Permanent plots as a means to monitoring forest dynamics and biodiversity

With the emphasis shifting from the one-time assessment of forest resources to the continuous monitoring of their changes, the question of installing permanent plots has become more and more acute across the world. This paper reviews some of the problems that arise when permanent plots are set up with the aim to monitor forest biodiversity and/or forest dynamics. The major advantages of setting permanent plots rather than having successive independent surveys are that (i) this reduces the imprecision in the estimates of change, and (ii) this provides a means to investigate the components of the changes. However there are several technical issues which always come to the surface and have to be discussed and solved according to the specific context and objectives : whether the plots should be physically demarcated in the light of the diffusion of global positioning systems (GPS); the choice between several alternative sampling designs : minimum size of the plot, cluster of plots vs. a single connected plot, network of medium-size plots vs. a few large plots; the minimum size of the sample trees; the way changes are estimated if the time step is long. (Résumé d'auteur