Overstory mortality as an indicator of forest health in California.

The interagency Forest Health Monitoring Program involves a network of about 4200 forest plots on a triangular grid across the United States. We present data on recent mortality of trees ≥27.9 cm diameter from the first three years of measurements in California (1992-1994). Three plot designs were used to collect data representative of a 1-ha stand at each site; the designs differed primarily in total area sampled (0.067, 0.4 and 1.0 ha). Approximately 50 sites were visited each year yielding a total of about 150. Field tallies showed few cases of recent mortality in the smallest plot size. Cumulative distribution functions of recent dead tree densities in the 0.067-ha plots differed significantly from those generated by tallies from entire 1-ha stands. We conclude that an area of 0.067 ha is unsuitable to assess and monitor overstory mortality in Pacific Coast forests.