退化生态系统恢复与恢复生态学

恢复生态学起源于100a前的山地、草原、森林和野生生物等自然资源的管理研究,形成于20世纪80年代。它是研究生态整合性的恢复和管理过程的科学。恢复生态学的研究对象是在自然或人为干扰下形成的偏离自然状态的退化生态系统。生态恢复的目标包括恢复退化生态系统的结构、功能、动态和服务功能,其长期目标是通过恢复与保护相结合,实现生态系统的可持续发展。恢复生态学的理论与方法较多,它们均源于生态学等相关学科,但自我设计和人为设计是唯一源于恢复生态学研究和实践的理论。由于生态系统的复杂性,退化生态系统恢复的方向和时间具有不确定性,其恢复的机理可用临界阈值理论和状态跃迁模型进行解释。中国森林恢复中存在的问题包括：大量营造种类和结构单一的人工林忽视了生物多样性在生态恢复中的作用;大量使用外来种;忽视了生态系统健康所要求的异质性;忽略了物种间的生态交互作用;造林时对珍稀濒危种需要缺乏考虑;城镇绿化忽略了植被的生态功能等问题。此外,还介绍了生态恢复的方法、成功恢复的标准,并提出了恢复生态学的发展趋势：恢复生态学尚未形成理论和方法体系,要成熟还有很长的路要走;恢复生态学正在强调自然恢复与社会、人文的耦合;对森林恢复研究要集中在恢复中的障碍和如何克服这些障碍两个方面;鉴于生态系统复杂性和动态性,应停止期待发现能预测恢复产出的简单定律,相反,应该根据恢复地点及目标多样性而强调适应性恢复。     

生态系统的脆弱性与退化生态系统

生态系统的脆弱性是一个含义广泛的概念,是生态系统内固有的特性,脆弱性只能在干扰的状态下才显现出来．而干扰（包括自然干扰和人为干扰）又是引起退化生态系统的原因,种类的入侵和消亡、种类组成的变化、生态系统的多样性和稳定性、生产力、生态位的分化及生态系统小环境变化则是研究退化生态系统形成和恢复的重要内容,本文探讨脆弱性与退化生态系统诸方面的关系以及在植被恢复上的应用．     

生态阈值:概念、方法与研究展望

生态阈值概念是20世纪70年代提出的,主要指生态系统的几个稳态之间突然改变的点或区域。在阐明生态系统结构与功能的关系、构建区域可持续发展范式以及服务于生态系统管理和生态红线的划定中,生态阈值的检测和量化有着重要的理论和实践意义。该文首先梳理了前人关于生态阈值的概念、类型的一些提法,从预警研究角度提出可以从两个层次理解生态阈值概念:生态阈值点是系统从量变到质变的转折点,类似于红色界限;而生态阈值带可以理解为量变过程中不同稳态之间的转换区域,类似于黄色与橙色预警边界带。黄色生态阈值表示生态系统可通过自身的调节能力重新达到稳定状态;橙色生态阈值表示需要排除干扰因子使得生态系统重新达到平衡;而红色生态阈值为关键阈值点,超过此阈值,生态系统将发生不可逆的退化甚至崩溃。该文还总结了目前确定生态阈值的主要方法,主要是基于野外观测数据的统计分析与模型模拟方法。最后,基于生态系统服务、生物多样性保护与生态系统管理等几个当今生态学热点研究领域,简单总结归纳了生态阈值的研究现状,并提出生态阈值未来的3个研究难点和方向:1)开展针对生态阈值检测和量化的研究;2)关注生态阈值的尺度效应并加强野外观测;3)发挥生态阈值的预警作用,指导"生态红线"的划定和生态系统管理。     

恢复生态学研究的一些基本问题探讨

对恢复生态学的研究概况、基本概念、内涵与研究内容以及生态恢复的目标、原则、程序与技术进行了分析与探讨。指出恢复生态学应加强基础理论研究(包括生态系统的演替理论及干扰条件下生态系统的受损过程与响应机制研究等)和应用技术研究(包括土壤、水体、大气和植被恢复技术、生物多样性保护技术以及生态系统的组装与集成技术等).生态恢复与重建是指根据生态学原理,通过一定的生物、生态以及工程的技术,人为地切断生态系统退化的主导因子和过程,调整和优化系统内部及其与外界的物质、能量和信息的流动过程及其时空秩序,使生态系统的结构、功能和生态学潜力尽快地成功地恢复到原有的乃至更高的水平。     

