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Objectives: (1) To evaluate how ecosystem services may be utilized to either reinforce or fracture the planning and development practices that emerged from segregation and economic exclusion; (2) To survey the current state of ecosystem service assessments and synthesize a growing number of recommendations from the literature for renovating ecosystem service analyses. Methods: Utilizing current maps of ecosystem service distribution in Bushbuckridge Local Municipality, South Africa, we considered how a democratized process of assessing ecosystem services will produce a more nuanced representation of diverse values in society and capture heterogeneity in ecosystem structure and function. Results: We propose interventions for assessing ecosystem services that are inclusive of a broad range of stakeholders’ values and result in actual quantification of social and ecological processes. We demonstrate how to operationalize a pluralistic framework for ecosystem service assessments. Conclusion: A democratized approach to ecosystem service assessments is a reimagined path to rescuing a poorly implemented concept and designing and managing future social-ecological systems that benefit people and support ecosystem integrity. It is the responsibility of scientists who do ecosystem services research to embrace more complex, pluralistic frameworks so that sound and inclusive scientific information is utilized in decision-making.

Research on urban ecosystems rapidly expanded in the 1990s and is now a central topic in ecosystem science. In this paper, we argue that there are two critical challenges for ecosystem science that are rooted in urban ecosystems: (1) predicting or explaining the assembly and function of novel communities and ecosystems under altered environmental conditions and (2) refining understanding of humans as components of ecosystems in the context of integrated social-ecological systems. We assert that these challenges are also linchpins in the further development of sustainability science and argue that there is a strong need for a new initiative in urban systems science to address these challenges and catalyze the next wave of fundamental advances in ecosystem science, and more broadly in interdisciplinary and transdisciplinary science.

Urbanization dramatically affects hydrology, water quality and aquatic ecosystem composition. Here we characterized changes in diatom assemblages along an urban-to-rural gradient to assess impacts of urbanization on stream conditions in Beijing, China. Diatoms, water chemistry, and physical variables were measured at 22 urban (6 in upstream and 16 in downstream) and 7 rural reference stream sites during July and August of 2013. One-way ANOVA showed that water physical and chemical variables were significantly different ( p p > 0.05). Similarly, structural metrics, including species richness (S), Shannon diversity (H′), species evenness (J′) and Simpson diversity (D′), were significantly different ( p p > 0.05) between reference and urban upstream sites. However, diatom assemblages were very different among all sites. Achnanthidium minutissima was a consistent dominant species in reference sites; Staurosira construens var. venter and Pseudostaurosira brevistriata were the dominant species in urban upstream sites; and Nitzschia palea was the dominant species in urban downstream sites. Clustering analyses based on the relative abundance of diatom species, showed all the samples fit into three groups: reference sites, urban upstream sites, and urban downstream sites. Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed that concentration of K + , EC, TN, Cl − and pH were positively correlated with relative abundance of dominant diatom species in urban downstream samples; WT and F − were correlated with reference and urban stream diatom composition. Our results demonstrate that the composition of diatom species was more sensitive to urbanization than the water physical and chemical parameters, and that diatom assemblage structure metrics more accurately assessed water quality. Some species, such as Amphora pediculus and Cocconeis placentula were among the dominant species in low nutrients stream sites; however, they were considered to be high nutrient indicators in some streams in USA. We suggest using caution in applying indicator indices based on species composition from other regions. It is necessary to build a complete set of diatom species data and their co-ordinate environment data for specific regions.

There is an abundance of conceptual frameworks relevant to sustainability in urban systems. However, to advance urban ecological science and its application to sustainable urban transformations, key existing frameworks must be synthesized. This paper is a conceptual synthesis cast in essay form in order to encompass a broad range of relevant ideas. It starts from the premise that the familiar models of metropolitan and megalopolitan urban structure, of industrially driven urban development, and of the contrasts between urban and non‐urban lands are manifestly inadequate representations of evolving global reality. Such inadequacy is illustrated with examples from the United States and from China. Both the form and the interactions involved in contemporary urbanization and urban change suggest the need for a new integrated framework synthesizing two existing yet still evolving concepts: (1) The urban megaregion framework accommodates the spatial extent, interdigitation of contrasting land uses, and the linked spatial relations between nominally urban and nominally rural areas. (2) The new concept of the continuum of urbanity emphasizes the shifts in livelihood and lifestyle driven by regional and global teleconnections and their joint effects on local environments and landscapes. Together these frameworks suggest a common conceptual structure for addressing urban areas of different ages, sizes, forms, and dynamics in both urbanizing and urbanized areas in developing and developed countries and regions. The synthesis of frameworks points to empirical research needs, and has the potential to better match sustainability plans and actions with the diverse urban forms and dynamics now appearing around the world.

The ability to estimate and model future vegetation dynamics is a central focus of contemporary ecology and is essential for understanding future ecological trajectories. It is therefore critical to understand when the influence of initial post-disturbance regeneration versus stochastic processes dominates long-term post-disturbance ecological processes. Often, conclusions about post-disturbance dynamics are based upon initial regeneration in the years immediately after disturbances. However, the degree to which initial post-disturbance regeneration indicates longer-term trends is likely to be contingent on the types, intensities, and combinations of disturbances, as well as pre-disturbance ecosystem structure and composition. Our relatively limited understanding of why initial post-disturbance regeneration is sometimes a poor predictor of future ecosystem trajectories represents a critical gap in post-disturbance ecological forecasting. We studied the composition and density of regeneration of tree species following wind blowdown in 1997, wildfire in 2002, and compounded disturbances by blowdown and wildfire in subalpine forests of Colorado. We examined regeneration of Picea engelmannii, Abies lasiocarpa, Pinus contorta, and Populus tremuloides in 180 permanent plots across 12 sites (classified by pre-disturbance age and composition) in 2003, 2010, and 2015. At sites that were blown down but not burned, regeneration was dense and dominated by Picea and Abies. At these sites, regeneration observed from 2003 to 2005 (hereafter initial regeneration) was also highly predictive of regeneration 5–10 yr later. In contrast, at sites that were burned and sites that were blown down and burned, regeneration was less dense and dominated by a mix of species. At these sites, initial regeneration was a poor predictor of longer-term trends as species dominance and overall density fluctuated over the 13-yr period. These findings call into question our ability to confidently predict ecosystem trajectories based upon observations made in the years immediately after large, severe disturbances such as wildfires and compounded disturbances. As compounded disturbances become more common under climatically driven changes in disturbance regimes, post-disturbance ecosystem trajectories may become increasingly stochastic and unpredictable.

