Tree Stand Structure in the Forest–Mountain Steppe Transition Zone on the Slopes of the Kraka Massif (Southern Urals) and Its Determining Factors

Abstract

Ground-based laser surveys of the upper parts (from the ridge crests to the border of closed forests) of six steppe slopes of the mountains of the Southern and Northern Kraka massifs (Southern Urals) on a total area of 20.82 hectares were carried out. As a result, 3584 trees were identified in all studied areas, their morphometric parameters (crown height and size) and exact geographical position were assessed with an accuracy of 3–10 cm. It was shown that the closure and density of tree stands are extremely low in the upper third of the surveyed altitudinal profiles, and a local increase in these indicators is observed only on some slopes. It is also widely noted that these characteristics of forest stands increase sharply at a distance of about 2/3rd of the length of the profiles from the ridge crests. Measurements of the depth of the soil layer showed that the soils in the upper parts of the slopes are thin (on average 7–12 cm), and their average depth reaches 29 cm only on some slopes in places where the density of forest stands increases. Soil depth on sections of profiles remote from the ridge crests 1/4th to 2/3rd of their length gradually increases and reaches average values of 20–30 cm. We associate both local and stable (in the lower part) increase in the density of forest stands in the forest–mountain steppe transition zone with the increase in the thickness of the soil layer and the volume of moisture retained by it.