Measuring Techniques for Assessing Basal Area Increment of Forest Stands : Forest Inventories in Europe with Special Reference to Statistical Methods

1991

S. 70-81

2 Abb., 5 Tab., 3 Lit. Ang.

Unselbständiges Werk

200086348

The systematic control of biomass production plays an important role in forest management. Considering the high costs entailed by forest growth estimation, a cautious sample sizing is needed. The paper deals with the sample sizing in the assessment of one of the most important forest growth variables - the stand basal area increment - reporting illustrative applications relative to Abies alba (Mill.) stands in the northern Apennines (Italy). The results obtained adopting different measurements of individual tree basal area increment, by combinating a varying number of outside bark stem b.h. diameters with a varying number of stem b.h. radial increments, are presented: - at a single tree level, the error of basal area increment estimation tends to diminish significantly as a function of the number of b.h. radial increments measured, but not as a function of the number of b.h. diameters measured; - at a stand level, the differences among the estimation performed by different measurement combinations on each stem b.h. cross section are not significant, because their effect is annulled by the incremental variability among trees. Consequently, it is sufficient to collect one radial core only for each sample tree and, at the same time, it is very important to establish carefully the number of trees to be sampled. To this end, an operational strategy to define the number of sample trees is given. Sampling simulations, carried out in the investigated Abies alba stands, show that forest growth assessment requires a relatively large number of sample trees to reach a good level of statistical reliability.