Resilience Thresholds Research Articles

Fire, fuel composition and resilience threshold in subalpine ecosystem.

BackgroundForecasting the effects of global changes on high altitude ecosystems requires an understanding of the long-term relationships between biota and forcing factors to identify resilience thresholds. Fire is a crucial forcing factor: both fuel build-up from land-abandonment in European mountains, and more droughts linked to global warming are likely to increase fire risks.MethodsTo assess the vegetation response to fire on a millennium time-scale, we analyzed evidence of stand-to-local vegetation dynamics derived from sedimentary plant macroremains from two subalpine lakes. Paleobotanical reconstructions at high temporal resolution, together with a fire frequency reconstruction inferred from sedimentary charcoal, were analyzed by Superposed Epoch Analysis to model plant behavior before, during and after fire events.Principal FindingsWe show that fuel build-up from arolla pine (Pinus cembra) always precedes fires, which is immediately followed by a rapid increase of birch (Betula sp.), then by ericaceous species after 25–75 years, and by herbs after 50–100 years. European larch (Larix decidua), which is the natural co-dominant species of subalpine forests with Pinus cembra, is not sensitive to fire, while the abundance of Pinus cembra is altered within a 150-year period after fires. A long-term trend in vegetation dynamics is apparent, wherein species that abound later in succession are the functional drivers, loading the environment with fuel for fires. This system can only be functional if fires are mainly driven by external factors (e.g. climate), with the mean interval between fires being longer than the minimum time required to reach the late successional stage, here 150 years.ConclusionCurrent global warming conditions which increase drought occurrences, combined with the abandonment of land in European mountain areas, creates ideal ecological conditions for the ignition and the spread of fire. A fire return interval of less than 150 years would threaten the dominant species and might override the resilience of subalpine forests.

Psychische Komorbidität und Lebensqualität bei Patienten mit implantierbarem Kardioverter/Defibrillator (ICD)

Currently, the method of choice for protection against sudden cardiac death for high-risk patients is ICD treatment. The CIDS study could prove a significant advantage of ICD treatment compared to amiodarone therapy. However, the survival advantages can be affected by the negative side effects of ICD therapy. The therapeutic survival function of the device is, in general, associated with a consciously experienced, at the same time completely unexpected and unprepared intracardial shock experience. Within the first year after implantation, 30-50% of patients with an ICD for secondary preventative indications experience such a shock. The average shock application frequency per year (under normal conditions) is about 2.5 shocks. The experience of one or more ICD shocks is significantly associated with a decrease in quality of life. Particularly the experiencing of five or more intracardial shocks approaches the patient's psychological resilience threshold. Partners and relatives of ICD patients are, on the other hand, often helpless with respect to the demands of and stress associated with the ICD technology. In current clinical practice, the involvement of the partners in the treatment of ICD patients is generally a coincidence and is generally not systematic or target-oriented. Improved involvement of relatives can contribute to an improved prognosis. Cardiologists caring for ICD patients should be aware of the specific psychological aspects of ICD technology, integrate these aspects into the guidance and care of patients, and be able to identify and address pathologically negative affects and crises in ICD patients.

Multiple stressors in coupled river–floodplain ecosystems

Summary1. Riverine floodplains are highly complex, dynamic and diverse ecosystems. At the same time they are among the world’s most threatened ecosystems because of the pervasiveness of dams, levees and other factors such as rapid spreading of non‐native species. Hence, floodplains are ideal systems to study ecological impacts of multiple stressors at the local, regional and catchment scale.2. Concepts such as the subsidy‐stress hypothesis and the stress‐induced community tolerance concept have been formulated to study the effect of stressors on aquatic and terrestrial ecosystems, as well as on their functional linkages.3. Riverine floodplains are pulsed ecosystems with distinct flow, sediment, resource and thermal pulses – thereby creating distinct ‘windows of ecological opportunity’. Human modifications that truncate or amplify theses pulses will have cascading effects on river–floodplain interactions by shifting the thresholds of connectivity, resilience or resistance – causing drastic regime shifts.4. Most aquatic insects and pond‐breeding amphibians have complex life cycles with aquatic and terrestrial stages. They are exposed to different stressors in their aquatic and terrestrial realm. Because most life history functions of aquatic insects are restricted to a short terrestrial period, we need to fully integrate the ‘airscape’ into the future management of river–floodplain ecosystems.5. Riverine floodplains integrate and accumulate multiple stressors at the catchment level, as reflected by distinct catchment fingerprints. Based on the European Catchment Data Base we provide spatially explicit information on multiple stressors; a key prerequisite for setting priorities in conservation and management planning.6. Thematic implications: the management of stressed river and floodplain ecosystems is a major challenge for the near future and water managers worldwide. Management approaches need to be adaptive and embedded within a catchment‐wide concept to cope with upcoming pressures originating from global change.

