Using Pollen Data to Delimit Steppe Types

What is it about?

Here we investigated the surface pollen assemblages of meadow steppe, typical steppe and desert steppe along the ecological humidity gradient in Inner Mongolia, northern China. The results indicate that 1) 3 steppe types are clearly distinguished from northern temperate forests, and from each other based on the pollen data by using cluster analysis; 2) the distribution and relative abundances of xerophilous elements (e.g. Ephedra, Tamarix, Zygophyllaceae and Nitraria) could be also used to delimit 3 steppe types.

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Why is it important?

While grasslands are important constituents of the terrestrial ecosystem, their origins and developments in the geological past remain open. Modern grasslands can be clearly differentiated from forests based on the vegetation compositions and relative abundances of arboreal and non-arboreal taxa. Recognizing these vegetation types (forests or grasslands) in the geological past requires the data of plant fossils. Former studies mainly based on indirect evidence, such as faunas, and stable carbon isotopes suggested the existence of grasslands in different continents, while direct botanical evidence such as fossil remains of grasses, phytoliths and pollen assemblages were sparse. Of this direct evidence, pollen assemblages have the advantage of reflecting the vegetation compositions and as such are potential indicators for the presence of grassland vegetation in any specific area, while megafossils and phytoliths usually fail to provide enough data of vegetation compositions. However, due to a lack of investigations on the pollen assemblages of modern grasslands, the criteria used to establish the origin of grassland based on the pollen assemblages were varied and confused in former studies. Obviously, detailed knowledge of the relationship between modern grasslands and their pollen assemblages is critical for recognizing and understanding the origin and expansion of grassland in the geological past using fossil pollen assemblages. Hoyt (2000) had confirmed that North America prairies could be clearly differentiated from forest, and four types of prairies (i.e. tall-grass, mixed-grass, short-grass and desert grasslands) can be distinguished from each other using pollen data. Nevertheless, it is unclear whether the pollen assemblages from the surface soil and/or strata of Eurasia can be used to detect the occurrence of steppe, or even to further delimit various steppe types.

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