Determinants of delayed traumatic tree reiteration growth: Levels of branch growth control and insights for urban tree management, modeling and future research

The reiteration process involves the replication of large and complex modules of a tree structure. Reiteration may occur in sequential (i.e. normal) tree development but may also appear on old structures in response to a traumatic event (delayed traumatic reiterations, DTR), stress or internal constraints. This process is of prime interest in the context of managing trees located under electrical networks as DTR are the tree parts that will repeatedly be trimmed because of their interaction with electric wires.However, the determinants of DTR growth are still largely unknown. In order to identify the most important DTR growth determinants and their scale of action, we measured 1061 DTR in 285 trees of six species located in 11 cities in the province of Quebec, Canada, along a large climatic gradient. Nine explicative variables, four at the local scale (dealing with within crown light and water supply), three at the tree scale (ontogeny, urban surrounding environment and crown shape), and two at the geographic scale (regional temperature and precipitation), were used to explain DTR growth. Boosted regression trees were used to fit the complex response of DTR length to each individual variable and to quantify the influence of each variable and the influence of the three scales.Results enabled us to link the response of DTR growth to physiological processes and provide evidence of a mostly local control of DTR growth potentially influenced by a combination of water supply, light availability, and C reserves. Tree size had a relatively strong influence, while the urban environment and maintenance conditions had only a weak effect. Although the regional climatic conditions were found to affect DTR growth, their effects varied greatly among species. Based on our results, we provide some recommendations for the management and modeling of urban trees, and draw insight for future research.