Effects of Land Cover on Stream Ecosystems: Roles of Empirical Models and Scaling Issues

We built empirical models to estimate the effects of land cover on stream ecosystems in the mid-Atlantic region (USA) and to evaluate the spatial scales over which such models are most effective. Predictive variables included land cover in the watershed, in the streamside corridor, and near the study site, and the number and location of dams and point sources in the watershed. Response variables were annual nitrate flux; species richness of fish, benthic macroinvertebrates, and aquatic plants; and cover of aquatic plants and riparian vegetation. All data were taken from publicly available databases, mostly over the Internet. Land cover was significantly correlated with all ecological response variables. Modeled R² ranged from 0.07 to 0.5, but large data sets often allowed us to estimate with acceptable precision the regression coefficients that express the change in ecological conditions associated with a unit change in land cover. Dam- and point-source variables were ineffective at predicting ecological conditions in streams and rivers, probably because of inadequacies in the data sets. The spatial perspective (whole watershed, streamside corridor, or local) most effective at predicting ecological response variables varied across response variables, apparently in concord with the mechanisms that control each of these variables. We found some evidence that predictive power fell in very small watersheds (less than 1–10 km²), suggesting that the spatial arrangement of landscape patches may become critical at these small scales. Empirical models can replace, constrain, or be combined with more mechanistic models to understand the effects of land-cover change on stream ecosystems. Present address for L.C. Thompson: Wildlife, Fish and Conservation Biology Department, University of California, Davis, CA 95616.     

Linkages among land-use, water quality, physical habitat conditions and lotic diatom assemblages: A multi-spatial scale assessment

We assessed the importance of spatial scales (catchment, stream network, and sample reach) on the effects of agricultural land-use on lotic diatom assemblages along a land-use gradient in the agricultural Willamette Valley Ecoregion of Oregon. Periphyton, water chemistry, and physical habitat conditions were characterized for 25 wadeable streams during a dry season (July to September, 1997). Additional water chemistry samples were collected in the following wet season (February 1998) to assess seasonal effects of land-use on stream water chemistry. Percent agricultural land-use in the study catchments ranged from 10% to 89% with an average of 52%. Partial canonical correspondence analysis (CCA) with the first axis constrained by % agricultural land-use showed that % agricultural land-use at 3 spatial scales explained between 3.7%–6.3% of variability in the diatom species dataset. Monte Carlo Permutation tests indicated that the variance explained by % agricultural land-use was only significant at the spatial scale of the stream network with 10- and 30-m band width (p<0.05, 999 permutations). In addition to the effects of % agricultural land-use, partial CCAs with a forward selection option showed that water chemistry (e.g., SiO₂), reach-scale stream channel dimensions (e.g., width, depth, and slope), reach-scale in-stream habitats (substrates and filamentous algal cover in stream beds), and riparian vegetative buffer were all important with relation to diatom species assemblages. Percent of obligately nitrogen-heterotrophic taxa was the only diatom autecological metric that showed a significant but weak correlation with % agricultural land-use along the stream network (r=0.50), but not at catchment or sample reach scale. Correlation between % agricultural land-use and water chemistry variables varied among the spatial scales and between seasons. Physical habitat variables (log₁₀ erodible substrate diameters and stream reach slope) were significantly correlated with % agricultural land-use along the stream network but not at catchment or sample reach scale. Our data suggest that spatial scales are important in assessing effects of land-use on stream conditions but the spatial scale effects may vary between seasons. Direct linkages between agricultural land-use and lotic diatom assemblages were weak during summer base-flow time regardless of the spatial scales. Summer sampling may underestimate the effects of catchment land-use on stream conditions in areas where seasonal patterns are so distinctive as in the Willamette Valley.     

