人为活动影响下的生态系统反馈机制——塔里木河流域生态输水工程的效应分析

通过对塔里木河流域生态输水工程的效应分析，揭示了生态系统反馈机制的原理和特点，强调了负反馈机制的作用，即生态系统在受到外界影响或干扰后，通过一系列的自我调节功能来减轻这种干扰或影响的程度，并力图恢复到平衡或稳定状态。最后，探讨了生态系统反馈机制的作用和意义。     

基于遥感和GIS的青藏铁路生态累积效应研究

采用遥感和GIS技术,通过生态系统功能偏离累积指数、景观格局干扰累积指数、植被退化指数、生态阻隔累积指数和区域生态累积效应指数研究青藏铁路建设和运营对沿线生态系统的累积影响.结果表明,铁路建设和运营对沿线0～1 km直接影响区的生态服务功能、景观格局、植被覆盖和生态流均造成一定的累积影响,但以景观格局和生态流受到的影响最大,且对拉萨至唐古拉段的影响大于唐古拉至格尔木段,主要表现为对农田、草地、河流湿地和荒漠生态系统的影响.从铁路沿线＞1～5和＞5～10 km范围的间接或协同累积影响来看,拉萨至唐古拉段明显高于唐古拉至格尔木段.铁路建设运营对＞1～5 km范围的农田、荒漠和河流湿地生态系统仍存在一定负面影响,且以农田生态系统受到的负面累积影响最大,主要表现为拉萨和格尔木城市扩张对农田生态系统的干扰和占用.     

生态系统多稳态研究进展

阐述了生态系统多稳态的定义及其生态学意义,总结了生态系统的多稳态现象的不同产生机制,综述了多稳态的存在性及稳态转换的研究现状,探讨了未来的理论及应用研究前景.多稳态指的是在相同条件下,系统可以存在结构和功能截然不同的稳定状态.不同的稳态对应于不同的生态系统结构和功能,并且可产生不同的生态系统服务价值.系统的稳态不仅仅包括稳定的点吸引子,也可能是周期吸引子或者混沌吸引子.多稳态现象广泛存在于多种生态系统(海洋生态系统、湿地生态系统、干旱生态系统等)中.较强的正反馈作用是系统产生多稳态的主要原因.生态系统中的正反馈循环主要包括易化作用、过度开发以及冰盖反射等.大量的理论研究证实多稳态是系统中的一个普遍现象,但从实验角度的研究成果较少.生态系统的不同稳态有不同的吸引域,吸引域之间存在阈值.当干扰强度大于恢复力时,系统有可能越过阈值发生稳态转换.生态系统发生转换的预警指标包括方差的增加、干扰后的恢复速率以及偏度的变化.多稳态的未来研究重点在于:(1)多稳态产生机制研究;(2)生态系统中多稳态的存在性检验;(3)生态系统恢复力及预警指标的定量评价研究;(4)多稳态理论在生态系统修复实践中的应用.     

干扰对牦牛坪景观格局及草地生态系统服务的影响

玉龙雪山高山草甸位于横断山区生物多样性保护关键地区,也是滇西北重要的生态旅游资源,提供了多种重要的生态系统服务,然而当下面临着放牧旅游复合干扰等多重压力。为明晰放牧和旅游干扰对玉龙雪山高山草甸景观格局及草地生态系统服务的影响,通过野外调查和遥感影像解译数据,区分出旅游、放牧和干扰交互区3个干扰类型区,并将草甸划分出重度、中度、轻度和未退化等4个级别。分别从调节、供给、文化服务等3个方面6个指标评估研究区生态系统服务,从景观数量组成(PLAND和PD指数)与景观空间结构(SHAPE和CONNECT指数)角度评估研究区的景观格局,运用冗余分析(RDA)探讨干扰影响下的景观格局对草地生态系统服务的影响。结果表明:(1)旅游干扰集中区域的未退化和轻度退化草甸斑块面积占比(PLAND)比其他干扰区低15%,中度和重度退化草甸面积占比则明显增加;放牧干扰集中区轻度退化草甸的斑块密度指数(PD)比其他干扰区域高2-7倍,斑块破碎化明显;(2)在干扰交互区和放牧干扰集中区,都出现了斑块形状指数(SHAPE)和斑块连接度指数(CONNECT)随着草甸退化程度增加而增加的现象,中度退化草甸斑块更破碎且连接度增加,进一步扩大分布范围的趋势明显;(3)景观组成特征对研究区生态系统服务作用明显,PD指数是研究区最重要的景观指标,PD越高景观越破碎,生态系统服务供给越差。旅游干扰集中区的生态系统服务更多受景观空间结构特征的影响,放牧干扰集中区的生态系统服务则主要受景观组成特征的影响。不同干扰区域景观组成与结构的差异对草地生态系统服务的供给的影响,可作为景区草地资源保护与景观规划管理的参考。     

