Changing climatic averages and variance: Implications for mesophication at the eastern edge of North America's Eastern deciduous forest

Abstract

Observed conversion of xerophytic warm genera species to mesophytic cool genera species in North America's Eastern Deciduous Forest (EDF) suggests species composition is in disequilibrium with recent climatic warming. However, increasing annual average temperatures is an oversimplification of long-term climatic change and the importance of climate variance is often neglected. Seven-year moving averages and standard deviations of annually averaged maximum temperatures, minimum temperatures, daily precipitation, and vapor pressure deficits (VPD) in West Virginia, USA were quantified over a 111-year period of record (1906-2016). Maximum temperatures decreased significantly (-5.3%; p < 0.001), minimum temperatures increased significantly (7.7%; p < 0.001), and precipitation increased (2.2%; p = 0.107). Additionally, maximum temperature variance decreased (-17.4%; p = 0.109), minimum temperature variance decreased significantly (-22.6%; p = 0.042), and precipitation variance increased significantly (26.6%; p = 0.004). Results indicate a reduced diurnal temperature range and significant reductions in estimated VPD (10.3%; p < 0.001) that imply increased relative humidity, cloud cover, and soil moisture that may support increasingly abundant mesophytic cool genera species. Feedback mechanisms associated with extensive changes in land use, fire suppression, and browser population may have exacerbated climatic changes. Long-term assessments of changing climatic averages and variance are needed to ensure sustainability of forest ecosystem services, health, and productivity in a swiftly changing climate across the broader EDF region and similar temperate forest ecosystems globally.