Spatial pattern dynamics of subalpine secondary forests over eighteen years on the eastern Qinghai–Tibet Plateau, China

: Revealing the dynamic changes in tree spatial patterns holds significant implications for the restoration practices of natural secondary forests. We analyzed the dynamics of tree spatial patterns using 18 years (2005–2023) of repeated survey data from a 4-ha subalpine natural secondary forest on the eastern Qinghai–Tibet Plateau, China. The results showed: (1) Tree density decreased by 40.31% over time. The dominant tree species, Minjiang fir ( Abies fargesii var. faxoniana ), exhibited an expanding population with abundant young individuals and few old trees. In contrast, the pioneer species Betula albosinensis , Acer sinense , and others exhibited declining population trends. (2) Dominant tree species showed aggregated patterns at small scales (< 15 m), and their aggregation scales decreased after 18 years. (3) Spatial associations varied in species pairs over 18 years. B . albosinensis and Minjiang fir changed from repulsion to independence, while B . albosinensis and A. sinense changed from attraction to independence. However, Minjiang fir and Picea asperata exhibited no spatial association at either census. (4) We found that density-dependent mortality occurred in both the Minjiang fir and B . albosinensis populations at different periods throughout the survey. Intense competition prevailed in the subalpine natural secondary forests. Therefore, thinning can help alleviate this competition. Our study provides long-term evidence for successional pathways and species-specific dynamics in subalpine natural secondary forests, informing future restoration planning.