Summer Branch Drop (SBD) refers to the sudden failure of mature branches during summer, often in the absence of strong winds or visible external signs of structural instability. This phenomenon has been associated with heat, water stress, increased branch weight, internal wood decay, and site-related stress factors. Although widely referenced in arboriculture literature, SBD remains inconsistently defined, and its underlying mechanisms are still not fully understood. This knowledge gap is especially significant because the unpredictable nature of SBD can limit the effectiveness of routine tree inspections and complicate the timely identification of risk-mitigation measures.

Building on previously documented cases of SBD in Portuguese urban trees, this work proposes an integrated framework for urban tree-risk assessment. Rather than describing isolated failure events, the aim is to discuss how information obtained from visual inspection, dendrometric characterisation, phytosanitary assessment, non-destructive diagnostic methods, and site-condition analysis can be combined to support more robust decision-making in municipal tree management.

The proposed approach considers SBD as a multifactorial process resulting from the interaction of biological, structural, and environmental factors. These factors should be understood as interacting components that may reduce branch mechanical safety margins and increase uncertainty in routine tree-risk assessment.

Visual assessment remains essential in tree inspection; however, SBD cases show that it may be insufficient when deterioration is internal, localised, or poorly expressed externally. In this context, non-destructive techniques, such as acoustic tomography and drilling resistance, can provide complementary information on the presence and severity of internal wood degradation, contributing to a more objective interpretation of mechanical strength loss. The integration of biological information, including the identification of decay fungi when present, further reinforces the need to connect phytosanitary diagnosis with biomechanical interpretation.

Overall, SBD assessment requires a multidisciplinary, evidence-based framework capable of integrating tree morphology, structural defects, internal wood condition, biological agents, environmental stressors, and site constraints. The systematic incorporation of these procedures into municipal monitoring programmes may reduce uncertainty in tree failure assessment, improve the prioritisation of interventions, and support technical decisions that balance public safety with the conservation of valuable urban trees.