STRESS AND ECOSYSTEMS 



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Fig. 7 Model and simulation of the effects of a chronic stressor 

 (continuous cutting at 1-year intervals) on tropical terrestrial 

 ecosystems [data from Ewel (1971a)]. (For identification of 

 symbols, see Fig. 2.) Cutting is a type 4 stress (see Fig. 5). As 

 structure is continuously removed, the system develops a steady 

 state at a lower amount of biomass. 



Stressors can also weaken systems and make them more 

 susceptible to further stress. Woodwell and Brower (1967), for 

 example, reported aphid population explosions induced by gamma 

 radiation stress. The same phenomenon occurs in mangroves stressed 

 by high salinity, frost, or alterations in drainage patterns (Lugo and 

 Patterson Zucca, 1977). Involved in these responses are additive 

 and/or synergistic effects among stressors vv^hich accelerate energy 

 losses and rapidly reduce the system's capacity to negotiate more 

 stress. 



STRESS AND ECOSYSTEM COMPLEXITY 



Ecologists use a variety of indexes to measure ecosystem 

 response to stressors. Much attention has been placed on finding 

 relationships betvi^een environmental change and species diversity or 

 the stability of the system. [Consult the work of Baker (1970) and 



