Sampling measures of tree diversity

The monitoring of tree diversity and forest structure is a key pre-requisite for understanding and managing forest ecosystems. This paper addresses the question whether and how tree diversity measures can be estimated as extensions of existing forest resource inventories. The sampling simulator CRANCOD was employed to compare the precision of angle count and fixed radius plot sampling with respect to nine representative diversity indices. The sampling methods were compared (a) in their overall precision in terms of estimating diversity indices and (b) in their ability to provide precise estimations for three different forest types independent of the spatial inventory scale, e.g. inventories at stand or enterprises level or national forest inventories. The results indicated that most of the spatially explicit indices are more precisely estimated by fixed radius plots. Interestingly the superiority of fixed radius plot sampling to angle count sampling increases significantly with increasing diameter differentiation of forests. However, basal area, basal area related diversity indices and Pielou's segregation index can be estimated by angle count sampling with at least the same precision as from fixed radius plots. This provides options for situations where discarding angle count sampling is not possible because permanent sampling designs are in place or the importance of forestry summary statistics exceeds that of tree diversity by far. (c) 2010 Elsevier B.V. All rights reserved.