Growing stock of tree and shrub species across elevation zones in Slovenia: comparative analysis and developmental characteristics

Abstract

Slovenian forests are among the most species-rich in Europe, with 71 native tree species recorded. Despite this high diversity, two species—European beech (Fagus sylvatica) and Norway spruce (Picea abies)—dominate the growing stock, together accounting for 60% of the total volume. The growing stock of trees and shrubs above the 10 cm DBH (diameter at breast height) threshold increases with elevation, with the highest elevation zone reaching 398 m³/ha. In contrast, the Shannon–Wiener diversity index for trees and shrubs above 10 cm DBH decreases as elevation increases. A similar pattern is observed for the Shannon–Wiener index of small trees and shrubs (below the 10 cm DBH threshold), although values in the lowest elevation zone are slightly lower. The proportion of Norway spruce in the growing stock of trees above 10 cm DBH increases markedly with elevation, rising from 10.2% in the lowest elevation zone (<300 m) to 49.4% in the highest zone. In recent years, European beech has become the dominant species in the growing stock of both trees and shrubs above 10 cm DBH, as well as small trees and shrubs below 10 cm DBH, indicating a likely further increase in the proportion of beech in future growing stock development. In elevation zones below 700 m, the growing stock of small trees and shrubs contains a substantially higher proportion of thermophilous broadleaved species—particularly manna ash (Fraxinus ornus), hop hornbeam (Ostrya carpinifolia), the non-native black locust (Robinia pseudoacacia), and shade-tolerant hornbeam (Carpinus betulus)—compared to their proportion in the growing stock of trees and shrubs above 10 cm DBH. In the growing stock of small shrubs across Slovenia and within all elevation zones, common hazel (Corylus avellana) predominates. Its growing stock proportion is highest in the 700–1000 m elevation zone (91.3%) and lowest in the lowest elevation zone (61.9%).