Beech buffers: Microclimate regulation in temperate old-growth forests, surroundings and forest edge

• Old beech forests effectively contribute to landscape cooling and moistening. • Even on hot and dry days, old forests show a significant microclimatic regulation. • Canopy cover and dense understory are important for buffering of critical extremes. • Distance from the forest edge affects microclimate, so buffer zones are important. • UNESCO World Heritage beech forests provide unique opportunities for research. Central European forests are increasingly threatened by the climate crisis. Microclimatic and hydrological self-regulation are key to forest stability, with old forests especially effective. This study analysed the microclimatic performance of old beech forests in Germany, component parts of a UNESCO World Heritage Site. Four component parts (Grumsin, Hainich, Kellerwald, and Serrahn) were monitored for about one year from May/June 2022 using data-loggers to assess maximum temperature (Tmax) and water vapor pressure deficit (VPDmax) across core and buffer zones, forest edges, and open land. Tmax in beech forests approached 40 °C, while non-forests exceeded 46 °C. The highest VPDmax was recorded in non-forests, exceeding 7 kPa, whereas forest interiors maintained lower atmospheric dryness. Denser canopy cover near the forest edge correlated with lower Tmax, higher humidity, and reduced VPDmax. A collapsing spruce stand in Kellerwald was 4.5–6 °C warmer than the neighboring old-growth beech forest, showing the cooling role of intact forests. The reduction in VPDmax, a key factor in tree survival during dry periods, underscores the importance of maintaining mature forests. Dense canopy, understorey, and wide buffer zones are essential for stabilizing microclimate under climate change. Expanding and preserving old-growth forests mitigates climate-related stresses and sustains ecological functionality.