Stable isotope composition in tree rings of Fagus sylvatica L. saplings reflects environmental variation induced by silviculture and microsite factors

Natural regeneration of tree species is sensitive to silvicultural interventions. This study aimed to investigate the effects of different cutting intensities and local topographic and soil conditions on the composition of stable carbon (delta C-13) and oxygen (delta O-18) isotopes in wood of young beech (Fagus sylvatica L.) trees. Beech saplings in the regeneration layer were sampled in summer 2018 at three study sites in Dinaric fir-beech forests in the karst area of Slovenia. Three different cutting intensities were performed in 2012: i) no cutting (control), ii) 50% cutting of the stand's growing stock creating thinned stands, and iii) 100% cutting of the stand's growing stock creating 0.4 ha canopy gaps. We show that delta C-13 increased along the gradient of cutting intensity. On average, delta C-13 values in the tree rings were similar to 2 parts per thousand increased in trees from canopy gaps than from closed control stands. Furthermore, delta C-13 was higher on south-facing slopes characterized by higher air temperatures and lower relative humidity compared to north-facing slopes of karst sinkholes. Additionally, the results suggest a dependence of delta O-18 on interannual and cross-site climatic variations, particularly in the case of summer precipitation amount. delta O-18 also responded to soil depth, with beech individuals exhibiting lower values on deeper soils, presumably characterized by higher soil water availability compared to shallow soils. The results are discussed in the context of future climate change, as many beech-dominated forests on karst terrain in the Dinaric Mountains are particularly affected by climate warming and drying due to prolonged and reoccurring summer droughts, intensified large-scale disturbances, and often shallow soils with low water storage capacity.

Automated summary

This study investigated the effects of different cutting intensities and local topographic and soil conditions on the composition of stable carbon and oxygen isotopes in wood of young beech trees. The results showed that the carbon isotope increased with cutting intensity, and the oxygen isotope was influenced by climatic variations and soil depth. These findings have implications for the future climate change impact on beech-dominated forests in the Dinaric Mountains.