Effect of riparian land use on contributions of terrestrial invertebrates to streams

Since terrestrial invertebrates are often consumed by stream fishes, land-use practices that influence the input of terrestrial invertebrates to streams are predicted to have consequences for fish production. We studied the effect of riparian land-use regime on terrestrial invertebrate inputs by estimating the biomass, abundance and taxonomic richness of terrestrial invertebrate drift from 15 streams draining catchments with three different riparian land-use regimes and vegetation types: intensive grazing — exotic pasture grasses (4 streams), extensive grazing — native tussock grasses (6 streams), reserve — native forest (5 streams). Terrestrial invertebrate drift was sampled from replicated stream reaches enclosed by two 1 mm mesh drift nets that spanned the entire channel. The mean biomass of terrestrial invertebrates that entered tussock grassland (12 mg ash-free dry mass m^–2 d^–1) and forest streams (6 mg AFDM m^–2 d^–1) was not significantly different (p > 0.05). However, biomass estimated for tussock grassland and forest streams was significantly higher than biomass that entered pasture streams (1 mg AFDM m^–2 d^–1). Mean abundance and richness of drifting terrestrial invertebrates was not significantly different among land-use types. Winged insects contributed more biomass than wingless invertebrates to both pasture and tussock grassland streams. Winged and wingless invertebrates contributed equally to biomass entering forest streams. Land use was a useful variable explaining landscape-level patterns of terrestrial invertebrate input for New Zealand streams. Evidence from this study suggests that riparian land-use regime will have important influences on the availability of terrestrial invertebrates to stream fishes.     

The SER Standards,cultural ecosystems,and the nature‐culture nexus—a reply to Evans and Davis

Evans and Davis claim the SER Standards use a “pure naturalness” model for restoration baselines and exclude most cultural ecosystems from the ecological restoration paradigm. The SER Standards do neither. The SER Standards consider both “natural” ecosystems (that are unequivocally not cultural) and “similar” cultural ecosystems as suitable reference models. Furthermore, Evans and Davis propose assessing whether a cultural ecosystem exhibits “good, bad, or neutral impacts from humans on ecosystems” as the basis for reference models. We argue that such an approach would overlook the indispensability of native ecosystem benchmarks to measure human impacts and provide a springboard for social‐ecological restoration.     

Land Reform and Land-Use Changes in the Lower Amazon: Implications for Agricultural Intensification

Land tenure has been considered one of the key factors that define patterns and change in land-use systems. This paper examines the implications of land reform for household decisions regarding patterns of land use, agricultural intensification, and forest conservation. We look at an Amazonian caboclo settlement in the Lower Amazon that had experienced land reform by the end of the 1980s. Results show that defined land tenure is not enough to guarantee agricultural intensification and forest conservation. In fact, several factors working at different scales are affecting land-use change in the region. At the settlement level, privatization of upland forest has led to an overall increase in cultivated land—pasture and annual crops—and increasing deforestation rates. However, at the farm-property level, different systems of agricultural production—intensive, extensive, or abandonment of land—occur according to availability of labor, and capital, and access to different natural resources.     

High potential, but low actual, glycine uptake of dominant plant species in three Australian land-use types with intermediate N availability

The traditional view of the nitrogen (N) cycle has been challenged since the discovery that plants can compete with microbes for low molecular weight (LMW) organic N. Despite a number of studies that have shown LMW organic N uptake by plants, there remains a debate on the overall ecological relevance of LMW organic N uptake by plants across ecosystems with different N availabilities. We here report patterns of glycine N uptake by plants from three different Australian land-use types with intermediate N availability and low inherent glycine concentrations in the soil. Using ¹⁵N labeled tracers, we tested the potential of these plants to acquire glycine in ex-situ laboratory experiments and attempted to validate these results in the field by determining actual uptake of glycine by plants directly from the soil. We found in the ex-situ experiments that plants from all three land-use types were able to take up significant amounts of glycine. In contrast, glycine uptake directly from the soil was minimal in all three land-use types and ¹⁵N tracers were largely immobilized in the soil organic N pool. Our study confirms that the potential for LMW organic N uptake by plants is a widespread phenomenon. However, our in-situ experiments show that in the three land-use types tested here plants are inferior competitors for LMW organic N and rely on NH ₄ ⁺ as their main N source. In contrast to several previous studies in arctic, alpine and even temperate ecosystems, our study suggests that in ecosystems with intermediate N availability, mineral N is the plants’ main N source, while LMW organic N is of less ecological relevance to plant N nutrition.     

