Time-lapse digital cameras reveal contrasting environmental controls of leaf phenology in different caatinga...

Leaf phenology in Tropical Dry Forests (TDF) is strongly influenced by environmental factors; however, responses may vary according to edaphic, structural, and floristic differences. The Caatinga, one of the largest continuous TDF in the Americas, exhibits pronounced hydric seasonality and encompasses distinct physiognomies such as the carrasco (deciduous shrubland) and crystalline caatinga (xeric shrubland). Studies addressing phenological variation among these two vegetation types remain limited and largely based on direct human observation. Our study aimed to advance the understanding of phenological dynamics in Caatinga TDF by investigating the climatic factors influencing leaf production and fall in woody communities of carrasco and crystalline vegetations using repeated digital photographs. Daily monitoring (2020-2024) provided green chromatic coordinate time series. Climatic drivers of Caatinga phenology (photoperiod, precipitation, temperature, and atmospheric moisture) were analyzed using principal component analysis and temporally structured generalized additive models. Woody communities of crystalline caatinga and carrasco exhibited distinct phenological strategies reflecting different responses to climatic variability. Leaf phenology in both areas was mainly driven by precipitation but was also associated with temperature. Carrasco showed more stable and predictable dynamics, with lower interannual variation in start of growing season (SOS), end of growing season (EOS), and length of growing season (LOS), retaining leaves about 20 days longer and responding to relief of hydrothermal stress at the end of the dry season. Crystalline caatinga was highly sensitive to rainfall irregularity and precipitation pulses. These results suggest that crystalline caatinga is more vulnerable to increasing climatic variability, whereas carrasco appears more resilient.