Using An Elevation Gradient As A Surrogate For Climate Warming To Understand The Effects On Wood Anatomy And Water Relations Of Fraser Fir (ABIES FRASERI) Christmas Trees

Fraser fir (Abies fraseri) Christmas trees are an important part of the agro-economyof Western North Carolina, accounting for $100 million dollars in annual sales. Inorder to assess how warming-driven stressors of climate change could affect thesetrees, I examined water relations and wood anatomy of Fraser fir Christmas treesalong an elevation gradient from 664 m to 1228 m. Low elevations exhibited thehighest daytime maximum temperatures and higher associated evaporative demand(greater vapor pressure deficit, VPD) than the middle and high elevations, whilehigh elevations experienced greater cloud cover and immersion than the lowerelevations, as expected. Stomatal conductance varied over site and season, showinga strong response to VPD and temperature changes. Diurnal water potentialslikewise displayed a change over the season and with elevation, with the lowestwater potential at the low elevation in the early growing season. In the mid-seasonthe high elevation trees exhibited the lowest water potential because of a high VPD.Trees did not experience enough water stress to induce embolism in the currentfield sites and conditions. Hydraulic conductivity did not exhibit a change acrosselevations. From an anatomical perspective, xylem lumen area was similar amongall sites. The tracheid count, however, differed among sites with the fewestcells/mm2 at the low elevation. Middle elevations had the greatest cell wallthickness but neither differences in the tracheid anatomy was great enough tochange alter the hydraulic conductivity. Trees across elevations tended tocompensate for warming by physiology, namely stomatal control, rather than adjustanatomy. With climate warming, dryer soil, and lower relative humidity,physiological functioning will decrease and low elevation farms may experiencelonger periods of stress during the growing season.