Benthic macroinvertebrates in Swedish streams: community structure, taxon richness, and environmental relations

Spatial scale, e.g. from the stream channel, riparian zone, and catchment to the regional and global scale is currently an important topic in running water management and bioassessment. An increased knowledge of how the biota is affected by human alterations and management measures taken at different spatial scales is critical for improving the ecological quality of running waters. However, more knowledge is needed to better understand the relationship between environmental factors at different spatial scales, assemblage structure and taxon richness of running water organisms. In this study, benthic macroinvertebrate data from 628 randomly selected streams were analysed for geographical and environmental relationships. The dataset also included 100 environmental variables, from local measures such as in-stream substratum and vegetation type, catchment vegetation and land-use, and regional variables such as latitude and longitude. Cluster analysis of the macroinvertebrate data showed a continuous gradient in taxonomic composition among the cluster groups from north to south. Both locally measured variables (e.g. water chemistry, substratum composition) and regional factors (e.g. latitude, longitude, and an ecoregional delineation) were important for explaining the variation in assemblage structure and taxon richness for stream benthic macroinvertebrates. This result is of importance when planning conservation and management measurements, implementing large-scale biomonitoring programs, and predicting how human alterations (e.g. global warming) will affect running water ecosystems.     

Interaction of Press and Pulse Disturbance on Crayfish Populations: Flood Impacts in Pasture and Forest Streams

Interactions between press and pulse disturbances can significantly impact benthic macroinvertebrate (crayfish) populations. Press disturbances such as land-use change can make crayfish more vulnerable to the detrimental effects of pulse disturbances, by changing the habitats available to crayfish. The impact of a pulse disturbance, a major flood (1 in 28 years return period), on crayfish (Paranephrops planifrons) was significantly greater in pasture than native forest streams. Population densities of crayfish in three forest and three pasture streams had been measured seasonally for 2 years prior to the flood and many crayfish had been marked with individually identifiable tags. Low numbers of marked crayfish were recaptured after the flood in the forest streams, but no marked crayfish were identified in any pasture stream. Crayfish densities in one pasture stream declined from an average of 5 m^–2 prior to the flood to <1 m^–2 soon after the flood and it took 3 years for the population to show evidence of recovery. Macrophytes and cobbles, the dominant habitats of crayfish in pasture streams, did not appear to provide stable refugia during the flood. Habitat stability was linked to the riparian zone in forest streams where undercut banks, tree roots, and pools were important habitats for crayfish. Frequent pulse disturbance could affect population persistence of refugia-dependent species when the pressure of land-use change affects the stability of habitats, but this may only be evident over long time scales.     

Counting on β-Diversity to Safeguard the Resilience of Estuaries

Coastal ecosystems are often stressed by non-point source and cumulative effects that can lead to local-scale community homogenisation and a concomitant loss of large-scale ecological connectivity. Here we investigate the use of β-diversity as a measure of both community heterogeneity and ecological connectivity. To understand the consequences of different environmental scenarios on heterogeneity and connectivity, it is necessary to understand the scale at which different environmental factors affect β-diversity. We sampled macrofauna from intertidal sites in nine estuaries from New Zealand’s North Island that represented different degrees of stress derived from land-use. We used multiple regression models to identify relationships between β-diversity and local sediment variables, factors related to the estuarine and catchment hydrodynamics and morphology and land-based stressors. At local scales, we found higher β-diversity at sites with a relatively high total richness. At larger scales, β-diversity was positively related to γ-diversity, suggesting that a large regional species pool was linked with large-scale heterogeneity in these systems. Local environmental heterogeneity influenced β-diversity at both local and regional scales, although variables at the estuarine and catchment scales were both needed to explain large scale connectivity. The estuaries expected a priori to be the most stressed exhibited higher variance in community dissimilarity between sites and connectivity to the estuary species pool. This suggests that connectivity and heterogeneity metrics could be used to generate early warning signals of cumulative stress.     

