Some recent papers on resilience…
1) Information network topologies for enhanced local adaptive management. by Örjan Bodin and Jon Norberg in Environmental Management 2005 35(2):175-93.
We examined the principal effects of different information network topologies for local adaptive management of natural resources. We used computerized agents with adaptive decision algorithms with the following three fundamental constraints: (1) Complete understanding of the processes maintaining the natural resource can never be achieved, (2) agents can only learn by experimentation and information sharing, and (3) memory is limited. The agents were given the task to manage a system that had two states: one that provided high utility returns (desired) and one that provided low returns (undesired). In addition, the threshold between the states was close to the optimal return of the desired state. We found that networks of low to moderate link densities significantly increased the resilience of the utility returns. Networks of high link densities contributed to highly synchronized behavior among the agents, which caused occasional large-scale ecological crises between periods of stable and high utility returns. A constructed network involving a small set of experimenting agents was capable of combining high utility returns with high resilience, conforming to theories underlying the concept of adaptive comanagement. We conclude that (1) the ability to manage for resilience (i.e., to stay clear of the threshold leading to the undesired state as well as the ability to re-enter the desired state following a collapse) resides in the network structure and (2) in a coupled social-ecological system, the system-wide state transition occurs not because the ecological system flips into the undesired state, but because managers lose their capacity to reorganize back to the desired state.
2) Eutrophication of aquatic ecosystems: Bistability and soil phosphorus by Steve Carpenter in PNAS online.
Eutrophication (the overenrichment of aquatic ecosystems with nutrients leading to algal blooms and anoxic events) is a persistent condition of surface waters and a widespread environmental problem. Some lakes have recovered after sources of nutrients were reduced. In others, recycling of phosphorus from sediments enriched by years of high nutrient inputs causes lakes to remain eutrophic even after external inputs of phosphorus are decreased. Slow flux of phosphorus from overfertilized soils may be even more important for maintaining eutrophication of lakes in agricultural regions. This type of eutrophication is not reversible unless there are substantial changes in soil management. Technologies for rapidly reducing phosphorus content of overenriched soils, or reducing erosion rates, are needed to improve water quality.
The paper shows that risks from nutrient accumulation are increasing and difficult to reverse or deal with:
Widespread eutrophication by anthropogenic nutrient inputs is a relatively recent environmental problem. Intensive fertilization of agricultural soils and associated nonpoint inputs of phosphorus increased through the middle of the 20th century. Analyses presented here show that it could take 1,000 years or more to recover from eutrophication caused by agricultural overenrichment of soils. In principle, eutrophication is reversible, but from the perspective of a human lifetime, lake eutrophication can appear to be permanent unless there are substantial changes in soil management. Technologies for rapidly reducing the phosphorus content of overenriched soils, or reducing erosion rates, could greatly accelerate improvements in water quality.
3) New paradigms for supporting the resilience of marine ecosystems by Terence Hughes, David Bellwood, Carl Folke, Robert Steneck and James Wilson in Trends in Ecology & Evolution. 2005 – 20(7) 380-386.
Box 1. Regeneration and hysteresis
What are the prospects for the recovery of damaged marine ecosystems? Marine organisms have many adaptations for coping with recurrent natural disturbances. However, chronic human impacts are analogous to press experiments, in which a manipulation is sustained. Consequently, a return to original conditions is impossible unless the major ongoing drivers (e.g. runoff of sediment, excess nutrients and fishing pressure) are reduced.
Many conservation and management practices imagine that if current stressors can be relieved, the ecosystem will automatically revert from an altered state to its original wilderness condition within a few years or decades. This approach ignores the recent emergence of a wealth of archeological and historical information about the profound changes wrought to marine ecosystems by human activities, especially harvesting. Moreover, marine ecosystems exhibit varying degrees of hysteresis; that is, their recovery follows a different trajectory from that observed during decline. Some systems have changed to the extent that they can effectively no longer converge to the original assemblage. From a complex systems perspective, they have crossed a threshold into a new state or domain of attraction that precludes return to the original state. The consequences for management are profound: it is easier to sustain a resilient ecosystem than to repair it after a phase shift has occurred.
Changes in species composition during recovery arise, in part, because of differences in life histories. For long-lived marine species (e.g. whales, turtles, dugongs, sharks and reef-building corals), recovery following controls on overfishing or pollution is necessarily slow. For example, populations of the seacow Dugong dugong have declined by 97% over the past three decades along 1000 km of coastline in tropical Queensland, Australia.
Assuming that hunting, incidental netting and habitat degradation can all be curbed, recovery of this species back to the levels of the 1970s (which were already severely depleted) will take at least 120–160 years, constrained by the limited annual growth rate of seacow populations of 2–3%. Similarly, recovery from increasingly frequent episodes of coral bleaching has favored short-lived species that can quickly recolonize after disturbances. All of the major fishing grounds worldwide have also seen a shift to weedier, fastgrowing species that are inherently less resilient and more prone to environmental fluctuations.
Alternate ecological states can be maintained by density-dependent mortality (e.g. owing to altered predator–prey ratios) or by density thresholds required for reproductive success. For example, regeneration of coral reefs can be inhibited by a surfeit of coral predators, by recruitment failure, and by blooms of toxic or structurally resilient algae that resist herbivory and smother juvenile corals. The concept of hysteresis recognizes that localized short-term reductions of human impacts will not ensure recovery to a pristine state. Similarly, the lack of recovery of collapsed fisheries a few years after fishing has eased does not prove that something else must have caused the decline.
