Estimation of the leaf area index of the pine forest stands within Northern Steppe of Ukraine conditions

Assimilation part of forest ecosystems play an important role in the global carbon cycle and forming net-primary productivity. However, knowledge on leaf area index (LAI), that affect carbon fluxes is lacking, especially within territory of Steppe zone of Ukraine. We studied twenty Scots pine (Pinus sylvestris L.) plantations different age in pure and mixed stands to examine the changes in LAI. The method for determining samples mass and volume was to random select of needles from green fraction from different crown parts. The next step was in weighing and the volume determination of the samples by the xylometric method. Pine stands within temporary sample plots represent different age structure and function in the following types of forest condition: very dry (A0) and dry (A1) bir, dry (B1), fresh (B2) and moist (B3) subir, dry (C1), fresh (C2) and moist (C3) suhrud, rarely – in the hrud condition. The obtained results of model trees biometric parameters show their approximate values to the average indexes of the temporal sample plots on which they were selected. The variation of the weight of needle samples in fresh and completely dry states depending on the age of the model trees is analyzed. Parameters of the needle area and ratio of fresh and dry weight to the total surface area of needle samples is calculated. The average value of needle biomass in completely dry states and the needles surface area of the of needles on the study plots is defined. The calculated LAI of pine stands varies from 1.1 to 3.36 m²/m². The dependence of LAI on the model tree age is established. There is the increase of the trend line for young trees, stabilization and then decrease this parameter up to 90 years old is defined. The maximum LAI index is characterized for a pure 83-year-old pine plantation of pine, with I class bonitat, that grows under dry suhrud conditions. The minimum LAI is recorded for the mixed pine stand in age of 9 years, with III class bonitat, which function in dry hrud conditions. Calculation of LAI of Scots pine stands showed that it depends on the type of site conditions and stand age.