短期极端干旱事件干扰后退化沙质草地群落恢复力稳定性的测度与比较

利用对不同沙漠化程度的6个沙质草地群落样地的调查资料,并通过构建恢复力指数,尝试性地对沙漠化过程草地群落在经历约为0.5个生长季的短时间尺度极端干旱事件干扰后、在当年后0.5个生长季表现出的恢复力稳定性进行了定量测定与比较。结果表明:6个不同退化程度沙质草地群落在降水条件恢复后具有反应快速和补偿生长的能力,从而表现出良好的恢复力,即使最严重沙漠化程度的群落也恢复到甚至超过了其在干旱前的状况。各群落恢复力综合指数在2.21-1.16之间,分别以多度、高度、盖度和生物量指标计算的恢复力分指数在4.69-1.23,1.21-0.98,1.59-1.15和1.28-1.00之间,基本呈随沙漠化程度提高而减小的趋势。恢复力指数的计算结果表明,在经历短时间尺度干旱事件干扰后,所研究的退化沙质草地群落具有以较强的恢复力维持植被稳定的倾向和能力。群落之间的比较显示,恢复力随沙漠化程度的发展而降低。对群落恢复力来源与构成进行的分析表明,以多度指标计算的恢复力分指数最大,显示各群落都有充足的种源条件和土壤种子库为群落恢复力提供基本保障条件;群落恢复力不仅来源于1年生植物,也来源于多年生植物;一些群落的优势物种在恢复过程中发生了快速转换。通过综合分析本研究以群落内部生态过程为基础对群落恢复力进行的数量测定结果以及对该群落在同一干旱事件干扰下的抵抗力进行的已有研究结果,认为退化沙质草地群落较低的抵抗力和较高的恢复力都说明了植被稳定性对降水条件的依赖不可替代和无法超越。因而,群落在短时间尺度上具有随降水波动的必然性和不稳定性,而在较长时间尺度上又具有主要由群落恢复力所维持的稳定性;恢复过程中发生的群落优势物种快速转换现象是生物多样性的表现形式之一,进一步证明生物多样性对维持生态系统功能和促进植被稳定性具有重要作用,是植被生态系统的一个基本特征。     

景观生态学与退化生态系统恢复

退化生态系统的恢复是一项艰巨任务,它需要考虑到所要恢复的退化生态系统的结构,多样性和其动态的整体性和长期性。现在对于退化生态系统恢复研究已经要使生态学家们关注受损生态系统的理论和实际问题。退化生态系统恢复所面临的挑战是理解和利用生态演替理论来完成并加速恢复进程。恢复的主要目标是建立一个自维持的,由不同的群落或生态系统组成的能够满足不同需要如生物保护和粮食生产需要的景观。景观生态学关注于大的空间尺度的生态学问题。景观生态学研究方法可以为退化生态系统恢复实践提供指导。在解决退化生态系统的恢复问题时,景观生态学的方法在理论和实践上是有效的。景观生态学中的核心概念和其一般原理斑块形状、生态系统间相互作用、镶嵌系列等都同退化生态系统的恢复有着密切的关系。如恢复地点的选择和适当的恢复要素的空间配置。在评价退化生态系统的恢复是否取得成功,利用景观生态学也具有重要的意义。景观生态学理论如景观格局与景观异质性理论,干扰理论和尺度理论都能够指导退化生态系统的恢复实践。同样地,退化生态系统的恢复可以为景观生态学的研究提供非常恰当的实验场。寓景观生态学思想于退化生态系统恢复过程是一种新的有效途径。     

恢复生态学的理论与研究进展

简介了恢复生态学中常用的生态学原理,以及在其自身发展过程中产生的状态过渡模型及阈值、集合规则、参考生态系统、人为设计和自我设计、适应性恢复等理论;从生境、种群、群落、生态系统、景观尺度层面,以及将全球变化与人类干扰纳入生态恢复范畴等方面介绍了恢复生态学的研究进展与主流认识。在此基础上,对恢复生态学的发展障碍与发展趋势进行了评述。     

