Leading Plant Families in Grasslands of Inner Asia Along the Aridity Gradient

The distribution patterns of plant families along the aridity gradient with regard to their role in the floristic composition and the structure of grasslands in Inner Asia have been studied. We have determined the relationships between the aridity, diversity, and activeness of 35 leading plant families using the Thornthwaite index on the basis of formalized analysis of 6256 relevés. The analyzed range of the aridity gradient covers 88% of the gradient represented in Eurasia. Communities are analyzed from subalpine tall-grass meadows in the hyper humid areas of the Altai-Sayan mountains to the deserts of Central Asia. Different results had been obtained when comparing family–species spectra with different levels of aridity considering species composition and importance values (activeness). The correlations between the aridity index and 35 families in 16 synoptic relevés indicate that, of the ten most rich families, Asteraceae, Chenopodiaceae, Fabaceae, and Poaceae show a strong positive relationship with the aridity index; the family Brassicaceae shows a moderately positive relationship with aridity index; the family Ranunculaceae shows a strong negative relationship with aridity index; and Apiaceae, Caryophyllaceae, and Rosaceae have a moderately negative relationship with aridity index. The correlation analysis of the importance values of the 35 families with the aridity index showed that Asteraceae, Fabaceae, and Poaceae are not associated with the aridity gradient, suggesting their significant ecological and phytocoenotic heterogeneity. Among other top families, Chenopodiaceae and Brassicaceae have strong positive relationships with aridity; Caryophyllaceae, Lamiaceae, and Ranunculaceae have a strong negative relationship with aridity; and Apiaceae and Rosaceae have a moderately negative relation. The use of species constancy and abundance in taxonomic spectra analysis can take into account the phytocoenotic importance of plants. This approach can be used to search for indicators of climatic processes, including those related to the aridification of Inner Asia.