Climatic conditions strongly control the geographic distribution of treelines; long-term in situ climatic measurements at the treeline are still rare. While microclimatic differences between trees and shrubs at treeline ecotones are already well established and explained, supporting empirical data remain limited. In this study, we compared in situ microclimate measurements in the canopy, stem, and root zones of tree and shrub plots of Juniperus squamata Buch.-Ham. ex D.Don at the treeline ecotone of Jiaozi Mountain, Yunnan, China, in 2022. Although the shrubs experienced higher wind speeds compared to the trees at the treeline ecotone, the short stature of shrubs created warm stem and soil temperatures that are more suitable for plant growth and survival. Shrub distribution at higher elevations may be due to higher soil temperatures. The inability of shrubs to grow upright may be attributed to the fact that their canopy is limited by lower temperatures above the canopy during the frost season. This can provide new insights into the mechanisms of treeline formation.