SAMPLING METHODS FOR ESTIMATING CHANGE IN FOREST RESOURCES

Changes in forest resources have been estimated in a variety of ways. This paper focuses on extensive forest surveys rather than on sentinel -site investigations. The sampling design and plot design used are key to precise estimates of change. Alternative sampling designs include temporary surveys, Continuous Forest Inventory, and Sampling with Part ial Replacement. Each can be used in conjunction with stratified sampl ing or double sampling for stratification. Plot designs can involve va riable-radius or Bitterlich sampling for trees, and fixed-area plots f or most attributes. In extensive surveys, it is efficient to group plo ts into clusters. Plots must be sampled at a frequency that is commens urate with the rate of change, degree of interest, and funding availab le. Often, plots are less than a hectare in size and spaced widely acr oss the population. Continuous Forest Inventory, with or without strat ification, is efficient for estimating current values, net change, and components of change. Much work remains in scaling to understand land scape-level interactions and to identify stressors and indicators of f orest health and sustainability.