Presentation on theme: "Walter E. Westman Bioscience 1978 Measuring the inertia and resilience of Ecosystems."— Presentation transcript:
Walter E. Westman Bioscience 1978 Measuring the inertia and resilience of Ecosystems
Introduces five characteristics of intertia and resilience Comments upon how they can be measured and/or modelled Examples mainly on terrestrial plants
1. go through the five characteristics –Definitions –Examples 2. Provide some points for discussion outline
definition: Resistance to change, how much force need to cause a certain change Example: how much radiations (this example is from the 1960s!) is needed to reduce to species richness by 50% => Varies for different plant assemblages intertia
Predictive index of inertia (aquatic) (Cairns and Dickson 1977) Product of: 1.Degree of adaptions of indigenous organisms to environmental fluctuations 2.Redudancy in function 3.Cleansing capacity- turbulence etc 4.Chemical buffering capacity 5.Proximity of to threshold (cold to warm water fishery) 6.Degree of effective management
Definition: the time required to restore a particular characteristic of the ecosystem (recovery rate) Example: - After mining, the time required to attain percentage similarity of plant species composition to e.g. 85% of original or climax vegetation -Disturbed tropical forest, extrapolated recovery time to climax state (from seed weights) Wet forest=1000 years, dry forest 150 years Elasticity
Amplitude Definition: Zone from which the ecosystem will return to initial state=> tresholds Examples: –Maximum stocking density to maintain pasture –Minimum fallow time after swidden agriculture to restore soil fertility –Oil exposure to plants threshold number (> 8-12 times), that when the plants cannot recover –Fire frequency, when below a certain treshold, a different species composition develops Problems with measuring=> modelling, disturbance treshold, frequency of clearcuts pending on dispersal etc.
Hysteresis Definition- degree to which the path of restoration is an exact reversal of path to degredation Example: Pattern of restoration/succession after grazing, incomparison with the order of disappearance
Definition: degree to which stable state established after distrubance differs for original steady state Stable state: mean species composition from one year to the next does not differ more than x % etc. Example: hsitorical records/modelling Compare measures of ecosystem structure and functioning, foliage cover, biomass, net production etc..) Malleability
How does the concepts here relate to other definitions of resilience? Raul: Inertia =resistance and not the same as resilience Elasticity= engeneering resilience Amplitude=related to ecological resilience Hysterises: Mallebility: two different stable states, equilibria, their difference in function Points to discuss:
What kind of view of the ecosystem does the paper apply? Key-words, stable state, climax community, succession How can the concepts be applicable when studying large marine systems like the Barents Sea ecosystem?