气候变暖背景下森林土壤碳循环研究进展

由人类活动引起的温室效应以及由此造成的气候变暖对森林牛态系统的影响已引起人们的普遍关注.森林土壤碳循环作为全球碳循环的重要组成部分,是决定未来陆地牛物嘲表现为碳源/碳汇的关键环节,揭示这一作用对于准确理解全球变化背景下陆地生态系统碳循环过程具有重要的指导意义.本文主要通过论述影响土壤碳循环过程的5个方面(土壤呼吸、土壤微生物、土壤酶活性、凋落物输入与分解、土壤碳库),综述了近10 a来全球气候变暖对土壤碳循环过程的影响.近年来,尽管已开展了大量有关土壤碳循环对气候变暖的响应及反馈机制的研究,并取得了一定的成果,但研究结果仍然存在很大的不确定性.整合各种密切关联的全球变化现象,完善研究方法和实验手段,加强根际微生态系统碳循环过程与机理研究将是下一步研究的方向和重点.参70     

生态系统服务研究的问题与展望

生态系统服务的研究是当前资源经济学和生态经济学的研究热点之一。通过分析生态系统服务的概念辨析,认为从生态系统功能的定义过渡到生态系统服务定义的过程中,在关注生态系统整体性的同时忽略了生态系统要素之间的相互作用,导致生态系统服务的评估中可能存在着重复估值或者估值不全面等风险。针对目前的很多生态系统的评估对生态系统的耗损贬值和环境退化所造成的负效益的忽略,以及对人类活动的干扰和气候变化等对生态系统服务产生影响研究不足,提出在今后的研究中应该在深入理解生态系统的复杂生态学机制的基础上,结合数学模型模拟在不确定性下的各种风险损失,加强对生态系统服务的时空动态分析,重视在气候变化、经济发展、环境污染、城市化以及人类活动的过度放牧和过度开垦引起的水土流失、环境退化、荒漠化等土地利用变化的干扰时生态系统服务的变化和反馈,更进一步分析和预测生态系统服务的损益和响应研究;通过长期的试验监测揭示生物多样性和生态系统的关系,测度出土地利用和环境变化对生物多样性的影响和边际效益,及其对生态系统服务的影响的弹性值,实现生态系统服务的精确估值;关注生态系统服务对人类福利的影响,尤其重视贫困地区和生态脆弱区的生态系统服务对减小贫困的研究,建立科学的生态补偿机制,实现可持续发展。     

典型杀虫剂类内分泌干扰物对水生溞类的毒性效应研究进展

内分泌干扰物(endocrine disrupting chemicals, EDCs),尤其是具有内分泌干扰效应的杀虫剂,因能显著影响水生生物的生长发育和生殖系统,其潜在生态毒性效应引起了人们的广泛关注。溞类在水生生态系统食物链中起着重要的连接作用,更易受到水体中残留的杀虫剂类EDCs的影响,其毒性效应在水生生态系统毒理学研究中有着重要的意义。本文重点综述了杀虫剂类EDCs对溞类产生的生长发育毒性和生殖毒性,从酶活性变化角度分析由此产生的氧化应激和神经毒性,并在基因表达水平上揭示其毒性作用机制,发现杀虫剂类EDCs通过扰乱神经系统和内分泌系统发挥作用,并展望了杀虫剂EDCs在联合毒性、多代效应的研究前景,旨在为研究杀虫剂类EDCs对大型溞的毒性作用和生态环境风险评估提供依据。     