The ecological concept of disturbance has scarcely been applied in urban systems except in the erroneous but commonplace assumption that urbanization itself is a disturbance and cities are therefore perennially disturbed systems. We evaluate the usefulness of the concept in urban ecology by exploring how a recent conceptual framework for disturbance (Peters et al. 2011 , Ecosphere , 2, art 81) applies to these social–ecological–technological systems (). Case studies, especially from the Long‐Term Ecological Research sites of Baltimore and Phoenix, are presented to show the applicability of the framework for disturbances to different elements of these systems at different scales. We find that the framework is easily adapted to urban and that incorporating social and technological drivers and responders can contribute additional insights to disturbance research beyond urban systems.

Governance is key to sustainable urban transitions. Governance is a system of social, power, and decision‐making processes that acts as a key driver of resource allocation and use, yet ecologists—even urban ecologists–seldom consider governance concepts in their work. Transitions to more sustainable futures are becoming increasingly important to the management of many ecosystems and landscapes, and particularly so for urban systems. We briefly identify and synthesize important governance dimensions of urban sustainability transitions, using illustrations from cities in which long‐term social–ecological governance research is underway. This article concludes with a call to ecologists who are interested in environmental stewardship, and to urban ecologists in particular, to consider the role of governance as a driver in the dynamics of the systems they study.

Socioecological theory, developed through the study of urban environments, has recently led to a proliferation of research focusing on comparative analyses of cities. This research emphasis has been concentrated in the more developed countries of the Northern Hemisphere (often referred to as the “Global North”), yet urbanization is now occurring mostly in the developing world, with the fastest rates of growth in sub-Saharan Africa. Countries like South Africa are experiencing a variety of land-cover changes that may challenge current assumptions about the differences between urban and rural environments and about the connectivity of these dynamic socioecological systems. Furthermore, questions concerning ecosystem services, landscape preferences, and conservation – when analyzed through rural livelihood frameworks – may provide insights into the social and ecological resilience of human settlements. Increasing research on urban development processes occurring in Africa, and on patterns of kinship and migration in the less developed countries of the “Global South”, will advance a more comprehensive worldview of how future urbanization will influence the progress of sustainable societies.

Older, economically troubled urban neighborhoods present multiple challenges to environmental quality. Here, we present results from an initiative in Baltimore, Maryland, where water-quality improvements were rooted in a socioecological framework that highlighted the interactions between biogeophysical dynamics and social actors and institutions. This framework led to implementation of best management practices followed by assessment of changes in human perception, behavior, and education programs. Results suggest that such an initiative can improve both water quality (eg reductions in nitrogen and phosphorus runoff) and quality of life (eg increased involvement in outdoor recreation by residents and improvements in student environmental literacy and performance) in urban neighborhoods. However, proposed solutions to the water-quality problems in such neighborhoods have (1) typically emphasized the need for stormwater facilities that are difficult to build and maintain and (2) comprehensively addressed neither the issues related to aging infrastructure and hydrologic complexity nor the benefits derived from linkages between resident perception of environmental improvements and behavior and water-quality outcomes.

The contrast between ecology in cities and ecology of cities has emphasized the increasing scope of urban ecosystem research. Ecology in focuses on terrestrial and aquatic patches within cities, suburbs, and exurbs as analogs of non‐urban habitats. Urban fabric outside analog patches is considered to be inhospitable matrix. Ecology of the city differs from ecology in by treating entire urban mosaics as social–ecological systems. Ecology of urban ecosystems incorporates biological, social, and built components. Originally posed as a metaphor to visualize disciplinary evolution, this paper suggests that the contrast has conceptual, empirical, and methodological contents. That is, the contrast constitutes a disciplinary or “local” paradigm shift. The paradigm change between ecology in and ecology of represents increased complexity, moving from focus on biotic communities to holistic social–ecological systems. A third paradigm, ecology for the city, has emerged due to concern for urban sustainability. While ecology for includes the knowledge generated by both ecology in and ecology of , it considers researchers as a part of the system, and acknowledges that they may help envision and advance the social goals of urban sustainability. Using urban heterogeneity as a key urban feature, the three paradigms are shown to contrast in five important ways: disciplinary focus, the relevant theory of spatial heterogeneity, the technology for representing spatial structure, the resulting classification of urban mosaics, and the nature of application to sustainability. Ecology for the city encourages ecologists to engage with other specialists and urban dwellers to shape a more sustainable urban future.

Numerous mechanisms driving alien plant invasions have been described in a rapidly growing body of literature. However these are frequently case specific, making generalizations across species and systems difficult. A number of conceptual approaches have been proposed to help synthesize the literature, stimulating healthy debate among scientists. We build on these syntheses, presenting an expanded framework that incorporates the processes contributing to invasions, and the context within which they must interact. We also provide a model template into which the framework we develop is incorporated, illustrating both with examples. Our general framework includes three contributing processes: these are (1) the characteristics of the introduced species, (2) system context, within which the invasion takes place, and (3) the features of the receiving habitat. System context refers to the influences arising outside of the receiving environment, both spatially and temporally. Each contributing process is comprised of specific mechanisms, drawn from literature on invasion ecology and other related fields. The framework invokes relevant mechanisms for a specific species or situation. Although, a number of frameworks already consider the characteristics of the invading species or those of the receiving habitat, they seldom include all possible characteristics of both. We propose that these approaches alone are inadequate to provide a comprehensive understanding of the invasion process, without explicitly examining the context within which the invasion takes place. The model template we present relates the contributing processes described for a particular invasion, to the change in habitat from one state to another. Each of the contributing processes defined in the framework modulates the degree to which the habitat is changed. We suggest that these additional tools and the explicit inclusion of all three contributing processes, provide for further synthesis and improved understanding of invasions by alien plants.

