Increased Growth Synchrony of Red Spruce in Response to Acid Deposition Recovery and Climate Change across its Southern Range Extent, Southeastern USA

Abstract

In a complex system of natural and human-caused disturbance, shifting climate, and documented, widespread decline and recovery of red spruce populations prior to and following the United States (US) Clean Air Act and amendments (CAAA) — all within the last century — a better understanding of the potential influence of these disturbances on the climate sensitivity and resiliency of red spruce under projected future conditions is needed. We investigated the potential recovery of annual growth in southeastern US red spruce populations following the CAAA and the influence of this recovery vs. ongoing climate change. Using a recently collected network of red spruce tree-ring data from across the southern Appalachian range, we examined temporal trends in stand-level growth and climate sensitivity in the context of acidic (acid) deposition and recovery and modern climate change. We demonstrated that in recent decades, spruce growth is becoming synchronous and climate sensi-tive in conjunction with a reduction in acid deposition coupled with changes in climate conditions. The emergence of synchronous growth across sites is a new phenomenon that highlights the potential of and the need for region-wide management. Our results provide a temporal perspective that can aid future management strategies in an era of reduced air pollution and a changing climate.