Habitat patchiness,ecological connectivity and the uneven recovery of boreal stream ecosystems from an experimental drought

Ongoing climate change is increasing the occurrence and intensity of drought episodes worldwide, including in boreal regions not previously regarded as drought prone, and where the impacts of drought remain poorly understood. Ecological connectivity is one factor that might influence community structure and ecosystem functioning post‐drought, by facilitating the recovery of sensitive species via dispersal at both local (e.g. a nearby habitat patch) and regional (from other systems within the same region) scales. In an outdoor mesocosm experiment, we investigated how impacts of drought on boreal stream ecosystems are altered by the spatial arrangement of local habitat patches within stream channels, and variation in ecological connectivity with a regional species pool. We measured basal ecosystem processes underlying carbon and nutrient cycling: (a) algal biomass accrual; (b) microbial respiration; and (c) decomposition of organic matter, and sampled communities of aquatic fungi and benthic invertebrates. An 8‐day drought event had strong impacts on both community structure and ecosystem functioning, including algal accrual, leaf decomposition and microbial respiration, with many of these impacts persisting even after water levels had been restored for 3.5 weeks. Enhanced connectivity with the regional species pool and increased aggregation of habitat patches also affected multiple response variables, especially those associated with microbes, and in some cases reduced the effects of drought to a small extent. This indicates that spatial processes might play a role in the resilience of communities and ecosystem functioning, given enough time. These effects were however insufficient to facilitate significant recovery in algal growth before seasonal dieback began in autumn. The limited resilience of ecosystem functioning in our experiment suggests that even short‐term droughts can have extended consequences for stream ecosystems in the world's vast boreal region, and especially on the ecosystem processes and services mediated by algal biofilms.     

A call for applying trophic structure in ecological restoration

Ecological restoration projects have traditionally focused on vegetation as both a means (seeding, planting, and substrate amendments) and ends (success based upon primary productivity and vegetation diversity). This vegetation‐centric approach to ecological restoration stems from an historic emphasis on esthetics and cost but provides a limited measure of total ecosystem functioning and overlooks alternative ways to achieve current and future restoration targets. We advocate a shift to planning beyond the plant community and toward the physical and biological components necessary to initiate autogenic recovery, then guiding this process through the timely introduction of top predators and environmental modifications such as soil amendments and physical structures for animal nesting and refugia.     

集合种群理论在生态恢复中的应用

环境问题的改善是生态与环境学家所面临的挑战之一 ,其核心是生态系统的稳定性和平衡性遭到极大的破坏 ,最明显的表现是生境破碎和栖息地丧失。本文探讨了集合种群理论的形成与成因 ,概述了该理论发展的最新成果及应用前景。在集合种群理论应用于生态恢复实践的论述中 ,阐述了一些原则性问题 ,包括集合种群平衡观、最小可存活集合种群、最适斑块密度以及高质量生境斑块等 ,以求在人们设计物种保护和恢复对策时 ,有一定的指导价值。     

Linking biodiversity and ecosystems: towards a unifying ecological theory

Community ecology and ecosystem ecology provide two perspectives on complex ecological systems that have largely complementary strengths and weaknesses. Merging the two perspectives is necessary both to ensure continued scientific progress and to provide society with the scientific means to face growing environmental challenges. Recent research on biodiversity and ecosystem functioning has contributed to this goal in several ways. By addressing a new question of high relevance for both science and society, by challenging existing paradigms, by tightly linking theory and experiments, by building scientific consensus beyond differences in opinion, by integrating fragmented disciplines and research fields, by connecting itself to other disciplines and management issues, it has helped transform ecology not only in content, but also in form. Creating a genuine evolutionary ecosystem ecology that links the evolution of species traits at the individual level, the dynamics of species interactions, and the overall functioning of ecosystems would give new impetus to this much-needed process of unification across ecological disciplines. Recent community evolution models are a promising step in that direction.     

