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Changes in the composition, structure, and altitudinal distribution of low forests at the upper limit of their growth over the past 50 years have been studied in the Tylaisko-Konzhakovsko-Serebryanskii Massif (the Northern Urals). The qualitative and quantitative assessment of these changes has been made on the basis of descriptions, photographs, and maps made in 1956 and 2005. The results show that the upper boundary of low forests on the majority of slopes has ascended. Considerable changes have occurred in the composition, density, and height of the tree layer in the communities that formed the upper low-forest boundary in 1956. Among a fairly large number of tree species growing in the subgoltzy belt (Picea obovata, Larix sibirica, Pinus sibirica, and Abies sibirica), the birch Betula tortuosa has expanded most actively, whereas the proportions of P. obovata and especially L. sibirica in low forests have decreased. These changes are explained by climate warming and increasing humidity.

The composition and structure of tree stands near the timberline have been studied on different slopes and at different elevations in the Tylaisko-Konzhakovsko-Serebryanskii Massif, the North Urals. It has been found that the upper limits of tree stands with different degrees of canopy closure have risen considerably (by about 100 m of elevation) since the mid-19th century, although the formation of these stands started as early as the late 18th century. Woodless areas in the eastern part of the massif started to be colonized by Larix sibirica in the late 18th to early 19th centuries; those in the western part, by Picea obovata in the mid-19th century; and in the southern part, by Betula tortuosa in the late 19th century. Analysis of meteorological data provides evidence for warming and increasing humidity of the climate since the late 19th century. Favorable climatic changes that facilitated the expansion of the forest have taken place both in the summer (prolongation of the growing period) and in winter seasons (increase of air temperature and precipitation). The observed differences in the composition and dynamics of tree stands between the studied areas of the mountain range are most probably explained by different requirements of tree species for the depth of snow cover and the degree of soil freezing.

When using the compiled database on net primary production (NPP) and biomass of Betula L. genus of Eurasia, transcontinental regularities of changing NPP of wood story from the North to the South according to the bell-shaped curve with a maximum in the subzone of before-forest-steppe are stated, while the NPP of roots and forest understory increases monotonically within the total zonal gradient. In the direction from the Atlantic and Pacific coasts to the continentality pole in Siberia, NPP of stems, branches and all the above-ground part decreases, while NPP of foliage, roots and understory increases. Thus, wood story NPP decreasing offsets by understory one increasing, and vice versa. Productivity of birch foliage, expressed by the ratio of above-ground NPP to foliage one, declines as growth conditions make worse both in the direction of ocean shores to the continentality pole and in direction from the optimal conditions for birch forest growth in the subzone of before-forest-steppe to pessimal conditions both of the tundra in the North and of the Himalayan mountains in the South.

First transcontinental changes in fractional composition of sample tree biomass of larches (Larix Mill.) and two-needled pines (subgenus Pinus) are reported, taking into account their regional differences by age, tree height, stem diameter, and volume, as well as tree density. All components of the tree biomass of larches and pines monotonically increases from the North to the South. Dynamics of pine biomass in the direction from the Atlantic and Pacific coasts to the continentality pole in Siberia is characterized by monotonous decrease of all components, including the roots. The latter is in contradiction with the change of the larch root biomass across the same gradient of climate continentality, which, unlike the mass of pine roots, is not reduced, but increased. The system of the transcontinental dependencies obtained allows its use in estimating forest biomass based on the local data of a tree enumeration per ha.

Changes in the altitudinal position of the timberline in high mountain areas of the Nether-Polar Urals and basic factors that influence such changes have been revealed on the basis of comparison of the age structure of Siberian larch (Larix sibirica) and arctic birch (Betula tortuosa) tree stands and photographs made in different years. On the mountain slopes studied, an upward shift of the timberline took place in areas covered in winter with thick snow (in the late 18th century), with Siberian larch being the pioneer species. Larch began colonizing areas with a thin snow cover in the 20th century. Birch appeared later and has since strengthened its positions. The increase in winter temperatures and precipitation facilitated the expansion of the forest.

The correlation between climatic changes and the numbers of trees in the generations of Siberian spruce (Picea obovata Ledeb.) in subgoltsy tree stands of the Southern Urals was analyzed over the past 200 years. The results showed that the most abundant generations appeared in 1809–1816, 1821–1827, 1839–1845, 1850–1867, 1875–1887, 1891–1896, 1900–1904, 1911–1918, 1923–1932, 1944–1952, 1958–1966, and 1975–1995. Their formation proved to be related to the improvement of thermal conditions of the warm season during the five to seven years before and after the emergence of trees and conditions of the cold season in the year of their emergence, as well as to the periods of increased snow depth in late April in the years 27–32 of tree growth.

Methodical approaches to forest biomass and net primary production estimating are studied and their regression models are designed. By means of combining these models and State Forest Account database of 305 forest enterprises of the Ural region the total forest biomass (9.11 billion tons) and net primary production (542 million tons) are calculated. The models and calculating algorithms are involved into the information system on the base of the Software AG platform Natural, which allows to estimate and to re-calculate forest biomass and net primary production on some territory in automatic mode.

Relationships between stem diameter and phytomass of trees and their parts (single- and multistemmed growth forms) have been studied at different altitudinal levels of the present-day upper treeline ecotone on the Iremel’ Massif, the Southern Urals. The time course of changes in the structure and phytomass of birch–spruce stands during the past centuries has been reconstructed. It is shown that the expansion of forests to the mountains in this period has occurred against the background of rise in summer and winter temperatures and increase in the amount of solid precipitation in the Southern Urals.