恢复力视角下的乡村空间演变与重构

乡村生产、生活、生态空间重构是中国乡村发展转型的重要途径。恢复力是指系统吸收干扰、经历变化和重组后,仍然保持原有功能、结构、特性和反馈的能力。梳理社会-生态系统恢复力、乡村社区恢复力、空间恢复力相应概念,借助宏观生态学领域中的恢复力相关概念阐释乡村空间演变过程,可以在深化乡村空间演变与重构理论内涵的同时更有效的理解乡村空间的演变过程和重构目标。乡村空间重构并不只是国土或规划层面的景观空间优化,而需要站在强化社会-生态系统恢复力的角度,从乡村空间演化机制入手,提升乡村空间演化动力从而驱动空间重构。将乡村空间的演变阶段嵌入社会-生态系统适应性循环过程中,将作为当前国际研究热点的社会-生态系统恢复力研究引入乡村地理学研究领域,从而进一步扩展了学科研究视角,完成乡村空间演变与重构的理论抽象。     

地下生态系统对生态恢复的影响

生态系统破坏与退化的加剧使生态恢复成为全球性的挑战课题,近年来生态恢复的研究已逐渐由地上向地下部分转移,地下部分对生态系统退化所起的作用、机理和过程已倍受关注。本文通过探讨恢复生态学的关键概念,从土壤、地下水循环、生物系统3个方面探讨了地下生态系统对生态恢复的作用机理和反馈机制。针对目前的研究现状,指出地下生态系统研究中存在的问题,并提出今后需要深入研究的几个方向:1)生态系统退化程度的诊断及其标准;2)基于诊断标准,针对不同退化生态系统类型选定恢复的目标植物群落,如何改善土壤性质,确定土壤性质的改善程度;确定地下水位及土壤含水量的阈值;如何有效选择、引入和接种土壤生物;3)生态系统地上和地下部分整合及恢复过程中监测指标的确定。     

新型生态系统理论及其争议综述

澳大利亚Richard J Hobbs教授等近年提出的新型生态系统(Novel Ecosystems)理论认为,由于人类作用,地球生态系统经历了前所未有的变化,很多生态系统已经越过不可逆转的阈值,不可能恢复到原有状态,形成了新的生态系统,其生物要素、非生物要素和系统功能等都发生了显著改变;人类应该面对现实,必须反思传统生态保护和生态恢复的行为、政策和思维;应该致力新型生态系统的特征、属性和演替规律的研究,在管理、规划、政策、组织和技术等方面的创新。新型生态系统理论引起了很大争议。质疑者认为,由于自然作用力和人类的持续扰动,地球生态系统一直在不断变化,所以一直都是"新"的,根本没必要贴上"新型"标签;该理论基本概念模糊,理论模型不精确,缺乏严密的逻辑推理,还很不成熟;该理论无助于生态保护和生态恢复的实践,会扰乱人们的思想,没有实践价值。不过,支持者和质疑者都承认地球上很多生态系统的确遭到严重破坏,已经发生深刻演替,极有必要对这类系统的非线性机制、系统阈值、恢复力、新范式,以及破坏后的所有特征等开展研究,应该理性选择合适的修复方法,理性分析人工干预的程度及其成功的可能性,科学制定行动方案和优选标准。跟踪国际前沿,开展新型生态系统理论研究有助于丰富我国恢复生态学理论以及创新工程实践。     

典型红壤区自然生态修复的适用性

自然修复主要通过封山育林、禁止农作、禁牧禁伐措施,减少人类对环境的扰动,利用自然生态环境的自我演替能力,恢复生态环境,实现生态平衡。自然修复作为一种成本低、无污染的生态修复手段很早就受到人们重视,但关于自然修复适用范围的研究较少。为了正确认识自然修复的适用性,选择了我国南方红壤地区长期遭受严重土壤侵蚀危害的福建省长汀县为研究对象,通过对长期自然修复样地的监测资料分析,发现在坡度条件为20%—30%下,当植被覆盖度低于20%的退化阈值时,严重的土壤侵蚀引发的土壤肥力损失将导致生态系统自我退化,自然修复不仅无法改善当地的生态系统,反而会引起生态系统的进一步恶化。由此可见,自然修复并不适合所有的生态系统,当生态系统退化到一定程度时,退化生态系统必须通过人工干预来修复。因此,必须探索适合当地的生态修复模式,在生态系统退化突破阈值时,红壤丘陵区应通过恢复土壤肥力、促进自然植被覆盖度增加、综合提高生态系统健康水平。     

Perspectives for ecosystem management based on ecosystem resilience and ecological thresholds against multiple and stochastic disturbances