Coastal wetland restoration through the lens of Odum's theory of ecosystem development

Advancing ecological restoration assessments requires a more detailed consideration of species interactions and ecosystem processes. Most restoration projects rely on a few metrics not always directly linked with ecological theory. Here, we used Odum's theory of ecosystem development to assess and compare the ecosystem structure and services of created marshes (4–6 years old) with preexisting, reference marshes in a brackish water region of the Mississippi River Delta. We built ecosystem models for created and reference marshes that integrated large datasets of stomach contents, stable isotopes, and taxa abundances. Despite strong resemblance in community structure, created marshes were at an earlier succession stage compared to the reference marshes, having lower biomass (including exploited species), higher biomass turnover and production, less dependence on detritus, lower material cycling, and less energy flowing through specialist pathways. Although preserving preexisting marshes should be a priority, created marshes may still be an important tool for the restoration of coastal areas and their ecosystem services. In addition, our results show that comparisons of species biodiversity alone may fail to capture essential differences in ecosystem processes between habitats, which reinforces the importance of ecosystem modeling approaches to assess restoration projects.     

演替理论与植被恢复

《昆明-蒙特利尔全球生物多样性框架》提出要高质量保护和恢复各30%的土地,最大化地实现保护生物多样性和缓解气候变化的目标,而演替理论和植被恢复可以为实现30%的保护和恢复目标服务。演替理论是植被生态学中的核心理论,演替是指在一个地点上由一群不同物种组成的生命体的结构或组成随时间而变化的过程;植被恢复是以植物种植、配置为主,恢复或重建植物群落或天然更新恢复植物群落的过程,植被恢复是生态系统结构和功能从简单到复杂、从低级向高级变化的过程,最终目的是建立健康稳定的植物群落。演替是植被恢复的基础,植被恢复被视为对演替过程的操纵,以达到恢复受损植被生态系统的目标。演替理论可以指导植被恢复,而植被恢复对演替理论的发展有益。演替按裸地性质可以分为原生演替和次生演替,有研究建议将恢复过程视为第三演替,这将有助于理解通过人为干预促进植被恢复成功的管理选择,特别是通过强调退化生态系统中的环境和生物遗存的管理选择。此外,该文还提出了植被恢复理论和演替理论未来可能重点关注的科学和技术问题。     

生态系统服务理论与山水林田湖草生态保护修复的应用

科学有效的理论基础是推进山水林田湖草生态保护修复工程顺利实施的保障。探讨了生态系统服务理论在山水林田湖草生态保护修复中的应用,以“压力-状态-响应”为主线构建了不同时空尺度上山水林田湖草与生态系统服务之间的关系认知框架,分析了山水林田湖草系统修复工程中生态系统服务研究的关键问题：（1）山水林田湖草系统修复工程区主要生态系统服务的时空演变规律与驱动机制;（2）山水林田湖草系统修复工程区多种生态系统服务之间的权衡与协同关系;（3）山水林田湖草系统修复工程区生态系统服务集成与生态系统管理策略;（4）山水林田湖草系统修复工程调控及其尺度效应;（5）探索优质生态产品价值实现机制,阐述了生态系统服务理论在山水林田湖草系统修复中的现实意义,以期有效推动山水林田湖草生态保护修复工程从科学到实践的深入。     

Knowing when (not) to attempt ecological restoration

Here we argue that there are two important steps in the decision process to restore ecological system that are often ignored. First, consideration of restoration is in response to observed change in a system, but ecological systems can fluctuate widely in their normal dynamic. Thus, there is an imperative to interpret ecological change; shifts in community structure that represent “typical” fluctuations in a properly functioning ecosystem do not warrant restoration, while change associated with phase shift in the system may well demand restoration action. Second, where restoration effort is warranted, it needs to be determined whether management responses are likely to be successful within resource constraints. Where ecological change involves pronounced hysteresis, even massive effort may have little chance in effecting recovery to a preferred ecosystem state. Theory and models indicate that consideration of the characteristic length scales (CLSs) of ecological systems provides an unambiguous interpretation of ecological change, enabling differentiation of “typical” fluctuations from phase shift, and here we show that CLSs can be calculated for real communities from their species' dynamics, and that their behavior is as predicted from theory. We also show that for ecological systems where local interactions and forcings are well understood, validated simulation models can provide a ready means to identify hysteresis and estimate its magnitude. We conclude that there are useful tools available for ecologists to address the key questions of (1) whether restoration attempts are warranted in the first place and, if they are, (2) whether it is practical to pursue them.     