Economic Lessons of the Kobe Earthquake

The earthquake that struck the Japanese port city of Kobe on January 17, 1995, was the most severe quake ever to strike a modern urban area. It has become the most studied, analyzed, and discussed natural disaster in history. What I propose to add to this dialogue is an economist's overview of what he saw in Kobe 19 months after the event and what he learned during the ensuing 6 months.

Lack of native species recovery following severe exotic disturbance in southern Californian shrublands

Summary 1. Urban and agricultural activities are not part of natural disturbance regimes and may bear little resemblance to them. Such disturbances are common in densely populated semi‐arid shrub communities of the south‐western US, yet successional studies in these regions have been limited primarily to natural successional change and the impact of human‐induced changes on natural disturbance regimes. Although these communities are resilient to recurrent and large‐scale disturbance by fire, they are not necessarily well‐adapted to recover from exotic disturbances. 2. This study investigated the effects of severe exotic disturbance (construction, heavy‐vehicle activity, landfill operations, soil excavation and tillage) on shrub communities in southern California. These disturbances led to the conversion of indigenous shrublands to exotic annual communities with low native species richness. 3. Nearly 60% of the cover on disturbed sites consisted of exotic annual species, while undisturbed sites were primarily covered by native shrub species (68%). Annual species dominant on disturbed sites included Erodium botrys, Hypochaeris glabra, Bromus spp., Vulpia myuros and Avena spp. 4. The cover of native species remained low on disturbed sites even 71 years after initial exotic disturbance ceased. Native shrub seedlings were also very infrequent on disturbed sites, despite the presence of nearby seed sources. Only two native shrubs, Eriogonum fasciculatum and Baccharis sarothroides, colonized some disturbed sites in large numbers. 5. Although some disturbed sites had lower total soil nitrogen and percentage organic matter and higher pH than undisturbed sites, soil variables measured in this study were not sufficient to explain variations in species abundances on these sites. 6. Non‐native annual communities observed in this study did not recover to a predisturbed state within typical successional time (< 25 years), supporting the hypothesis that altered stable states can occur if a community is pushed beyond its threshold of resilience.

Coping with complex and dynamic systems. An approach to a transdisciplinary understanding of coastal zone developments

Complexity and uncertainty play important roles in coastal management. Economic development may push the coastal system beyond its resilience thresholds as a result of interactions between environmental and socio-economic processes. The concepts in this paper link processes of system change, natural evolutionary processes observed in coastal zones, to processes of social evolution. An indicator based on calculating an ecological footprint for coastal zones is presented to guide decision-making in spatial and economic planning. The suggested indicator may support a range of methods linking economic valuation and environmental impact analysis.

Ecological impacts of global change on drylands and their implications for desertification

Potential impacts of global change on dryland ecosystems are reviewed from four perspectives. First, results are reviewed from recent research on vegetation change, land degradation and desertification. The role of disturbances and low recurrence events in triggering non-linear changes by driving ecosystems beyond their resilience thresholds is outlined. Particular attention is paid to the development of spatial structures as feedbacks that tend to buffer degradation. Secondly, the synergetic operation of climatic and anthropogenic forcing factors of dryland degradation is discussed in the light of some case histories. Changes in one group of those factors often render the ecosystems particularly sensitive to changes of those in the second group. Thirdly, off-site effects of dryland degradation are summarized, including feedbacks to the atmosphere, changes in biological diversity and downstream impacts in river catchments. Finally, the implications of global change for land degradation control policies are outlined. The importance of prevention is emphasized, as well as the need to carefully consider where to apply rehabilitation and restoration. Prevention includes soft and cheap measures based on management practices, while restoration calls for massive and expensive interventions on soil or vegetation. © 1998 John Wiley & Sons, Ltd.