Urban areas are growing in size and importance; however, we are only beginning to understand how the process of urbanization influences ecosystem dynamics. In particular, there have been few assessments of how the land-use history and age of residential soils influence carbon (C) and nitrogen (N) pools and fluxes, especially at depth. In this study, we used 1-m soil cores to evaluate soil profile characteristics and C and N pools in 32 residential home lawns that differed by previous land use and age, but had similar soil types. These were compared to soils from eight forested reference sites. Residential soils had significantly higher C and N densities than nearby forested soils of similar types (6.95 vs. 5.44 kg C/m2 and 552 vs. 403 g N/m2, P

Despite a growing recognition that the solutions to current environmental problems will be developed through collaborations between scientists and stakeholders, substantial challenges stifle such cooperation and slow the transfer of knowledge. Challenges occur at several levels, including individual, disciplinary, and institutional. All of these have implications for scholars working at academic and research institutions. Fortunately, creative ideas and tested models exist that provide opportunities for conversation and serious consideration about how such institutions can facilitate the dialogue between scientists and society.

While exotic plant invasions are thought to lead to declines in native species, the long-term impacts of such invasions on community structure are poorly known. Furthermore, it is unknown how exotic plant invasions compare to invasions by native species. We present data from 40 yr of continuous vegetation sampling of 10 fields released from agriculture to examine the effects of invasions on species richness. The effects of both exotic and native species invasions on species richness were largely driven by variations among fields with most species not significantly affecting species richness. However, invasion and dominance by the exotics Agropyron repens, Lonicera japonica, Rosa multiflora, Trifolium pratense and the native Solidago canadensis were associated with declines in richness. Invasions by exotic and native species during old field succession have similar effects on species richness with dominance by species of either group being associated with loss of species richness. Exotic species invasions tended to have stronger effects on richness than native invasions. No evidence was found of residual effects of invasions because the impacts of the invasion disappeared with the decline of the invading population. When pooled across species, heavy invasion by exotic species resulted in greater loss of species richness than invasion by native species. Studies of invasion that utilize multiple sites must account for variability among sites. In our study, had we not included field as a factor we would have incorrectly concluded that invasion consistently resulted in changes in species richness.

Urban areas are heterogeneous. Transitions in architecture and building density, vegetation, economic activity, and culture can occur at the scale of city blocks. Ecologists have been criticized for treating the city as homogeneous and urbanization as one-dimensional. To develop ecological understanding of integrated human–natural systems, the fine-scale heterogeneity of their built and natural components must be quantified. There have been calls for the integration of the biophysical and human components of systems, but here we provide a new tool to quantify this integrated heterogeneity by reconceptualizing urban land-use and land-cover classification approaches. This new tool, High Ecological Resolution Classification for Urban Landscapes and Environmental Systems (HERCULES), balances detail and efficiency and is flexible, allowing it to be used for interdisciplinary research, with ancillary datasets, and across urban systems.

Our understanding of the dynamics of urban ecosystems can be enhanced by examining the multidimensional social characteristics of households. To this end, we investigated the relative significance of three social theories of household structure—population, lifestyle behavior, and social stratification—to the distribution of vegetation cover in Baltimore, Maryland, USA. Our ability to assess the relative significance of these theories depended on fine-scale social and biophysical data. We distinguished among vegetation in three areas hypothesized to be differentially linked to these social theories: riparian areas, private lands, and public rights-of-way (PROWs). Using a multimodel inferential approach, we found that variation of vegetation cover in riparian areas was not explained by any of the three theories and that lifestyle behavior was the best predictor of vegetation cover on private lands. Surprisingly, lifestyle behavior was also the best predictor of vegetation cover in PROWs. The inclusion of a quadratic term for housing age significantly improved the models. Based on these research results, we question the exclusive use of income and education as the standard variables to explain variations in vegetation cover in urban ecological systems. We further suggest that the management of urban vegetation can be improved by developing environmental marketing strategies that address the underlying household motivations for and participation in local land management.

Urban ecological studies have had a long history, but they have not been a component of mainstream ecology until recently. The growing interest of ecologists in urban systems provides an opportunity to articulate integrative frameworks, and identify research tools and approaches that can help achieve a broader ecological understanding of urban systems. Based on our experience in the Baltimore Ecosystem Study (BES), Long-term Ecological Research project, located in metropolitan Baltimore, Maryland, USA, we identify several frameworks that may be useful in comparative urban studies, and may be worthy of consideration in other integrative urban ecosystem studies: (i) spatial patch dynamics of biophysical and social factors; (ii) the watershed as an integrative tool; and (iii) the human ecosystem framework. These frameworks build on empirical research investigating urban biota, nutrient and energy budgets, ecological footprints of cities, as well as biotic classifications aimed at urban planning. These frameworks bring together perspectives, measurements, and models from biophysical and social sciences. We illustrate their application in the BES, which is designed to investigate (i) the structure and change of the urban ecosystem; (ii) the fluxes of matter, energy, capital, and population in the metropolis; and (iii) how ecological information affects the quality of the local and regional environments. Exemplary results concerning urban stream nutrient flux, the ability of riparian zones to process nitrate pollution, and the lags in the relationships between vegetation structure and socio-economic factors in specific neighbourhoods are presented. The current advances in urban ecological studies have profited greatly from the variety of integrative frameworks and tools that have been tested and applied in urban areas over the last decade. The field is poised to make significant progress as a result of ongoing conceptual and empirical consolidation.

