Fog interception in spruce-fir and mixed northern hardwood forests of Great Smoky Mountains National Park, Southeast USA

Abstract: Fog interception is a significant component of the water balance of Southern Appalachian spruce-fir forests in the Southeast USA. Here, fog interception rates are quantified for spruce-fir and northern hardwood trees in Great Smoky Mountains National Park (GSMNP), Tennessee and North Carolina, as a precursor to examining how interspecific differences in fog interception could affect catchment water balances if there is widespread vegetation change from spruce-fir to hardwoods. A water-balance approach was implemented, based on paired open-site (rainfall) and beneath-canopy (throughfall) electronically recording tipping-bucket rain gauges that were in place in the spruce-fir zone of GSMNP from May to November 2021. Comparing identified fog interception events to actual conditions captured by a webcam, 90% of verifiable events had conditions that were either clearly or potentially favorable for fog interception. Estimated fog interception gain ranged from averages of 0.24 to 0.69 mm day⁻¹, representing 3 to 8% of rainfall. Results are consistent with the expectation of higher fog interception gain for spruce and fir than for birch, the representative hardwood species. Quantification of fog interception rates provides valuable information about ecohydrological processes in ecologically significant Southern Appalachian spruce-fir forests.