Linking social and ecological systems: management practices and social mechanisms for building resilience

1. Linking social and ecological systems for resilience and sustainability Fikret Berkes and Carl Folke Part I. Learning from Locally Devised Systems: 2. People, refugia and resilience Madhav Gadgil, Natabar S. Hemam and B. Mohan Reddy 3. Learning by fishing: practical engagement and environemntal concerns Gisli Palsson 4. Dalecarlia in Central Sweden before 1800: a society of social and ecological resilience Ulf Sporrong Part II. Emergence of Resource Management Adaptations: 5. Learning to design reslilient resource management: indigenous systems in the Canadian subarctic Fikret Berkes 6. Resilience and neotraditional populations: the caicaras of the Atlantic forest and caboclos of the Amazon (Brazil) Alpina Begossi 7. Indigenous African resource management of a tropical rain forest ecosystem: a case study of the Yoruba of Ara, Nigeria D. Michael Warren and Jennifer Pinkson 8. Managing for human and ecological context in the Maine soft shell clam fishery Susan S. Hanna Part III. Success and Failure in Regional Systems: 9. Resilient resource management in Mexico's forest ecosystems: the contribution of property rights Janis B. Alcorn and Victor M. Toledo 10. The resilience of pastoral herding in Sahelian Africa Maryam Niamir-Fuller 11. Reviving the social system-ecosystem links in the Himalayas Narpat S. Jodha 12. Crossing the threshold of ecosystem resilience: the commercial extinction of northern cod A. Christopher Finlayson and Bonnie J. McCay Part IV. Designing New Approaches to Management: 13. Science, sustainability and resource management C. S. Holling, Fikret Berkes and Carl Folke 14. Integrated management of a temperate montane forest ecosystem through holistic forestry: a British Columbia example Evelyn Pinkerton 15. Managing chaotic fisheries James M. Acheson, James A. Wilson and Robert S. Steneck 16. Social mechanisms and institutional learning for resilience and sustainability Carl Folke, Fikret Berkes and Johan Colding Index.

Usefulness of the human carrying capacity concept in assessing ecological sustainability of land-use in semi-arid regions

The carrying capacity concept was developed from animal ecology, and applied to rangeland management in order to assess sustainable livestock stocking rates. In it, long-term ecological sustainability was not a well developed criterion. Early applications of carrying capacity concepts to agricultural land-use have been much criticised, but recent developments provide useful insights. The proposed definition of human carrying capacity is ‘the maximum level of exploitation of a renewable resource, imposing limits on a specific type of land-use, that can be sustained without causing irreversible land degradation within a given area’. Hence, it is a property of the ecosystem only. The definition is primarily aimed at maintaining ecosystem productivity and resilience, i.e. avoiding irreversible land degradation. The human carrying capacity is based on the sustainable supply of natural resources and on resilience thresholds of the ecosystem. The level of maximum sustained exploitation of natural resources can also be expressed as maximum sustainable agricultural production levels, or sustainable population densities based on such production levels. Such applications require careful definitions of the assumptions and conditions involved. Absolute assessments of human carrying capacity have limited value only, particularly in semi-arid regions. However, comparing human carrying capacity levels with current exploitation rates of natural resources provides a useful framework to consider the ecological aspects of sustainable land-use.

The influence of below-average rainfall on the vegetational traits of a patch-grazed semi-arid grassland

The effect of below-average rainfall on the species basal cover of semi-arid grassland varies between patches representing different stages of degradation. Total basal cover of patches in good condition increased in contrast to patches in poor condition, due to increases in basal cover of high ecological status species. Patches in poor condition expanded at the expense of less degraded patches. Long-term patch over-utilisation stresses the vegetation beyond a threshold of drought resilience. Consequently, the absence of livestock grazing did not prevent retrogression of patches in poor condition in times of drought. The following hypothesis was formulated: semi-arid vegetation which has retrogressed beyond a threshold of drought resilience can not rest–recover. Recovery trends in above-average rainfall seasons will be reversed in subsequent below-average rainfall seasons due to the instability of the retrogressed vegetation and lack of resilience to even minor droughts.