Biocomplexity was introduced to most ecologists through the National Science Foundation's grant program, and theliteratureintended to introducethat program.Thegeneralities ofthat literature contrast with the abstract and mathematical sophistication of literature from physics, systems theory, and indeed even of pioneering ecologists who have translated the conceptintoecology.Thissituationleavesamiddleground,thatisbothaccessibletoecologists ingeneral,andcognizantofthefundamentalsofcomplexity,tobemorecompletelyexplored. To help scope this middle ground, and to promote empirical explorations that may be located there, we propose a non-exclusive framework for the conceptual territory. While recognizing the deep foundations in the studies of complex behavior, we take ecological structure as the entry point for framework development. This framework is based on a definition of biocom- plexity as the degree to which ecological systems comprising biological, social and physical components incorporate spatially explicit heterogeneity, organizational connectivity, and historical contingency through time. These three dimensions of biocomplexity - heterogene- ity, connectivity, and history - will be explored as axes of increasing complexity. Basing the description of spatial heterogeneity on either patch or continuous quantification, complexity of spatial structure increases as quantification moves from simple discrimination of patch typesandthenumberofeachtypetoassessmentofconfigurationandthechangeinthemosaic throughtime.Organizationalcomplexityreflectstheincreasingconnectivityofthebasicunits that control system dynamics. At the simple end of the axis, the functional connectivity between units is low, and the processes within a unit are determined by structures or other processes within that unit.Atthehighestlevelofcomplexityalongthisaxis,unitsina mosaic interact through fluxes of energy, matter, organisms, or information, and the structure and dynamics of the mosaic can be altered by those fluxes. Temporal relationships in the system range from direct contemporary ones to indirect and historically contingent ones. The influence of indirect effects, legacies, the existence of lagged effects, and the presence of slowly appearing indirect effects constitute increasing temporal complexity. This framework embodies some features of both the structural approach to complexity and the approach of complexity of explanations that we extracted from the literature. It leaves the issue of what levels of each axis result in complex behavior as an important question for further research.

Although ecologists want to conduct research in urban systems, cultural constraints, spatial complexity, and institutional agendas limit the establishment of ecological experiments. Recent approaches using household landscaping have begun to tackle these obstacles; others, including adaptive management, restoration, reclamation, and wetland construction, reveal overlaps between ecological experiments and urban design. “Designed experiments” propose going beyond current strategies to partner with urban designers, landscape architects, and architects to insert architecturally designed experiments into the urban mosaic. The interdisciplinary approach of designed experiments exploits the aesthetics and functions of urban design, balancing ecological goals with important design factors such as context, public amenities, and safety. Designed experiments represent a novel way for ecologists to help improve urban environments by providing a means with which to work with urban designers in creating attractive, practical, and replicated experimental designs that generate quality ecological data from metropolitan sites.

As defined by Ascher, biocomplexity results from a “multiplicity of interconnected relationships and levels.” However, no integrative framework yet exists to facilitate the application of this concept to coupled human–natural systems. Indeed, the term “biocomplexity” is still used primarily as a creative and provocative metaphor. To help advance its utility, we present a framework that focuses on linkages among different disciplines that are often used in studies of coupled human–natural systems, including the ecological, physical, and socioeconomic sciences. The framework consists of three dimensions of complexity: spatial, organizational, and temporal. Spatial complexity increases as the focus changes from the type and number of the elements of spatial heterogeneity to an explicit configuration of the elements. Similarly, organizational complexity increases as the focus shifts from unconnected units to connectivity among functional units. Finally, temporal complexity increases as the current state of a system comes to rely more and more on past states, and therefore to reflect echoes, legacies, and evolving indirect effects of those states. This three-dimensional, conceptual volume of biocomplexity enables connections between models that derive from different disciplines to be drawn at an appropriate level of complexity for integration.

Specialization can become detrimental to a discipline if it fosters intellectual isolation. A bibliographic analysis of several research areas in plant ecology (invasion biology, succession ecology, gap/patch dynamics, and global change effects on plants) revealed that plant ecologists do not regularly make use of the findings and insights of very similar studies being conducted in other research subdisciplines, nor do they try to make their findings and insights easily accessible to researchers in other areas. Invasion papers were least likely to be cross-linked (6%) with other fields, whereas gap/patch dynamics papers were most likely to be cross-linked (15%). This tendency toward intellectual isolation may be impeding efforts to achieve more powerful generalizations in ecology by reducing the number of potentially productive exchanges among researchers. In this paper, we illustrate this problem using the example of several speciality areas that study vegetation change. We argue that, rather than characterizing studies of vegetation change on the basis of what distinguishes them from one another, plant ecologists would benefit from concentrating on what such studies have in common. As an example, we propose that several speciality areas of plant ecology could be reunified under the term ecology of vegetation change. Individual researchers, journals, and ecological societies all can take specific steps to increase the useful exchange of ideas and information among research areas. Promoting rapid and more effective communication among diverse researchers may reduce the proliferation of narrow theories, concepts, and terminologies associated with particular research areas. In this way, we can expedite our understanding of the ecological mechanisms and consequences associated with plant communities. (c) 2004 Elsevier GmbH. All rights reserved.

Recent experimental and simulation results, and competition-based ecological theory, predict a simple relationship between species richness and the invasibility of communities at small spatial scales – likelihood of invasion decreases with increasing richness. Here we show data from 42 continuous years of sampling old field succession that reveal quite different dynamics of plant invasion. Contrary to experimental studies, when richness was important in explaining invasion probability, it was typically positively associated with species invasion. Invasion of several species had a unimodal response to resident species richness, which appeared to be a mixture of compositional influences and a richness effect. Interestingly, invasions by native and exotic species did not fundamentally differ. Control of species invasion in this system is individualistic, caused by a variety of community-level mechanisms rather than a single prevailing richness effect.

