Remeasured US forest plots showed small mortality-driven tree community warming of 0.014-0.018 C per decade in West and East, 2001-2025; species permutation did not separate it from turnover

Question: do the western US tree thermophilization results of Rosenblad et al. (2023, PNAS) repeat in the same states in a new period and in the eastern US? Approach: we used USDA Forest Inventory and Analysis annual plots that were measured two times (2001-2025) and fully forested both times: 18,020 western plot pairs in the original 2000-2018 design, 14,358 western pairs with a second survey in 2019-2025, and 107,691 and 55,139 eastern pairs (second survey to 2018 and 2019-2025). A species thermal index (STI) is the mean 1981-2010 nClimGrid temperature of the plots where each species occurs. We calculated the basal-area-weighted community temperature index (CTI) and its parts from mortality, growth, recruitment and harvest, and compared CTI change with local warming and recorded disturbance. Intervals come from a spatial block bootstrap. Results: the CTI increased by 0.018 [0.008, 0.029], 0.015 [0.004, 0.025], 0.016 [0.002, 0.029] and 0.014 [0.003, 0.025] C per decade, which is 4-11% of the local warming trend. Natural mortality gave the largest part in all four samples. In the West, plots with insect disturbance changed 7-9 times faster in both periods; in the East, insect disturbance gave no clear difference, and recruitment and harvest lowered the CTI. The western rate was about half of the published 0.039 C per decade. The links to local warming and to north-facing slopes did not repeat. When STI values were randomly permuted among species, the observed changes were inside the permutation distribution (p = 0.63-0.74), because a few abundant species control the CTI. Limitations: the eastern result depended on the STI version (intervals included zero with basal-area-weighted or median STI); STI ranges are cut at the US border; disturbance codes are coarse; we could not apply the original tree-distance rule. Conclusion: a small CTI increase repeated, mainly through mortality, but these data do not show that thermal niche, rather than species-specific disturbance, selected the species that died.