land use

Study: Forest Fires in Sierra Nevada Driven by Past Land Use not Climate Change

Researchers from the University of Arizona and Penn State studied fire regimes in the Sierra Nevada Mountain of California for the period 1600 to 2015 and found that land use changes, not climate, were the principal controlling factors.

This result was apparently a surprise to the researchers since they set out to correlate climate with the fires.

“Initially, we did work to see if we could develop long-lead forecasts for fire in the area — six to 18 months in the future — using climate patterns such as El Niño,” said Alan H. Taylor, professor of geography, Penn State. “This would be a significant help because we could place resources in the west if forecasts indicated it would be dry and the southeast would be wet. However, the climate relationships with fire did not consistently track.”

“We were expecting to find climatic drivers,” said lead co-author Valerie Trouet, a UA associate professor of dendrochronology. “We didn’t find them.”

The researchers used tree ring data from 29 sites, historical documents, and 20th Century records of areas burned.

From the UofA press release:

For the years 1600 to 2015, the team found four periods, each lasting at least 55 years, where the frequency and extent of forest fires clearly differed from the time period before or after. The team found the fire regimes corresponded to different types of human occupation and use of the land: the pre-settlement period to the Spanish colonial period; the colonial period to the California Gold Rush; the Gold Rush to the Smokey Bear/fire suppression period; and the Smokey Bear/fire suppression era to present. Finding that fire activity and human land use are closely linked means people can affect the severity and frequency of future forest fires through managing the fuel buildup and other land management practices — even in the face of rising temperatures from climate change.

From the Penn State press release:

Early fires, because they were more frequent, with less fuel build-up, were “good” fires. They burned through the forest, consumed understory fuels and left the majority of trees unharmed. The Native American mosaic of burned and unburned areas prevented fires from continuously spreading.

From 1776 to 1865 the second fire regime, characterized by Spanish colonialism and the depopulation of Native Americans in the area, shows more land burned. European settlers brought diseases against which Native Americans had no immunity and the population suffered. The Spanish built a string of missions in California beginning in 1769 and relocated remaining Native Americans to the mission areas. In 1793, there was a ban on burning to preserve forage, disrupting the pre-colonial Native American burning practices. The incidence of fires became more sensitive to drought and the fire regime changed, creating the time when fires were largest and most closely coupled with climate.

The third fire period is from 1866 to 1903 and was initiated by the California gold rush, when thousands of people poured into the area. Settlement by large numbers of new immigrants began to break up the forest fuel and the creation of large herds of animals, especially sheep, removed large amounts of understory and changed the fire regime.

The fourth fire period began in 1904 and is linked to the federal government’s policy of fire suppression on government lands. The reason pre-colonial and Spanish colonial fire levels were so much higher than today is that the current fire regime is one of suppressions with an extremely low incidence of fires compared to the past. However, suppression over the last century has allowed fuel to build up on the forest floor and opened the door for “bad” fires that destroy the forest canopy and burn large areas of land.

(UofA press release, Penn State press release, paper abstract )

This finding contradicts an alarmist story printed in the Arizona Daily Star this past October (see third reference below).


See also:

Wildfires and Warming – Relationship not so clear
Claim: “Worsening Wildfires Linked to Temp Rise

Media hype about forest fires and global warming
Mega-fires in Southwest due to forest mismanagement

Bioreactor landfills – advantages and disadvantages

Tony Davis reports in the Arizona Daily Star that the “Arizona Department of Environmental Quality wants to make this the 15th state nationally to secure Environmental Protection Agency permission to start issuing permits for what’s known as ‘bioreactor landfills.’” (See story here.) I think the next sentence in the story is a misstatement: “They use liquids to react with garbage and speed the decomposition of methane gas that radiates from landfills everywhere.” It is not the methane that decomposes, it is the organic material in the garbage that decomposes to produce methane, more quickly in the case of bioreactor landfills.

The whole idea behind bioreactor landfills is to speed up natural decomposition of the contained organic material by providing conditions that favor increased microbial action. This is accomplished by circulating water, or air, or both through the landfill.

To find out more about these landfills, I recommend a site sponsored by the Florida Department of Environmental Protection and the U. S. Environmental Protection Agency. In Florida, these agencies are running two experimental bioreactor landfills as a bioreactor demonstration project. The site contains a detailed report of results and a video.

Claimed advantages of bioreactor landfills over conventional landfills:

1. Reduced potential for pollution. This presumably comes from recirculating water (called “leachate”) within the landfill to collect toxic metals and other harmful substances rather than have such substances gradually get into the ground beneath the landfill.

2. Increased energy recovery and reduced greenhouse gas emissions. The enhanced microbial action produces methane faster so that it is easier to collect.

3. Extended life for landfill. Decomposition of organic matter decreases the mass and allows the landfill to be used longer.

4. Lower long-term maintenance costs.

Claimed disadvantages of bioreactor landfills:

1. They use more water and the increased moisture could make the landfill less stable.

2. Initial costs are higher because of installation of water/air circulating system and monitoring system.

3. Bioreactor landfills tend to produce more hydrogen sulfide gas (H2S) which smells like rotten eggs.

My overall impression is that the advantages outweigh the disadvantages, and bioreactor landfills are a better way to deal with solid waste. However, it remains questionable whether or not this emerging technology is right for Arizona because of the increased water requirement. The costs and benefits should be carefully weighed.