The present distribution of terrestrial vegetation is a highly complex mosaic resulting from the interplay of many factors. The natural coevolution of climate, soils, and biotic species through complex feedback loops has also been shaped, at an escalating rate, by human influences
over the past million years. Significant anthropogenie factors include the incidence of disturbance processes such as fire, selective harvest of plant and animal species, domestication of a remarkably scant number of plant and animal species and both purposeful introduction
and accidental redistribution of species well beyond their source biomes. A basic understanding of the current web of life and associated abiotic feedback through various cycles is at the core of global earth systemscience.A number of process models have been developed
to understand the nature of fluxes occurring between the geosphere, biosphere, hydrosphere, and atmosphere. For each model, a specific set of parameters has been developed to represent the significant attributes of the system. For those models that seek to operate at
large spatial- or temporal-scales, this parameterization of land-cover attributes generally necessitates classification in order to compress the breadth of natural diversity
into a finite number of manageable classes and to do this at spatial scales commensurate with the process to be modeled. Inherent limitations to the development of a successful classification, for a given purpose, are (1)