Ecosystem resilience is the inherent ability to absorb various disturbances and reorganize while undergoing state changes to maintain critical functions. When ecosystem resilience is sufficiently degraded by disturbances, ecosystem is exposed at high risk of shifting from a desirable state to an undesirable state. Ecological thresholds represent the points where even small changes in environmental conditions associated with disturbances lead to switch between ecosystem states. There is a growing body of empirical evidence for such state transitions caused by anthropogenic disturbances in a variety of ecosystems. However, fewer studies addressed the interaction of anthropogenic and natural disturbances that often force an ecosystem to cross a threshold which an anthropogenic disturbance or a natural disturbance alone would not have achieved. This fact highlights how little is known about ecosystem dynamics under uncertainties around multiple and stochastic disturbances. Here, we present two perspectives for providing a predictive scientific basis to the management and conservation of ecosystems against multiple and stochastic disturbances. The first is management of predictable anthropogenic disturbances to maintain a sufficient level of biodiversity for ensuring ecosystem resilience (i.e., resilience-based management). Several biological diversity elements appear to confer ecosystem resilience, such as functional redundancy, response diversity, a dominant species, a foundation species, or a keystone species. The greatest research challenge is to identify key elements of biodiversity conferring ecosystem resilience for each context and to examine how we can manage and conserve them. The second is the identification of ecological thresholds along existing or experimental disturbance gradients. This will facilitate the development of indicators of proximity to thresholds as well as the understanding of threshold mechanisms. The implementation of forewarning indicators will be critical particularly when resilience-based management fails. The ability to detect an ecological threshold along disturbance gradients should therefore be essential to establish a backstop for preventing the threshold from being crossed. These perspectives can take us beyond simply invoking the precautionary principle of conserving biodiversity to a predictive science that informs practical solutions to cope with uncertainties and ecological surprises in a changing world.     

Quantifying resilience of multiple ecosystem services and biodiversity in a temperate forest landscape

Resilience is increasingly being considered as a new paradigm of forest management among scientists, practitioners, and policymakers. However, metrics of resilience to environmental change are lacking. Faced with novel disturbances, forests may be able to sustain existing ecosystem services and biodiversity by exhibiting resilience, or alternatively these attributes may undergo either a linear or nonlinear decline. Here we provide a novel quantitative approach for assessing forest resilience that focuses on three components of resilience, namely resistance, recovery, and net change, using a spatially explicit model of forest dynamics. Under the pulse set scenarios, we explored the resilience of nine ecosystem services and four biodiversity measures following a one‐off disturbance applied to an increasing percentage of forest area. Under the pulse + press set scenarios, the six disturbance intensities explored during the pulse set were followed by a continuous disturbance. We detected thresholds in net change under pulse + press scenarios for the majority of the ecosystem services and biodiversity measures, which started to decline sharply when disturbance affected >40% of the landscape. Thresholds in net change were not observed under the pulse scenarios, with the exception of timber volume and ground flora species richness. Thresholds were most pronounced for aboveground biomass, timber volume with respect to the ecosystem services, and ectomycorrhizal fungi and ground flora species richness with respect to the biodiversity measures. Synthesis and applications. The approach presented here illustrates how the multidimensionality of stability research in ecology can be addressed and how forest resilience can be estimated in practice. Managers should adopt specific management actions to support each of the three components of resilience separately, as these may respond differently to disturbance. In addition, management interventions aiming to deliver resilience should incorporate an assessment of both pulse and press disturbances to ensure detection of threshold responses to disturbance, so that appropriate management interventions can be identified.     

Accounting for ecosystem alteration doubles estimates of conservation risk in the conterminous United States

Previous national and global conservation assessments have relied on habitat conversion data to quantify conservation risk. However, in addition to habitat conversion to crop production or urban uses, ecosystem alteration (e.g., from logging, conversion to plantations, biological invasion, or fire suppression) is a large source of conservation risk. We add data quantifying ecosystem alteration on unconverted lands to arrive at a more accurate depiction of conservation risk for the conterminous United States. We quantify ecosystem alteration using a recent national assessment based on remote sensing of current vegetation compared with modeled reference natural vegetation conditions. Highly altered (but not converted) ecosystems comprise 23% of the conterminous United States, such that the number of critically endangered ecoregions in the United States is 156% higher than when calculated using habitat conversion data alone. Increased attention to natural resource management will be essential to address widespread ecosystem alteration and reduce conservation risk.     

