Using a Mensuration Approach with FIA Vegetation Plot Data to Assess the Accuracy of Tree Size and Crown Closure Classes in a Vegetation Map of Northeastern California

The accuracy of the Lassen-Modoc vegetation map was assessed using data from a grid of permanent Forest Inventory and Analysis (FIA) plots in conjunction with a fuzzy logic approach. This paper presents the results for the Modoc National Forest. The main foci of this paper are the methods and results for assessing the accuracy of tree size and crown closure classes using a mensurational approach based on calculations made from the plot data. This approach proved very useful in conjunction with fuzzy accuracy methods. Higher error rates reported for crown closure classes may be due to a variety of factors including error associated with crown closure modeling methods, error associated with crown closure calculations for a plot, and the variability of crown closure within a plot. Using the FIA data has proven to represent a cost-effective means of generating accuracy assessment information based on a probability sample.