While exotic plant species often come to dominate disturbed communities, long-term patterns of invasion are poorly known. Here we present data from 40 yr of continuous vegetation sampling, documenting the temporal distribution of exotic plant species in old field succession. The relative cover of exotic species decreased with time since abandonment, with significant declines occurring 20 yr post-abandonment. The number of exotic species per plot also declined with time since abandonment while field-scale richness of exotics did not change. This suggests displacement occurring at small spatial scales. Life history types changed from short-lived herbaceous species to long-lived woody species for both native and exotic plant species. However, shrubs and lianas dominated woody cover of exotic plants while trees dominated native woody cover. The species richness of exotic and native species was positively correlated at most times. In abandoned hay fields, however, the proportion of exotic plant cover per plot was inversely related to total species richness. This relationship suggests that it is not the presence, but the abundance of exotic species that may cause a reduction in community diversity. While the development of closed-canopy forest appears to limit most introduced plant species, several shade-adapted exotic species are increasing within the fields. These invasions may cause a reversal of the patterns seen in the first 40 yr of succession and may result in further impacts on community structure.

The ecosystem is a fundamental ecological concept that is not as simple as it first appears. We explore three key dimensions of the concept that make it both complex and broadly useful—its basic definition, its application via models to concrete or specific situations, and its metaphorical connotations as used in general communication within the domain of science and with the public at large. Clarity in identifying what the dimensions are and how they are related can help to maintain the rigor of the concept for specific scientific uses while also allowing enough flexibility for its use in the integration of scientific principles, as well as in public discourse. This analysis of the ecosystem as a multidimensional concept is likely to be generalizable to other important concepts in ecology.

Forest fragmentation leads to a dramatic increase in forest edge, and these edges may function as traps and concentrators for wind-borne nutrients and pollutants. We assessed the influence of forest edges on atmospheric deposition and subsequent inputs to the forest floor in deciduous-forest fragments in the eastern United States. To quantify these inputs, we collected throughfall—water that has passed through the forest canopy—from edge and interior zones of forests adjacent to open fields. During the 1995 growing season, atmospheric input (wet and dry deposition) of sulfur to forest edge zones was elevated compared with input to forest interiors. Throughfall fluxes of dissolved inorganic nitrogen and calcium were also greater at edges than interiors. The mean edge increases ranged from 17% to 56% for the nutrients and pollutants we measured. When we manipulated the structure of forest edges by removing all vegetation below half the canopy height, throughfall flux in the edge zone declined sharply and was less than that of the respective interior zone. Changing the vegetation structure of the edge also shifted the zone of highest throughfall flux farther into the interior of the forest. Our data suggest that forest edges can function both as significant traps for airborne nutrients and pollutants from adjoining agricultural or urban landscapes and effective concentrators of below-canopy chemical fluxes. These enhanced fluxes may have cascading effects on soil-nutrient cycling, microbial activity, seedling dominance, and other ecological processes near forest edges.

A key goal of conservation biology is to prevent the spread of exotic species. Previous work on exotic invasion has two limitations: (1) the lack of a spatially explicit approach and (2) a primary focus on the net effect of invasion by examining invasive species already present in the community. We address these limitations by focusing on the arrival of a potential invader into a community and use a spatially explicit approach to quantify the flow of seeds from the surrounding landscape into the interior of a forest. We hypothesize that the structure of forest-edge vegetation influences how the edge mediates seed flux. To test our hypothesis, we experimentally altered vegetation structure within 20 m of the edge to create two edge treatments: thinned and intact. We quantified the flux of seeds moving into the forest interior across the two treatments. We used seed traps randomly arrayed on transects from 5 to 50 m into the forest. More seeds crossed the thinned treatment than crossed the intact treatment to reach the forest interior. In addition, seeds that crossed the thinned treatment dispersed farther into the forest than those that crossed the intact treatment. These results were consistent throughout the period of maximum autumn dispersal, including periods before and after leaf drop. Our results show that the structure of vegetation on the edge interacts with the flux of wind-dispersed seed across the edge. We demonstrated that an edge with intact vegetation can function as a physical barrier to seed dispersal. Therefore, the structure of vegetation on edges can influence the function of edges as barriers to seed flux into the forest interior.

We investigated the influence of differing patch types on the germination, growth, and survival of two species of tree seedlings in a catastrophic, old-growth forest windthrow. We documented environmental conditions, and experimentally introduced seeds, transplanted seedlings, and manipulated litter and herbivore access to determine the effects of patch types during initial forest regrowth. Among patch types defined by substrate condition and exposure, we found significant differential influence of patch type on germination of seeds of a common colonizer, Betula alleghaniensis. Patch types that provided exposed mineral soil allowed greater germination than other patch types, regardless of light availability. Germination of Acer rubrum varied among patch types in a fashion similar to that of B. alleghaniensis, although differences among patch types were not significant. Litter can also be the basis of patch classification. Both type and amount of litter significantly influenced emergence of seedlings, with broad-leaf litter (in amounts typical of intact forest) producing greater inhibition of emergence than amounts of conifer needles typical of intact forest. Survival and performance of fenced and unfenced Acer rubrum seedlings transplanted into different patch types reflected influences of both herbivory and competition with existing vegetation. Survival was lowest where the Acer seedlings were most apparent to mammalian herbivores. Growth of Acer seedlings was greater when they were protected from herbivory and free of competition from surrounding vegetation. These findings demonstrate that patch types offer different suitability as regeneration microsites during early tree life history stages. Because these patch types are common and easy to recognize, the differences in species' responses may be sufficiently general to apply in other disturbances of this type. If general species responses to patch types can be combined with knowledge of propagule abundance and patch abundance, it could provide a basis for improved understanding of post-disturbance regeneration, via patch influences.

