Global and local factors in earth surface systems

Abstract

Earth surface systems are controlled by a combination of global factors (laws, principles and relationships that apply everywhere and always) and local factors which are place- and time-contingent. Formal arguments, framed in the context of the state factor model of soils and ecosystems, show that where the scales of the global and local components are sufficiently different, global or local dynamics can be discovered without considering the other. However, the same arguments show that the total, aggregated system cannot be understood without accounting for both the local and global components. The system dynamics cannot be recovered from the global or local controls alone. Local forms of spatial analysis provide both the conceptual and operational means to frame global factors within the spatial and historical contingency expressed in local controls. Applications have been limited in environmental sciences, but the potential is high. Entropy-based approaches also hold promise and may allow estimates of the relative contributions of global and local controls. An example of application to forest succession in the southeastern US coastal plain is designed to examine the relative importance of laws governing successional pathways with or without regular fires and of the local spatial and temporal contingencies, which control fire regime. The analysis shows that global laws governing forest succession account for about 80% and local contingencies associated with fire frequency for about 20% of the system connectance entropy.