The second analytical stage involves entering the ecosystems diagram with 

 each primary ecological alteration. The PEA indicates a direct effect in the 

 ecosystem on storages of materials (soil salts, nutrients, detritus, micropore 

 water, surface water); transformers (primary producers, various consumers); or 

 on pathway regulators (ground cover, shade, flowing water). Quantifying the 

 magnitude and duration of the PEA provides the initial point of reference 

 needed to determine and evaluate the first ecosystem component affected. When 

 an access point into the model has been identified and the initial alteration 

 has been quantified with respect to duration, magnitude, and direction of 

 change, the second phase terminates and stage three begins. 



The third stage constitutes the "heart" of the methodology. All the 

 analytical decisions regarding the (1) magnitude, (2) duration, (3) probabil- 

 ity of occurrence, (4) subsequent second-, third-, and fourth-order effects, 

 (5) synergistic properties, and (6) "significance" of the PEAS are determined 

 here, relative to the predetermined scale of review. Depending on the magni- 

 tude and duration of the initial disturbance, secondary alterations may be 

 systematically identified by checking, on the respective system diagram, 

 altered energy/material pathways and altered energy/material storages or 

 transformers. Tertiary alterations may be similarly identified. The proce- 

 dure followed in conducting a PEA analysis can be summarized by the following 

 synopsis. 



Given a primary ecological alteration, the operator enters the model at a 

 specific storage, transformer, or input. An estimation of the PEA magnitude, 

 direction of change, and duration has been established as a result of the PEA 

 determination phase and permits a judgment as to what the initial component 

 (storage, transformer, or input) change will be. The resultant change, either 

 an increase or decrease, will be for that particular component as a generated 

 result of the PEA's. In addition, some estimate of duration of change, either 

 long or short term, may be indicated. The first order or level of altera- 

 tion(s) for that specific PEA has now been determined. The operator now 

 notices that one or more pathways emerge from the initial storage, trans- 

 former, or input which has just been changed by the PEA. These pathways lead 

 to other model components and represent either (1) material /energy flows into 

 other system storages, outputs, or transformers or (2) a regulatory function 

 of other ecosystem processes. Every pathway must be examined individually, 

 with respect to characteristics of the activity and the ecosystem, and evalu- 

 ated as to importance to the ecosystem. The evaluation process considers many 

 aspects, the most important of which are: probability of event occurrence, 

 magnitude of change, direction of change, synergistic effects, and counteract- 

 ing processes. If a particular link is determined to be unimportant or 

 incapable of altering the subsequent system storages or ecological processes 

 which it leads to, then further consideration of that pathway is unnecessary 

 and the analysis is terminated. 



If, however, the magnitude, direction, and/or duration of a change is 

 such that important alterations (third-order) are still evident, then the 

 operator must continue the analysis by following subsequent linkages. 

 Storages, outputs, .and/or transformers that are connected to such linkages 

 must also be examined to determine if significant increases or decreases in 



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