The Thicket Structure Explains Sorbaria sorbifolia ’s Ability to Be a Transformer in the Secondary Range

The patterns of formation of thickets of the invasive vegetatively mobile shrub Sorbaria sorbifolia were studied. The study was carried out in urbanized southern taiga pine forests—forest parks of Yekaterinburg. The density, length and diameter of shoots, and their volume were determined in the center and on the periphery of three thickets of S. sorbifolia on 60 plots of 0.25 m 2 . The age of 64 shoots was determined by annual tree rings. In the ontogeny of an individual shoot up to 5–7 years, growth is slow, the maximum growth rate is reached at 7–15 years; after 15 years, the morphological parameters of shoots cease to increase noticeably. The average length and diameter of the shoot are 2 times greater from the periphery to the center of thickets, and the volume of one shoot is 8–9 times greater. The total volume of shoots per unit area is 6–6.5 times higher in the center of thickets than in the periphery. Young (1–5 years old) shoots absolutely predominate in the marginal zones. In the center of the thickets, there is a significant proportion of cohorts whose age is more than 10 years, but shoots aged 1–5 years make up more than half of all shoots. It was concluded that the ability of S. sorbifolia to manifest the properties of a transforming plant in the secondary range can be satisfactorily explained by the special structure of its thickets, which have no analog in the forest communities of the Middle Urals.