景观对河流生态系统的影响

从景观的视角研究河流生态系统,是目前河流生态学中受到广泛关注且发展迅速的内容之一。流域内多尺度景观强烈影响河流的理化及生物特征,已成为共识,但有关量度、整合景观与河流生态系统二者之间联系的理论体系与方法的建立尚处于起步阶段。对景观组成与空间格局影响河流生态系统的机制与途径进行了系统总结,提出了该领域研究中的主要难题,即如何识别景观中人为因素和自然因素的协变现象,如何衡量多空间尺度景观对河流生态系统的交互影响,如何理解景观阈值的不确定性。为克服当前研究面临的困难与挑战,填补已有知识的不足,提出今后研究的重点方向:河流景观分类系统的改进;更具代表性时空数据的采集;新型景观指标的开发与应用;微观尺度数据与宏观尺度数据的整合等。     

Looking to the Future of Ecosystem Services

Ecosystem services—the benefits that people obtain from ecosystems—are essential to human existence, but demands for services often surpass the capacity of ecosystems to provide them. Lack of ecological information often precludes informed decision making about ecosystem services. The Millennium Ecosystem Assessment (MA) was conceived in part to provide the necessary ecological information to decision makers. To this end, the MA set out to address the stated needs and concerns of decision makers and examine the ecological dynamics and uncertainties underlying these concerns. To improve our understanding of their information needs and concerns, we interviewed 59 decision makers from five continents. The respondents indicated that although most people generally agree about the ideal state of the planet—free of poverty and extreme inequality, replete with cultural and biological diversity—they often disagree about the best way to achieve these goals. Further, although nonspecialists are generally concerned about the environment and may have a good understanding of some of issues, they often have a more limited grasp of the ecological dynamics that drive the issues of concern. We identify some of the principal uncertainties about ecosystem dynamics and feedbacks that underlie the concerns of decision makers. Each of the papers in this special feature addresses these ecological feedbacks from the perspective of a specific discipline, suggesting ways in which knowledge of ecological dynamics can be incorporated into the MA’s assessment and scenario-building process.     

Fractal properties of forest spatial structure

The definition of fractal dimension of natural objects, which enables to deal with scale dependence of fractal dimension is discussed. Abrupt changes of fractal dimension of spatial structure of terrestrial ecosystems are considered in the context of hierarchical paradigm. On this ground the procedure is proposed for segmentation of a territory, which takes into account the scale dependence of spatial variability of ecological parameters. Using remotely sensed data — normalized difference vegetation index (NDVI) and thermal radiation in the infrared band — fractal dimensions and critical scales are evaluated for different forest types with the help of software, developed for this purpose. The results obtained corroborate the potentialities of fractal approach in ecology. These methods and results can be used for discrimination of remotely sensed data; but further investigations, including detailed comparison of fractal characteristics of remotely sensed forest images with results of on-site field studies are necessary to validate them.     

新疆焉耆盆地人类活动与气候变化的效应机制

通过对新疆焉耆盆地及其周边近40a(1973—2014)的气候变化趋势检测、LUCC和生物量估算,探讨气候变化和人类活动的生态效应机制,研究区域陆地生态系统演变及其归因。分析结果表明:(1)焉耆盆地山区和平原区降水变化都有明显的突变点,并呈现增加趋势,蒸发量在山区减少,在平原区波动性减少趋势;(2)LUCC分析表明,山区裸地面积减少5.40%,冰川面积减少3.36%,高地植被面积增加8.76%;同时平原区天然绿洲面积增加1.96%,沙漠面积减少1.62%,水域面积减少1.30%,人工绿洲面积增加15.41%,湿地面积增加1.27%;(3)山区陆地生态系统对区域气候变化非常敏感,其中降水变化是决定山区地表植被生存状态和分布的重要因素;(4)人类活动的推动作用和有益气候变化的支撑是绿洲平原区生态系统好转的原因,其中人口急剧增加和社会经济快速发展,导致绿洲平原区生态系统结构及其时空分布的主要因素。焉耆盆地及其周围区域陆地生态系统的演变对气候变化和人类活动有明显的时空尺度效应,其反应程度各不相同。     

