For many regions of the Earth, anthropogenic climate change is expected to result in increasingly extreme climate conditions. However, contemporary analyses rarely consider the implications of change in variance of climate indices over time. This is of concern given little is known about how increasing (or decreasing) climate variance may affect short and long-term ecosystem productivity. Forest ecosystems may be particularly susceptible given specialized species niche adaptations. Investigations in the Eastern Deciduous Forest (EDF) biome stretching from the eastern (north-east West Virginia) to the midwestern United States (mid-Missouri; the western edge of the Biome) were undertaken to quantify rates and directions of climate variable changes including variance. Analyses included long-term data sets (e.g. 1906-2016) from multiple locations using historic climatology, global change modeling, and other regional data sources.
Results/Conclusions
A cross-system EDF analysis during growing season months showed that mean net ecosystem exchange (NEE, umol/m-2/s) was -5.76, -3.22 and -3.52 in 2009 during a period of extreme wetness, and -4.68, -2.18, and -0.09 respectively, in 2012 (extreme drought) at ecosystem flux sites in Harvard forest, Morgan Monroe forest, and central Missouri, respectively. This finding suggests that at the western edge of the EDF net ecosystem exchange (NEE) may be more adversely impacted (relative to east) by ongoing increased precipitation, precipitation variance and excessive wetness. In the eastern portion of the EDF, analyses showed an increasingly wet and temperate climate characterized by warming minimum temperatures, cooling maximum temperatures, and increased annual precipitation that have accelerated during the second half (1959 to 2016) of the period of record relative to the first half (1958-2016). Trends also appear to be elevation dependent and may be accelerating with increasing forest age and increases in atmospheric moisture. Median air temperature and dew point values decreased with elevation at a rate of 5.2ºC km-1 and 3.5ºC km-1, respectively consistent with decreasing vapor pressure deficits (-0.30kPa km-1). Results imply that excessive (persistent) wetness may become the primary ecosystem stressor associated with climate change in the distinct Appalachian region of the EDF. Ultimately, collective results indicate rapidly changing (spatially heterogeneous) climate variance throughout the EDF. This work therefore serves as an alert to the need for studies of potential impacts of climate variance on forest ecosystem health and productivity. This is important 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.