Sensitivity in annual growth of Midwestern conifers to multiple dimensions of winter and spring climate

Anthropogenic climate warming is altering the ecosystem function of temperate and boreal forests. A number of studies have indicated a rise in overall ecological productivity due to a lengthening growing season, particularly into early spring. However, interactions between temperature and precipitation remain understudied with respect to their combined impacts on the responses of trees to warming in spring. Here, I examine the sensitivity of common Midwestern conifers to multiple dimensions of climate during the early growing season. I combine tree-ring chronologies, satellite observations, and daily climate records to examine relationships among early season weather, leaf-out phenology and annual growth rates. In multiple species of common Midwestern conifers growing across heterogeneous landforms, I found a universal sensitivity of annual tree-ring widths to both temperature and precipitation in winter and spring. My results suggest that the effects of warmer air temperatures may be offset if heavy precipitation suppresses soil temperatures and delays the onset of cambial activity. Amidst the recent pluvial affecting the Midwest region, the sensitivity of forests to warming air temperatures may be modified by the fraction of precipitation that falls as rain versus snow. These results underscore the competing pressures faced by forests to respond to dramatic recent changes in winter and spring climate.