USDA Forest Service
 

Pacific Southwest Region

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How the Maps and Data tables were made


We start with a map of vegetation burn severity that is derived from an index of relative change between pre- and post-fire LANDSAT imagery. The satellite imagery derived index was calibrated with field data collected after 18 fires that burned in the Sierra Nevada from 2001-2004. More information on the methods used to derive the satellite index may be found in Miller and Thode, 2007 (.pdf 2.4Mb). The vegetation burn severity map that we use is graduated into 7 classes of severity that correlate with the percent of tree basal area lost in the fire. Here is an example: Moonlight Fire 2007 - Plumas National Forest (.pdf 5.9Mb).

Moonlight Fire 2007 - Plumas National Forest.  Percent of Basal Area Mortality.  Zero percent: 2237 acres.  Zero to 10 percent: 6303 acres.  Ten to 25: 4774 acres.  25 to 50: 5879 acres.  50 to 75: 5523 acres.  75 to 90: 4195 percent.  Greater than 90 percent: 36328 acres.  Unmapped: 263 acres.

Which of these classes are in a deforested condition?

To answer that question, we made field observations on two fires, the Boulder Fire (2006, Plumas National Forest) and the Hunter Fire (2006, Mendocino National Forest). Using GPS locator devices, a team of professional foresters visited points on the ground in different severity classes. They concluded that the 3 highest severity classes should be considered "deforested condition", while all other classes should be considered "forested". How does this conclusion compare to field plot data collected to develop the technique, assess its accuracy, and expand its use to other geographic areas?

BA_Category n % of plots with less
than 10 % canopy cover
% of plots with less
than 20 % canopy cover
7 (>90%) 345 85 % 90 %
6 (75%-90%) 63 56 % 63 %
5 (50%-75%) 116 37 % 50 %
4 (25%-50%) 139 27 % 39 %
3 (10%-25%) 110 6 % 19 %

Most of the area considered to be in a deforested condition had less than 20 % canopy cover. This data was collected in the first growing season after the fire.

To determine what kind of vegetation burned, we used vegetation maps available online from the USDA Forest Service Pacific Southwest Region. Major forest types were grouped into forest type groups for the Post Fire Condition Reports, for the logic see the Grouping Logic page.

The table category "treatments not permitted" is derived from a land suitability GIS layer. These land areas include proclaimed wilderness areas, wild and scenic rivers, research natural areas, and a few other special designations.

Other GIS layers needed to complete the work include ownership and slope.

USDA Forest Service - Pacific Southwest Region
Last Modified: Wednesday, 15 May 2013 at 17:36:10 CDT


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