森林净生态系统生产力及其生物影响因子研究进展

在全球大气二氧化碳浓度上升的背景下,陆地生态系统碳循环及碳汇功能研究得到了广泛的关注,日益成为今后的政治和外交的重大议题之一.净生态系统生产力(net ecosystem production, NEP)是生态系统光合固定的碳与生态系统呼吸损失的碳之间的差值;或者为生态系统净的碳积累速率.NEP 的研究整合生态系统地上和地下部分,把生态系统碳循环的影响因子有机地联系了起来.当NEP为正值时,说明生态系统为碳汇,NEP为负值则表明生态系统为碳源.随着植物和土壤相互联系及其对生态系统过程研究的深入,NEP已经成为生态系统碳循环研究的核心概念之一.以森林NEP为出发点,综述了国内外的最近的 NEP 研究进展,分析了 NEP 研究的科学意义;探讨了植物群落组成/生物多样性、土壤微生物群落、大型/土壤动物和人为的管理或干扰等生物因子对NEP的影响.根据综述研究提出未来研究应在:(1)土壤生物过程、土壤食物网及其与地上部分植物/动物相互作用对NEP的影响;(2)自然林生物多样性的竞争/共存机制与生态系统碳吸存稳定性;(3)人工林固碳潜力和不同植物功能群(灌草层)对生态系统碳动态影响等方面加强,以期为全面认识生物因子对森林生态系统系统固碳现状、机制和潜力提供理论基础.     

生态库原理及其在城市生态学研究中的作用

几十年来,生态学工作者一直把研究的重心放在生态系统内部结构和功能的辨识和调控上,很少注意生态系统与其外部环境之间的关系.由于生态系统的外部环境对生态系统至关重要,而且不同生态系统的外部环境具有许多相似或共同之处,为便于调控和研究生态系统与其外部环境的相互依赖关系,刘建国1986年提出了生态库(ecopool)的概念.本文将对生态库的概念进行拓广,并试图阐明生态库对其主体生态系统(tar- get ecosystem)的作用机理及其所产生的效应以及生态库原理在城市生态学研究中的应用.     

荒漠河岸生态系统退化机理的定量分析

通过野外监测资料,采用聚类分析与主成分分析法,分析了荒漠河岸生态系统退化的内外因素与驱动力、植被退化的环境主导因子与生态退化程度,结果表明:(1)地质、地貌与气候条件等因素的影响,塔里木河下游生态系统存在脆弱和不稳定性是其退化的内因,外界干扰则是其退化的外在因素。人为干扰则是其退化发生的驱动力,起因于人口的增加、需求的增长。(2)在此过程中导致植被受损的环境主导因子是水,植被退化是人类干扰作用于植被赖以生存的环境主导因子所致。(3)其不同河段的生态退化可以归为三类:潜在沙漠化类(轻度退化),轻度沙漠化类(中度退化),中度或重度沙漠化类(重度退化),其中第三类型,土壤条件与其它两类差异较大,表现出土壤退化的滞后现象。     

基于放射源理论的区域生态系统评价方法

研究区域生态系统定量评价方法对区域生态系统的建设与保护具有十分重要的意义。从放射源理论出发,首次将生态影响距离、生态源及生态影响效应的概念引入分析评价中,提出了区域生态系统的定量评价方法,并建立了基于景观空间格局的区域生态系统生态影响的定量计算公式。甘垛镇新庄片和横泾镇沿荡片的应用实例表明,该方法原理简明、结果直观,为区域生态系统的科学评价提供了定量评价方法。     

Application of an ecological framework linking scales based on self-thinning.