Fish community responses to drying disturbances in an intermittent stream: a landscape perspective

1. Refugia are critical to the persistence of individuals, populations and communities in disturbed environments, yet few studies have considered how the position of refugia within the landscape interacts with the behavioural responses of component species to determine the influence of disturbance events on mobile animals. 2. An 18‐month quantitative electrofishing survey was undertaken on the Selwyn River, a stream that is intermittent in its middle reaches, to determine how the direction and distance to refugia affect the response of fish populations to drying, and how landscape context interacts with flow permanence to produce spatial patterns in communities. 3. Overall, the propensity of fish to take refuge in perennial reaches during drying episodes, and the rate and extent of recolonization from these refugia upon rewetting, depended upon the direction and distance to refugia and the behaviour of component species. 4. In the upper river, Canterbury galaxias (Galaxias vulgaris), upland bullies (Gobiomorphus breviceps) and brown trout (Salmo trutta) migrated upstream to permanent water as the stream dried from the bottom up, but frequent drying and slow recolonization by most species combined to produce a fish community in intermittent reaches that was quantitatively and qualitatively different to that in neighbouring perennial reaches. 5. In the lower river, fish did not appear to migrate downstream to permanent water as the stream dried from the top down, but a lower frequency of drying episodes and faster recolonization by upland bullies and eels (Anguilla spp.) from downstream refugia allowed the fish community in intermittent reaches to converge with that in neighbouring perennial reaches during prolonged wetted periods. 6. Longitudinal patterns of increasing fish density and species richness with flow permanence are interpreted as the product of species‐specific responses to drying events and the spatial position of refugia within the riverscape.     

How ecological neighbourhoods influence the structure of the scavenger guild in low arctic tundra

Aim How the ecological neighbourhoods of coast and forest affect arctic tundra ecosystems is a pressing question as the circumpolar tundra belt is shrinking under global warming. Mobile facultative scavengers are likely to negatively impact tundra biodiversity as dominant competitors or predators, if they spill over into tundra. Here, we provide the first quantitative assessments of the structure of a scavenger guild in low arctic tundra with emphasis on how it changes along spatial gradients from neighbouring ecosystems (i.e. forest and coast) and with altitude (i.e. productivity gradients). We also assess the likelihood of interactions between guild members that may negatively impact vulnerable tundra species. Location North‐eastern part of Norway. Methods Extensive records of scavenger prevalence were obtained by deploying automatic digital cameras at experimental carcasses in tundra regions covering several thousand square kilometres and three winters in northern Norway. Main conclusions We found short‐range neighbourhood effects of forest and coast within the tundra scavenger guild. Species richness declined steeply with decreasing distance from the neighbouring ecosystems, in particular subarctic forest, and with increasing altitude. Bird species with strongholds in forest (golden eagle Aquila chrysaetos and hooded crow Corvus cornix) or along the coast (white‐tailed eagle Haliaeetus albicilla) were mostly responsible for short‐range neighbourhood effects on guild structure. However, the two most abundant guild members, the common raven Corvus corax and the red fox Vulpes vulpes, exhibited no spatial patterns within the range of neighbourhoods and altitudes examined. There was a clear diurnal segregation in the use of carcasses between birds and mammals reducing the likelihood of direct interactions between these two taxa. Presence of red fox appeared to exclude the arctic fox Vulpes lagopus, the only endemic tundra species within the guild, from carcasses.     

Factors affecting the fate of Pacific lamprey carcasses and resource transport to riparian and stream macrohabitats

