Categorising biogeographical data in the MaarjAM database.

Ecological categories

The habitat classification implemented in the MaarjAM database uses three hierarchical levels (from general to specific): specific ecosystem features, biome, habitat.

The category ‘specific ecosystem features’, which currently has five levels, is a flexible category allowing researchers to address particular ecological patterns of interest. For the purpose of the questions addressed in this paper, it is used for distinguishing between structurally and functionally different ecosystems such as forests and grasslands (cf. McNaughton et al., 1989), and to characterize the dynamic status of the ecosystem (in the current paper, we distinguish early successional natural ecosystems and anthropogenic ecosystems - cultivated ecosystems or various disturbed ecosystems). One level ‘culture’ is used for records originating from cultures of Glomeromycota if no information about the ecosystem of origin was available. Further specific categorizations may be created to address future questions.

The category ‘biome’ represents the largest ecological classification unit that is convenient to recognize globally. Habitats within a biome function in a broadly similar way. There are several parallel classifications of biomes, ranking from very coarse in scale to rather specific (Lomolino et al., 2005; Mace et al., 2005). The WWF classification of terrestrial ecoregions within 14 biomes and eight biogeographic realms (Olson et al., 2001), also applied in the Millennium Ecosystem Assessment (Hassan et al., 2005), was used as a starting point. However, in order to interpret the distribution of AM fungi in a more precise ecological context, the original classification was further refined to include altogether 27 biomes as follows: tropical moist broadleaf forest; subtropical moist broadleaf forest; tropical dry broadleaf forest; subtropical dry broadleaf forest; tropical coniferous forest; subtropical coniferous forest; temperate broadleaf and mixed forest; temperate coniferous forest; boreal forest; tropical grasslands and savannas; subtropical grasslands and savannas; tropical shrublands; subtropical shrublands; temperate shrublands; temperate seminatural grasslands; temperate natural grasslands; temperate cultivated permanent grasslands; flooded grasslands and savannas; montane grasslands; montane shrublands; tundra; Mediterranean forest, woodland and scrub; deserts and xeric shrublands; mangroves; other wetlands; anthropogenic ecosystems.

In the case of tropical and subtropical forests (moist and dry broadleaved and coniferous forests), grasslands and shrublands, we distinguished between tropical and subtropical biomes. We also distinguished grasslands from shrublands. The biome ‘Temperate grasslands, savannas and shrublands’ was split into four units. Temperate shrublands was retained, but three types of grasslands were distinguished: natural, seminatural and cultivated permanent grasslands. Such a distinction is fundamental because natural grasslands represent zonal vegetation (such as steppes in Eurasia and prairies in North America); while seminatural grasslands, whose flora and fauna is spontaneous, have developed from natural vegetation in the presence of long term moderate human impact (such as many European pastures and wooded meadows developed in naturally forested areas, cf. Poschlod & WallisDeVries, 2002); and cultivated permanent grasslands have been artificially created by humans and maintained over several years. Montane grasslands and shrublands are treated as different biomes. In addition to mangroves, we included the category ‘other wetlands’, which combines several azonal wetland biomes across the globe. In addition, we introduced the category ‘anthropogenic ecosystems’ to represent a variety of ecosystems in heavily human influenced areas (agricultural, industrial and urban areas). Currently, the MaarjAM database contains records from 15 biomes.

The category ‘habitat’ refers to the vegetation/ecosystem/ ecoregion/habitat type where sampling was conducted. If present, a description from the original publication was usually retained; however, if it was lacking or insufficient, wherever possible a specification was provided on the basis of other information available in the publication or elsewhere.

Environmental categories

Climatic zones were defined primarily according to temperature, but also moisture balance. These zones generally correspond strongly to vegetation boundaries. Walter (1994) distinguished nine climatic zones: equatorial (always moist and lacking temperature seasonality); tropical (summer rainy season and cooler winter dry season); subtropical (highly seasonal arid); mediterranean (winter rainy season and summer drought); warm temperate (occasional frost, often with summer rainfall maximum); nemoral (moderate climate with winter freezing); continental (arid with warm summers and cold winters); boreal (cold temperature with cool summers and cold winters); polar very short, cold summers and long, very cold winters).

For simplicity, a modification of Walter’s (1994) system with five broad climatic zones corresponding to zones by Holdridge (1967) is used in the MaarjAM database: tropical s.l. (equatorial and tropical); subtropical s.l. (subtropical, mediterranean and warm temperate); temperate s.l. (temperate, nemoral and continental); boreal; polar. There are currently no data in MaarjAM from the latter two zones.

References

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