Coniferous and broad-leaved mixed forest has the optimal forest therapy environment among stand types in Xinjiang

The mountainous natural forest resources in Xinjiang are rich and unique, offering vast prospects for forest therapy tourism. However, the scientific understanding on the quality of forest therapy environment in different stand types is still not clear. During the period of June to August in 2022 and 2023, four stand types (evergreen coniferous forest, deciduous coniferous forest, deciduous broad-leaved forest, and coniferous and broad-leaved mixed forest), as well as a non-forest land were selected in six representative natural protected areas in Xinjiang. From the four dimensions of atmospheric, thermal, light, and acoustic environments, nine environmental indicators including negative air ion concentration (NAIC), air oxygen content (AOC), airborne bacteria content (ABC), particulate matter 2.5 concentration (PM2.5), particulate matter 10 concentration (PM10), human comfort index (HCI), light intensity (LI), ultraviolet radiation intensity (URI), and noise level (NL) were selected. The Forest Therapy Environment Quality Index (FTEQI) was developed through principal component analysis to comprehensively evaluate the quality of forest therapy environment in different stand types. The findings revealed that coniferous and broad-leaved mixed forest excelled in improving NAIC and HCI, coupled with reducing ABC, PM2.5, PM10, and NL, followed by evergreen coniferous forest. The deciduous broad-leaved forest displayed the highest AOC, while coniferous and broad-leaved mixed forest exhibited the lowest LI and URI. In terms of the FTEQI, the coniferous and broad-leaved mixed forest was at Level I, which was extremely beneficial to human health; the evergreen coniferous forest and deciduous coniferous forest were at Level II; the deciduous broad-leaved forest was at Level III; whereas non-forest land was at Level IV. Therefore, the forest therapy environmental quality was optimal in the coniferous and broad-leaved mixed forest, followed closely by evergreen coniferous forest and then deciduous coniferous forest, among different stand types. In the process of constructing healthcare forests or upgrading stands, priority should be given to the mixed planting model of coniferous and broad-leaved tree species, to maximize the forest therapy benefits. When developing forest therapy tourism in mountainous forests of Xinjiang, it is advisable to select the coniferous and broad-leaved mixed forest, evergreen coniferous forest, and deciduous coniferous forest, with their understory space being reasonably utilized to conduct diverse forest therapy activities.