1. Anadromous fish transport marine-derived nutrients to freshwaters during spawning migrations with potential implications for stream food webs. While many studies have explored the role of marine-derived nutrients instream ecosystems (particularly via Pacific salmonids [Oncorhynchus spp.]), relatively few have examined the spatial distribution and patchiness of non-salmonid fish carcasses or rates of transport to the riparian zone.
2. We radio-tagged and released 144 mature Pacific lamprey (Entosphenus tridentatus) prior to spawning and tracked the fate of post-spawn carcasses in two inland Columbia River basin streams to characterise spatial distribution of carcasses and marine-derived nutrient deposition. We found that 27 and 40% of lamprey that could be assigned a fate were moved into the riparian zone adjacent to stream segments exhibiting higher velocity conditions with larger substrates. Conversely, lamprey with instream fates were associated with depositional microhabitats and woody debris dams. Estimated carcass loading rates varied by more than an order of magnitude among habitats. These patterns probably reflect a combination of processes influencing the likelihood of carcass removal (e.g. by predators or scavengers, or stranding) and factors affecting the distribution of carcasses remaining within the stream.
3. Our results demonstrate substantial transport of lamprey carcasses across the stream-riparian ecotone and a non-random distribution of carcasses within streams, patterns which probably influence how resources enter stream and riparian food webs. More broadly, the results suggest local and landscape-scale hydrogeomorphic factors, along with species-specific traits and phenology, affect the distribution and potential roles of fish carrion in stream food webs.

     

溪流生态系统潜流带生态学研究概述

最近一、二十年,对潜流带研究的逐渐开展已使人们充分认识到潜流带在溪流生态系统结构、功能和生态过程中的重要意义。潜流带是溪流地表水和地下水相互作用的界面,占据着在地表水、河道之下的可渗透的沉积缓冲带、侧向的河岸带和地下水之间的中心位置。有关潜流带重要性的近期研究进展增进了我们对溪流生态学的理解,大大扩展了水生生物生境的物理空间以及生物相互作用和生产力存在的区域。潜流带生境包含多样化的、丰度很高的动物区系,其常常控制着溪流生物生产力和生态过程。潜流带对溪流生态系统的潜在重要性来自于生物学和生物地化活动。潜流带在溪流有机物的分解和水质净化等生态过程中发挥着重要的作用。潜流带是溪流集水区内各种环境特征的综合表征体,它能够反映周围景观的环境条件及其变化,集水区内的自然或人为干扰,都会影响到潜流带的水文循环、理化特征、生境分布、营养结构和基本生态过程。因此,对溪流生态系统的综合管理必须包括潜流带。最后对潜流带生态学研究现存的主要问题及未来研究展望提出了几点看法。     

Tracing energy flow in stream food webs using stable isotopes of hydrogen

1. Use of the natural ratios of carbon and nitrogen stable isotopes as tracers of trophic interactions has some clear advantages over alternative methods for food web analyses, yet is limited to situations where organic materials of interest have adequate isotopic separation between potential sources. This constrains the use of natural abundance stable isotope approaches to a subset of ecosystems with biogeochemical conditions favourable to source separation. 2. Recent studies suggest that stable hydrogen isotopes (δD) could provide a robust tracer to distinguish contributions of aquatic and terrestrial production in food webs, but variation in δD of consumers and their organic food sources are poorly known. To explore the utility of the stable hydrogen isotope approach, we examined variation in δD in stream food webs in a forested catchment where variation in δ¹³C has been described previously. 3. Although algal δD varied by taxa and, to a small degree, between sites, we found consistent and clear separation (by an average of 67‰) from terrestrial carbon sources. Environmental conditions known to affect algal δ¹³C, such as water velocity and stream productivity did not greatly influence algal δD, and there was no evidence of seasonal variation. In contrast, algal δ¹³C was strongly affected by environmental factors both within and across sites, was seasonally variable at all sites, and partially overlapped with terrestrial δ¹³C in all streams with catchment areas larger than 10 km². 4. While knowledge of isotopic exchange with water and trophic fractionation of δD for aquatic consumers is limited, consistent source separation in streams suggests that δD may provide a complementary food web tracer to δ¹³C in aquatic food webs. Lack of significant seasonal or spatial variation in δD is a distinct advantage over δ¹³C for applications in many aquatic ecosystems.     

