Tree height, growth rate and stand density determined by ALS drive probability of Scots pine mortality

Understanding how particular stand factors shape patterns of forest mortality is crucial for supporting forest management as well as creating appropriate adaptation strategies in the era of climate change. Until recently, many stand characteristics such as tree height, height increment, and stand density were measured by traditional field methods. However, the current use of remote sensing tools opens up new possibilities for forest monitoring and measurements. Thus, the research objective was to assess the influence of selected tree and forest variables measurable by ALS-top height, top height increment, and stand density-on the probability of Scots pine stands' mortality. We focus on the Katowice region in southern Poland, which experienced extensive drought -induced mortality in 2015-2021. For this area, we acquired data from two ALS acquisitions to determine the stand top height, top height increment, and stand density. We found that the probability of tree mortality is most strongly driven by stand height and height growth rate. Moreover, the highest probability of mortality was observed in the densest stands. Through the identification of a core set of stand characteristics that predispose forests to mortality, this work can inform future research on forest structure under accelerated mortality. Bitemporal ALS allows for a brief overview of height increment trends over large regions. Therefore, detecting trends in height increment using ALS can help us assess vulnerability to disturbance and provide an effective approach for early detection of tree stress and mortality signs.

Automated summary

Understanding the impact of stand factors on forest mortality is crucial for forest management and adaptation strategies in the face of climate change. By using remote sensing tools, the influence of tree and forest variables on the probability of Scots pine stands' mortality was assessed. In the Katowice region of Poland, the most significant factors affecting tree mortality were found to be stand height and height growth rate, with the highest mortality probability observed in the densest stands. Identifying key stand characteristics that predispose forests to mortality can contribute to future research on forest structure.