Transformation of cover vegetation in mire sites by draining in the Ob-Tom divide

In the north of the forest-steppe zone and in the south of south-taiga zone drainage ofpeat bogs occurs. In order to study changes in their cover vegetation, a research washeld in the Ob-Tom Divide (West Siberia, Russia) in 2000-2002. The transformation wasthe most remarkable in the fens and their plant associations become an indicator ofchanging the hydrological regime of the peat bog on the whole. Both smooth and catastrophicsuccessions were revealed in vegetation communities of mires depending on thephase of draining. Slight changes of the cover vegetation, generally affecting the periphery,were marked only on large bogs with a thick peat deposit. On small ones, mostlycavin, the transformation was expressed more distinctly. The weakening of the mireforming process by draining resulted in strengthening the forest-forming process. A weakdraining results in the appearing of seedlingsand strengthening the draining results ingradual forming the tree layer on the previous fens.In the plant communities ecological species groups are changing: hydrophilic andhygrophilous groups are replaced by hydromesophilic and mesophilic ones. The portionof hydrophilic (Carex limosa, Sphagnum majus, S. jensenii, etc.) and hygrophilous wetlandspecies (Eriophorum vaginatum, Sphagnum angustifolium, etc.) reduces to theircomplete disappearance. Then hydromesophilic and mesophilic forest-mire and forestspecies (Pleurozium sherberi, Dicranum polysetum, etc.) recolonize there, gradually becomingdominant species in plant communities. Mosses as rootless plants react sharplyto the changing of moisture regime by draining, so changes in moss cover structure andcontent are more abrupt. Strong draining results in complete disappearance of sphagnummosses from the phytocenosis and in replacing them by forest Bryopsida mosses. Ondead areas of cover, formed by wetland species dying out, spots of various lichens fromgenus Cladonia appear. Pine and birch forest litter coenosis form in catastrophic successions.The changing of moisture in mire sites was estimated by using L.G. Ramenskiyecological scales. The amplitude of moistening in the fens sites is from 4-9 degrees onthe periphery of large wetland areas to 13-20 degrees on small cavin bogs. In most ofexamined sites the changes of fens moisture conditions to typical forest and meadowconditions occur

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