Vegetation reconstruction methods in comparison

A widespread and the earliest vegetation reconstruction method is the phytosociological approach (e.g., Heer 1855, Saporta & Marion 1878, Saporta 1881, Kirchheimer 1957). In this syntaxonomical concept, palaeoabiotic factors (e.g., substrate and trophy characters, groundwater table, salinity, etc.) are also considered to different degrees. In this method, several palaeophytocenological markers are usually selected based on their abundance, physiognomical and taxonomical characte; on this basis the defined palaeovegetation units (including their nearest living relatives (NLRs) environmental datasets) have been correlated to suitable extant vegetation units and/or subunits. Mai (1995, p. 498-603) presented most of the published vegetation types and their synonyms, thus providing a detailed overview of zonal and azonal phytosociological units in current use for the Paleogene and Neogene of Europe. In contrast, the IPR-vegetation analysis is designed to indicate major zonal vegetation types, i.e., BLDF, MMF, BLEF, etc. that are reflected in fossil assemblages. The analysis does not consider abundances of taxa and abiotic factors are not differentiated beyond the discrimination of zonal versus azonal taxa.

Another common method that can help to interpret the structure of an ancient plant cover is a geoelement analysis. This approach has been methodologically derived from a phytogeographical approach and has been used to evaluate and show the migration and extinction of fossil taxa in the Paleogene and Neogene (e.g., Unger 1847, Heer 1855, 1859; Ettingshausen 1851, 1869, 1885; Mai 1995, Kvaček et al. 2011). This method analyses the habitat ranges of the most similar relatives (MSRs) analogues of fossil taxa and clusters them into several defined element groups and/or subgroups, such as tropical-subtropical elements (A), holarctic elements (B) and others (C) (sensu Mai 1995, p. 239-240). The proportion of the defined geoelements/groups can indicate a general vegetation character of fossil assemblages based on the representation of the most abundant geoelement group. Kvaček et al. (2011) noted an almost identical percentage proportion of the geoelement groups A and B (36 % vs. 59%) and percentages of the BLE and BLD components (35% vs. 52 %) sensu the IPR-vegetation analysis in the mastixioid flora of Arjuzanx (France). This fact can be simply explained by a similar methodological background of both methods: (1) to some degree corresponding taxonomic-physiognomic definitions of the geoelements A and B and the BLE and BLD components in the IPR-vegetation analysis and (2) the quantitative analysis.

Both the phytosociological approach and the geoelement analysis are weakly empirical methods, whereas the IPR-vegetation analysis includes botanical, sociological, and ecological input/information as well as quantitative evaluation.

A relatively new method is the “reconstruction of vegetation transects” developed by Bertini & Martinetto (2008, 2011). It was first applied on selected Messinian to Piacenzian floras from North and Central Italy. This method also evaluates an integrated fossil plant record and distinguishes physiognomic-taxonomic scoring parameters that are similar to the IPR-vegetation analysis such as azonal, zonal, extrazonal habitats, leaf type categories, growth forms. In addition, and differing from the latter analysis, it includes pollination types (Bertini & Martinetto. 2011, tables 2, 3). As opposed to the IPR-vegetation analysis, this new method considers “representative taxa” defined by their appropriately weighted abundance-percentage datasets. By incorporating the abundance factor into reconstructions of the fossil plant cover (which also reflects standard geobotanical methods), it can help to more closely and reliably correlate hypothetical fossil azonal and zonal vegetation types to suitable living vegetation units. As mentioned above, the IPR-vegetation analysis excludes taxa abundances because they are usually strongly biased because taphonomic factors differ strongly among the organ assemblages (leaves versus fruits and seeds versus pollen) (Kovar-Eder et al. 2008, p. 109). The application of the IPR-vegetation analysis on empirically (botanically) defined modern vegetation units from SE China and Japan, including the cluster analysis of the results, have proved that no significant differences exist between empirically defined vegetation types that consider abundances and the predicted vegetation types by the IPR-vegetation analysis (Teodoridis et al. in press).

Martinetto & Vassio (2010) recently developed a special quantitative vegetation reconstruction method called the “Plant Community Scenarios” focusing only on carpo-deposits (sensu Gee 2005). This method makes use of the CENOFITA 1.2 database (Martinetto & Vassio 2010). It has been introduced and tested for the flora of Ca’ Viettone, Italy. As the “reconstruction of vegetation transects” method, several scoring groups are applied such as different leaf type categories, plant habitus and ecology. Contrary to all the other methods, this one includes tentative corrections for taphonomical biases induced by different size and production rates of plant parts (Martinetto & Vassio 2010, tables 2, 3).