Tree rings are a key terrestrial archive providing insight into past climate and environmental variability at annual resolution, and from local to hemispheric scales. Tree ring proxies are also important as indicators of plant physiological responses to changing climatic conditions and for further understanding of long-term ecological processes. In this broad context we welcome contributions using one or more of the following approaches to either study the impact of environmental change on trees and forest ecosystems or to assess and reconstruct past environmental change: i) traditional dendrochronological methods including studies based on tree-ring width and density, ii) stable isotopes in tree rings and specific plant compounds including compound-specific isotope analysis (CSIA), iii) quantitative wood anatomy, iv) sapflow, dendrometer and related monitoring data analyses, and v) mechanistic modeling, from seasonal to multi-century and from local to hemispheric scales.