Low‐clouds and fog moderate the diurnal temperature range (DTR) through radiative effects. Consequently, frequent foggy events make montane cloud forests (MCFs) stable and unique. However, high‐resolution observations in the forest understory are rare. To investigate the DTR variation in elevations, we surveyed the Central Cross‐Island Highway in central Taiwan along the altitude of 0–3,000 m across both the non‐cloud forest and MCFs. The results from paired weather stations revealed that the DTR increases significantly with altitude in open fields but not in the forest's understory. Furthermore, the continuous observations in altitude indicate that smaller DTRs were found in both open field and understory sites in the MCF compared with those in low‐ and high‐altitude sites. The DTR discontinuity highlights the indispensability of MCF for the mountain ecosystem. Further simulating the integrative effect of the climate and land‐use change on fog is crucial for the ecoclimate in mountainous regions. Plain Language Summary: The diurnal temperature range (DTR), regulated by canopy and fog, is critical to the ecosystem. During the day, fog and the canopy block downward solar radiation to prevent the increase in temperature. At night, fog and the canopy trap long‐wave radiation to reduce the rate of temperature decline. Observational data indicate that DTR increases significantly with altitude in open fields but not in the understory. Therefore, the difference in DTR between open fields and the understory is more significant at a higher altitude. Furthermore, the difference in the DTR is smaller at midaltitude (1,250–2,000 m), which is most likely related to the presence of montane cloud forests. DTR discontinuity in altitudes highlights the value of montane cloud forests. Key Points: A relatively great variance of daily temperature range between the open fields and understory at high altitudesCanopy shade efficiently moderates the diurnal variability and the elevational variation of daily temperature rangeThe fog and low cloud create altitudinal discontinuities in daily temperature range [ABSTRACT FROM AUTHOR]