A ring-width based approach for disturbance detection and reconstruction

Identifying releases from suppression represents one of the most fundamental dendroecological procedures for quantifying forest disturbance histories. The reconstruction of past disturbances has often been hindered by difficulties in disentangling disturbance pulses from other climatic and biological signals encoded in tree rings. A long-time disturbance chronology would provide a deeper understanding of forest biogeochemical cycles, especially the carbon cycle, and, eventually, a better representation of complex stand dynamics. Additionally, after identification, their removal from a ring-width series could better represent the climatic signal encoded in tree rings, hence providing a better representation of the climatic drivers shaping forest growth. This is even more relevant considering current global change, which is posing serious threats to the future of our forests. Here we present a new methodology to detect, reconstruct and, if necessary, remove non-climatic disturbance-induced growth releases from ring-width series. The case study focuses on common juniper, coming from two sites located in the Finnish and Swedish tundra. While the Swedish site showed no sign of major disturbances, the Finnish site was heavily affected by an outbreak of the Autumnal moth (Epirrita autumnata) in the last Century. This event is represented by an abrupt growth release in the ring-width chronology, clearly detectable in the species’ ring-width pattern. The process, involving the boundary-line release criteria for disturbance detection, allowed us to reconstruct past major disturbance events over more than 1500 years and, by removing them when present, to obtain virtually disturbance-free chronologies. As a result, climate-growth correlations after the disturbance removal improved for every variable we tested over the last 120 years, suggesting a clearer climatic signal representation. This protocol can be applied to several other contexts, from natural to artificial forest stands, in both shrub and erect tree species, where disturbances play a crucial role in ecosystem dynamics. Standardized release criteria would allow more accurate comparisons of disturbance histories among sites, species, and even across landscapes, providing new insights into disturbance regimes and dynamics for a better representation of past, present, and future evolution of forest ecosystems.