Photosynthesis is a vital source of energy in nature. Various techniques for measuring photosynthesis intensity in plants enable comparisons across different plant species and provide insights into the unique characteristics of photosynthesis in vegetation. The research aims to study the photosynthesis intensity in woody plants. The plant leaf exterior square was calculated using the measurement of mass. The exterior square of the vegetation needles was calculated by the M. Ya. Oskretkov’s equation. The analysis of the photosynthesis intensity was performed on vegetation growing in the Botanical Garden of the Sciences Academy in the Uzbekistan Republic (ASRUz). Investigations were conducted three times from May to September (15th–25) from 7:30–9:00 a.m., in the bright weather, at t = 20–28 °C all year round. Statistical processing for the collected results was made to find the dynamics of changes in the intensity of photosynthesis in plant species Acer campestre L., Betula pendula Roth, and Robinia pseudoacacia L. According to the research results, less photosynthesis intensity is found in the plant species growing in mild climates. The analysis of photosynthesis intensity dynamics showed that in the first year, the average level of decrease in the photosynthesis intensity from May to September was 41.3% in the plant Acer campestre L., 1.2% in the plant Betula pendula Roth, and 7.6% in the plant Robinia pseudoacacia L. Plant species from the continental climate area in mountainous conditions showed a high photosynthesis intensity.