Conserving Biodiversity in a Human-Dominated World: Degradation of Marine Sessile Communities within a Protected Area with Conflicting Human Uses

Conservation research aims at understanding whether present protection schemes are adequate for the maintenance of ecosystems structure and function across time. We evaluated long-term variation in rocky reef communities by comparing sites surveyed in 1993 and again in 2008. This research took place in Tigullio Gulf, an emblematic case study where various conservation measures, including a marine protected area, have been implemented to manage multiple human uses. Contrary to our prediction that protection should have favored ecosystem stability, we found that communities subjected to conservation measures (especially within the marine protected area) exhibited the greatest variation toward architectural complexity loss. Between 1993 and 2008, chronic anthropogenic pressures (especially organic load) that had already altered unprotected sites in 1993 expanded their influence into protected areas. This expansion of human pressure likely explains our observed changes in the benthic communities. Our results suggest that adaptive ecosystem-based management (EBM), that is management taking into account human interactions, informed by continuous monitoring, is needed in order to attempt reversing the current trend towards less architecturally complex communities. Protected areas are not sufficient to stop ecosystem alteration by pressures coming from outside. Monitoring, and consequent management actions, should therefore extend to cover the relevant scales of those pressures.     

A regional perspective on the effects of human disturbance on the termites of Sundaland

The remains of the rainforests of Sundaland are threatened by logging,burning and conversion to agriculture. In this study theeffects of different levels of disturbance and recovery on termites wereexamined. This was carried out on a regional scale and incorporated sixdifferent disturbance effects. Termites were found to be strongly effected bydisturbance, particularly by complete removal of the forest canopy. Recoveryfrom severe disturbance is discussed and we find that completely cleared andfarmed land, when left fallow near to a source area of primary forest for over50 years, can completely recover its termite assemblage andassociated ecosystem services. Over larger areas termites do not recover fromdisturbance events for millennia. The conservation implications of our findingsare discussed, with reference to both the conservation of species and ofecosystem services. We propose that most Sundan termite species can be conservedin a relatively small area. However, termite composition and ecosystem processesthroughout the region may be altered forever, if current widespread rainforestdestruction is not halted.     

Impacts of biological invasions on disturbance regimes

Human management activities have altered the frequency and intensity of ecosystem disturbance often with enormous impacts on landscape structure and composition. One additional and under-appreciated way in which humans have altered disturbance regimes is through the introduction of invasive non-native species, themselves capable of modifying existing disturbance regimes or introducing entirely new disturbances. In many cases, modifications of disturbance regimes results in maintenance of ecosystems in a new or transitional state. There is now evidence that alteration of disturbance regime may be the most profound effect that a species or functional group can have on ecosystem structure and function.     

Measures of resilience: the response of coastal sage scrub to fire

Measures of four components of resilience are developed and used to quantify the response of coastal sage scrub to fire in southern California: (1) elasticity (rate of recovery following disturbance), (2) amplitude (threshold of disturbance beyond which recovery to the original state no longer occurs), (3) malleability (extent of alteration of the new stable-state from the original) and (4) damping (extent and duration of oscillation in an ecosystem parameter following disturbance). Vegetation and soil properties measured before fire, and for the first 5–6 yr after fire on four coastal (Venturan association) and four inland (Riversidian association) sites of coastal sage were used to follow changes. In addition, results from a simulation model of post-fire succession in Venturan coastal sage scrub (the FINICS model of Malanson) were used to examine resilience behavior over a 200 yr period. Resilience behavior of coastal sage scrub is critically influenced by the presence of a competitive mix of inherently strongly and weakly resprouting species. Sites dominated by weak resprouters exhibit lower elasticity and less damping of year-to-year fluctuations in composition in the early post-fire years. Sites with a mixture of weak and strong resprouters have a lower threshold of disturbance (amplitude) before species extirpation occurs, a result intensified by a higher frequency of disturbance. Malleability is also greater in these systems under higher disturbance frequency.Nomenclature follows. P.A. Munz, 1974. A Flora of Southern California. Univ. California Press.     

The maintenance of evolutionary equilibrium in Late Ordovician benthic marine invertebrate faunas

An upper evolutionary limit on species equilibrium number (S of MacArthur & Wilson) has been postulated but never demonstrated. Results of the present study indicate that an S of about 10 was attained very rapidly in a Late Ordovician benthic marine invertebrate faunal succession. This S value was then maintained for perhaps five million years within a marine environment that did not remain uniform but changed progressively from relatively deep to shallow water. Most importantly, significant taxonomic and presumed trophic changes that accompanied the gradual habitat alteration seem to have had a negligible effect on the plateau-like limit to species equilibrium number. We conclude from these preliminary results that the maintenance of evolutionary equilibrium in an open ecosystem strongly suggests a long-term component of biotic resiliency, at least within this one marine ecosystem, and perhaps in many others. The reasons for this resiliency remain to be explored.