Plants, in their interaction with the environment, synthesize organic compounds that are considered beneficial for human health in the practice of forest therapy. This study describes seasonal changes in the production and activity of volatile organic compounds in two emblematic southern Chilean trees. Phytochemical profiles were obtained by gas chromatography-mass spectrometry, total phenolic content was determined by the Folin–Ciocalteu method, and antioxidant activity was measured by ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate)) and DPPH (2,2-diphenyl-1-picrylhydrazyl) assays, in Peumus boldus and Cryptocarya alba leaves obtained from Nonguén National Park (Chile). Climatic data were recorded. The results show that the phytochemical richness of P. boldus reached the highest value in autumn, while C. alba showed a slight decrease in summer. The four seasons presented a broad core of constitutive compounds including monoterpenes and monoterpenoids, in both species. ABTS assay showed that antioxidant activity in P. boldus was significantly higher in autumn, while in C. alba, the highest value was reached in winter. DPPH assay showed highest antioxidant activity in spring in P. boldus, and in C. alba it occurred in winter. The highest phenolic accumulation was scored in spring for P. boldus, and in autumn for C. alba. Here we provide the first glimpse of the dynamics of phytochemical variation in response to the seasonal changes occurring in two trees of the southern forest. Further investigation is required to fully understand the emission dynamics in response to seasonal changes, and its contribution to human health through the practice of forest therapy.