Growth Features of Siberian Elm on Brown Soils of the Astrakhan Semi-Desert

The article presents the current state assessment and suggests the methods for additional moisture supply of soils under stable tree plantations of Siberian elm (Ulmus pumila L.) on brown soils of semi-desert. The research area belongs to the arid zone. This is a treeless zone of dry steppe and semi-desert, where about 1,000 ha of plantations with a predominance of elm of different species have been planted since 1949–1953: shade clumps, pasture protection strips, massifs, separated forest stands. The soils are brown desert-steppe alkaline sandy loam and light clay-loam in combination with solonetz (10 %). Siberian elm stands form plantations of different ages and for different purposes. The research is based on biomonitoring materials and field experiments using standard forest inventory techniques. Test sites of a rectangular shape with an area of 0.4 ha were laid out in order to study the Siberian elm stands. We described in detail the location of the test sites, the soil composition thereon, and gave a comprehensive assessment of the growth and durability of the plantations. It is shown that the stand state is determined by 2 sets of factors: zonal-edaphic and pastoraleconomic. Viable stands of Siberian elm at the age of 57–64 have been preserved on sandy loam and dark-colored soils located in micro- and inter-hill depressions. The dynamics of soil moisture under plantations is largely independent of the tree location method. Satisfactory indicators of growth and durability of plantations depend on the level of availability of soil moisture and the degree of its salinity. The moisture supply of soils under elm plantations can be increased by using melt water runoff in hollows and micro-depressions and increasing the growing space of a tree to 25 m2. Formed elm plantations respond positively to the presence of resting animals. The “alliance” relationship between the stand and livestock does not arise immediately, but rather from a certain age of the stand and the moment it forms a certain structure of the tree layer, which should be provided by forest cultivation and silvicultural measures in conjunction with the regulation of pasture load. There is a positive effect of resting animals at the appropriate load on the growth, state and durability of the Siberian elm stands.