Quantifying relationships between land‐use gradients and structural and functional indicators of stream ecological integrity

1. Modification of natural landscapes and land‐use intensification are global phenomena that can result in a range of differing pressures on lotic ecosystems. We analysed national‐scale databases to quantify the relationship between three land uses (indigenous vegetation, urbanisation and agriculture) and indicators of stream ecological integrity. Boosted regression tree modelling was used to test the response of 14 indicators belonging to four groups – water quality (at 578 sites), benthic invertebrates (at 2666 sites), fish (at 6858 sites) and ecosystem processes (at 156 sites). Our aims were to characterise the ecological response curves of selected functional and structural metrics in relation to three land uses, examine the environmental moderators of these relationships and quantify the relative utility of metrics as indicators of stream ecological integrity. 2. The strongest indicators of land‐use effects were nitrate + nitrite, delta‐15 nitrogen value (δ¹⁵N) of primary consumers and the Macroinvertebrate Community Index (a biotic index of organic pollution), while the weakest overall indicators were gross primary productivity, benthic invertebrate richness and fish richness. All indicators declined in response to removal of indigenous vegetation and urbanisation, while variable responses to agricultural intensity were observed for some indicators. 3. The response curves for several indicators suggested distinct thresholds in response to urbanisation and agriculture, specifically at 10% impervious cover and at 0.1 g m^?3 nitrogen concentration, respectively. 4. Water quality and ecosystem process indicators were influenced by a combination of temperature, slope and flow variables, whereas for macroinvertebrate indicators, catchment rainfall, segment slope and temperature were significant environmental predictor variables. Downstream variables (e.g. distance to the coast) were significant in explaining residual variation in fish indicators, not surprisingly given the preponderance of diadromous fish species in New Zealand waterways. The inclusion of continuous environmental variables used to develop a stream typology improved model performance more than the inclusion of stream type alone. 5. Our results reaffirm the importance of accounting for underlying spatial variation in the environment when quantifying relationships between land use and the ecological integrity of streams. Of distinctive interest, however, were the contrasting and complementary responses of different indicators of stream integrity to land use, suggesting that multiple indicators are required to identify land‐use impact thresholds, develop environmental standards and assign ecological scores for reporting purposes.     

Assessing stream channel restoration: the phased recovery framework

Channel reconfiguration is one of the most common and costly stream restoration techniques, though its effectiveness is frequently questioned. Project monitoring often tracks changes in macroinvertebrate communities and other responses for a 5‐year period. However, channel reconfiguration is a documented disturbance to stream ecosystems, suggesting that this form of restoration initiates succession over longer time frames than monitoring typically captures. To address the role of succession in stream ecosystem recovery, we developed the Phased Recovery Framework (PRF) which proposes benchmarks represented by predictable habitat structure and community composition based on project age. The PRF was tested across nine stream restoration projects in western Montana, ranging in age from 1 to 18 years, each paired with an established reference system. We tested for differences in channel form, habitat character, and macroinvertebrate community composition. While restoration established desired channel form, most biotic variables had not recovered to reference condition even for the oldest projects. Across all sites, phases of the PRF were poor predictors of response. However, analyzing responses to reconfiguration independently for sites in watersheds with unimpaired water quality versus those experiencing excessive nutrient enrichment (i.e. impaired sites) indicated that biological variables converged on reference conditions at unimpaired sites, but diverged across impaired reaches. These large‐scale anthropogenic influences may play a stronger role in recovery than do changes to channel form and need to be incorporated into project design and success criteria. Assessment of the PRF suggests that short‐term monitoring is not likely to produce reliable indicators of effectiveness without incorporating locally appropriate change associated with watershed impairment and successional progression.     

Organizational capacity and ecological restoration

Organizations entrusted with responsibilities and resources to repair ecosystems have for many decades pursued their defining purpose against long odds created by a host of inherent challenges, notably the long time frames required for ecological recovery and landscape-level stressors. Global change compounds these challenges, increasing shocks to the operating environments of these organizations. Interest in assessing organizational capacity to respond to system shocks (i.e. resilience) productively has been strong in many fields, though not in the restoration arena. The objectives of this paper are to build awareness of the importance of organizations for achieving the aims of restoration and to spur organizational research to strengthen the restoration sector. I summarize research on organizations relevant to the restoration sector and with this foundation propose a framework for assessing the capacity of restoration organizations. The proposed framework is an adaptation of models used in other sectors, based on five critical capacities: situation awareness, governance and leadership, internal resources, external relations, and change readiness. We can assess the extent to which an organization possesses each capacity by eliciting feedback about functions linked to each capacity. Devising assessment tools from this framework requires attention to key realities of the restoration sector including prevalence of short-term funding, effect of externalities on restoration outcomes, dependence on partnerships of multiple organizations for complex and large restorations. Exploration into assessment approaches for restoration organizations highlights a major knowledge gap that, if addressed, could enhance the reliability of restoration as a global and local strategy for improving ecosystems services.     