Summary 1 Forest edges, which are prominent features in the north-eastern United States landscape, may control the flux of organisms between forest and non-forest habitats. Previous studies have described edge structure rather than function, as determined by interaction with such fluxes. 2 The function of the forest edge may be linked to the structure of its vegetation. We tested this hypothesis by experimentally altering the structure of the vegetation at two deciduous forest edges in Millbrook, New York, USA. Intact and thinned plots were established at each edge and we determined whether the structure of the edges influenced the flux of herbivores, as measured by herbivore damage to transplanted tree seedlings. 3 Herbivore damage to seedlings at site 1 was affected by edge vegetation structure and by distance from the edge. The edge structure effect was due to herbivory by voles, which was significantly greater in the intact than in the thinned treatment. Regardless of treatment, voles damaged seedlings only on the edge and 30–40 m from the edge and did no damage in the forest interior (90–100 m), whereas deer damaged significantly more seedlings in the forest interior than on the edge. At site 2, where vole damage was concentrated on the edge, damage to seedlings was affected only by distance from the edge, not edge structure. 4 The two dominant herbivores, white-tailed deer and meadow voles, preferentially damaged different seedling species. In addition, tree seedlings browsed by deer resprouted more frequently than those clipped by voles. Our results suggest that both edge structure and distance from the edge influence herbivore activity and, as a result, influence the spatial arrangement, density and composition of populations of tree seedlings during regeneration in forest fragments.

We approach the benefits and burdens of interdisciplinary research (IDR) from the perspective that science involves both constructive and critical approaches. The constructive aspect generates concepts, theories, and data to understand the observable world, while criticism tests the internal consistency of understanding and its fit to the observable world (Pickett and others 1994). IDR is the linkage of phenomena, research approaches, and conceptual tools that had previously been pursued independently (Parker 1993). Such linkages produce new research questions, new approaches to problems, new theories, and new generalizations. Therefore, IDR emphasizes the constructive aspect of science.

The ground-layer vegetation of a forest-old field edge gradient was sampled lo determine the effects of the edge on spatial patterns of plant species and community attributes. Species showed individualistic responses to the forest edge, with peak abundance at different spatial positions rclalive to the edge. Principal components analysis rcstilted in three a\es which explained a total of 63.2'J^> of the variation within the data set. The first two PCA axes were related to distance to the forest edge. The third separated plots into those that were dominated by Solidago ccmadensis. and those that were dominated by Solidago juncca. All population- and community-level attributes varied along the edge gradient. Species richness, Shiinnon-Wiener diversity, and total percent cover increased from the forest to the edge, with slight declines 60 m from the edge in the field. Among-plot heterogeneity was higher at the edge than in either the forest or the field. Exotic species had peak abundance within 20 m of the edge inside the forest and are restricted to the edge. Mosi population- and community-level attributes showed edge responses on both sides of the edge. This emphasizes the need to study edges as gradients that include both disturbed and undisturbed habitats.

Large, infrequent disturbances (LIDs) can have significant impacts yet seldom are included in management plans. Although this neglect may stem from relative unfamiliarity with a kind of event that rarely occurs in the experience or jurisdiction of individual managers, it may also reflect the assumption that LIDs are so large and powerful as to be beyond the ability of managers to affect. However, some LIDs can be affected by management, and for many of those that cannot be affected, the resilience or recovery of the system disrupted by the disturbance can be influenced to meet management goals. Such results can be achieved through advanced planning that allows for LIDs, whether caused by natural events, human activities, or a combination of the two. Management plans for LIDs may adopt a variety of goals, depending on the nature of the system and the nature of the anticipated disturbance regime. Managers can choose to influence (a) the system prior to the disturbance, (b) the disturbance itself, (c) the system after the disturbance, or (d) the recovery process. Prior to the disturbance, the system can be managed in ways that alter its vulnerability or change how it will respond to a disturbance. The disturbance can be managed through no action, preventive measures, or manipulations that can affect the intensity or frequency of the disturbance. Recovery efforts can focus on either managing the state of the system immediately after the disturbance or managing the ongoing process of recovery. This review of the management implications of LIDs suggests that management actions should be tailored to particular disturbance characteristics and management goals. Management actions should foster survival of residuals and spatial heterogeneity that promote the desired recovery pattern and process. Most importantly, however, management plans need to recognize LIDs and include the potential for such disturbances to occur.

We studied the patterns and mechanisms of regeneration of a 400-ha wind- throw in an old-growth beech-hemlock forest caused by a tornado on 31 May 1985. Starting in 1986, and over a period of six growing seasons, we recorded percent cover and density of woody stems, and monitored seedling demography of nearly 5000 seedlings in the windthrow and adjacent forest. Plant community response to the disturbance was dramatic: by August of 1986, species richness, tree seedling density and total percent cover were significantly greater in the windthrow than in the adjacent forest. Shade-intolerant herbs (e.g., Erechtites hieracifolia) and shrubs (e.g., Rubus allegheniensis) established and rapidly increased in abundance during the first 3 yr, but began declining by the 5th yr of the study. Tree seedlings established in decreasing amounts through the 6 yr of the study, and the young tree canopy was dominated in 1991 by seedlings and sprouts that established prior to 1987. Fagus grandifolia, a shade-tolerant species that established via advanced regeneration, was dominant the first 3 yr, but was surpassed in the 5th yr by Betula alleghaniensis, a species of intermediate tolerance that established from seed germination just before or shortly after the disturbance. Tsuga canadensis seedling densities were initially high, but deer browsing prevented substantial growth and a drought in 1988 caused heavy mortality of browsed seedlings. Regeneration thus differed from the predictions of the gap and Hubbard Brook models of forest regeneration (which predict dominance by shade-intolerant species), and the severity model (which predicts dominance by shade-tolerant species). The differences point out important influences of availability of propagules and the impact of herbivory; and the need for more attention to models that incorporate multiple contingencies.

In their recent article in TREE, Ramalho and Hobbs [1] call for a more mechanistic urban ecology that better incorporates the dynamic nature of urban areas in both time and space. We agree with their goals, but we feel that their assessment of urban ecological research was elementary and misrepresents the actual state of the science. Urban ecologists [2] are fully aware that modern cities do not develop as concentric rings, but instead grow in the spatially and temporally complex, non-linear ways that Ramalho and Hobbs emphasize [1].

