Highly branched arabinan-rich pectic polysaccharides, containing 84% of arabinose, was extracted from wood greenery of Abies sibirica L. The structure of arabinan was studied by the 1D and 2D NMR spectroscopy. The macromolecule backbone was represented mainly by RG-I (molar ratio GalA:Rha∼1.3:1) patterns with high degree of rhamnose branching. Side chains were comprised of 1,5-linked α-l-Araf residues (the major part of polymer mass), 1,3,5-di-O- and 1,2,3,5-tri-O-linked α-l-Araf residues, confirming the presence of highly branched 1,5-α-l-arabinan. Although most l-Araf were in α-anomeric form, minor terminal β-l-Araf-(1→… was detected. 1,4-β-d-linked Galp residues found in the side chains account for minor AG-I or 1,4-galactan, as compared to arabinan. A tentative structure was proposed. Polysaccharides obtained from Siberian fir greenery were screened for biological activity. Galacturonan had a strongest stimulating effect on germination and growth rate of seeds, germs and roots of Triticum aestivum, Avena sativa, and Secale cereale.