Forest composition and diversity buffer microclimates and enhance productivity

Trees can buffer forest ecosystems against climate extremes, creating microenvironments that support diverse plant communities. We asked how diverse tree communities could influence the above- and below-ground moisture environment, thereby linking tree diversity and ecosystem function. To address this question, we integrated remotely sensed forest structure, growth inventories, microclimate measurements, and leaf-level physiology in a forest biodiversity experiment. We found that fast-growing, early successional tree species buffered daily amplitudes of vapor pressure deficits (VPD) within forest plots, increasing the annual wood production of slow-growing, shade tolerant tree species. In assemblages with more stable microclimates, several tree species showed increased leaf water content and reduced physiological stress. Plots with reduced amplitude in VPD had greater complementarity and overyielding relative to those with higher variability. A mechanistic understanding of how tree diversity and community composition contribute to VPD amplitude and overyielding can inform conservation and restoration efforts in a rapidly changing world.