Tree mortality is shaped by tree characteristics, silvicultural treatments, and environmental conditions, the influences of which can change during stand development. In the southeastern United States, loblolly pine ( Pinus taeda ) plays a critical role in providing timber production and ecosystem services. Understanding the impacts of abiotic and biotic factors on tree mortality is essential for ecological forecasting and adaptive forest management in the region. Survival analysis, focusing on time-to-event, provides a useful tool for assessing the long-term dynamics of factor influence on tree mortality. In this study, we evaluated the impacts of tree, stand, and climatic factors on tree mortality of loblolly pine over a 18-year study period using survival analysis. Furthermore, we divided the study period into three time intervals to evaluate how these impacts vary at different stages of stand development. Data were collected from culture-by-density field trials across three physiographic regions, resulting in a total of 47,485 unique trees and 221,270 repeated observations. Results showed that larger and dominant trees generally have a lower tree mortality risk, whereas the risk increases with higher site quality, greater stand density, and the presence of disturbances. Intensive management shows a greater mortality risk than operational management. Notably, tree size, dominance and region have significant impacts only in older stands. Regional variation in mortality can be partially explained by climate extremes, including acute extreme cold stress (lower 10-year minimum January temperatures) and heat stress (higher annual mean temperatures). This research provides insights on tree mortality dynamics and its impact factors as well as a quantitative tool for forest managers to assess tree mortality in sustainable forest management.
Senevirathne et al. (Tue,) studied this question.