Barnes and Roderick developed a generic, theoretical framework for vegetation modeling across scales. Inclusion of a self-thinning mechanism connects the individual to the larger-scale population and, being based on the conservation of mass, all mass flux processes are integral to the formulation. Significantly, disturbance (both regular and stochastic) and its impact at larger scales are included in the formulation. The purpose of this paper is to illustrate how this model can be used to predict patch and ecosystem dry mass, and consequently system carbon. Examples from pine plantations and mixed forests are considered, with these applications requiring estimates of system carrying capacity and the growth rates of individual plants. The results indicate that the model is relatively simple and straightforward to apply, and its predictions compare well with the data. A significant feature of this approach is that the impact of local scale data on the dynamics of larger patch and ecosystem scales can be determined explicitly, as we show by example. Further, the general formulation has an analytic solution based on characteristics of the individual, facilitating practical and predictive application.     

Meta-analysis of the effects of upstream land cover on stream recovery

Unpredictable or variable ecosystem recovery from disturbance presents a challenge to conservation, particularly as the scale of human disturbance continues to increase. Theory suggests land-cover and disturbance characteristics affect recovery, but individual studies of disturbance and recovery frequently struggle to uncover generalizable patterns because of high levels of site-specific variation. To understand how land-cover, disturbance type, and disturbance duration influence ecosystem recovery, we used studies documenting recovery of 50 streams to perform a global meta-analysis of stream recovery from disturbances that affect water quality (e.g., oil spill, fire, wastewater). We extracted upstream natural and urban land-cover percentages for each site and performed model selection and averaging to identify influences on recovery completeness. Most streams improved following the end of a disturbance (median 240% of disturbed condition) but did not recover fully to baseline predisturbance condition within the studied period (median study period 2 years; median recovery 60% of baseline). Scale of disturbance in time and space did not predict recovery, but sites with higher percentages of upstream natural land cover had less complete recovery relative to sites with more urban or agricultural cover, possibly due to higher baseline conditions in these streams. Our findings suggest impacts to systems with low anthropogenic stress may be more irreversible than impacts to already modified systems. We call for more long-term evaluations of ecosystem response to disturbance and the inclusion of regional references and predisturbance reference conditions for comparison. A more thorough understanding of the role of the surrounding landscape in shaping stream response to disturbance can help managers calibrate expectations for recovery and prioritize protection.     

Change in plant spatial patterns and diversity along the successional gradient of Mediterranean grazing ecosystems

In this study, we analyze the complexity of plant spatial patterns and diversity along a successional gradient resulting from grazing disturbance in four characteristic ecosystems of the Mediterranean region. Grazing disturbance include not only defoliation by animals, but also associated disturbances as animal trampling, soil compaction, and mineralization by deposition of urine and feces. The results show that woodland and dense matorral are more resistant to species loss than middle dense and scattered matorral, or grassland. Information fractal dimension declined as we moved from a dense to a discontinuous matorral, increasing as we moved to a more scattered matorral and a grassland. In all studied cases, the characteristic species of the natural vegetation declined in frequency and organization with grazing disturbance. Heliophyllous species and others with postrate or rosette twigs increased with grazing pressure, particularly in dense matorral. In the more degraded ecosystem, only species with well-adapted traits, e.g., buried buds or unpalatable qualities showed a clear increase with grazing. Indeed, the homogeneity of species distribution within the plant community declined monotonically with grazing impact. Conversely, the spatial organization of the characteristic plants of each community increased in the better-preserved areas, being also related to the sensitivity of the species to grazing impact. The degree of autocorrelation of plant spatial distribution at the species level and the information fractal dimension at the community level allow us to quantify the degree of degradation of natural communities and to determine the sensitivity of key species to disturbance.     

