Macroclimate and canopy characteristics regulate forest understory microclimatic temperature offsets across China

Forest microclimates can contrast substantially from the macroclimate outside forests. These microclimates regulate understory biodiversity and ecosystem functions. Studies have quantified the global patterns and driving factors of forest understory temperature offsets, but data from China were almost missing, making the global assessment incomplete. To fill this knowledge gap, we quantitatively synthesized 494 paired observations from China extracted from 91 publications to quantify mean (Tmean), maximum (Tmax) and minimum temperature offsets (Tmin). Results showed that (1) forest canopies significantly buffered understory Tmean and Tmax against macroclimatic temperature, with average offsets of 1.0 and 1.5 degrees C, respectively, while understory Tmin offsets were not significantly different from zero; (2) forest type (broadleaved, mixed, vs. coniferous) and forest location (rural vs. urban) did not affect Tmean, Tmax or Tmin offsets, but climate zone and season showed significant impacts; and (3) macroclimatic temperature, wind speed, tree height and canopy density also impacted temperature offsets, although their effects varied among Tmean, Tmax and Tmin. Our results complement the global assessment of forest buffering capacity, and reiterate the necessity for incorporating microclimatic variability into future bioclimatic modelling of species demography and distributions.