Aastaring

Aastaring is the annual growth ring of a tree, visible in a cross-section of wood. In Estonian forestry and dendrochronology literature, the term denotes the tissue formed by the cambium during one year of growth and used to infer environmental conditions in the past. Each aastaring typically comprises two parts: earlywood, produced in the spring with large, thin-walled cells that are lighter in color, and latewood, formed later in the growing season with smaller, thicker-walled cells that are darker. The distinct combination of these zones creates the visible ring.

The width and density of aastaring vary with climate, water availability, temperature, and site conditions. Favorable years with ample moisture and warmth tend to produce wider rings, while drought, cold spells, or nutrient limitations yield narrower rings. In temperate regions trees usually form one clear ring per year, whereas tropical forests may show less pronounced seasonality and fewer distinct rings. Some trees can produce false or missing rings if growth is interrupted, complicating interpretation.

Aastaring are central to dendrochronology, the science of dating wooden materials and reconstructing past climates. By cross-dating rings from multiple trees, researchers align growth patterns to build long chronological sequences. Ring-width measurements serve as climate proxies and help calibrate radiocarbon dating. Limitations include regional growth suppression, disturbance, or long-term changes in wood properties, which require careful sampling, preparation, and statistical analysis.