Nitrogen regulation of the climate-carbon feedback: evidence from a long-term global change experiment

Modeling studies have shown that nitrogen (N) strongly regulates ecosystem responses and feedback to climate warming. However, it remains unclear what mechanisms underlie N regulation of ecosystem-climate interactions. To examine N regulation of ecosystem feedback to climate change, we have conducted a warming and clipping experiment since November 1999 in a tallgrass prairie of the Great Plains, USA. Infrared heaters were used to elevate soil temperature by an average of 1.96 degrees C at a depth of 2.5 cm from 2000 to 2008. Yearly biomass clipping mimicked hay or biofuel feedstock harvest. We measured carbon (C) and N concentrations, estimated their content and C:N ratio in plant, root, litter, and soil pools. Warming significantly stimulated C storage in aboveground plant, root, and litter pools by 17%, 38%, and 29%, respectively, averaged over the nine years (all P < 0.05) but did not change soil C content or N content in any pool. Plant C:N ratio and nitrogen use efficiency increased in the warmed plots compared to the control plots, resulting primarily from increased dominance of C4 plants in the community. Clipping significantly decreased C and N storage in plant and litter pools (all P < 0.05) but did not have interactive effects with warming on either C or N pools over the nine years. Our results suggest that increased ecosystem nitrogen use efficiency via a shift in species composition toward C4 dominance rather than plant N uptake is a key mechanism underlying warming stimulation of plant biomass growth.     

Moss species benefits from breakdown of cyclic rodent dynamics in boreal forests

Bryophytes have increased in abundance in northern regions, and climate changes have been proposed to account for this change. However, changes in the population dynamics of microtine rodents may also contribute to changes in bryophyte abundance. New evidence indicates a tendency for microtine rodent population oscillations to change from periodicity of 3-5 years to become irregular or acyclic. The impact on ecosystem functioning is potentially great. We study the impact of variation in microtine rodent population characteristics, such as cycle length and amplitude, on the population dynamics of the boreal, clonal moss Hylocomium splendens. We use experimental and observational demographic data to construct 127 scenarios representing all combinations of disturbance type (gap formation and/or clipping), period (cyclic with 4, 6, 12, or 24 years between rodent peaks; or acyclic with constant or stochastically varying annual disturbance severity) and disturbance severity (fraction of individuals affected by disturbance in each year relative to the maximum disturbance carried out in the field experiment; seven levels). Population data collected in the field during 13 years were used as a baseline scenario. By subjecting all scenarios to stochastic matrix modeling, we demonstrate considerable impact of microtine rodent on the population dynamics of H. splendens, most notably when rodent populations fluctuate with short periods and high peak disturbance severities. Under the same average disturbance severity, H. splendens population growth rates are highest in acyclic scenarios and are progressively reduced with increasing peak disturbance severities (i.e., with increasing period). Stochastic elasticity analyses show that in less variable environments mature segment survival contributes more to the population growth rate, while in more variable environments the regeneration pathway (branching of older parts of the plant) plays a stronger role, inevitably leading to lower population fitness. Our results support the hypothesis that breakdown of cyclic rodent population dynamics accentuates increase in the abundance of H. splendens and other large bryophytes in boreal forests in Norway, observed empirically in recent years and primarily ascribed to climatic change.     

Marine-derived nutrients, bioturbation, and ecosystem metabolism: reconsidering the role of salmon in streams

In coastal areas of the North Pacific Ocean, annual returns of spawning salmon provide a substantial influx of nutrients and organic matter to streams and are generally believed to enhance the productivity of recipient ecosystems. Loss of this subsidy from areas with diminished salmon runs has been hypothesized to limit ecosystem productivity in juvenile salmon rearing habitats (lakes and streams), thereby reinforcing population declines. Using five to seven years of data from an Alaskan stream supporting moderate salmon densities, we show that salmon predictably increased stream water nutrient concentrations, which were on average 190% (nitrogen) and 390% (phosphorus) pre-salmon values, and that primary producers incorporated some of these nutrients into tissues. However, benthic algal biomass declined by an order of magnitude despite increased nutrients. We also measured changes in stream ecosystem metabolic properties, including gross primary productivity (GPP) and ecosystem respiration (ER), from three salmon streams by analyzing diel measurements of oxygen concentrations and stable isotopic ratios (delta O-O2) within a Bayesian statistical model of oxygen dynamics. Our results do not support a shift toward higher primary productivity with the return of salmon, as is expected from a nutrient fertilization mechanism. Rather, net ecosystem metabolism switched from approximately net autotrophic (GPP > or = ER) to a strongly net heterotrophic state (GPP < ER) in response to bioturbation of benthic habitats by salmon. Following the seasonal arrival of salmon, GPP declined to <12% of pre-salmon rates, while ER increased by over threefold. Metabolism by live salmon could not account for the observed increase in ER early in the salmon run, suggesting salmon nutrients and disturbance enhanced in situ heterotrophic respiration. Salmon also changed the physical properties of the stream, increasing air-water gas exchange by nearly 10-fold during peak spawning. We suggest that management efforts to restore salmon ecosystems should consider effects on ecosystem metabolic properties and how salmon disturbance affects the incorporation of marine-derived nutrients into food webs.     

