Root-closed forest ecosystem formation above forest boundary in Northern Urals mountains

The purpose of this work is to determine the length of the root systems of Siberian stone pine undergrowth (Pinus sibirica Du Tour) growing in the mountain tundra of the Northern Urals and to establish regression relationships with its aboveground parameters and age. The studies were carried out in the belt of mountain stony shrub-moss-lichen tundra at an altitude of 1010–1040 m above sea level on the plateau of the «Tri Bugra» mountain massif (59°30ʹ N, 59°15ʹ E). Consideration of environmental conditions and undergrowth of woody plants was carried out on 30 registered plots with a size of 5×5 m. P. sibirica is absolutely dominant (6,0 thousand specimens per ha) in the undergrowth. Its constant almost annual renewal began in the end 60s XX century. It was revealed that under the conditions of mountain tundra, the length of the root systems of all studied age groups of P. sibirica undergrowth exceeds its height by 1,2…1,5 times, and the area of soil nutrition (field of root competition) exceeds the area of projective crown cover by more than 10 times. A statistically significant relationship between the length of roots and the age (R2 = 0,78) of the undergrowth and its height (R2 = 0,92) are established. Regression equations are obtained. At the current rates of climate warming and the growth of P. sibirica trees, the revealed dependences make it possible to predict for the mountain tundra of the Northern Urals mosaic formation of primary underground-closed forest associations (woodlands) with characteristic forest relationships in 20–25 years, and communities with multiple interweaving of root systems in 40–50 years.