国内外主要湾区生态系统特征、修复理论与技术模式

通过总结粤港澳大湾区、东京湾区和旧金山湾区等国内外主要湾区的生态系统特征、生态修复理论和实践研究进展,在辨析生态修复概念内涵的基础上,基于Meta-Analysis及综合分析方法,分析了生态系统退化机制及驱动因子,归纳总结湾区生态修复的主要理论基础、技术模式及案例。结果表明:(1)国内外三大主要湾区的生态系统特征为森林占比最高,其次是农田和草地占比,城镇占比第三。森林一般分布在湾区外围,城镇分布在湾区内核河口三角洲附近。(2)湾区生态修复理论包括以恢复生态学、景观生态学和复合生态系统生态学为基础的三种修复理论,生态修复的类别分为补救修复、改善修复、生态恢复和复垦等。(3)湾区生态修复技术模式包括主动修复、被动修复和重建等三类技术模式。在总结梳理生态修复理论和技术模式的基础上,结合当前国内生态修复存在问题,本文提出我国和广东省开展生态修复实践的建议和展望,以期为粤港澳大湾区生态修复提供一定的理论指导。     

生态恢复中生态系统服务的演变:趋势、过程与评估

经过10余年的发展,生态系统服务已经成为生态恢复研究关注的前沿和热点。生态恢复改变了生态系统格局与过程,对生态系统服务的产生和提供具有重要影响。但是目前对于生态系统服务在生态恢复过程中的演化仍缺少系统性研究。对国内外相关研究的最新成果进行综述,总结了生态系统服务评估中框架的构建和方法的选择(参数转移法、系统模型法和定量指标法),介绍了生态恢复对生态系统服务的促进作用、生态系统服务的演变过程以及不同生态系统服务间的协同与权衡关系,分析了社会经济因素对生态恢复和生态系统服务维持的影响。最后结合我国生态恢复实践,提出未来生态恢复和生态系统服务研究可以从深化作用机制研究、推动服务评估创新、增强研究成果应用3方面深化和拓展。     

湖泊生态恢复的基本原理与实现

当前我国湖泊污染及富营养化问题非常严重。湖泊治理的一个有效途径就是恢复水生植物,通过草型湖泊生态系统的培植来达到控制富营养化和净化水质的目的。但是,迄今为止,只有在局部水域或滨岸地区获得成功,恢复的水生植物主要是挺水植物或漂浮植物。鲜有全湖性的水生植物恢复和生态修复成功的例子。原因是对湖泊生态系统退化及其修复的机理了解甚少。实际上,环境条件不同决定了生态系统类型的不同,只有通过环境条件的改变才能实现生态系统的转变。利用草型湖泊生态系统来净化水质,其实质是利用生态系统对环境条件的反馈机制。但是,这种反馈无法从根本上改变其环境条件,因此其作用是有限的,不宜过分夸大。以往许多湖泊生态修复的工作之所以鲜有成功的例子,原因就是过于注重水生植物种植本身,而忽视了水生植物生长所需的环境条件的分析和改善。实施以水生植物恢复为核心的生态修复需要一定的前提条件。就富营养化湖泊生态恢复而言,这些环境条件包括氮磷浓度不能太高,富含有机质的沉积物应该去除,风浪不能太大以免对水生植物造成机械损伤,水深不能太深以免影响水生植物光合作用,鱼类种群结构应以食肉性鱼为主等等。因此,在湖泊污染很重或者氮磷负荷很高的情况下,寻求以沉水植物为核心的湖泊生态恢复来改善水质是不切实际的。为此,提出湖泊治理应该遵循先控源截污、后生态恢复,即先改善基础环境,后实施生态恢复的战略路线。