Something is odd about Cal Fire’s state Tree Mortality maps

We examined a place near Santa Ysabel, off Highway 78 in San Diego County that we know well. What we found was disturbing.

1. Much of the area designated as having 40 – 15 dead trees per acre is either California sage scrub or chaparral (where there are no trees), or non-native grassland with a few scattered oaks. The white square in the first image represents one square acre for reference. The X on the second Google Image and the corresponding Tree Mortality Viewer map marks the approximate location of the square.

2. In oak woodland areas where there are actually trees, the estimate of tree mortality doesn’t seem to come close to what is actually on the ground.

3. We question the likelihood of having 40 – 15 dead, mature oaks on a single acre, especially in the upper range.

Whatever measurements the state is using, they appear to be based on crowded mixed-conifer forests. Where there are no conifers, the program seems to have a major hiccup.

We have discussed the inaccuracy of the maps with others in the field and they have confirmed the problems are statewide. This is an important issue because land and fire management decisions are likely being made based on these maps.

The state needs to conduct ground-truthing of their computer generated data if they intend to develop policy that reflects what is actually occurring.

The Tree Mortality Viewer can be seen here.


Santa Ysabel acre
The area in which Cal Fire indicates there are 40 – 15 dead trees per acre. Most of the area in view is California sage scrub, chaparral, or non-native grassland with a few oaks. White square represents one square acre for reference.


Santa Ysabel Trees Google with X
Much of the terrain to the right of Highway 79 is not forested, but rather California sage scrub and chaparral. X marks the approximate location of the square acre in the previous photo.
Santa Ysabel Trees
Above: The state’s Tree Mortality Viewer map. The X marks the approximate spot for the square acre in the above photo. Red designates areas that supposedly have 40 – 15 dead, mature trees (oaks) per acre. Other colors: Orange (15-5 dead trees per acre), Yellow (5 or less dead trees per acre).


Addendum August 17, 2018

The more we look, the more errors we find in the state’s conclusions.

Below is the image of the state’s Tree Mortality Viewer of an area in the Cleveland National Forest above Corona, California that supposedly has 15-40 dead trees per acre (see solid red polygon). If we use a mid range of 25 dead trees, we are talking about 12,000 dead trees in the area.

Dead trees Trabuco via TMV
Claimed tree mortality in the Cleveland National Forest.

Now, compare the image with two from Google Earth showing the same red polygon outlined in white.

Trabuco Dead Trees error
The overall view of the approximately 500 acre “dead tree” polygon.
Trabuco Dead Trees error close up
Close-up of polygon where Cal Fire indicates there are supposedly 15-40 dead trees per acre. Nearly all of this area is covered with chaparral with very few trees, all of which are quite healthy.

The area shown in the photos is a chaparral ecosystem with oaks, big cone Douglas firs, and a few other few species in canyon areas. The Google image confirms our field observations. Dead trees are not an issue there.

The disconnect between what is on the ground and what the state says exists via their Dead Tree Viewer is not unusual. We have found the same problem in several other areas we have examined as mentioned above for San Diego County.

Why are these inaccuracies so important to point out?

Government policy is being made based on these inaccurate maps. This, despite that fact that the most devastating wildfires in California have little to nothing to do with dead trees.

The map below shows the full Cal Fire tree mortality map for California. We have added the perimeters of all the state’s most devastating wildfires up to October 2017. Nearly all (16 out of 17) of the most devastating wildfires in California (i.e. greatest loss of life and property) have little to nothing to do with forests and dead trees. We define a devastating fire is defined as at least 500 structures burned and 1 fatality or more.

We have inserted a map showing San Diego County to expand the southern California perspective.

Tree Mortality 12 FINAL

Where do the most devastating wildfires occur? The most devastating fires occur where planning agencies have put communities in harm’s way and because our communities are composed of flammable homes. Add climate change and we have the perfect storm.

Shrubs and trees grow. Growth is natural. Dense habitats are necessary for biodiversity. When these habitats catch fire, they burn. Fire is hot. In crown fire ecosystems like chaparral and lodgepole pine forests, everything gets incinerated. That’s the natural pattern. The problem is that we’ve inserted ourselves in flammable habitats and still do not address the main reason homes ignite – by embers that can travel a mile or more from the fire front.

The California legislature continues to focus in the wrong direction. This is illustrated by what Senator Bill Dodd (D – Napa) was quoted as saying in the Los Angeles Times, “Why are we talking about anything else other than reducing the fuels in our state?” The final response by the state legislature to the devastating fires in 2017? They passed legislation to log forests in the Sierra Nevada, far from where the devastating wildfires occurred.

By blaming Nature (“fuel”), we are merely reaffirming the same approach that got us into this situation. Here’s the letter we sent to Governor Brown and the state legislature explaining why their approach is misguided. We also provide 12 policy suggestions that will save lives and property.

Here’s the science.

Here’s our excellent book on wildfire in California.

Here’s a great video on why homes burn and the best way to respond by USFS fire scientist Jack Cohen.

A full set of recommendations on how to make your home fire safe can be found here.

If you live in California, please write to your state legislators (Assembly and Senate) and let them know. Find who yours is here.

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