Crown condition, needle mass, and sapwood area relationships of Norway spruce (Picea abies)

Crown-condition assessment, hypothesized to estimate needle losses following damage from several sources, one of which might be air pollution, suffers from the subjective notion of a standard "healthy" tree. On the other hand, the foliage biomass - sapwood area ratios are reported to depend on a number of factors, e.g., site quality, stand density, crown class, and tree ring width conductivity. The authors hypothesize that early sapwood area might help to even better estimate needle biomass of Norway spruce (Picea abies (L.) Karst.) and to help standardize crown-condition assessment. Thirty-six Norway spruce trees at two Austrian sites, from three age-classes, three crown classes, and two crown-condition classes were felled. Needle mass, cross-sectional area, sapwood area, and early sapwood area (i.e., sapwood area excluding latewood) were measured. The results of this study indicate that indeed early sapwood area is a good estimator of foliage, independent of site, age, crown class, and crown condition. The ratio between early sapwood area and cross-sectional area could be a good estimator for crown condition and thus help to standardize crown-condition assessments by different surveyors.