Dynamics of parcel structure of forest phytocoenoses in regenerating spruce population in boreal birch forests
Regularities of dynamics of parcel structure associated with spruce regeneration was found in sorrel birch forests and bilberry birch forests 40-115 years old based on 20 years long studies at 12 sampling plots (Yaroslavl Oblast, Northern forest experimental station of the Institute of Forest Science). We analyzed growing stages by the 10 years age groups of the birch edificatory story. Birch forests with early and late spruce regeneration were studied, with the 20-30 years or later spruce regeneration after birch establishment on a cutting. The dynamics of parcel structure was studied in five groups of parcels recognized by similarity of the wooden stories structure, including: B1-Sou (birch with open undergrowth of spruce), B1-Scu (birch with closed undergrowth of spruce), B1-S2 (birch with closed second story of spruce), B1-S2o (birch with open second story of spruce), B1 (birch with no spruce story). At the stage of 41-50 years we found high patchiness in the structure of phytocoenose with up to 120 parcels of predominantly (63%) open and closed undergrowth per 1 ha. Birch forest at transition to maturation at 51-70 years has decreased parcel number from 112 to 80, with further diminishing to 11 parcels dominated with B1-S2 at the age of 71-90 yrs. Mono-parcel structure of the birch forest destructs at the old-growth stages at 91-115 years due to appearance of young spruce undergrowth. The parcel sizes was related to the structure of birch forests.