Vitality characterization of stressed trees based on non-destructive and real-time monitoring of stem water content

The detection of stem water content is necessary as it is an important indicator for measuring woody plant vitality. However, the relationship between stem water content, determined by non-destructive, real-time, and long-term monitoring, and woody plant vitality remains undefined. In this study, the response of woody plant vitality to stem water content under different stress (freeze–thaw, pest, or drought) was analysed by mining the dynamic characteristics of the stem water content in different woody plants at the temporal scales of year, month, and day. Compared with unstressed trees, stressed trees had contrasting diurnal patterns. The stem water content in Populus koreana Rehd. during the freeze period was much lower than that during the thaw period, and opposite diurnal variation trends were observed during the freeze and thaw periods. The stem water content in infected Lagerstroemia indica was lower than that in uninfected L. indica, and the amplitude of the diurnal variation curve was lower in infected than in uninfected L. indica. Under drought stress, the more severe the water shortage, the lower the stem water content in Malus micromalus. When it was below a certain threshold, the diurnal variation trend was opposite to that without water shortage. In conclusion, stem water content dynamics can be used to evaluate the cold, pest, and drought response of trees, which could monitor tree health and guide forest assessment.