We explored local variation in rate of plant succession by computing three contrasting measures of change for 10 New Jersey old fields through the first 18 yr after abandonment. We found that all three measures, euclidean distance in ordination space, turnover analysis, and regression analysis of species loss from the initial cohort, showed the same trend of decrease in the rate of plant succession with time. However, we did not find a monotonic decrease, and the specific years of transient increase differed with the analytical measure used. Both turnover and regression analysis showed that those old fields that had previously been planted in orchard grass (Dactylis glomerata) had a much lower initial change than fields previously in soybeans, or soybeans and sorghum, but this difference dissolved after 10 yr of succession. The study fields compared favorably to other mesic successions and agreed with the general pattern of more rapid rate decrease in mesic compared to xeric successions. Our results echo ...

Marhovian chains are probabilistic matrix models used to simulate the dynamics of systems in which each transition depends upon the present state of the system, but is independent of the pathway that brought the system to its present state. Their application to ecological succession has not been especially fruitful. Appropriate Markovian models could be used to test successional hypotheses analogous to the Marhovian assumptions. However, serious mathematical and empirical difficulties thwart the development of adequate models, primarily because of the importance of historical and spatial factors in succession.

We studied the effects of litter ofthe annual grass Setariafaberii, the perennial herb Solidago spp. (mostly S. canadensis), and leaves of the hardwood tree Quercus alba on a successional plant community. We also assessed light interception by these litter types in the laboratory. Light extinction followed the Beer-Lambert exponential law. Solidago litter had the highest transmittance constant and Quercus litter the lowest. The three types of litter produced different light mosaics at the microsite (0.8 cm diameter) scale. In the field, all three litter types affected community structure, but the effect of Quercus was the strongest. Litter reduced the density of the two dominant grasses, Setaria faberii and Panicum dichotomiflorum. Quercus and Setaria litter resulted in biomass compensation (i.e., fewer but larger individuals) by S. faberii but not by P. dichotomiflorum, which probably was always outcompeted by S. faberii. Solanum carolinense, the main dicot in the community, was unaffected by litter addition. Setaria and Solidago litter enhanced the establishment of Erigeron annuus, but Quercus litter reduced it. Litter reduced the number of flowering individuals of S. faberii and the number of seeds per plot; Quercus litter increased the production of seeds per individual. We conclude that species-dependent effects of litter on plant populations may significantly alter interspecific interactions and change plant community structure through direct and indirect effects.

We discuss the dynamics of plant litter, the effects of litter on the chemical and physical environment, the direct and indirect effects of plant litter on plant populations and communities, and different adaptative traits that may be related to litter accumulation. The production of litter depends primarily on the site productivity, but other properties of the environment, as well as chance, may introduce important variation. The existence of time lags between the production of plant organs and their transformation into litter appears as a relevant character of litter dynamics seldom included in models. Herbivory, and other processes that destroy biomass or reduce productivity, may reduce the amount of litter produced. The destruction of litter encompasses a complex of interactions. The main processes, including physical and chemical degradation, consumption by invertebrates and decomposition, are differentially affected by the environment and by the physical and chemical characteristics of the litter itself. The relative importance of those processes varies among systems.

Urbanization is a massive, unplanned experiment that already affects large acreages and is spreading in many areas of the United States (Alig and Healy 1987). Urban areas are conservatively defined as those with human populations denser than 620 individuals/km2 (United States Bureau of Census 1980, Bourne and Simmons 1982). In 1989, 74% of the United States population (203 million people) resided in urban areas and that number is expected to increase to >80% by the year 2025 (Fox 1987, Haub and Kent 1989). The increase in urban population throughout the country has resulted in the conversion of cropland, pastures, and forests into urban and suburban environments

Ecologists and paleoecologists have become increasingly aware that the temporal and spatial scales of the two disciplines overlap considerably and provide complementary information. Pollen and macrofossil evidence from thousands of radiocarbon-dated sites worldwide indicate that species respond to environmental change independently, that communities are relatively open assemblages, and that instability and change characterize Quaternary environments and biotas. The extended temporal view provided by paleoecology also enables detection of the occurrence, intensity and changing frequency of periodic and unique events such as disturbances and environmental fluctuations. As these insights contribute to our understanding of a dynamic environment and biota, they may help to increase our ability to anticipate future changes in communities.

The roles of disturbance and resource availability in influencing species richness and plant abundance were examined by conducting a factorial experiment for 2 yr in an old field in New Jersey, USA, dominated by goldenrods (Solidago spp.). Replicate plots were treated by (1) adding macronutrients, (2) adding water, (3) tying back tall herbs to increase light to ground layer species, and (4) creating gaps in the vegetation by disturbing the soil with a hand trowel early in the growing season. Nutrient additions increased the cover of the herbaceous canopy and enhanced the dominance of Solidago spp. Water additions also increased canopy cover during the second growing season, a year with low seasonal rainfall. Light enrichment as a consequence of canopy manipulations resulted in the competitive release of subcanopy species, primarily Fragaria virginiana. Other subcanopy dominants were limited by different resources; Hier- acium pretense responded most strongly to water and Rumex acetosella to nutrients. These differences in limiting resources may be responsible for the continued coexistence of these three subcanopy species. Additionally, we observed marked seasonal and yearly fluctuations in the severity of resource limitation which might serve to favor different species in this community at different times. Species richness was decreased by light enrichment alone, whereas light with irrigation interacted to increase species richness. Nutrient additions had little direct effect on species richness. A single small disturbance at the beginning of the growing season had little impact on species richness or abundance. Relative to the influence of resources, small-scale dis- turbance plays only a minor role in this community. Our results suggest that nonequilibrium organization of old-field communities can occur via a shifting resource base in the absence of natural disturbances.

An emerging generalization from theoretical and empirical studies on conservation biology is that high levels of environmental stochasticity increase the likelihood of population extinction. However, coexistence theory has illustrated that there are circumstances under which environmental stochasticity can increase the chance of population persistence. These theoretical studies have shown that the sign of the effect of environmental stochasticity on population persistence is determined by interactions between life history and environmental stochasticity. These interactions mean that the stochastic and deterministic rates of population growth might differ fundamentally. Although difficult to demonstrate in real systems, observed life histories and variance in the vital rates of populations suggest that this phenomenon is likely to be common, and is therefore of much relevance to conservation biologists.

