THE MISSING TAIL AND OTHER CONSIDERATIONS FOR THE USE OF FIRE HISTORYMODELS

This paper reviews methods used for testing the fit of the cumulative form of a negative exponential distribution to the cumulative distribu tion of forest age-classes. It is shown that existing methods can lead to a greater chance of falsely rejecting the fit of the negative expo nential model and inferring that fire frequencies have changed through time. This results when the old-age tail of a negative exponential di stribution is mathematically assumed to be present at the end of the a ge-class distribution. In reality, the tail is censored from sample di stributions of forest age-classes. Censoring alters the shape of a cum ulative age-class distribution from the straight line expected for a s emi-log graph of the cumulative negative exponential model. A solution to this problem is proposed that restricts the tests-of-fit to the po rtion of the negative exponential distribution that overlaps with the data to be tested. The cumulative age-class distribution can then be c ompared directly with the cumulative of a truncated negative exponenti al distribution. Considerations for interpreting a poor fit are then d iscussed.