Errori nella stima degli incrementi di volume in alberi forestali

Periodic tree and stand increments are often estimated retrospectively from measurements of diameter and height growth of standing trees, through the application of various simplifications of the general formula for volume increment rates. In particular, the Hellrigl method and its various formulations have been often suggested in Italy. Like other retrospective approaches, the Hellrigl method is affected by a systematic error, resulting from the assumption as a reference term of conditions at one of the extremes of the period considered. The magnitude of the error introduced by different formulations has been assessed in the present study through their application to mensurational and increment measurements from the detailed growth analysis of 107 Picea abies trees. Results are compared with those obtained with a new equation, which makes reference to the interval mid-point. The newly proposed method makes it possible to drastically reduce the error in the estimate of periodic tree increments, and especially its systematic component. This appears of particular relevance for stand- and national level applications.