Sivolapov A.  

Structure of clonal Populus alba L. micropopulations in floodplains Khopyor and Don rivers

In floodplains of Khopyor and Don rivers poplar stands are typical floodplain forests, pioneers and aboriginals of woody and shrubby plants along the rivers courses. White poplar (Populus alba L.) is met as groups, clumps, small plots of the same clone up to 1.5 ha. White poplar is a forest former of floodplain stands. It shows its important role in forming of biocenosis in river floodplains.
As for regime and duration of flooding, white poplar is timed to the floodplains of short-term and seldom average flooding.
Along the main river course sedge and blackberry micropopulations are formed. In the central part blackberry-nettle-kirkazon natural white poplar stands are formed. In near terrace part nettle and blackberry white poplar stands are formed.
White poplar micropopulations are more frequently met in near course and central floodplain, on slopping dunes and even plots of the relief. On sandy alluvial dunes white poplar forms highly productive stands. Thus, in Khopyor nature reserve, quartel 93 according to the data of a permanent sample plot white poplar´s maximum volume at the age of 130 was 1640 m3/ha; average tree height – 44 m, average diameter on breast height – 92 cm. On the depth of 1.1 m soil pit showed humus horizon of 50 cm thichness. This poplar plot is registered as a plus stand.
In the central floodplain they are met on typical oakery soils. Ecological row of these poplar stands is in fresh and moist growing conditions, in rows of fertility C-D-E by P.S.Pogrebnyak’s classification.
Clonal micropopulations of white poplar are differed by sex. Rsearches showed that male trees occupy higher plots of microrelief and the number of male trees is 15-50 % higher than of female trees.
Investigation of the structure of clonal micropopulations of natural white poplar stands by bark design showed that in central floodplain longitudinal-chinked (typical) forms and in near course floodplain dark-coarse-fark forms prevail. In near terrace floodplain sometimes biogroups of pectinate-bark form are met.
Investigations of physical and mechanical properties of wood showed that its specific gravity in pectinate-bark form reaches 530 kg/m3, in typical and dark-coarse-bark form – 410 - 430 kg/m3, that is 100 kg less than in pectinate-bark form.
Study of histological tissue composition showed that in dark-coarse-bark form the content of mechanical tissue is 10-15% higher than in typical and pectinate-bark forms and is 65%.
The length of woody fiber (libriform) in pectinate-bark form is 0.20-0.30 mm less than in typical and dark-coarse-bark forms (1.30 mm).
So, the study of white poplar clonal micropopulations in floodplains of Khopyor and Don rivers allowed to highlight 3 groups of edaphic ecotypes, 3 forms by bark design, which differ by qualitative description of wood and peculiarity of sex dimorphism.
Valuable stands and trees of white poplar are registered as plus ones and represent gene pool of this woody species for further breeding and propagation.


Abstracts file: Sivolapov A..doc

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