Introduction and assumptions

In this chapter we take you through the process of calculating baseline mortality, and comparing it to observed mortality to assess the sustainability of four sample forests. We present four case studies, each of which utilizes a dataset from a different forest type and region of the world.

The use of the baseline mortality approach to assess forest health is dependent upon some important underlying assumptions that must be considered for appropriate use of the method and interpretation of results, and which include the following (we first mentioned these in Chapter 1, but it is worth repeating here): (1) The method generally is applicable only at the landscape scale to minimize the influence of individual stand peculiarities and sampling artifacts. It may, however, be appropriate at the stand level if the stand is fully stocked, and is properly sampled (i.e., sample plots are large enough or sufficiently numerous to provide an adequate representation of all diameter/size classes and species of trees in the forest. The plots must be randomly selected to remove sampling bias). (2) The method used to quantify observed mortality assumes that dead trees remain identifiable to species for about the same time that it takes for the living trees to grow into the next diameter class. Therefore, the decay rate and the growth rate must be taken into account when determining the optimum width of the diameter classes.