Structure and regularities of tree stand development in flood­plain forests of Mari El Republic

Results of long­term studies conducted in flood­plain forests of Mari El Republic are presented. These forests are of vast diversity of species, age, and spatial structure of stands. It is found that there are three phytocenotical layers in the flood­plain forests, English oak Quercus robur L. and tillet Tilia cordata L. are dominants in the layers. All the tree species, with the exception of Scots pine Pinus sylvestris L. and the European white birch Betula pendula L., have an ontogenetic structure. The best vitality is typical for tillet, the worst – for the European white elm Ulmus laevis L. and English oak. The trees of Scots pine and English oak are the highest ones in the stands. High correlation between the height of trees (all species) and their diameter is revealed. It is demonstrated that there is a quantity of undergrowth in flood­plain forests, where tillet typically dominates as it is well adapted to growing under the canopy. In some temporary inundated areas, self­seeding spruce Picea abies (L.) H. Karst. and fir Abies sibirica Ledeb. trees spring up and successfully grow under the stand canopy. Young oaks, birches, and aspens Populus tremula L. grow well in the canopy openings only or after a complete death of the stand. Currently phytocenotic processes in the flood­plain forests are going with dominating positions of tillet