Continuously monitoring the phenological dynamics and growth patterns of trees through TreeTalkers in a mixed and multi-layered broadleaved Mediterranean forest

In recent years, the consciousness that climate change influences forest health and vitality has increased, encouraging the development of methods and instruments for remote forest monitoring and assessment. Data routine and IoT (Internet of thing) instruments have been proposed and tested to assess tree functional traits. Here, we applied the TreeTalker technology in a broadleaved mixed and multi-layered Mediterranean forest. The Tree Talkers (TTs) devices collect real-time data on tree dynamics, ensuring continuous monitoring of tree ecophysiological features (e.g., monthly, weekly, daily, hourly). Using real-time TTs data, we investigated the phenological dynamics and growth patterns of two important tree species, Quercus cerris L. and Fagus sylvatica L. Tree phenology was measured through a spectrophotometer that intercepts the amount of light penetrating the crown (crown transparency). The light transmitted through the forest canopies, and its spectral components (measured by a spectrometer), were used to monitor the leaf phenological activity, while the radial growth was measured through a radial trunk growth sensor which measures the distance to the tree bark with an infrared ray. TTs give information on stem growth and, thus, on the formation of tree rings and the basal area index. In particular, we compared the tree growth patterns of the two species in two spring seasons (2021 and 2022) to highlight differences in growth rates and their relationships with forest structural parameters.Moreover, the environmental variables, such as air temperature (C°) and relative humidity (%), were also tested as drivers of reactivation to understand whether there are significant differences in the phenological seasons and the effects on tree growth. Despite the two species showed different growth rates, differences were small between the two years. In 2021, both species showed low values of tree growth in April-May and high values in October. By contrast, in 2022, Quercus cerris L. maintained the growth rates recorded in 2021, while Fagus sylvatica L. had lower growth values compared to 2021. The main challenges were associated with weather conditions, revealing a significant influence on the recording of tree dynamics.