Human activities affect Earth's life support systems so profoundly as to threaten many of the ecological services that are essential to society. To address this challenge, a new science agenda is needed that integrates people with the rest of nature to help chart a more sustainable trajectory for the relationship between society and the biosphere. This paper describes Earth Stewardship, an initiative of the Ecological Society of America to provide the scientific basis for actively shaping trajectories of social-ecological change to enhance ecosystem resilience and human well-being. Principles for moving toward these goals include simultaneous attention to multiple scales and issues; consideration of both ecological and socioeconomic consequences; alignment of incentives with stewardship behavior; strengthening peoples' connections to valued places; and using demographic transitions as new opportunities for stewardship. Past experience provides guidelines for fostering Earth Stewardship. Early attention to sustainable pathways before problems emerge generally provides more cost-effective solutions than attempting to remediate entrenched problems. Defining sustainable pathways by assessing tradeoffs among alternative options requires careful attention to fine-scale processes, interactions, and feedbacks and to larger-scale controls and constraints. Many opportunities occur locally, through development of practices that match the properties of resources with the needs of their users. Substantial challenges remain at larger scales, including maintaining the diversity, productive capacity, and resilience of nature, which are essential for long-term human welfare. The knowledge needed to inform stewardship requires an interdisciplinary science that draws on the observations, skills, and creativity of a wide range of natural and social scientists, practitioners, and civil society. New questions and solutions will emerge when these groups work together to formulate the issues, design the research, and co-produce the observations, knowledge, and concepts that form the basis for solutions. The goal of Earth Stewardship is not to protect nature from people; rather it is to protect nature for human welfare.

Given that ecological effects of disturbance have been extensively studied in many ecosystems, it is surprising that few quantitative syntheses across diverse ecosystems have been conducted. Multi-system studies tend to be qualitative because they focus on disturbance types that are difficult to measure in an ecologically relevant way. In addition, synthesis of existing studies across systems or disturbance types is challenging because sufficient information needed for analysis is not easily available. Theoretical advances and improved predictions can be advanced by generalizations obtained from synthesis activities that include multiple sites, ecosystems, and disturbance events. Building on existing research, we present a conceptual framework and an operational analog to integrate this rich body of knowledge and to promote quantitative comparisons of disturbance effects across different types of ecosystems and disturbances. This framework recognizes individual disturbance events that consist of three quantifiable components: (1) environmental drivers, (2) initial system properties, and (3) physical and biological mechanisms of effect, such as deposition, compaction, and combustion. These components result in biotic and abiotic legacies that can interact with subsequent drivers and successional processes to influence system response. Through time, a coarse-scale quasi-equilibrial state can be reached where variation in drivers interacting with biotic processes and feedbacks internal to the system results in variability in dynamics. At any time, a driver of sufficient magnitude can push the system beyond its realm of natural variability to initiate a new kind of event. We use long-term data from diverse terrestrial ecosystems to illustrate how our approach can facilitate cross-system comparisons, and provide new insights to the role of disturbance in ecological systems. We also provide key disturbance characteristics and measurements needed to promote future quantitative comparisons across ecosystems.

Summary 1. By the end of this decade, the majority of people will live in cities and suburban areas. Urban areas, including suburbs and exurbs, are expanding rapidly worldwide. 2. Plant ecology has largely ignored cities, or has primarily focused on the discrete urban green spaces within cities. 3. Plant ecology is increasingly engaging urban ecosystems as integrated natural-human systems, in which human agency is part of the complex of feedbacks. 4. Linking plant ecology with urban design (architecture, landscape architecture, civil engineering and urban planning) can help to integrate research and understanding of plants into the structure of cities, and to make use of urban design projects as ecological research tools. 5. Synthesis . A cycle of ecological design illustrates the linkage of plant ecological research with the ongoing transformation of urban systems by urban designers and civil society. Quality of life, human health, public appreciation of ecological processes in cities, and scientific understanding can all be enhanced by participating in a cycle of ecological urban design.

CADENASSO, M.L., S.TA. PIcKETr (Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545) AND PJ. MoRiN (Department of Ecology, Evolution, and Natural Resources, 14 College Farm Road, Cook College, Rutgers University, New Brunswick, NJ 08901). Experimental test of the role of mammalian herbivores on old field succession: community structure and seedling survival. J. Torrey Bot. Soc. 129:228-237. 2002.-When elucidating plant community dynamics, investigators have focused on plant-plant and plant-environment interactions and on the characteristics of individual plants. The role of animals has been relatively neglected. Herbivory may affect vegetation dynamics by altering community composition and structure and by influencing the performance of species. Therefore, herbivory can be an important factor in succession. We experimentally tested the role of mammalian herbivores in two fields at the Hutcheson Memorial Forest Center in central New Jersey. Both fields were released from active cultivation, one at the beginning of the experiment and the other 17 years earlier. Large exclosures (5 X 5 m) were used to exclude mammalian herbivores, and open units of the same size were used as controls. The effect of herbivore exclusion on the structure and composition of the plant community was analyzed. In addition, tree seedlings of three species-Acer rubrum, Cornus florida, and Juniperus virginiana-were planted in the experimental units in both fields. These species typically invade earlyto mid-successional old fields. The survival of these individuals was calculated and, using height as an indicator, their performance assessed. Herbivore exclusion primarily influenced the structure of the plant community rather than its composition. Percent cover of species and species richness of all plants were not affected by herbivory, but in one field the relative cover of exotics was greater in the exclosures. The height profile of the plant community in the exclosures was significantly taller than the community in the open plots. The survival and growth of planted A. rubrum and C. florida seedlings was significantly greater when protected from herbivores. In contrast, the survival and growth of J. virginiana seedlings was not affected by herbivores. Growth and survival of J. virginiana did differ by the field they were planted in, suggesting that physiological constraints may be more important than herbivory for this species. These results reenforce that herbivorous mammals play a key role in old field succession, particularly in the pivotal shift of dominance from herbaceous to woody cover.