Assessment of Summer Branch Drop: A Case Study in Four Portuguese Cities

Abstract

This paper addresses the problem of summer branch drop (SBD) in urban forests, namely through detecting the causes of this unpredictable event, aiming at preventing and increasing the control of this phenomenon, while using the most recent methodologies to detect wood deterioration, namely visual tree assessment (VTA), drilling resistance, and acoustic tomography, in an isolated and associated way. The study considers events in the cities of Arcos de Valdevez in Viana do Castelo district (Site 1), Ponte de Lima in Viana do Castelo district (Site 2), Montemor-o-Novo in Évora district (Site 3), and Paços de Ferreira in Porto district (Site 4), targeting trees of public interest. Given the phytosanitary condition recognized using nondestructive equipment, a set of measures for the preservation of the tree elements and their history are suggested. SBD is mostly related to internal degradation. A VTA diagnosis, applied in isolation, could lead to an incorrect prognosis of the internal degradation. So, it is important to confirm of the presence of biotic agents through equipment (acoustic tomography and drilling resistance). Even with instrumental diagnostics, for reducing the subjectivity of the approach to estimating the SBD, a global analysis is necessary, including dendrometric parameters, predisposing or inciting factors, lower tree defences against internal degradation due to environmental conditions, and biotic agents.