Fuel Load and Forest Fires – Watts Up With That?

Don Healy

Over the past several years, I have been corresponding with many local journalists regarding the cause of the recent increase in forest fires in the U.S. Using the written word alone has garnered only modest success. While a few now mention fuel load in their articles, the mention is cursory at best with them harping back to increasing temperature as the driving force. Concluding that are more graphic approach was necessary I decided to use a period of Covid isolation to enhance my limited skills using the charting functions of Microsoft Excel. The following is the result when comparing U.S. data on acres burned to temperature and to fuel load:

Examining the situation from this perspective makes it very clear that fuel load is by far the dominant factor. This also confirms what we were taught by the forestry professors at Oregon State University in the late 1960s.

The rationale behind the chart and the sources for the data are as follows: The graph compares the number of acres burn in U. S. forest fires in recent decades to the two major conditions responsible for this increase, temperature and fuel load. The dashed orange “acres burned” line on the graph illustrates the increase in the acreage of forest fires that has occurred in the U.S. in the past four-plus decades. This data comes from the U.S. Interagency Fire Center. (Source: https://www.nifc.gov/fire-information/statistics/wildfires) This record used to extend back to the 1920s but was recently amended to cover the period from 1983 to the present, due to concerns about the earlier methods of determining burned acreage. Unfortunately, the Agency has nothing to replace this earlier data. Many are using this amending of the prior record to conclude that earlier periods, particularly the 1920s and 1930s, experienced fewer fires than were originally recorded. That assumption appears unwarranted in light of other peer-reviewed studies, the logs of some of the earlier Spanish and English explorers, anecdotal evidence from many of the early settlers, and even an account by Mark Twain during his visit to Tacoma in the 1880s. However, the data in this graph has been limited to currently approved data.

Upper solid blue line on the chart is the volume of merchantable timber on all ownerships in the U.S. and was obtained from the surveys conducted by the U.S.F.S. every ten years covering both hardwood and softwood timber species. (Source:  United States Department of Agriculture Forest Resources of the United States, 2017A Technical Document Supporting the Forest Service 2020 RPA Assessment Sonja N. Oswalt, W. Brad Smith, Patrick D. Miles, and Scott A. Pugh. https://research.fs.usda.gov/treesearch/57903) The dots on this line represent the precise data results from the surveys.

This record actually extends back to 1953 and shows that from 1953 to the last survey in 2017, merchantable timber volumes have increased by 60%. The U.S.F.S. inventory figures for 2017 were 985,238 million cubic feet. Therefore each digit on the left vertical axis represents 100,000 cubic feet. Not having any data on total biomass, the timber inventory figures have been used as a proxy for total fuel load. In reality, the fuel load increase is probably much greater than indicated since non-merchantable trees, shrubs and grasses, some highly invasive, have not been included. Going forward, the CO2 fertilization effect may further impact the fuel load situation by both increasing the growth rate of virtually all plant life, and its ability to increase the drought resistance of plants and trees. As an example, red alder trees are growing about 20% faster than they were in 1950.

The center dashed green line charts the change in the average annual temperature in the contiguous U.S. from 1983 to the present in degree F. This data is from the National Weather Service. (Source: https://www.ncei.noaa.gov/access/monitoring/national-temperature-index/time-series/anom-tavg/1/0) This graph was designed to show visually how much temperature has increased within the framework of normal human existence. The top horizonal blue dashed line is at 130 degrees F., slightly below the highest temperature record in Death Valley, and the bottom horizontal dashed magenta line represents -50 degrees F, (the coldest recorded was actually -70 degrees F.) In virtually all reporting today monitoring climate, temperatures are shown in tenths of a degree that greatly magnifies very small changes. It is important to compare data such as temperature changes, fuel load and acres burned on scales equitable for that comparison.

Comparing these three elements on a rational scale shows that acres burned tracks fuel load rather closely, while the small change in temperature is barely noticeable. However, most media and official reports stress the role of increasing temperature, with seldom a mention of the fuel load issue. If we are to deal effectively with the forest fire issue it is imperative that we get the foundational data correct first so we can develop effective strategies to deal with this major threat to mankind.