Observed Changes in West Virginia’s Land Use, Forest Species Composition, and Climate

Relatively few studies have simultaneously addressed observed changes in climatic averages and variability, land use, and forest species composition that jointly influence land-atmosphere interactions. West Virginia (WV), USA represents a quintessential region to do this since old growth hardwood forests were cleared for timber extraction, agricultural development, and settlement near the turn of the 20^th century. In 1909 it was estimated that agriculture and pasture lands comprised 72% of WV’s land area, but farm abandonment resulted in rapid afforestation with forest cover estimated at 64% and 79% in 1949 and 1979, respectively. Forest cover remained steady (~79%) through the 2013 forest inventory analysis, but the forest species composition shifted from oak (Quercus spp.) to maple (Acer spp.) species in response to a positive-feedback loop more commonly referred to as mesophication. For example, in 2013, oaks and maples represented approximately 46% and 5% of larger trees (>50.8 cm in diameter) and 5% and 27% of smaller trees (5.1 to 10.2 cm in diameter), respectively suggesting mesophication will continue. Oaks and maples have different hydraulic architectures that may reflect an evolutionary trade-off between hydraulic conductivity (i.e. water use) and drought vulnerability suggesting that climate change in WV is increasing water availability and reducing drought severity. Seven year moving averages and standard deviations of observed maximum temperatures, minimum temperatures, precipitation, and modeled vapor pressure deficits (VPD) were quantified and averaged across WV (n = 18) over a 111 year period of record (1906-2016). Results showed that maximum temperatures decreased significantly over the period of record (-5.3%; P = 0.000), minimum temperatures increased significantly (7.7%; P = 0.000), 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 with less temperature variance that is further supported by significant reductions in modeled VPD (-10.3%; P = 0.000), which is a key ecosystem driver of photosynthesis, water vapor flux, and plant productivity. Therefore, feedback mechanisms associated with simultaneous changes in climatic averages and variability, land use (e.g. afforestation), and forest species composition may have reduced drought severity in WV with regional implications for water, energy, and carbon transfer.