Nature - autonomous learning

212 the dis/unity of geographyBox 4.5 EQUILIBRIUM ONTOLOGIESUntil fairly recently, the belief that biophysical systems tendedtowards ‘equilibrium states’ was common in physical geography.In simple and very general terms, the equilibrium idea proposes thatthe various components of biophysical systems adjust to oneanother over time so that they form a relatively stable relationship.Indeed, this relationship is considered to be so stable for manybiophysical systems that any disturbance or external ‘forcing’ willultimately be compensated for as the system trends back to anequilibrium state (a so-called ‘homeostatic reponse’). For instance,in geomorphology it was a long-standing truism that landformsevolved over time in response to dominant environmental processes.Likewise, biogeographers assumed for many decades that‘climax communities’ were the norm in the plant world. Climaxcommunities are those assemblages of plant life that are most fullyadapted to the prevailing environmental conditions (like climate),albeit modified by local variations in soils, relief etc. In practice,physical geographers have utilised a range of equilibrium ideas intheir research. But we can make a broad distinction between ideasof static (or steady-state) equilibrium and more dynamic (or slowchanging)equilibrium. From the late 1970s, geomorphologists inparticular began to modify and challenge these ideas. For instance,Schumm (1979) identified intrinsic and extrinsic thresholds.Thresholds are points in which an environmental system undergoesa sudden change, without there necessarily being any alteration inthe flows of matter and energy entering and leaving the system.After this sudden change the system may attain a new equilibrium.Subsequent to the threshold idea taking hold in parts of physicalgeography, complexity theory, chaos theory, quantum mechanicsand the so-called ‘new ecology’ have been drawn upon to informphysical geographers’ ontological assumptions. These days it isaccepted that many environmental systems do not conform toequilibrium behaviour. Equilibrium and post-equilibrium thinking inphysical geography speaks directly to the third definition of the term