Thermal Limits and Sensitivity of Brosimum rubescens Taub. (Moraceae): Implications for Monodominance in a Warming Climate

ABSTRACT Understanding temperature tolerance is key to predicting tropical trees' responses to global warming. However, the thermal limits of monodominant tropical forests remain understudied, leaving their vulnerability to climate change unclear. This study examined the thermal safety margin, tolerance parameters of PSII ( T 5 , T 50 , T 95 ), leaf traits (e.g., leaf water mass content, leaf thickness, stomatal conductance), and temperatures of Brosimum rubescens Taub. (Moraceae) seedlings during the dry season in southern Amazonia, a rapidly warming and drying region. We analyzed 60 seedlings and found that open‐canopy conditions reduced thermal tolerance, with leaf temperatures surpassing T 50 in over 40% of seedlings under a 3°C warming scenario. The closed‐canopy area exhibited more effective leaf cooling driven by trait plasticity; however, this cooling was not sufficient to maintain leaves within safe thermal limits. When temperatures exceeded 40°C, PSII performance declined sharply, particularly in the open‐canopy area, resulting in reduced thermal safety margins. Overall, our findings suggest that these effects may hinder the natural regeneration of B. rubescens , potentially affecting its role as a monodominant species and gradually influencing local dynamics and biodiversity in the long term, in response to warming and prolonged dry seasons in southern Amazonia.