Preemptive and Salvage Harvesting of New England Forests: When Doing Nothing Is a Viable Alternative

Abstract:  One unexpected consequence of natural disturbances in forested areas is that managers often initiate activities that may impose greater ecosystem impacts than the disturbances themselves. By salvage logging areas affected by windstorms or other impacts, by harvesting host trees in advance of insect infestation or disease, or by preemptively harvesting forests in an attempt to improve their resilience to future disturbances and stresses, managers initiate substantial changes in the ecosystem structure and function. Much of this activity is undertaken in the absence of information on the qualitative and quantitative differences between disturbance impacts and harvesting. To provide insight for such decisions we evaluated the ecosystem consequences of two major disturbance processes in New England (U.S.A.)—intense windstorms and invasive pests and pathogens—and contrasted them with impacts from preemptive and salvage harvesting. Despite dramatic physical changes in forest structure resulting from hurricane impacts and insect infestation, little disruption of biogeochemical processes or other ecosystem functions typically follows these disturbances. Indeed, the physical and organic structures produced by these disturbances are important natural features providing habitat and landscape heterogeneity that are often missing due to centuries of land use. From an ecosystem perspective there are strong arguments against preemptive and salvage logging or the attempt through silvicultural means to improve the resistance or resilience of forests to disturbance and stress. There are often valid motivations for salvage or preemptive logging including financial considerations, human safety, and a desire to shape the long-term composition and resource-production characteristics of forests. Nonetheless, there are many ecological benefits derived from leaving forests alone when they are affected or threatened by disturbances and pest and pathogen outbreaks.     

Modeling the forest transition: forest scarcity and ecosystem service hypotheses.

An historical generalization about forest cover change in which rapid deforestation gives way over time to forest restoration is called "the forest transition." Prior research on the forest transition leaves three important questions unanswered: (1) How does forest loss influence an individual landowner's incentives to reforest? (2) How does the forest recovery rate affect the likelihood of forest transition? (3) What happens after the forest transition occurs? The purpose of this paper is to develop a minimum model of the forest transition to answer these questions. We assume that deforestation caused by landowners' decisions and forest regeneration initiated by agricultural abandonment have aggregated effects that characterize entire landscapes. These effects include feedback mechanisms called the "forest scarcity" and "ecosystem service" hypotheses. In the forest scarcity hypothesis, forest losses make forest products scarcer, which increases the economic value of forests. In the ecosystem service hypothesis, the environmental degradation that accompanies the loss of forests causes the value of ecosystem services provided by forests to decline. We examined the impact of each mechanism on the likelihood of forest transition through an investigation of the equilibrium and stability of landscape dynamics. We found that the forest transition occurs only when landowners employ a low rate of future discounting. After the forest transition, regenerated forests are protected in a sustainable way if forests regenerate slowly. When forests regenerate rapidly, the forest scarcity hypothesis expects instability in which cycles of large-scale deforestation followed by forest regeneration repeatedly characterize the landscape. In contrast, the ecosystem service hypothesis predicts a catastrophic shift from a forested to an abandoned landscape when the amount of deforestation exceeds the critical level, which can lead to a resource degrading poverty trap. These findings imply that incentives for forest conservation seem stronger in settings where forests regenerate slowly as well as when decision makers value the future.