Dendrochemistry, the chemical analysis of precisely dated tree rings, provides a dynamic record of change both for the landscape and within the living tree. It helps to answer a broad range of questions from the timing of releases of chemical pollutants for environmental forensics to how healthy trees maintain their nutritional needs and resilience under various soil conditions and stress from pests and pathogens. Forest Service scientists and partners in an international team studying Pollution Investigation by Trees (PIT) are using high-resolution x-ray fluorescence analysis (EDXRF) to assess the timing and spatial extent of potentially toxic chemicals released into the environment. This technique can identify very low levels of metals at 0.05-mm intervals along a wood sample. The scientists are developing a guide for the detection and interpretation of dendrochemical markers for forensic investigations. Recently, PIT used EDXRF to track a plume of chlorinated solvent through groundwater by dendrochemical patterns. In another study, Forest Service scientists based at the agency's Northern Research Station and PIT partners used EDXRF to identify the internal processes of tree maturation and infection that affect dendrochemical patterns of calcium, potassium, and zinc-chemical elements that are essential for healthy trees. This high-resolution analysis provides insight for management of both human and forest health.