COMMON PATTERNS OF ECOSYSTEM BREAKDOWN UNDER STRESS

Ecosystems, despite their diversity, respond to stress in similar ways . The major pressures which cause the transformation of systems from h ealthy states to pathological states are classified into four groups: physical restructuring, overharvesting, waste residuals;and the introd uction of non-native species. Signs of Ecosystem Distress Syndrome (ED S) are briefly examined in three contrasting ecosystems: desert grassl ands, the: Great Lakes, and the Baltic Sea. The issue is raised as to the difficulty in discerning between healthy ecosystems, recovering fr om a natural disturbance, and those ecosystems that have lost their or iginal resilience due to anthropogenic stress. Knowledge of site histo ry and a rigourous monitoring program are important in the evaluation of EDS. An assessment of how ecosystem services are affected is indica tive of the consequences to the human component of ecosystems. Managem ent strategies which are employed to mitigate the signs of EDS are usu ally initiated after resilience is lost or the ecosystem has transform ed to an alternate, stress-induced, stable stare. It is proposed that preventive strategies measure signs of EDS that serve as early warning signals, combined with ''fitness tests'' that measure ecosystem respo nse to natural perturbations. The fitness test for ecosystems is based on the premise that unstressed systems are more resilient to natural disturbances than stressed systems.