Showing papers by "Stephen R. Carpenter published in 2002"

Resilience Management in Social-ecological Systems: a Working Hypothesis for a Participatory Approach

Abstract: Approaches to natural resource management are often based on a presumed ability to predict probabilistic responses to management and external drivers such as climate. They also tend to assume that the manager is outside the system being managed. However, where the objectives include long-term sustainability, linked social-ecological systems (SESs) behave as complex adaptive systems, with the managers as integral components of the system. Moreover, uncertainties are large and it may be difficult to reduce them as fast as the system changes. Sustainability involves maintaining the functionality of a system when it is perturbed, or maintaining the elements needed to renew or reorganize if a large perturbation radically alters structure and function. The ability to do this is termed "resilience." This paper presents an evolving approach to analyzing resilience in SESs, as a basis for managing resilience. We propose a framework with four steps, involving close involvement of SES stakeholders. It begins with a stakeholder-led development of a conceptual model of the system, including its historical profile (how it got to be what it is) and preliminary assessments of the drivers of the supply of key ecosystem goods and services. Step 2 deals with identifying the range of unpredictable and uncontrollable drivers, stakeholder visions for the future, and contrasting possible future policies, weaving these three factors into a limited set of future scenarios. Step 3 uses the outputs from steps 1 and 2 to explore the SES for resilience in an iterative way. It generally includes the development of simple models of the system's dynamics for exploring attributes that affect resilience. Step 4 is a stakeholder evaluation of the process and outcomes in terms of policy and management implications. This approach to resilience analysis is illustrated using two stylized examples.

Ecological futures: building an ecology of the long now1

Abstract: Ecosystem dynamics unfold into the future but are understood by examining the past. A forward-looking ecology, which assesses a broad range of possible future ecosystem states, is the complement of long-term, historical approaches to ecology. Together they are the ecology of the long now. The “long now” of ecosystems includes historical influences that shape present ecologies, and the future consequences of present events. As a step in testing theories by their consequences, prediction is widely used in ecology. Ecologists have developed, criticized, and improved many predictive theories. Ecologists also have developed many empirical relationships that are potentially useful in forecasting. Eutrophication is an example of a problem for which ecologists created fundamental understanding, predictive capability, and new options for management. Ecologists frequently justify their research funding through appeals to improved predictability. This goal is sometimes attainable and in any case motivates a considerable body of insightful research. However, in many cases of environmental decision making, what ecologists cannot predict is at least as important as what can be predicted. It is important to assess the full range of changes in ecosystems that may plausibly occur in the future, and the implications of these changes. The paper discusses some ways that ecological information can be used to improve understanding of the future consequences of present choices.

Pathways of organic carbon utilization in small lakes: Results from a whole-lake 13C addition and coupled model

Abstract: In many small aquatic ecosystems, watershed loading of organic C exceeds autochthonous primary production. Although this allochthonous organic C has long been thought of as refractory, multiple lines of evidence indicate that substantial portions are respired in the receiving aquatic ecosystem. To what extent does this terrestrial C support secondary production of invertebrates and fish? Do current models adequately trace the pathways of allochthonous and autochthonous C through the food web? We evaluated the roles of allochthonous and autochthonous organic C by manipulating 13 C content of dissolved inorganic C in a small, softwater, humic lake, thereby labeling autochthonous primary production for about 20 d. To ensure rapid and sufficient uptake of inorganic 13 C, we enriched the lake with modest amounts of N and P. We constructed a carbon flow model based on the ambient and manipulated levels of 13

Multiple states in river and lake ecosystems.

Abstract: Nonlinear models of ecosystem dynamics that incorporate positive feedbacks and multiple, internally reinforced states have considerable explanatory power. However, linear models may be adequate, particularly if ecosystem behaviour is primarily controlled by external processes. In lake ecosystems, internal (mainly biotic) processes are thought to have major impacts on system behaviour, whereas in rivers, external (mainly physical) factors have traditionally been emphasized. We consider the hypothesis that models that exhibit multiple states are useful for understanding the behaviour of lake ecosystems, but not as useful for understanding stream ecosystems. Some of the best-known examples of multiple states come from lake ecosystems. We review some of these examples, and we also describe examples of multiple states in rivers. We conclude that the hypothesis is an oversimplification; the importance of physical forcing in rivers does not eliminate the possibility of internal feedbacks that create multiple states, although in rivers these feedbacks are likely to include physical as well as biotic processes. Nonlinear behaviour in aquatic ecosystems may be more common than current theory indicates.

Stocking piscivores to improve fishing and water clarity: a synthesis of the Lake Mendota biomanipulation project

Abstract: 1. A total of 2.7 × 10 6 walleye fingerlings and 1.7 × 10 5 northern pike fingerlings were stocked during 1987-99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha -1 and stabilised at 4-6 kg ha -1 throughout the evaluation period. 2. Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3. Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300-600 kg ha -1 prior to the die-off and the fish stocking, to about 20-40 kg ha -1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4. During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5. In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6. The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the diversity of fishing opportunities have improved for walleye, northern pike and, more recently, yellow perch.

Comparisons of P-Yield, Riparian Buffer Strips, and Land Cover inSix Agricultural Watersheds

Abstract: Riparian buffer strips may protect streams from phosphorus (P) pollution. We compared 2 years of daily P-yield (μg m−2 day−1) from six southeast Wisconsin watersheds with contrasting riparian buffer attributes. Of the variables measured, mean daily P-yield was most closely correlated with the variability in riparian patch size. Variability in P-yield was most closely correlated with characteristics of the riparian buffer, such as percent wetland land cover, riparian continuity, and stream sinuosity. During the most extreme events, mean P-yield was negatively correlated with the percentage of wetland land cover in the upland watershed. Correlations suggest that riparian continuity may influence P-loading in these watersheds. Our results corroborate the importance of continuity and uniformity of riparian buffers as moderators of P flow from upland agricultural lands into streams.

Temporal, spatial, and taxonomic patterns of crustacean zooplankton variability in unmanipulated north‐temperate lakes

Abstract: We quantified the spatial and temporal variability of crustacean zooplankton abundance at annual time steps with 261 lake-years of data from 22 lakes in three regions of central North America. None of these lakes had been experimentally manipulated. Using a nested three-way analysis of variance, we apportioned variance among years, 1

Optimal phosphorus loading for a potentially eutrophic lake

Abstract: We are concerned with the management of ecological and economic systems with threshold responses and with several time scales. Although optimal control of such systems is seldom attainable, the form of such optimal controls provides important insights for more practical schemes. Here we optimize the expected discounted net benefits of phosphorus (P) loadings for a potentially eutrophic lake. The benefits accrue to agricultural interests from activities that result in loading, and costs accrue to other interests from the resulting deterioration of water quality. We extend the 1999 results of S. R. Carpenter, D. Ludwig, and W. A. Brock to account for dependence of P recycling upon the concentration of P in sediments. We obtain optimal policies using methods of dynamic programming with two state variables. We find a strong interaction between economic and ecological parameters in determining the optimal policy: the economic discount rate determines whether the time horizon is long or short, and this in turn strongly influences the magnitude of the optimal loadings. Simple policies that neglect dynamics of P in the sediments are inadequate unless the time horizon is short and the dynamics are slow. A stochastic model is essential if there are substantial random fluctuations in loadings. Uncertainty in the determination of the critical P density that triggers recycling cannot be neglected. Our results may be interpreted as a quantitative precautionary principle that takes account of both economic and ecological aspects of the management of the lake. Our results may also be used to illustrate economic ideas such as sustainable development, natural capital, option values, and income.