Cronosequences of vegetation a bioclimatic theory for interpreting the patterns of relict vegetation types
de Mera, Antonio Galán; Vicente Orellana, José A.
Based on the meteorological data of 855 stations of the world, and using the total humidity index (HT), the mean annual temperature (T), and the number of months with the minimal absolute temperature lower than 0 °C (nma < 0), a climatic model predicting vegetation types has been established. As a result, 13 different tropical vegetation types have been obtained: desert (DT), semidesert (SMT), dry savanna (SS), steppe with deciduous trees (ET), high tropical mountain with disperse periglacial vegetation (AMT), humid savanna (SH), coniferous forests or espinal (BAT), dry high tropical mountain 'dry Puna' (PS), laurel-type forests (BL), high continental tropical mountain with disperse periglacial vegetation (AMTC), rain forests with palm communities (PL), rain forests with arborescent fern communities (PLM), and humid high tropical mountain with long grass 'humid puna' and 'paramo' (PH). Thirteen extratropical vegetation types have also been included: Tundra or high mountain grasslands (T), wooded tundra or high mountain disperse forest (TA), Artic and Subantartic disperse scrubs (MDS), Taiga or coniferous forest (TG), mixed forest with coniferous and deciduous trees (MXCC), temperate deciduous forest (BCT), temperate steppe with deciduous trees (ETC), desert with Mediterranean character (DM), semidesert with Mediterranean character (SMM), sclerophyllous vegetation with Mediterranean character (VM), steppe with disperse scrubs with Mediterranean character (VAL), high mountain grasslands with Mediterranean character (AMM) and Mediterranean mixed forest with coniferous and deciduous trees (MXCE). As a consequence of the climatic convergence of different territories, which is presented in a similarity dendrogram (Cluster Analysis), an essay of the origin and evolution of the vegetation, which we synthesize in the hypothesis of the cronosequences of vegetation, is presented. A cronosequence of vegetation is the succession on time of different types of vegetation, due to climatic changes.