城市景观格局演变的生态环境效应研究进展

快速城市化过程剧烈影响着下垫面变化,直接带来了交通拥挤、资源短缺、环境污染、生态恶化等诸多问题,所有这些问题的出现均与景观格局演变密切相关,研究城市景观格局演变及其生态环境效应正在成为全社会关注的热点.系统总结了城市化过程对景观格局演变的影响,分析了城市景观格局演变的热环境效应、水环境效应、生态服务效应,以及城市生态用地与生态安全格局设计等方面的研究进展.指出了目前城市景观演变与生态环境效应研究中存在的问题与不足:(1)现有研究侧重于景观格局演变的量化分析和景观格局指数的计算,较少关注景观格局演变对生态环境及其区域生态安全的影响;(2)城市景观格局演变与热岛效应研究多局限于两者数理统计关系的分析,对于城市热环境形成的机理缺乏深入研究;(3)城市景观格局演变与大气环境效应方面更多研究关注绿地及其空间布局在吸收和降解大气污染物、固体颗粒物方面的作用,对城市景观格局演变的大气环境综合效应以及大气灰霾效应影响机理重视不够;(4)如何通过合理设置生态用地,有效提高城市生态服务功能和保障城市生态安全,目前仍缺乏深入而又系统的研究.下一步的研究中,需要综合多尺度的景观信息来揭示城市景观的演变机理和环境效应,构建基于城市空间扩展和生态服务效应评价的城市生态空间优化决策模型,探讨城市生态空间优化模式与安全格局.     

Ecological engineering: A field whose time has come

Ecological engineering is defined as “the design of sustainable ecosystems that integrate human society with its natural environment for the benefit of both.” It involves the restoration of ecosystems that have been substantially disturbed by human activities such as environmental pollution or land disturbance; and the development of new sustainable ecosystems that have both human and ecological value. While there was some early discussion of ecological engineering in the 1960s, its development was spawned later by several factors, including loss of confidence in the view that all pollution problems can be solved through technological means and the realization that with technological means, pollutants are just being moved from one form to another. Conventional approaches require massive amounts of resources to solve these problems, and that in turn perpetuates carbon and nitrogen cycle problems, for example. The development of ecological engineering was given strong impetus in the last decade with a textbook, the journal Ecological Engineering and two professional ecological engineering societies. Five principles about ecological engineering are: (1) It is based on the self-designing capacity of ecosystems; (2) It can be the acid test of ecological theories; (3) It relies on system approaches; (4) It conserves non-renewable energy sources; and (5) It supports biological conservation. Ecology as a science is not routinely integrated into engineering curricula, even in environmental engineering programs, while shortcoming, ecologists, environmental scientists, and managers miss important training in their profession—problem solving. These two problems could be solved in the integrated field of ecological engineering.     

Mapping ecosystem functions to the valuation of ecosystem services: implications of species–habitat associations for coastal land-use decisions

Habitats and the ecosystem services they provide are part of the world’s portfolio of natural capital assets. Like many components of this portfolio, it is difficult to assess the full economic value of these services, which tends to over-emphasize the value of extractive activities such as coastal development. Building on recent ecological studies of species–habitat linkages, we use a bioeconomic model to value multiple types of habitats as natural capital, using mangroves, sea grass, and coral reefs as our model system. We show how key ecological variables and processes, including obligate and facultative behaviors map into habitat values and how the valuation of these ecological processes can inform decisions regarding coastal development (habitat clearing). Our stylized modeling framework also provides a clear and concise road map for researchers interested in understanding how to make the link between ecosystem function, ecosystem service, and conservation policy decisions. Our findings also highlight the importance of additional ecological research into how species utilize habitats and that this research is not just important for ecological science, but it can and will influence ecosystem service values that, in turn, will impact coastal land-use decisions. While refining valuation methods is not necessarily going to lead to more rational coastal land-use decisions, it will improve our understanding on the ecological–economic mechanisms that contribute to the value of our natural capital assets. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A social and ecological assessment of tropical land uses at multiple scales: the Sustainable Amazon Network

Science has a critical role to play in guiding more sustainable development trajectories. Here, we present the Sustainable Amazon Network (Rede Amazônia Sustentável, RAS): a multidisciplinary research initiative involving more than 30 partner organizations working to assess both social and ecological dimensions of land-use sustainability in eastern Brazilian Amazonia. The research approach adopted by RAS offers three advantages for addressing land-use sustainability problems: (i) the collection of synchronized and co-located ecological and socioeconomic data across broad gradients of past and present human use; (ii) a nested sampling design to aid comparison of ecological and socioeconomic conditions associated with different land uses across local, landscape and regional scales; and (iii) a strong engagement with a wide variety of actors and non-research institutions. Here, we elaborate on these key features, and identify the ways in which RAS can help in highlighting those problems in most urgent need of attention, and in guiding improvements in land-use sustainability in Amazonia and elsewhere in the tropics. We also discuss some of the practical lessons, limitations and realities faced during the development of the RAS initiative so far.