A methodological approach to potential vegetation modeling using GIS techniques and phytosociological expert-knowledge:: application to mainland Portugal

An attempt to obtain a consistent spatial model of natural potential vegetation (NPV) for the mainland Portuguese territory is reported. Spatial modeling procedures performed in a Geographic Information System (GIS) environment, aimed to operationalize phytosociological expert-knowledge about the putative distribution of potential zonal forest communities dominant in the Portuguese continental territories. The paradigm for NPV assumed was that of RIVAS-MARTINEZ (1976) and RIVAS-MARTINEZ et at. (1999), which presupposes, for a given territory, a univocal correspondence between a uniform combination of bloclimatic stage and lithology, given a biogeographical context, and a unique successional sequence leading to a single climax community (i. e. a vegetation series (VS)). Information issued from both literature and a team of phytosociologists possessing detailed knowledge about Portuguese vegetation, namely about forests and its serial vegetation, was acknowledged as a starting point for the construction of such a habitat-vegetation correspondence model. First, a bloclimatic map concerning the "Worldwide Bioclimatic Classification System" (WBCS) of RIVAS-MARTINEZ (1981-2004), obtained by multivariate geostatistical interpolation issuing from the work of MESQUITA (2005), was set. Several partial matrices, one for each biogeographical Province, combined such habitat statements to VS. Initial incoherence due to vagueness of statements led to an important amount of both superimposition of VS and habitat gaps in the matrices. Further rearrangement of the table according to known field distribution of VS by experts allowed setting an approximate univocal correspondence VS-habitat. Finally, an intersection of bloclimatic, lithology and biogeographic maps yielded over a thousand habitat combinations to be associated each to a single VS through implementation of the matrices as a set of rules. Again, inconsistencies were solved likewise, but this time by direct observation of the map by experts. Keeping of phytosociological consistency and fidelity to information on actual vegetation field distribution was always mandatory during the process.