest landscape restoration (FLR) programs. Differences in environmental conditions, species composition, dynamics, and landscape context from old growth forests may exacerbate climate impacts on second growth stands. We compile data from 112 studies on the effects of natural climate variability, including warming, droughts, fires, and cyclonic storms, on demography and dynamics of second growth forest trees and identify variation in forest responses across biomes, regions, and landscapes. Across studies, drought decreases tree growth, survival, and recruitment, particularly during early succession, but the effects of temperature remain unexplored. Shifts in the frequency and severity of disturbance alter successional trajectories and increase the extent of second growth forests. Vulnerability to climate extremes is generally inversely related to long‐term exposure, which varies with historical climate and biogeography. The majority of studies, however, have been conducted in the Neotropics hindering generalization. Effects of fire and cyclonic storms often lead to positive feedbacks, increasing vulnerability to climate extremes and subsequent disturbance. Fragmentation increases forests’ vulnerability to fires, wind, and drought, while land use and other human activities influence the frequency and intensity of fire, potentially retarding succession. Comparative studies of climate effects on tropical forest succession across biogeographic regions are required to forecast the response of tropical forest landscapes to future climates and to implement effective FLR policies and programs in these landscapes.     

Climatic thresholds shape northern high‐latitude fire regimes and imply vulnerability to future climate change

Boreal forests and arctic tundra cover 33% of global land area and store an estimated 50% of total soil carbon. Because wildfire is a key driver of terrestrial carbon cycling, increasing fire activity in these ecosystems would likely have global implications. To anticipate potential spatiotemporal variability in fire‐regime shifts, we modeled the spatially explicit 30‐yr probability of fire occurrence as a function of climate and landscape features (i.e. vegetation and topography) across Alaska. Boosted regression tree (BRT) models captured the spatial distribution of fire across boreal forest and tundra ecoregions (AUC from 0.63–0.78 and Pearson correlations between predicted and observed data from 0.54–0.71), highlighting summer temperature and annual moisture availability as the most influential controls of historical fire regimes. Modeled fire–climate relationships revealed distinct thresholds to fire occurrence, with a nonlinear increase in the probability of fire above an average July temperature of 13.4°C and below an annual moisture availability (i.e. P‐PET) of approximately 150 mm. To anticipate potential fire‐regime responses to 21st‐century climate change, we informed our BRTs with Coupled Model Intercomparison Project Phase 5 climate projections under the RCP 6.0 scenario. Based on these projected climatic changes alone (i.e. not accounting for potential changes in vegetation), our results suggest an increasing probability of wildfire in Alaskan boreal forest and tundra ecosystems, but of varying magnitude across space and throughout the 21st century. Regions with historically low flammability, including tundra and the forest–tundra boundary, are particularly vulnerable to climatically induced changes in fire activity, with up to a fourfold increase in the 30‐yr probability of fire occurrence by 2100. Our results underscore the climatic potential for novel fire regimes to develop in these ecosystems, relative to the past 6000–35 000 yr, and spatial variability in the vulnerability of wildfire regimes and associated ecological processes to 21st‐century climate change.